ocP/73.1
ONCHOCERCIASIS CONTROL IN THE VOLTA RIVER BASIN AREA
REPORT OF THE PREPARATORY ASSISIANCE ilISSION IO THE GOVERNTIENTS OF: : . .;,. DAHOHEY GHA}IA IYORY COAST TALI NIGER TOGO UPPER VOLTA
THE AUSPICES OF THE UNITED NATIONS DEVELOPMENT PROGRAMME ( UNDP), FOOO AND AGRICULTUBE THE UNITED NATTONS ( FAO ), TNTERNATIONAL BANK FOR RECONSTRUCTTON AND DEVELOPMENT ( IBRD l, TH ORGANTZATTON ( WHO I
GENEVA 1973
I ocP/73.'.|
* rlj
ONCHOCERCIASIS CONTROL IN THE VOLTA RIVER BASIN AREA
Report of the Mission for Preparatory Assistance to the Governments of :
DAHOMEY, GHANA,IVORY COAST, MALI NIGER, TOGO and UPPER VOLTA
Presented bY:
UNITED NATIONS DEVELOPMENT PROGRAMME
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS ( ASSOCIATE AGENCY }
INTERNATIONAL BANK FOR RECONSTRUCTION AND DEVELOPMENT
WORLD HEALTH ORGANIZATION GENEVA ( EXECUTING AGENCY } 20 August 1973 -I.-
COI.ITEITS
Page ii Synopsis .
INTRODUCTION
CHAPTER I The Programme area: Physical, hurnan and econonic geography 7
CHAPTER II Onchocerciasis: Parasite and disease L7
CHAPTER III onchocerciasis: Vectors and transnissi.on 2L
CHAPTER IV Epideniotogy of onchocerciasis and socio-econonic aspects of the disease ' . 27
CHAPTER V Prograrnne for the control of onchocerciasis and plan of operation 43
CHAPTER VI Anticipated socio-econornic benefits and proposals for economic development of the areas freed frorn the disease ' 53
CHAPTER VII Structure and management of the Onchocerciasis Control Programne 81
Appendix List of technical annexes 85
The boundaries and designations shown on the maps and used in the text of this report and its annexes do not imply the expression of any opinion what- soever on the part of the United Nations and their specialized agencies con- cerning the lega1 status of any country or territory or of its authorities, or concerning the delimitation of its frontiers.
Unless otherwise stated all costing estimates relate to values and the exchange rate for the US dollar as 1n July 1972. - 11 -
SYNOPS I S
Following a number of prelimlnary steps, it was decided rn 1970 at the request of the Governments of Dahomey, Ghana, Ivory Coast, Mali, Nrger, Togo and Upper Volta, to prepare a strategy for a programme desti,ned to control onchocerciasis in the Volta River Basin area, The Preparatory Assistance Mission which resulted was set up by the World Health Organization in association with the Food and Agriculture Organization over the period 1971-73 and was financed by the United Nations Development Programrne.
The present report covers this preparatory work and sets out the proposed strategy.
The main objectives of the Programme envisaged are twofold: to combat a disease that is widespread and severe in the area, and to remove a maJor obstacle to economic development.
Onchocerciasis is an infection by a parasitic filarial (threadlike) worm, Onchocerca volvulus, transmitted in the programne area by the bite of an infected female blackfly of the species Simulium damnosum. The fly itself becomes i.nfected by biting an infected human host. Both man and fly are therefore essential elements in the life cycle of the parasite.
The clinical manifestations of onchocerciasis include intensely itchlng rashes, wri-nkling, thickening and depigmentation of the skin, the characteristic skin nodules in which the adutt- worms are to be found, and eye lesions leading to bli,ndness as the most serlous consequences of the disease. Heavrly-infected patients often lose weight and suffer from debilitation.
The larvae of the insect vector, S. damnosum, can develop only in fast-flowing rivers. Onchocerciasis is therefore a disease of the fertile areas flanking the rapids of rivers, hence its common name "river blindness", Moreover, apart from its role as a vector of disease, the blackfly constitutes an intolerable nuisance, the average number of bites per man per day sometimes amount to several thousand, although only a smal1 proportion of these result in infections. -l I'
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L i The savanna area of the Volta River basrn rs one of the worst endemic onchocerciasis zones in the world. On the basis of surveys carried out by the national health services, it j-s estimated that over 1 million of the 10 miltron j-nhabitants of the area covered by the programme (nearly 7OO OOO tm2) are infected by onchocerciasis, and that of these at teast 70 OOO are blind or have a serious impairment of sight.
Apart from the great personal sufferlng i.t causes, onchocerciasis has a two- fold destructive eeonomic effect: not only i-s there a reduction in the productive
capacity of those afflicted by the disease, but the blind and near-blind become a charge on society; inhabitants of the fertile valleys flanking the rivers migrate to poorer lands that are overcropped and, far from y1eldlng marketable produce, do not provlde an adequate means of subsistence. Furthermore, the persistent and critical effects of drought 1n the sahel and the savanna, follow:-ng the failure of the rains in L972 for the fifth successrve year, have greatly I complicated the already precartous socio-economrc balance in the VoIta River basin atea.
Among the measures to control onchocerciasis that have been considered are:
(a) Mass chemotherapy. Unfortunately, the two avarlable drugs of proved value - suramin and drethylcarbamazrne - may have dangerous side-effects, and can therefore be admlnistered only under close medr.cal supervlsron. This precludes therr use for mass chemotherapy ln populatrons whose access to medlcal care is mj,nimal. Research to frnd safer onchocercj-cida1 drugs rs under way, but has not yet resulted in a definitrve solution.
(b) Brological control of the vector, usr.ng known predators, parasites, and pathogens of S. damnosum. This method i.s under study, but as yet rs far from berng of practlca} significance.
(c) Protection of the potential human host by chemical or physical barriers. The vector usually bites below the knee, and in theory the use of an effectlve insect repellent or protectrve clothing would i-nterrupt the transmission of onchocerciasis. While such measures have a Iimited value in speciaJ. circumstances, their mass apptication in the programme area would be quite impracticable.
Elimlnation of the insect vector by chemicals offers the sole means at present available for preventing the disease, This cannot be achieved by an attack on the edult fly because an lmmense area would have to be treated with lnsecticides - the flight-range of the fly may, rn favourable clrcumstances, extend to as much as I5o km. i
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OnIy one line of attack remains: namely, to destroy the blackfly larvae in the circumscri.bed sites in which they mature. Fortunately, the physiorogical requirements of the larvae are such as to make such a method of control eminentty feasible. Attached to their submerged supports, they depend on the fast-flowing water to bring them oxygen for their respiration and parti.culate matter, for their nutrition. Particles suspended in the water are ingested indiscriminately, whether or not they are of nutritive value, and ingestion of a chemi.cal larvicide in adequate concentration results in the destruction of the larvae.
The desiderata for a chemical compound lethal to the larvae are: (a) tnat it shourd not undury affect other forms of life ("non-target fauna"), especially fish that are of economic importance; (b) that it should soon be decomposed i.n the biological envj-ronment (biodegradability); and (c) ttrat it should be possi.ble to apply it to rivers in such formulations as will result in its ingestion by the larvae together with other suspended particulate matter, The two compounds that best meet these requirements are Abate1 and methoxychlor. Atthough DDT is also effective against the Simulium larva, its chemical stabllity and consequent persistence preclude its use.
Because of the inaccessibility by land of many of the breeding sites of Simulium, the only feasible method of applying the larvicide is frorn the air. In the case of large rivers that are sufficiently straight, light planes can be used, but narrow twisting waterways and those overhung by forest require the use of hellcopters. In the rainy season, when the rivers flow swiftly, a single applica- tion may eliminate the Simulium larvae for up to 50 km downstream. In the dry season, relatively fast-flowlng stretches of river may be interrupted by areas of still water, in which case each of these stretches must be treated separately.
Because of the long life of the adult worm in the human host, sufferers from onchocerciasis may remain infective for as long as 15 years even if not re-infected. The duration of a campaign to prevent the disease by elj.ninating its insect vector must therefore be not less than this length of time after the last new case in the programme area.
The strategy, cost and organizati-on of the control campaign are presented in the report. For its execution, co-ordination of field operations will be assured by a headquarters at ouagadougou, Upper Volta, which is centrally situated in the programme
I This is a proprietary name. "Temephos" is under consideration by the International Organization for Standardization as a non-proprietary name for this compound. I'
-v- area and in one of the most severely affected of the seven countries involved. The effects of the larviciding operations on the presence of Sirnulium will be under continuous surveillanee and will incl-ude repeated tests of larval suscepti.bility to the compounds used as well as periodic hydrobiologicat studies of typical treated stretches to ensure that the biological equilibriun of the rivers is not seriously disturbed' The impact of the campaign on the prevalence and severity of the disease will also be continuously monitored by epidemiological teams.
The repopulation ana/or settlement of the uninhabited fertile areas freed from the disease is a major objective of the Onchocerciasis Control programme. Such actiofr would also permit development measures to be taken in areas of high population density]. It is expected that major reclamation of deserted land witl be possible some 1g npnths after the start of insecticide treatment in the zone concerned. A series of reclamation plans based on the development of agriculture and stock raising has been studled and costed for the guidance of the Governments of the programme area.
cLinicaL, entomological, parasitologicar, sociological, economi.c, and agronomic studies of the overall consequences of onchocerciasis in the programme area have shown not only that control of the vector, and hence of the disease, is feasible but that - in addition to the relief of suffering, whi-ch must universally be recognized as an end 1n itself - wide-ranging socio-economic benefits would be made possible by the exptoitation of lands that are now deserted although fertile.
It is planned to l-aunch the Programme - which will last about 20 years - in 1974 aftet the endorsement by all concerned of the strategy proposed. Rrnds in the region of US$ 12O million will be required to finance the programme and a Special F\rnd for Onchocerciasis is being established.
As Executing Agency, WHO will assume technical responsibitity for the Programme in conjunction wlth the Governments involved.
The executive organ of the Programme wifl be the Steering Committee for Onchocerciasis Control in the Volta Rj-ver Basin area, representing the four sponsoring agencies (UNOp, FAO, IBRD and !!HO). -1-
II.ITRODUCTION
The problem
This report deals with a disease that affects over a million people i.n the
Volta River basin area covering nearly 7OO OOO square kilometers i.n seven countries of West Africa. The disease is onchocerciasis, or river blindness, wtrich is propagated by a species of the blackfly (Simulium damnosum) that breeds in rapidly flowing seetions of the rivers. The disease brings with it debilitation, misery and blindness and constitutes for the area the most important single deterrent to human settlement and the subsequent economic development of many fertiLe valLeys, which lie uninhabited and unproductive. This situation inhibits the development of the vast savanna belt of the Volta River basin area, and countless thousands of famllies have left productive ancestral lands to crowd the adjacent areas where 1ow- yielding, poor soil predominates.
For populatlons dependent on agriculture and cattle-raising the situation is economically crippling. Furthermore, the persistent and critical effects of drought in the sahel and the savanna, following the failure of the rains in L972 for the fifth successive year have gravely complicated the already precarious socio- economic balance in the Volta River basin area, resulting in a population movement towards the south.
The first steps
Awareness of the extent of the problem had been steadily developing, particularly in the minds of the national authorities concerned, when in 1968 the Wor1d Health Organization (WHO) in joint sponsorship with the United States Agency for Inter- national Development (USAID) and the Organisation de Coordination et de Coop6ration pour Ia Lutte Contre les Grandes krd6mies (OCCGE) convened a technical conference in Tunis to consider the problem of onchocerciasis. The Tunis meeting brought together the world's leading experts on onchocerciasis and its insect vectorsrand its major objective was to assess whether the control of onchocerciasis is possible with currently available methods.l
The conference concluded that control is technically feasible, and that the chances of obtaining successful and lasting effects would be greatest if the control were carried out in ecological zones sufficiently large to obviate the need for continuous protection of the whole area against reinvasion by the blackfly vector.
1 World Health Organization (1969) Report of a .ioint USAID/OCCGE/I{HO technical meetinq on t tv of is cont is, 1-8 July 1968, wHo,/oNCHO/69 -75 60 pp., 4 maps I'
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The possibility of launching a large-scale control progranme led the meeting to recommend that priority should be accorded to onchocerciasis in Africa, and specifically to an initial campaign in the severely affected area of the Volta River Basin involving adjolning parts of Dahomey, Ghana, Ivory Coast, Ma1i, Niger, Togo and Upper Vo1ta. The delineation of the area was dlctated not only by the high prevalence of onchocercal infection there but also by reason of the severity of the disease and the manifestly high rates of blindness. Moreover, certain field operations were already under way in the area; some success had already been achieved and significant entomologlcal, epidemiological and economic data accumulated. Above all, the recommendation regarding the area reflected the determination of the interested Governments, supported by public opinion, to cooperate in a control progratnme that was recognized to be a prerequisite for economic development, as well as for the health of future generations.
According thls priority to the area of the Volta River Basin in no way precludes the future extension of control operations to neighbouring onchocerciasis foci in the African savanna zone. Although further studies wil-1 be required before
extensions can be envisaged in some areas, the present scheme should serve as a basls for the forrnulation of operational patterns for subsequent expansions. Thus the Volta River basi.n scheme would constitute the cornerstone of future coordinated action against onchocerciasis and for the associated economic development in Africa south of the Sahara.
In April 1969 a further meeting was organized in Brazzaville by the WHO Regional Office for Africa to refi.ne further the approach needed to secure technlcal assis- tance for the proposed campaig.r.l Experts from the Government of Ghana, oCCGE and usArD, in addition to ltHo representatives, attended these discussions.
Requests from Governments
Shortly thereafter, in 1969 and in 1970, several of the lnterested countrles submitted formal requests - emanating from the highest authorities - to international and bj-lateral sources of assistance 1iab1e to be interested i-n supporting this great undertaking which was taking practical shape. Among those organizations were the Fonds Europ6en de D6veloppement (FED), the Food and Agriculture Organization of the United Nations (FAo), the International Bank for Reconstruction and Deveropment (rBRD), the united states Agency for rnternational Development (usArD) and the world
I World Health Organization (196e) xt onchocerciasis control ro rect n the Volta River Basi_n, Brazzavi1le, 30 April - 2 May 1969, 4 13, 36 -3-
Health Organization (WHO). Simultaneously the United Nations Development Programne (UNDP) manifested its interest in the subject, particularly as it was already financing a WHO onchocerciasis project i.n West Africa.l
Preparatory Assistance to the Governments (PAG Mission)
On the basis of the requests received and at the suggestion of IBRD, WHO and UNDP sponsored a planning meeting in Geneva in July 1970 wtrich brought together
representatives of the Conseil de lrBrtente12 th" Government of Ghana, and OCCGE, FAO, FED, IBRD, UNDP, USAID and UIIO. At this meeting terms of reference were drawn up for a missj.on designed to carry forward, on behalf of the seven Governments concerned, the essential preparatory work required for the definition of an overall strategy for the proposed onchocerciasis control programrne. Ttre Mission was scheduled to start 1n mid-1971 and initially programmed for one year - this was
later extended to cover the vfiole of the year 1972. The Administrator of IJNDP agreed to provide the necessary funds and accordingly nearly US$ O.2 million was allocated to WHO as the Executing Agency in association with FAO, which accepted responsibility for certain aspects of the work.
The PAG Mission received as its mandate3 a rnajor two-fold objective. In the health sector, it was requested to prepare a plan of work to achieve control of onchocerciasis over the entire recommended project zone, taking into account economic development of reclaimed areas I to work out the expected costs and benefits of the scheme; and to analyse the possible financial resources available. In the economic sector, the Mi.ssion was later cal1ed upon to identify areas wi.thin the project zone, which owing to their economic potential and location in relation to centres of population density, offered development possibilities; it was requested also to draft preliminary terms of reference for feasibility studies to be conducted later in these areas.
The Government of Upper Volta agreed to act as host to the PAG Mission and to place at its disposal premises at Ouagadougou for its headquarters which were set up in August 1971. Operating from Ouagadougou, the Mission has benefitted from the fuII collaboration and encouragement of the Government of Upper Volta and the Governments of the other six countries in which it has carried out its activj-ties.
t ,n" onchocerciasis Advisory Team GeffzZfn8) assigned to Northern Ghana, Togo and Upper Volta and operating from Bolgatanga, Ghana. 2 A consultative body in which the Goverrunents of Dahomey, Ivory Coast, Niger, Togo and Upper Volta participate.
3 The terms of reference of the PAG Mission are set out in Annex o-1. t"
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The staff of the Mission comprised a Chief of Mission, an entomologist, a general economist and an administrative officer, supplemented by short-term consul- tants on aerial larviciding operations, a project ptanning (costing) expert, a statistician, two human geographers, an agricultural production economist, an agricultural (costing) economist, an agriculturalist, a sociologist, a veterinarian and two development economists. In addition, the Mission received considerable support from the WHO regular research programmes, including operational research conducted with funds provided by the Governments of the Federal Republic of Germany and the United States of Amerlca.
Research undertaken by the Onchocerciasis Unit of the Ministry of Health of
Ghana, by the Centre Muraz and Ophthalmological Institute of OCCGE, and by ORSTOM1 has proved of invaluable help in the study of the disease and its vector and in the development of an appropriate methodology for epidemiological evaluation. The collectlon of data has been made possible through the cooperation of the departments of health, agriculture, economics and planning and their related bodies in all the countrj-es concerned. During its assignment the PAG Mission reinforced its affiliat:-ons with ancillary work in progress, such as the entomological studies being performed in northern Ghana, the FED campaign in the Com6e-Leraba region, OCCGE's Onchocerciasls Secti.on, and hydrobiological work on Lake VoIta.
Apart from the continuous technical contacts maintained by the PAG Mission with
1ocal and anternational bodies, a series of meetings took place during the PAG Missj-on's assignment to review progress and advise on the future work. Discussions of current problems, particularly in logistlcs took place at Ouagadougou in September
1971 between the Upper Volta authorities and representatives of WHO and FAO, with the participation of an IBRD representative. A revi-ew meeting was held at WHO head- quarters in Geneva in February a972, and thi-s was followed by a fuII project review meeting in Geneva in JuIy 1972. In October of the same year a planning meeting between the regi.onal and field representatives of UMP, FAO, IBRD and WHO was organized in Accra, Ghana.
The Steerlng Committee
Meanwhile, in Apr11 L972, the Director-General of FAO, the President of IBBD, the Administrator of LINDP and the Director-General of WHO decided in view of the importance and complexity of the scheme envisaged, to set up a Steering Committee for Onchocerciasis Control comprising a representative from each of the four agencies.
'Orfr." de 1a Recherche Scientifique et Technique Outre-Mer supported by the Government of France. -5-
The Steering Cornrnittee had a general mandate to ensure coordination of the action taken by the four agencies in the planning and implementation of the programme, and its detailed terms of reference are set out in Annex Q'2 to this report. The Conmittee held its first session in July L972 in Geneva and subsequent meetings in October 19?2 (New York), February 1973 (Geneva), May 1973 (Geneva) and JuIy 1973 (Rorne). The Steering Committee has thus been able to moni-tor the progress of work during the various preparatory phases, discuss technical, administrative, financial and logistic matters and review the forn and content of the present report.
Extension of the work in 1973
Among the major recommendations made by the Steering Committee at its first session was that the preparatory work phase should extend through 1973. Accordingly, an interim project covering the year 1973 was formulated to aLlow operational research to proceed in the form of field trialS in a pilot zone, to adjust the aerial spraying technique and refine its costing; the interim project also included the lnitiation of field trials with established drugs. Another important part of the work was establishing firm baseline data to enable progress to be continuously checked during the proposed Onchocerciasis Control Programme. In addition the interin project was requested to review the possible ecological changes that might ensue and suggest precautions that should be takeni and also to plan and launch the training programme for natlonal staff.
On the understanding that other financial assistance wouLd be forthcoming for the full prograrme scheduled to start in 1974, the Administrator of UNDP agreed to extend the fi.nancial support to the PAG Mission to maintain the interlm project in 1973. The sum allocated was approximatety US$ O.5 million, but this was later increased to nearly US$ O.6 miltion.
The docgment describing the scope of the 1973 interim project of the PAG Mission is presented as Annex O-3.
The report
The findings of the PAG Mission and other preliminary lnvestigations are combined to form this report which delineates the area in which it is proposed to implement the Onchocercj.asis Controt Programme and describes the main features of the progranme. The report then describes onchocerciasis, particularly its parasito- logical aspects, and the research efforts that will be needed to produce a safe drug to provide protection against infection and a cure for the disease. Then follows a description of the vector, its distribution, transmission of the disease and the method proposed for controlling Simulium damnosum, and of the broader epidemiological l"
-6- and socio-economic aspects of onchocerciasis, in particular the extent of the problem and its relationship to emigration and the desertion of land. The central feature of the report is the plan of operation for the Onchocerciasis Control Programme to- i gether with a costing analysis of each component. There follows a description of selected economic development projects demonstrating the potential economic benefits of the campaign and the report concludes with an outli.ne of the way i-n which, it is believed, the Programme should be organized and managed to ensure the greatest success. ;fr(*
This report is presented to the Governments of Dahomey, Ghana, Ivory Coast, , Ma1i, Niger, Togo and Upper Vo1ta in compliance with their initial requests for preparatory assistance in formulating a plan of work for onchocerciasis control rn the Volta River basin area which could lead to the repopulation, settlement and economic development of the reclaimed areas.
The report is also destined for the consideration of a Roundtable conference . which will bring together the seven Governments involved, the potential donors, multilateral and bilateral agencies and voluntary bodies to endorse the Programme formally and review the proposed strategy with a view to taking the decisions necessary for launching the Onchocerciasis Control Programme in 1924.
Those responsible for the report are consclous of the prolonged efforts that will be demanded of all concerned to achieve the success envisaged here. They are also mlndful of the magrritude of the resources required for the Onchocerciasis Control Programme, and for the economic development of the areas to be restored to present and future generations. Ttrese problems - like others that wil1 certainly arise in a scheme of this breadth of concept - will be solved only if the dedication of the seven Governments to this common cause 1s supported. by the cooperation of other countries and of the international community as a whole -7-
CHAPTER I
THE PROGRAMME AREA: PHYSICAL, HI]MAN AND ECONOMIC GEOGRAPHY
The prograrr" is situated almost entirely between latitudes 8o and 15o ".aa' north and longitudes 4o east to 8o west. It includes parts of Dahomey, Ghana, Ivory Coast, Mali, Niger, Togo, and most of Upper Volta, with a total area of nearly 7OO OOO square kilometres lying almost entirely within the savanna be1t. The central part of the programme area constitutes the upper watershed of the Volta River, with the tributaries of the Niger River in the north-east and the north-west and the upper watersheds of the Como6 and Bandama rivers in the south-west (Fig. t).
Cl imate
In this part of West Africa the delineation of the climatic zones depends on the total amount and length of rainfall, which, in turn, is influenced by the prevailing winds. A humid maritime wind, the monsoon, blows from the south towards the north-east, whi.Ie a continental dry wind, the harmattan, blows from the Sahara desert towards the south; where both winds meet violent storms are generated. The monsoon influence during the second and third quarters of the year extends northwards and the rainfall peak occurs usually in August in the savanna area. The harmattan, in its turn, dominates the monsoon during the fourth and the first quarters of the year and reaches the Atlantic coast in December or January. These seasonal influences determine the location of major climatic belts, which are broadly parallel to the coast in the central part of West Africa: the subdesertic zone lies north of latitude 20" north; the sahelian zone between latitudes 15o and 2Oo north; the equatorial zone south of latitude 8o north, and the sudanian zone between the equatorial and sahelian zones. Within these major climatic zones the annual average rainfall and the length of the rainy season (Figs 2 and 3) determine the characteristics of several vegetation belts, each with its own agricultural potential (Figs 4, 5, and 6 ).
The programme area lies entirely within the sudanian climatic zone. The northern part, with an annual average rainfall of about 60O mn to almost 1OOO mm but large variations in the amount from year to year, is covered by the sudanian savanna represented by a dry wooded savanna in the south and thorn bush in the north. Ttre southern part, with an average annual rainfall of IOOO mm or more, reach- ing 13OO mm in some places, is covered by the guinean savanna with forest galleries along the streams and rivers and oiI palms scattered or grouped in the humid lowlands.
1 The geographical features of the progranme area are described in greater detail in Annex I-1. l'' I
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In the extreme south of the programme area patches of dense forest are scattered throughout the guinean savanna, constituting a transition zone to the equatorial rain forest (fig. 4).
Geography and hydrography
The main mountainous area of West Africa is the Fouta Djallon where the Niger River has its source, but plateaux and cliffs of moderate elevation above sea level play a major role in delineating the watersheds of the large rivers and of their main tri.butaries. The north-eastern and south-eastern extensions of Fouta Djallon channel the Niger River and its first tributaries to the north-east, this area forming the watershed from which flow most of the Malian tributaries of the Niger River as well as the Bandama River and its western tributaries. The Banfora- Sikasso plateau gi-ves rise to the Como6 River and its main tributaries, to the Black Volta, and to one tributary of the Niger River. From the Bandiagara plateau flow a few sma1l tributaries of the Nlger River, while the Mossi plateau gives rise to the Whj-te and Red Voltas and their tributaries of Upper Volta as well as to the trlbutaries of the Niger River in Upper Vo1ta. From the Atakora scarp to the ea$t flow the Oti-Pendjari and its tributaries and the Dahomean tributaries of the Niger River.
Further south many rivers and streams originate from the hi1ly country of the central Ivory coast, from the Ashanti prateau of centrar west Ghana, Togo, and Dahomey, and from the southern slopes of the south-eastern extension of the Guinean range; these waters mostly flow directly into the Atlantic Ocean.
The Niger River flows north-east for more than 15OO kn before turning south- ea$t towards the bight of Benin: the river forms an interior delta nearly 5OO lsn long and it can be as much as 1OO km wide when the annual flood reaches thls detta. From Bamako to the Nigerian border the Niger flows mostly through flat country and hae ferv rapids but it does not constitute a major waterway in the area, being quite shallow for part of the year. A11 the other rivers mentioned are frequently interrupted by waterfalls and rapids and are entirely unsuitable for navigation.
In the progranme area particularly, on account of the very uneven seasonal digtribution of the rainfa11, many watercourses are very shallow or even completely dry during part or most of the dry season, and those that are permanent vary enormously in volume and flow rate from month to month (figs 7 and 8). These streams thus offer limited prospects for dry-season irri-gation and in manv areas water supply ls an acute problem during several months of the year. To mitigate this problem hundreds of sma11 dams have been bui-It during the past quarter of a century -9- for agro-pastoral purposes, and hundreds more are being planned. Two large lakes have also been created by daming the Volta River near Akosombo in Ghana, and the Bandama River near Kossou in the Ivory Coast (Fig. 7).
Soi.Is
Three main categories of soit are recognized in the central part of West Africa: north of tatitucle I5o north are the beige sandy soils, with usually loose sands in the desertic zone and fixed sands in the sahelian zone; south of lat+tude 15' north are the red ferruginous tropical soilsr of which two types occur: I. the dark red lateritic soils of the sudanian climatic zone: these soils are usually shallow, fragile, and easily eroded; their inherent fertility is low1 Z. the pale red, deep sandy soils covering the rocky skeleton of the equatorial climatic zone.
The Votta River basin area has mostly dark red soils but is far from homogeneous, in this respect. Rocks appear at the surface in some places while lateritic crusts are not uncommon on the plateau; some fertile brown soils are found and in the north-eastern part of the area there are sandy soi1s. The valteys of the main rivers and some of their tributaries have fertile or moderately fertile alluvia1 soils.
As a consequence of fundamental differences in the geological structure and the rnherent fertility of the various soils combined with the effects of htruran occupation, there i.s now a marked contrast between the plateau and valley areas across the pro- gramme area. Severe population pressure in the plateau areas - those with poor Iateritic soils as well as those with more fertile soils - has, as a result of over- cropping, led to the serious degradation of the upland soils. In many densely populated areas there is abundant evidence of sheet wash and even gully erosion, and with the loss of nutrients crop yields in crowded watershed areas have declined markedly. This is in contrast in many cases to the situation in neighbouring valleys where the soils have a much higher inherent fertility leve1 and therefore a much greater yi.eld potential, given proper management.
Populat ion distribut ion
In the central part of West Africa, as in most of the continent the population is very unevenly distributed, sparsely inhabited areas lying next to overpopulated ones (Fig. 9). This situation is as much the result of historical as of bioclimatic factors because with the exception of the subdesert and desert zones, which are unsuitable for dense settlement, and of the rain forest, which has long constituted an obstacle to human colonization, most of West Africa offers good opportunities for farming or ranchingr or both. I' I
-10-
The present population density distributi.on shown in Fig. 9 must be i.nter- preted with caution as averages were obtained for very large administrative units. A more accurate examination of the data for smaller areas at the country, district, or group of villages level, shows that 1n many instances the population distribution is patchy (Figs 10-12). The population and the area covered by the programme are shown in Table 1.
In the northern half of Ghana (Fig. 10) there are high population densitj.es in the plateau areas between the valleys of the White and Red Volta, the Sissili and the Kulpawn rivers, vtrile the valleys themselves are sparsely populated or even uninhabited. Relatively densely populated areas are also encountered in the Bawku district in the extreme north-east of the country, as well as around Tama1e in the centre and in the Wa and Lawra districts in the north-west, but most other parts of the Upper and Northern Regions have very 1ow population densities. On the other hand, the southern third of Ghana is densely populated.
In northern Ivory Coast (fig. 11) the population is nostly concentrated rn the Korhogo area which is immediately surrounded by sparsely populated zones including the almost entirely uninhabited valleys of the Bandama, Bou, Nzi, Como6, and Black Volta rivers. The central part of the country as well as some parts of the forest and coastal belts are much more densely populated. The patchy distribution pattern is definitely related to the locatlon of the various ethnic groups, but this does not explain why most of the valleys of the northern gulnean savanna zone have been abandoned.
In Upper Volta (Fig. 12), the high population densities of the central and northern parts of the Mossi plateau are explained by the political stability of the Mossi empire over the centuries. However, in the most heavily populated sectors including Ouagadougou, Yako, llaya and Ouahigouya, the population density reached a critical stage many years ago. Ttre inherently low so1I fertility, the erratic ralnfall, and the impossibility of allowing adequate fallow periods in the present- day agricultural pattern have resulted in serious food deficits and crop production has fa11en well below the minimum subsistence needs of the population. Consequently, both temporary and permanent emigration, which began a long time ago, are now proceeding at an ever lncreasing pace. Similar situations, but in more restricted areas, are also encountered in the valleys of the Bougouriba, and Black, Red and White Vo1tas. There, the situation is even more striking as entirely uninhabited fertile valleys are sj.tuated 1n the immediate vicinity of overpopulated eroded plateaux. -11 -
In Dahomey and Togo sone very densely populated areas are interrningled with almost empty ones. The main population concentrations are in the Dapango and Lama-llata areas in Togo and the Tangui6ta, Natitingou, and Boukomb6 areas in Dahoney. By comparison, many parts of the northern-central zone of Togo and most of central and northern Dahomey are very sparsely poputated or uninhabited, especially in the alluviaI valleys of the main rivers, the few foci of population being concentrated on the plateau and on rocky hill slopes where the soil fertility varies between medium and poor and erosion is a rnajor problem. On the other hand, the southern third of Togo and the southern fifth of Dahomey are very densely populated (F,ig. 9).
In southern MaIi the overpopulated areas are not as conspicuous as in the above-rnentloned countries but the abandonment of nost of the large val1eys, especially those of the Baou16, Bago6, and Banifing rivers, is nevertheless quite noticeable while relatively dense populations occur further north in areas with a lower and very uneven rainfall.
In southern Niger the population is relatively dense as most of the country is subdesertic. However, some parts of the extreme south along the valleys of the M6krou and La Tapoa are so sparsely inhabited that they have been transformed into a national game park, while other areas could support a much blgger population. This uneven utllization of the southernmost areas of Niger is of importance in view of the severe droughts that periodically affect the country and hinder agricultural and ranching development in many densely populated areas further north.
Ethnic groups and migratory movements
In the Volta River basin and the surroundi.ng region, the major ethnic groups belong to the Mande and Voltaic families, while Fulani are scattered through the programme area and representatives of the Hausa family are not uncommon in the north-eastern part of the area. other smaller unrelated groups are encountered in parts of northern Dahomey, Ghana, and Togo.
Among the main Mande family groups are the Bambara of MaIi, the Mali-nk6 of MaIi and the Ivory Coast, the Bwaba of Upper Volta and MaIi, and the Dioula of the Ivory Coast, Mali, and Upper Volta. To the Voltaic family belong the Bobo-Fing, the Mossi and the Gourmantch6 of Upper Volta, the Lobi of Upper volta, Ivory Coast and Ghana, the S6noufo of Ma1i, Ivory Coast and Upper Vo1ta, the Koulango of Ivory coast, as werl as the Manprusi and the Kusasi of Northern Ghana.
This brief perspective covers in fact a great variety of ethnic groups and sub- groups with different traditions and languages. T?re wide ranges of populatlon density can be partly explained by the fact that many of these groups in the past -L2- had few opporiunlties to increase in proportion to their needs the size of the zone they cultivate. However, traders of the Mande and Hausa families, and nomadic Fulani have always been widely scattered over the whole area. The recruj.tment of workers for the coffee, cocoa, and banana estates, or for the timber and mining cornpanies of the richer rain forest be1t, also j-nduced large populatlon movements. during the flrst half of this century, and this trend 1s gaining increasing importance as a result of urbanization and industrialization, the greatest movements being from the rural areas to the cities and from the savanna areas towards the coastal belt.
Furthermore, for nearly 25 years individual migrations have also taken place from the overpopulated plateaux to the underpopulated valleys, either in the same area or sometimes hr-rndreds of kilometres away, even in a neighbouring country. Many etbnic groups are involved in these colonization movements, but the most active of the migrants belong to the Mossi group of central Upper Volta whose menbers in some areas are already more numerous where they settle than the traditional owners of the land. Another j-mportant migration movement involves the Malink6 and Bambara of southern Mali who leave their country for the rvory coast.
The economy of West Africa
In principle the whole of West Africa stilI lives under a subsistence economy except i-n sma11 isolated zones si-tuated principally at the ports. The structure of the active population, with more than 80% employed in agriculture, strongly reflects the characteristlcs of under-development as does also the low per capita level of income. Agricultural production
The usual- distinction between agricultural production for sale and subsistence agriculture is more and more difficult to make in the northern zone of the programme area. In effect, this zone, in which the cultivation of cereals is the most important form of subsistence agriculture, has two different marketing systems: - the marketing of food crops for locaI consumption I distances for transport are short and carriage is not expensive, and in some areas of the zone the quantity of produce marketed IocaIIy is increasing; - the narketing of produce outside the locality requiring commercial organizations such as "Compagnie franqaise pour 1e D6veloppement des Fibres 1 textiles"- (CFDT) for cotton, and similar ones for groundnuts and rice.
I F"en"h Company for the Development of Textile Fibres.
t. - 13 -
It is therefore preferable to distinguish between these two methods of marketing instead of agricultural production for sale and subsistence agriculture, otherwise the importance of the traditional markets will be overlooked.
The sudanian part of the zone has certain homogeneous characteristics including a predominance of cereal crops with a short marketing chain and 1ow cash income potentral. While this is the overall situation j.n the zone, it is possible to distinguish between the eastern and western parts of the sudanian zone, the limit being the 4"15'west line of longitude passing through Bobo-Dioulasso in Upper Vo1ta. The zone to the qest is better watered than that to the east and has a denser network of permanent watercourses. As a result, the agriculturat economy in the western zone is based on crops with a longer marketing chainl that is, more crops of cotton, rice and groundnuts are grown. Cash crops, especially rice and cotton (sponsored by the CFDT), are being produeed in greatly increasing quantities in northern Ghana.
In the sudanian zone and up to approxinately the 4OO mm isohyet of the sahelian zone, millet and sorghum are the main subsistence crops. The transition from the mixed curtural systems (miIlet and sorghum mixtures) of the arid regions to the root crops of the wetter zones starts in this region. Here, traditionally, natural fallows are employed and are of long duration. Rice cultivation occurs sporadically in-the region near the rivers. Itre highest 1evel of agriculture in the progranme area is found in the western part of this zone. High yields, the use of organi.c fertitizer, and the integration of animal husbandry are common, and the most impor- tant food crops are cassava, yams, and maize.
By contrast, in the eastern zone food crops predominate and there is a short marketing chain, a high poputation density, and an unbalanced agrlculture. The main characteristics of the agriculture are that the soils are degraded and of low inherent fertility. There is a shortage of water, and the population is concentrated in densely populated areas. However, in the interior of the zone large areas are often found where the soils are superior, the population density very 1ow or the area uninhabited, and, superficially at least, the water resources better. These areas emphasize the differences between the valleys and the plateaux.
A number of large development projects have been started in an attempt to correct this imbalance between the vatleys and the plateaux through the development of new land (the Red and l{trite Volta scheme in Upper Volta), the introduction of new crops such as sugar cane (at Ferkess6dougou in the Ivory Coast, for example), large-scale production of rice (as in northern Ghana), or the improvement and -14- intensification of agricultural methods (the Atakora project in Dahomey). However, there are many diffi.culties, one of which is the high prevafence of disease in the development zones.
Animal husbandry
In the sudanian and sahelian zones it is possible to distinguish three types of animal husbandry: the nomadic system, transhumance, and livestock rearing by the village farmers.
There is considerable scope for increasing animal and milk production and there is no doubt that more intensive livestock systems integrate well with cropping and also improve the productlvity of the 1and. However, in addition to the control of diseases such as trypanosomiasi-s, ri.nderpest and pleuropneumonia, watering points must be established and pasture rotation introduced if the livestock and meat industry is to be developed. Once these measures are applied the sahelian-sudanian zone will be able to provide a reservoir of protein within the project zone. A meat factory is already in operation at Bolgatanga. Fishing
A11 the development plans for the prograrnme area emphasi.ze the importance of fish as a source of protein. It is necessary, however, to point out that in the zone studied the movement of animal protein between the north and south is conditioned by two important factors: distance and the availability of money.
Anlmal protein in the form of meat from the north can be transported to the south and marketed there at an economic price whl1e fish from the south, being more difficult to transport, becomes too expenslve in the north. As a consequence, there is a considerable deficit of animal protein in the north. Although there is a large traditional fish market at Mopti it is too smatl to correct this deficit. Industry
By far the most important industries in the programme area are those processing agricultural products and they are very unequally distributed. The processing industry in the north of the area lies almost entirely in the west of the sudanian :zone (Ma1i, and the Bobo-Dioulasso area of Upper Volta) with limited activity at Ouagadougou (an abattoir and cotton gin) to the east. In the guinean zone processing industry is found mostly to the west in the triangle formed by Korhogo, Ferkess6dougou, and Niakaramandougou 1n the Ivory Coast and in northern Ghana. The present industrial zone of West Africa j-s prlmarily situated along the coast outside the programme area. - L,/LG -
TABLE 1. AREA AND POPUI,ATION COVERED BY THE PROGRAMME
Area Total Approximate Country area covered by Estimated total population (h2) the programme population in (km2) prograrrme area
Dahomey Ltz 620 56 000 2 770 000 (1) 547 000
Ghana 234 377 98 000 8 546 000 (3) I 600 000
Ivory Coast 333 270 110 000 5 100 000 (2) I OOO OOO
Mali I 204 000 125 000 s 3oo ooo (r) 1 400 000
Niger 1 187 000 17 000 4 000 000 (2) 90 000
Togo 56 600 18 000 1 e56 OOO (2) 555 000
Upper Volta 274 0@ 230 000 5 42L OOO (1) 4 900 000
Total 3 405 867 654 000 33 093 000 10 092 000
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GC- ltl ut ,i c{ E9 =E()ff ()<<(J 9a 3() ol4aE|{ CE =2 =E l^* l'' TOTBOUGOU GANSE IOUROU 1500 1500- 350 :.:w 300 ELACK VOLTA 300 VOL|A NOIRE 250 250 200 200 150 150 100 100 50 50 0 0 JF MAIlIJ JFI!!AI\4JJASOND F MA IUJ JASOND LAIIA. I(ARA KAt{DI 1 500 350 w 300 DIAMONGOU 250 250 250 m0 200 200 150 150 't50 100 'r00 100 50 50 50 0 0 0 JF l\,lAl\4JJ ASOND JFMAMJJASOND JFIlIAIlIJJASOND s lIIABABAKOKO FERIGSSEDOUGOU SAfIIANDENI 300 ELACK VOLTA VOLTA NOIRE 250 200 200 150 150 100 100 50 50 N nffi JT MAIl/!JJASOND JFMAI\4JJASOND - J F IVAMJJ ASOND DIOILA GOUALA SANSANNE. TANGO 1500 1250 1250 1000 1000 750 750 500 500 250 250 0 0 J FIlIAI\4JJASOND FI\4AI\4JJASOND JF[/lAI\IJJASOND AVEBAGE MONTHLY IIAIEBFLOIT OF SECTIONS OF SOXIE STREAUS AND BIVERS OF THE PROGRATIIIIIE ASEA CHARACTEBISTIC ru / S. 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O;>. \,t J .it - 'll -L7- CHAPTER II ONCXIOCERCIAS I S : PAMSITE AND DISEASE Onchocerciasis is a parasitic disease caused by the filarial (threadlike) worm Onchocerca volvulus and transmitted by species of blackfly belonging to the family Simuliidae. ?he disease occurs in Africa, the Yemen and in parts of Central and South America. There are about 20 nnillion infected people in the world, the largest endenic areas being located in tropical Africa, where they extend across the conti- nent from Senegal to Ethiopia in the north and from Angola to Tanzania in the south. The Volta River Basin is one of the worst endemic onchocerciasis zones in the world. Because the blackfly vector requires fast-flowing rivers and streams for breeding, the distribution of onchocerciasis is essentially focal, causing the greatest suffering among the people rvho inhabit the fertile river valteys, hence its common name 'rriver blindness". The parasite The worms pass through several different stages of development to complete their life cycle (Fig. 13). The adult worms, males and females, live mainly in the skin of the human host where they frequently form visible and palpable nodules (Fig. 14) in uhich one or more pairs of wor:urs are coiled (Figs 15 and 16). The female worm produces millions of embryos, or microfilariae, during its life span which may be as long as 15 years (Fig. 17). The microfilariae invade the skin, where no further development takes place until they either die in the course of about 30 months or are ingested by a biting blackfly. When a female fly bites an infected person, it may take up microfilariae which develop into infective larvae within six to seven days under the climatic conditions of the progranme area. When the fly takes a meal of human btood the infective larvae are liberated on the skin of the host, penetrate, and develop in the human host into mature male and female worms, thus completing the life cycle of the parasite Neither O. volvulus nor its most important African vector, Simulium damnosum, can be regarded as uniform species. The most important dissimilarities are found between endemic areas in Ehe African forest and savanna zones. These differences in the parasite-vector complex are reflected in certain variations of the frequency and nature of the clinical manifestations of onchocerciasis in these two contrasting ecological zones. From the public health point of view, ocular lesions are most important and these occur more frequently and in a more severe form in the savanna area in $&ich the Volta River Ebsin is located. -18- The disease The clinicat rnanifestations of onchocerciasis are manifold. Most of the severe fesions are due to reactions to the presence of the microfilariae (Fig. 1g). Whl1e in the early stages of onchocerciasis the adult worms produce no detectable reaction and are neither visible nor pa1pable, in long-standing infections a large proportr-on of the adult worms can be found in characteristic nodules. rn African patients most of the nodules are located around the hips, on the sides of the chest wall and around the knees. Head nodules are common in Central America, but rarely occur in the African form of onchocerciasis. The frequency and severity of the clinical manifestations caused by the micro- filariae are closely associated with the intensity of the infection which in turn depends on the cumulative effect of the many reinfections and super-infections a resident in an endemi-c area receives year after year. The most important types of clinical manifestations are unsightly and intensely pruritic skin rashes (Fig. 19), chronic skin manifestations such as elephant's skin (fig. 20), atrophy and depigmen_ (Fig. tation 21), hanging groins and hernia, and a variety of eye lesions that may culminate in blindness. Some heavily infected patients have microfilariae in their urine. Among the residents of hyperendemic areas, chronic weight losses are not uncommon, making onchocerciasis at times a wasting disease. Eye lesions and blindness are the most seri.ous consequences of onchocerciasis. In sma11 communities in hyperendemic areas, more than lO% of the totat population may be blinct. If the age-specific prevalence of blindness is studied in greater detail, it may be found that as much as 3O-5O% of the adult male population is incapacitated by toss of vision (Fj-g. 22). Microfilariae are believed to invade the eye from the adjacent skln. They can easlly be found in small biopsies taken from the conjunctiva. Microfilariae can also be seen frequently by careful examination with an eye bi-omicroscope, the so- called srit lamp. rnvasion of the cornea is very common. when they die, a eellular reaction occurs vtrich produces opacities around the body. The chronic character of the dj-sease, with the deaths of large nrmlbers of worms over the years, eventually leads to a chronic sclerosing keratitis. The lesions often begin at the periphery of the cornea at approximatety the 3 o'cIock and 9 o,clock positions and progress in a tongue-1ike fashion bilaterally until they cover the tower half of the cornea and eventually the entire cornea. This chronic sclerosing keratitis is a very cornmon cause of brindness in onchocerciasis (see Figs.23-26). In addition to the lesions in the anterior eye, microfilariae can also invade the deeper parts of the globe where their death may cause an inflammatory reaction -19- of the iris, ciliary body, retina and choroid. The vitreous body and the lens may also become involved with clouding of the former and secondary cataracts i.n the latter. Alone and in combination, these disease processes may lead to various degrees of visual impairment and eventually to blindness in one or both eyes. Ttre diagnosis of onchocerciasis can be made by three nethods. The first, and historically the oldest, is the search for the characteristic nodules produced by the adult worms. T'l:ris method is nevertheless relatively insensitive because nodules are absent in the early stages of infection and may be too small or deep seated to allow detection by inspection and palpation even in the more advanced stages (Fig. 27). Ttre second and at present the most reliable diagnostic method depends on the demon- stration of microf.ilariae in the skin. The generally accepted technique is the skin snip. A tiny, superficial skin biopsy weighing not more than 1 rnilligran is taken with the help of a special punch with a cutting width of about 2 millimetres. This safe and fast nethod causes Iittle inconvenience to the patients and has proved to be of great value in mass examinations. The microfilariae emerging from the skin snip are easily recognizable under the 1ow power of a microscope; and the microfilarial density can be estimated by countlng their numbers (Fig. 28). In cases where onchocerciasis is suspected, but where either the characteristic clinical manifestations are absent or where microfilariae in the skin are too scanty to be revealed by a skin snip, an indirect tentative diagnosis can be nade by a third method (the Mazzotti test). After the ingestion of 50 milligrams of the micro- filaricidat drug diethylcarbamazine, which kills the larval worms, the inapparent infection may become overt by the development of itching skin reactions at the sites where microfilariae are present in low nr.mbers. The control of the parasite Two drugs are available for the treatment of onchocerciasis patients. The first is suralnin, a very effective macrofilaricide that kills the adult worms and has also some effect on the microfilariae. T?re second is diethylcarbamazj-ne which is a highly effective microfilaricide but has almost no effect on the adult worms. Both drugs can be recommended for individual treatment under the supervi-sion of an experienced physician. The toxic and allergic reactions they may produce in infected persons prevent their use in mass treatment campaigns. In view of the magnitude of the public health probletn caused by onchocerciasis and the inadequacies of the drugs now available for use against this disease, there is a pressing demand for new therapeutic agents suitable for use in mass treatment and prophylaxis. The current status of the chemotherapy of onchocerciasis is reviewed in Annex II-1. _20_ Surgical removal of the nodules harbouring the adult qrorms (denodulization, nodulectomy) may be a useful measure in indivldual patients, especially in those with head nodules. However, as it can rarely be expected that all adult worms are encapsulated in palpable nodules, the usual effect of denodulization is only a $uppressive one. Mass nodulectomy campaigns have been carried out in Guatemala and Mexico. Although these campaigns have undoubtedly reduced the prevalence of $evere ocular lesions, the method alone is considered inadequate as a means of lowering transmission rates in endemic areas because of the presence of many hidden and non-encapsulated worms. Oncfioce rco ,ol"ulus Adults rn subcutaneous ttssue Mrcrofrlarrae iFsous - cutan6s Adultes dans les ttssus Mrcrofrlarres / Subcutaneous tissue Tr ssus sous ' cutan6s / II I Enters skrn throuqh"au flv btte wound Traverse la peau ir'eu de Prqure Homo saprens lnfectrve staoe Microfrlarra in skir n Stade rnfectait Microftlatre der mr que Mrorates to head and oroboscrs Mi[re ftvers la tAte et [e proboscrs Penetrates stomach wall \ ( Sr mul r um Traverse la parot stomaca le (z-z;* - '-.'.;j 3rd staqe larva / stade Thoracrc muscles ."'x3-e Muscles, thoraciques 1st staqe larva ( 'formeiaucrssesausaoe form ) Larve 1"er stade ( ) €*.7 LIFE CYCLE 0F gNqHocERCA VoLVqLUS FIGURE; 13 CYCLE DE DEV ELOPPEMENT D' ONC HOCERQI\]IOIV U-LUS $ PATlENTtIlTHLABGEN0DULEcoNTAlNlNGNUMERoUSPA|RSoFADULT@(PHoToGBAPH.wHo) MALADE AVEC UN GROS NODULE CONTENANT DE NOMBREUI( COUPLES D'OruCNOCENCA VOLVU (PHOTOGRAPHIE,OMS) FIGURE:14 Cross-section of a nodule with coiled adult worms (scale in mm ) (photomicro- graph no 72-45008, AFIP ) Section transversale d'un nodule, avec vers adultes enchevetr6s ( 6chelle en mm ) FIGURE : 15 ( microphotographie n0 72-45008, AFIP ) 1 Dr. D. Connor; Armed Forces lnstitute of Pathology, Washington, D.C. Entanglement of male and female onchocerca volvulus digested out a nodule (scale in mm. ). Female worms are about 23-70 cm in length and between 27s"32s microns in width. The males are approximately 2.5 cm in length and 130-'150 microns in width ( photomicrograph n0 69-9753, AFIP ) Enchevetrement de m6les et de femelles d'Onchocerca volvulus obtenu par digestion FIGURE : 16 d'unnodule(6chelleenmm).Lesfemelleffimdelonget6ntre 275 et 325 microns de diam6tre. Les m0les ont environ 2.5 cm de long et 130 i 150 microns de diambtre ( microphotographie n0 69-9753, AFIP ) 1 Dr. D. Connor, Armed Force lnstitute of Pathology, Washington; D.C. t ;-- j*- iz. *7 :lI t'\ ril, -l l*-i it! NPHOTOMICROGRAPH OF A CROSS.SECTION OF A NODULE WITH A FEiIIALE ONCHOCERCA VOLVULUS SHOIIING THE UTERUS IYITH EIIIERYOS OF FILARIAE AT DIFFERENT SIAGES OF DEVELOPMENT (Dr. A.A. BUCK,JHU , r____== -'- ll,llcRoPHoToGRAPHlE D'UNE SECTI0N TRANSVERSALE D'UN NODULE AVEC UNE FEMELLE D'ONCHOCERCA VOLVULU! DONT L'UTERUS CONTTENT DES EMBRYONS DE FILAIRES A DTFFERENTS sTAoEs DE DEvELoppEMENT (Dr. A.A. BUCK,JHUII .tt High-power photomicrograph showing the long clear spaco (1&,15 microns) at the tail end with elongated terminal nuclei in a single row. These features are diagnostic of O.volvulus.The microfilariae msasure apppximately 300- 320 microns in length (photomicrograph n0 71-10072.AFlPI) Micrographie i fort grossissement,montrant le long dspaco clair (10.15 microns) situ6 i !'extr&nit6 caudale avec les noyaux terminaux allong6s dispos6s en une seul e rang 6e. Ces caract6ri st i ques permettent d' identif i er Les micro filaires mesurent environ $&320 microns de long (mi no 71. 10072,AHP11 oircHocEncA volvutus mcRoFtLA$A FIGUXE: 18 TICROFILAIRE D'ONCHOCENCA VOTVULUS I II.YEAR-OLD BOY UTITH SEVERE DERMATITIS CHARACTERIZED BY TTRI NIGI NG,THI CKENI NG,PAPULES AND DEPIGMENTATION OF THE SKIN ( Photograph n0 68-7912,AFlPl GARCON DE 11 ANS AVEC UNE DERITJIATITE ONCHOCEROUIENNE SEVERE CA RACTERI SEE PAR LE PI. I SSEMENT,L' EPA ISSI SSETUIENT ETi LA DEPIGMENTATION DE LA PEAU ET PAR LA PRESENCE DE PA. PULES (Photosraphie no 68'7912.AF|Pr) FIGURE: 19 1 Dr. D Connor , Armed Forces lnstitute of Pathology,Washington,D.C. tIlTH ADVANCED ONCHOCERCIASIS OF THE SKtN (PHOTOGRAPH No 72-4500C,AFtpr) PACHYDERIIIIE DU GENOU DROIT,AVEC NODULE SATLLANT,CHEZ UN HOIiME AGE DE 35 ANS PRESENTANT UI'IE ONCHOCERCOSE CUTANEE EVOLUEE (PHOTOGRAPHIE NO 72.45OOC,AFIP1) FIGUBE:20 ,1 SEVERE URINKLING AND DEPIGMENTATION OF THE IflEES IN A 3().VEAR.OLD PATIENT IIITH ADVANCED oNCHOCERCIAS|S 0F THE SK|N (N0. 6&10074,AFtp)* PLISSEMENT ET DEPIGMENTATION ACCUSES DE LA PEAU DES GENOUX CHEZ UN IUIALADE AGE DE 30 ANS PRESENTANT UNE ONCHOCERCOSE CUTANEE EVOLUEE (N0.6-8.1OO74,AFIP}* *Dr. D. Connor,Armed Forces lnstitute of Pathology,Washington,D.C" FIGURE: 21 I "( Blindness . 3/60 or 202400 in the better eye ffi C6cite <3/60 ou 20t400 dans le mr.lrlleur oerl Severely impaired vision < 6t60 or 20r200 rn the better eye fll]ilffiilIl Perte de vision grave 6260 ou 20r200 rlans le meillerir oeil lmpaired vision < 6/ 18 or 20t70 rn the better eye E Perte de vision <6/18 ou 20170 dans le meilleur oeil Prevalence of Q-qo_!ydus infection on the basis of skin biopsies Pr6valance de I onchocercose d apes I examen des bropsies dermrques Number in age group ( ) Nombre dans le qroupe d age (t3r) A9e r n yrart Age en ann6es AGE SPECIFIC PREVATENCE OF INFECTION. BLINDNESS AND TIIO CATEGORIES OF IMPA]RED VISION IN THREE VILLAGES ( BUJAN POPULATION 443; NAKONG POPULATION 221: BASIASAN POPULATION 140 ) lN AN AREA 0F HYPERENDEMIC ONCHOCERCTASTS tN THFVALLEY OF THE SISSILI RIVER PREVALENCE DE L INFECIION.DE tA CECIIE ET DE DEUX CAIEGORIES DE PERIE DE V]SION PAR GROUPE D AGE DANS TROIS VILLAGES ( BUJAN.443 HABITANTST NAKONG 221 HABITANIS: BASIASAN. 140 HABITANTS ) DANS UNE ZONE D ONCHOCERCOSE HYPERENDEMIOUE DE LA VALLEE DE LA SISSILI ",!7.2'+ FIGURE 23. 'SNOW STORM OPACITY' AT THE 9 O'CLOCK FIGURE 24. ADVANCING OCULAR ONCHOCERCIASIS, POSITION. EARLY STAGE OF OCULAR ONCHOCERCIASIS ' TONGUE-LIKE OPACITIES PROGRESSING TOWARDS THE ( OPACITE EN TEMPETE DE NEIGE I A LA POSITION 9 HEURES. CENTRE OF THE CORNEA ! STADE PRECOCE DE L'ONCHOCERCOSE OCULAIRE t ONCHOCERCOSE OCULAIRE EVOLUTIVE, OPACITES LIN- GUIFORMES PROGRESSANT VERS LE CENTRE DE LA CORNEE t FIGURE 25. ADVANCED OCULAR ONCHOCERCIASIS. FIGURE 26. FINAL STAGE OF OCULAR ONCHOCERCIASIS SCLEROSING KERATITIS HAS PROGRESSED TO INVOLVE WITH BLINDNESS DUE TO TOTAL OPACIFICATIOI{ OF THE THE ENTIRE LOWER HALF OF THE CORNEAI CORNEA I ONCHOCEFCOSE OCULAIRE EVOLUEE. 1.A KTRATITE STADE FINAL DE L'ONCHOCERCOSE OCULAIRE, AVEC SCLEROSANTE AFFECTE TOUTE LA MOITI€ INFERIEURE CECITE CAUSEE PAR L'oPACIFICATIoN ToTALE DE LA OE LA CORNEEI CORN€E I r D' A, A. Buck. Thc Johne Hopkinc University, Bsltimora, Marylend, USA. 80r1 6 870 ! '6 q ;60 o o E '6 I .EE50 E .= ;o .; E Eot0 I o o e d .Eo ,30 E -9 o i o o c ga@ o o o G L Percentage with nodulos Pourcontags des portours de nodules (COIBIIED POPULATIOII:13'1r3} ADJUSTXEITT IIODUI"E |rTO Snrr SNtp * BASED Ot{ RESULTS FmX il VILLAGES ltl TIG PR(EnAIIE AnEA I -.^..* pioRrEURs DERtlouEs BASEE rtuurc ; -zr ABAOUE DE COnfiELATIOII ETIIRE LA FREOT EIICE DES DE IIODU]ES EI CELE DES PomEUBS DE tlcnoFlulnEs I (PoPULATlot{ 13,113 HABITAITTS} i[n rrs oo-senvlnoirs FATIES olus li vir-r.lces Ix LA REGlot DU PmcRAtffi ToIAIE: .l 1 Dr. D. Connor,Armed Forces lnstitute of Pathology,llashington,D.C. I OF mcmfl mmAE OF OilGltOcEilC4 VO+W|-U,S, lPtptomisrosra[h lro z€07,AFtP ] iilCMPHOTOGNAPIIIE A FAIBIE G! TIONTRAilT UN GNAND ilOMRE DE (ticrophotographie n0 7&507.AFlPt ) FIGUE:28 :-.- ,.:,;j- J -.' A1!Il''' I _ -2r- CHAPTER III oNCHOCERCIASIS: VECTORS AND TRANSMISSION The vector: distribution and biologyl As stated in Chapter II, onchoeerciasis is transmitted by small blood-sucking flies of the Simuliidae family. In West Africa aII vectors of this disease belong to the Simutium damnosum complex2 of which seven forms are at present known in the Volta River basin area (Fig. 29). The northern limit of S. damnosum distribution in this area is latitude 15'N, while the southern limlt follows the edge of the coastal plain or, in its absence, the Atlantic coast. The females of S. damnosum lay their eggs in batches of about 25O at water- 1evel or up to 50 mm belos' the surface on partially submerged supports in fast- flowing (current speed of 50 to 2OO cmF) rivers and their large tributaries (Figs 30-32). Various types of support are used including tree branches, plants and rocks. The eggs hatch in 36-48 hours after laying and the young larvae immediately move down to the submerged part of the support. They mav also drift downstream and colonize completely immersed supports. These larvae (Fig. 33), whi-ch generally inhabit the upper 50 cm of the riverrs surface water, feed by filtering organicandotherparticIescarriedbythecurrent.Inthisrespect'@i= a fairly demanding species and will only inhabit those parts of the watercourse with a relatively high content of suspended nutritive particles. Under the prevailing conditions in the Volta River region the larval life-cycle lasts for some eight to ten days. At the end of this period the larvae moult into pupae after surrounding themselves with a cocoon attached to a submerged support. The pupae (Fig. 34) neither nove nor feed and this stage lasts about three days. The adults emerge from the pupae in an air bubble and take flight as soon as they reach the surface of the water. The males of S. damnosum feed exclusively on plant juices and thus play no role in the transmission of onchocerciasis. The females mate once in their life within a few hours of their emergence. The new-born females also feed on plant juices before taking a blood meal, usually the day after their emergence. At each blood meal they absorb about one milligram of blood, which exceeds the weight of the unfed S. damnosum female (Fig. 35). Each blood meal is followed by the maturation of the 1 - The distribution and biology of the vector in the Volta River basin area are described in greater detail in Annex III-1. 2 For the purpose of simplicity the S. damnosum complex is referred to under the collective term S. damnosum throughout this report. eggs to be laid three to flve days later and each laying is followed within 24 hours by a new blood meal. These cycles continue in the same way until the death of the female, whose life-span varies widely depending on environmental conditions. It has been estimated that, of lOO females taking their first blood meal, the number still surviving nine days later will be three in the forest area of the southern Ivory Coast as agai-nst 33 in the guinean savanna of southern Upper yolta, and 42 in the dry sudanian savanna in the centre of the country. The daily activity of S. damnosum females may be slowed down or stopped by tomperatures that are low (under 17") or too high (over 3O.C) as weII as by other unfavourable meteorological factors (strong winds, rain).] tne females bite outdoors from dawn till dusk and are particularty active in cloudj weather or in shady places. In the Volta River basin area the S. damnosum females trarle a marked preference for man, although they may feed on a number of other vertebr{tes, particularly in unin- habited areas. They bite not far from ground level ana { standing subject receives nearly 95% of the bites below the knee. The bite is not always noticed when received but it soon itches. When the females are numerous they (onstitute a major nuisance, quite apart from their vector potential, and may make worfk clifficult or impossible wtthout suitabl-e individual protection. In the Volta River basin area many watercourses onl flow during the rainy soason and at the beginning of the dry season, thus the istribution of S. damnosum varies considerably according to the season (Figs 36 and 37). Three main types of seasonal variations of S. damno populations have been observed (Fig. 38): (a) synchronic variation, when the ce of the vector i-s positively correlated with the water flowl (b) lnverse ariation, wi-th S. damnosum i occurring mostly, or only, during the dry seasoni (c) U modal variation, **" ,* periods vector is only abundant during of maximum and mi imum river flow. To each I water 1eveI and rate of flow of a river correspond preci e locations of the S. damnosui breeding places. Preliminary entornological surveys rela t" hydrological data thus allow accurate planning of S. damnosum control operation :O -t I Little is known so far about the adult resting pla s except just after emer- I gence or a short while before laying, when the unfed and gravid females are sometimes found in large numbers on vegetation near the larval si s. The females may travel I great when distances climatic conditions and vegetation )ver are favourable. Their i active dispersion may occur very rapidly over a distance rf up to 40 km around the I larval breeding sites throughout the year in rain forest lountry, and during the rainy season in the savanna. On the other hand, in the ry season in the savanna, S. damnosum adults remain in the i.mmediate vicinity of larval breeding sites, -23_ going further only where gallery forests afford cover (Figs 3g and 40). S. damnosum females may also travel di.stances of up to 15O km and more with favourable air currents especially those occuming with the shift of the intertropical front from the coast towards the interior at the beginning of each rainy season. These long flights ensure the annual repopulation of S. damnosum's temporary 1arval breeding sites in the savanna, when the watercourses flow again. Onchocerciasis transmission When the S. damnosum female bites a person infected with onchocerci.asis it absorbs dermal microfilariae at the same time as its blood mea1. Some of the ingested microfilariae succeed in passing through the flyrs stomach wall and penetrating its thoracic muscles, while others are digested along with the btood. Under the climatic conditions of the programme area the microfilariae that enter the thoracic muscles develop (Figs 4I and, 42) in six to seven days into infective larvae uhich may be deposited on the skin of the person bitten by a female blackfly during a subsequent blood meal. Some of the infective larvae will penetrate the body through the skin lesion made by the bite and develop into adult worms within a few months. Owing to a tack of synchronization between S. damnosum,s ovarian cycle and the larvaI development cycle of O. volvulus in the vector, the female flies can only transmit the parasite at the second and subsequent blood meals following that taken from an infected person. Therefore, if the first meal nas taken from an infected person transmi-ssion will only be possible at the third blood meal eight to ten days later. The relationship between parasite and vector varies according to the strain (or perhaps species). The savanna populations of S. damnosum are very tolerant of parasitism by o. volvulus larvae, but they are generarly mirdly infected (on average scarcely more than trrro infective 1arvae per infected female), whereas in the forest areas S. damnosum females may succumb to heavy parasitism, being often more severely infected (an average of about five infective larvae per infected female). The observed leve1 of parasitism does not seem to affect appreciably the dispersion and effective flight range of S. damnosum females. However, long-range active dls- persion involves mostly young nutliparous females, thus the numbers of o1d infective females, and consequentty transmission of O. volvulus to man, decrease rapidly as distance from breeding sites increases, especialry in the savanna zone. In the course of investigations on the chenotherapy of onchocerciasi-s, it has been noticed that the dermal microfilariae persisting after treatment with diethyl- carbamazine remain infective for Simulir.rm. The females can even be infected when the dennal microfilariae are so few as to be undetected during ordinary parasito- logical surveys. The development of automatic sampling procedures for adult S. damnosum popula- tions has not yet been successful, but thefemale'santhropophilic habit is exploited during field investigations on vector distribution and abundance and on the trans- mission of O. volvulus. Ttre surveys are made with f1y collectors who act as bait, catohing all the specimens that come to bite during a given time, wtrich, for epidemiological studies, is usually from 6 a.m. to 6 p.m. The results are expressed in bites p"r rarrr/d"y, in infective bites p", ot even in the theoretical ^^n/d^yt number of infective larvae deposited on man per year. S. damnosum, because it is anthropophilic and often has a long tife-span, is a very effective vector of onchocerciasis. Several hundreds to several thousands of infective bites p", have frequently ^unfy"ar been recorded during studies carried out in West African foci of endemic onchocerciasis. The interruption of transmission thus cal1s for the almost complete elimination of the vector and not just a simple reduction in its poputation size. Vector control 1 S. damnosum is attacked by a number of predators, parasites and pathogens. The larval and the pupal stages are very susceptible to sharp variations in rj.ver Ievel, since they are unable to tolerate for more than a few hours either dryness or submersion in deep water. Ttrese natural controlling forces 1ie behind the seasonal fluctuations of S. damnostun populations. Ttre use of Mermithidae parasites for controlling the vector is under study but it will probably be many years before this method becomes operational. Ttrese parasites usually affect only a certain proportion of the Simutium population and the anticipated degree of control would not be sufficient for the attack phase of the Onchocerciasis Control programme. If successful, however, this method could constitute a useful adjunct to maintenance measures. Because of their ecological requirements (food, current, immersed supports) S. damnosum Iarvae occupy restricted stretches of certain rivers and are plentiful in a limited number of sites. The mechanical destruction of these ma.jor larval breeding sites has been considered. The simplest solution would be the construction of dams downstream to transforrn fast flowing waters into still reservoirs. This method, while effective, is costly and can only be considered where a dam in itself is economically justified. It must also be remembered that each darn spillway may 1 The teehnical problems related to the control of S. damnosum in the Volta River Basin are described in greater detail in Annexes ITI-2, III-3 and III-4. - zs/ze - provide an excellent S. damnosum breeding site unless properly designed. The vector distribution has already been considerably expanded by a series of snall dams set up to meet farming and ranching needs; these have generated far more breeding places than they have destroyed. On the other hand, large dams destroy many more S. damnosum breeding sites than they give rise to while the large water reservoirs thus created might constitute a major obstacle to the dispersion of the fIv. The use of lnsecticides is at present, therefore, the only practicable means of controlling S. damnosun. Control of the adults night be possible, but would be difficult owing to their rapid dispersal over vast areas. Larval control is relatively easier and more effective since the breeding sites are restri-cted to certain areas. The application of insecticides upstream from the breeding sites to be destroyed enables the toxic particles to be carried by the current to the larvae which absorb them in filtering their food, thus ensuring a concentration of the toxicant within their body. Owing to these characteristics, Simulium larvae are much more susceptible tc insecticides than the great majority of other aquatic organisms, and their selective destruction is possible. The development of larvi- cide formulations that will remain in the upper layer of water also means that the toxicant can be concentrated in that part of the river wtrere S. damnosum larvae are to be found, increasing further the selective aspect of the treatment. So far the campaigns undertaken against S. damnosum in different parts of West Africa have been based on the use of DDT, weekly applications giving the best results. To avoid all risk of long-term environmental contamination, DDT is now being replaced by biodegradable insectj-cides that disappear spontaneously from the treated areas a few weeks after application. These new compounds, wttich are not toxic for man in routine use, have also been selected for their lack of acute toxicity at the concentrations that give effective control of the vector,l fot.ro.r- target fresh-water organisms, particularly fish and their natural food-chain. T?rus the elimination of S. damnosum larvae need not have far-reaching effects on the biological equilibriuur of the hydrographic network of the Volta River basin area, and will not interfere with the productivity of the Volta and Kossou lakes. The quantities used for controlling S. damnosum are, moreover, minimal, since the highest concentrations to be used are of O.1 mg per titre during 10 minutes, once a week. This corresponds to an average concentration in the water of the treated rivers of some O.l mg per cubic metre of water. 1 s"" Annex III-3. ! t 0f ( 1 i l o5 I I I otu =EEE d= =i-fa $ H! ,'-.-- ') H= i ;H I EE i v--6 I -B I OT= I e! sE I uo I it.\oiv i'l - I '2 i 5# z) (.ti OP I Ea? i EA I o= t L_tr tt \i ./' =E / =fl a\ 1* E 5=5.& l BO< . a-E: ra<*=.;3b- I FIGURES 30 .37 SIMULIUIUI DAMt\lOSt M EGG MASSES ( photognph Onchocerciasis Section. OCCGE, Bouak6 ) MASSES D'OEUFS DE SlMULlUltJl DAMNOSUM (photogmphie Seaion Onchocercose,OCCGE, Bouak6 ) SIMULIUM DAMM)SUM LAFVAE ( photognph Onchocerciasis Section, OGCGE, Bouak6 ) LARI/ES DE IIWUU'JI-QAUIQEUU ( photographie Section Onchocercose. OCCGE, Bouak6 ) llt'Jlt L|UM DAMI\IOSUIU PUPAE I plntograph Orchocerciasis Section. OCCGE, Bouak6 ] NYttfl{ES tr !!MU!!UU !A!l!!QSuU ( plplosmphie Section Orchocercose, OCCGE. Bouak6 ) FIGURES 33 .34 ";ai ' l\: - UTIFED AIID ttOOD.FED $Ilt tluli DAttU8Ut FEilALES I rcato in mrn I ( photognph, f,. D. Gomot, AFIP, lishingtou-Dt I FETEII"ES DE A .EUttl EI q)mEE { achelle m mm } ( photogrephie, t. D. Gonnor, I Flolfr: ti ! _i.-L< r ;'fdeiI,.: t {rL.'-\ ,L-;. .a ..4 t ..\ or '1 \ tlJ 7 .r'".r-.1 cc a ) ,'t a I ...... -..j' ti t L at a f iilil Horrzontal lrnes show the wrdth of the ilver dunng the dry and the ratny season respecttvely, whtle the black areas on the left represent schematrcally the seasonal vanatlons of the vector abundance accordrng to the water level. Les lrgnes hortzontales Indrquent la largeur de la rrvrlre pendant respecttvement la sarson sdche et la satson des plutes tandts que les zones norres sur la gauche repr6sentent sch6ma - trquement les vanatlons satsonntdres de l'abondance du vecteur en fonctron du nrveau de I eau. MAIN TYPES OF SEASOiIIAL VARIATIONS OF SIUULIII'I-OAUNOSIJI ABUNDANCE IN ITS BREEDING PTACES OF THt VOLTA RIVER BAS]N AEA PRINCIPAUX TYPES DE VARIATIONS SAISONNIERES DE L'ABONDANCE DE SIMULIUIII DAMNOSUM DANS SES GITES LARVAIRES DE LA REGION DU BASSIN DE LA VOLTA RAINY SEASON DRY SEASON SAISON DES PLUIES SAISON SECHE o .C C) a/a) Po, ;o (,E(Dr C, U) * o.r LOE od VI 9o )-h.E u>=G-- E(, frn 3E L- o->1= 6==6 9x aa Aa f,o UJr.tJ tso; #r "E E(9 -c_ il zz.oo lv \-. E0) e=A- Lo- c((D (oo Elr scHEtIlATlc DISPERSIoN 0F SIUUUUU DAUNQ$Uilr FEMALES FROM THETR LARVAL BREEDTNG PLACES tN THE THREE MAIN ECOLOGICAL ZONES OF WEST AFRICA DURING IHE DRY AND IHE RAINY SEASONS REPRESENTATTON SCHEMATTOUE DE LA DTSPERSTON DES FEMELLES DE S!MUL_!rJU lArrlU9lUU DEpUtS LEURS GITES LABVA!RESDANS LES TROIS PRINCIPALES ZONES ECOLOGIOUES D'AFRIOUE OCCIDENIALE" PENDANT LA SAISON DES PLUIES ET LA SAISON SECHE A B /: /; .t .e {o> .MONDON Lobr Brtrlqe Ponr de la Lobr H D_ Breedrng places qltes laruarres NIERIIIC: Drspergron area Zone de drspersron o.------l9L' RAINY SEASON DRY SEASON SAISON DES PLUIES SAISON SECHE OESERVED DISPERS]ON OF SIMULIUM DAMNOSUIU FEMALES FROii THEIR IARVAL BREEDlNG PLACES IN THE GUINEAN SAVANNA ZONE OF SOUTH-WESTERN UPPER VOLTA DURING THE DRY AND THE RA]NY SEASONS DI8PERSION OBSEBVEE DES FEMELLES DE SIMULIUM DAUNOSUTTI A PABTIB DE LEURS GITES LABVAIRES DANS LA ZONE DE SAVANE GU]NEENNE DU SUD.OUEST DE LA HAUTE.VOLTA" EN SAISON SECHE EI EN SAISON DES PtUtES FIGURE : 40 F l_ (_, {t - FUSI ltUSIAn LAn A ( " snrsaso hm ) (F ONCrcCmA \rOLVU-tE lN TIC IHIAOC ru9ct-S S SmttLm DAilUEIJil ( photonicrograph ffi.8orCd ) -saucisse LA8VE mE SIATE ( tomp ") D'OilGIOCERCA VOwU.IS DAtlS t^ES nECtES III)f,A- CI(UE IE $mIJtIl DAfit)Stil ( microdntogrsphie, Section Onchoceoso, OCCGE, Bodd ) THIRD lttlslAn LAnvAE ( inlsctive lom l tr OilCllOcffiA V(f,VlLtE lI{ Tlf BODY CAVIIV 0F Slfr.ltl[ DAt(Etfl ( plrtooicrograph, 0ncbcsrciasis Sectim,OCCGE, Bornld I l181,ESImElffi SIAE ( lom inleaame l D'9NelPmA lCIJlLUq DAilS l,A CAVIIE eIE tLE f $nfltf, DAt(EUt ( ntffi, occcB Bopki I FIGURES 41 .42 -27 - CHAPTM IV EPIDEMIOLOGY OF ONCHOCERCIASIS AND SOCIO-ECONOMIC ASPECTS OF THE DISEASE Prevalence of onchocerciasis and blindness in the programme area Population samples Data from 24O7 poputation units in the programme area, comprising a total of 5 600 OOOpersons, were available for epiderniological analysis. With the exception of 224 units for which only total figures by "canton" have yet been collected, the remaining 2183 units were individual villages and towns in the prograrnme area. This large body of data was derived from previous surveys made by the various health services of the seven countries incLuded in the programme. In these surveys, population samples had not been selected on a random basis and the diagnostic methods employed in different countries were not ldentical. In view of these dissinilarities, all data had to be adjusted and homogenized by special standardization procedures to allow a uniform presentation and a meaningful analysis. Population samples included in the study are listed in Table 2 and descri.bed in more detail in Annexes IV-I and IV-2. Diagnostic criteria for onchocerciasis Most of the epidemiologicaL data were gathered between 1968 and L972 by different teams, for dissimilar purposes, and often with unlj.ke methods. The recognition of onchocerciasis in mass examinations was based on two main criteria, i.e. detection of the typical onchocercal nodules by inspection and palpation, and demonstration of microfilariae of Onchocerca volvulus in routinely taken biopsies as described previously. Of these methods, the former is, as stated in Chapter II, less sensitive than the latter because many persons with early or mild infections have no detectable nodules. Since most of the prevalence data on onchocerciasis in Upper Volta are based on the detection of nodules only, these estimates are too low and not directly comparable with those obtained from other surveys in which skin biopsies have been employed as the diagnostic method. Therefore, adjustments have been made using data from population samples in which each individual had been examined independently once for the presence of nodules and again for microfilariae in skin biopsies. The method employed for converting nodule prevalence to skin snip prevalence is described in greater detail in Annex IV-1. _28_ Some data from the Ivory Coast were based on yet another diagnostic method. In certain areas persons were first examined for the presence of nodules and those found negative were then screened for microfilariae in skin snips. If neither nodules nor microfilariae xrere present, the Mazzottj- test, as described in .'t 'lChapter II, was used to detect clinically inapparent infections. The prevalenc'ki-of onchocerciasis was then calculated by combining the percentages of positives from aIl three diagnostic tests. In comparison to the simple adjustment from nodul. to'dki., snip prevalence, which gives conservative estimates, the third indirect method' detects between 5-L5% more infections. These data had to be presented in thetr originar form. They involve onry 49?9, or o.16%, of the approximatery three million persons examined, resulting therefore in an insignificant overestimation of the overall results that were used to map the frequency and distribution of onchocerciasis in the programme area. For this presentation, levels of endemicity were classified according to four broad categories: O-g.g%: sporadic cases; 10-39.9%: low endemicity; 4O-69%t medium endemicity; and 70% or more: high endemicity. Diagnostic criteria for blindness I{ith few exceptions, the diagnosj-s of blindness or severe visual impairment was made by a small number of experienced ophthalmologists. Their limited participation j.n routine examinations conducted in the programme area is reflected by the considerably smaller ophthalmologieal coverage of the territory, i.e. 963, or 40.@o of the 2407 population units, but this deficiency is often compensated for by studies in depth, dealing for example w"ith the relationship between the prevalence and intensity of infection wj-th Onchocerca volvulus and blindness, the natural history of oeular lesions, and the various etiologies of visual impairment that co-exist in endemic areas and may affect the same group of persons. Estimated prevalence of onchocerciasis and blindness While most of the programme area is well documented by prevalence surveys for onchocerciasis, there stil1 remain many sub-areas for which the presently available baseline data are insuffi-cient. Major deficiencies concern data on the prevalence of infection in the Togolese part of the area and in the Northern Begion of Ghana. The tota'l computed number of persons with onchocerciasis in the suryeyed areas of the programme area was about 85O OOO (Table 2). It is reasonable to estimate by extrapolation from these figures that the total number of infections might surpass one million if all the gaps in our present knowledge were filled. Incomplete inforrnation on blindness poses a much more serious problem. Blank areas include most of Upper Volta, with the exception of the Cercles of Banfora, -29- Di6bougou, Gaoua, Manga, Po, Ti6b61d and Zabrd, and most of northern Togo. The main body of information is based on crude prevalence data only and, with few exceptions, the age and sex composltions of the individual population samples are not known. Nevertheless, on the basis of the availabte data there are a minimum vision' of 35 OOO blind Persons and at least as many wlth severely impaired ical distribution of onchocerciasis and blindness All available data on onchocerciasis prevalence and frequency of blindness, together with the exact geographical position (longitude and tatitude) of the villages and towns from where they were obtained, were coded and transferred to an IHr[ 371/55 computer for storage and analysis. A special mapping programme using. the Calcomp plotterl made it possible to print maps corresponding exactly to a of each 1:1 OOO Ooo and 1:5 OOO OOO scale where the precise geographical location comnunity surveyed is shown together with the prevalence of infection and, if available, the frequency of blindness. Indivldual villages at least 3 km apart are plotted on the I:I OOO OOO naps while the smatlest distance for showing separate communities was adiusted to about 20 km on the smaller scale maps of 1:5 OOO OOO' For the latter, the computer selected from the cluster of overlapping villages that were bituated within a six arc minute area the one which had the highest prevalence. This representative figure is always printed in the centre of each corresponding six arc minute square. The computer mapping programme is flexible and permits continuous updating on the basis of i.ncoming information. Figure 43 shows the geographical distribution of onchocerciasis by levels of endemicity. Large hyperendemic areas with prevalence rates of more than 7O% are found between the Red and White Volta Rivers above and below the border between in Ghana and upper volta, along the sissili River and its many small tributaries Ghana, in the north-eastern regions of the Ivory Coast adiacent to the B1ack Volta and around the White Bandama and Bou Rivers in the north central parts of lvory coast. Towards the more arid regions in the north of upper volta, the prevaLence levels decrease gradually. A similar, but less pronounced tendency of declining infection rates can be seen as one moves away from the heartlands of the volta of River basin towards the east and west. The southern border of the savanna-type foci of onchocerciasis is less well defined and merges graduall,y with the endemic the forest-type of the disease. while the large scale map pictures the overall onchocerciasissituationintheprogrammearea,itdoesnotrevealtheextreme foeaLization of endemic onchocerciasis even within areas of generally high, medium and low endemicity. This aspect is dealt with in the following section of this chapterandillustratedinthemoredetailedmapsincludedintheatlasincorporated in Annex IV-3. ' C"rrfo".ria Computer Products, Inc. -30_ Although less comptete, the map showing the dlstribution and prevalence of blindness (Fig. ) comesponds relatively well with the endemicity levels of onchocerciasis presented in Fig. 43, with two notable exceptions, one in Mali and the other in Niger. In parts of these two countries, the frequency of brindness exceeds 4% arthough the corresponding prevalence rates were less than.* 7O% in Mali and even less than 40% in Niger. The most likely reasons for theql apparent discrepancies nay be the following: dissimilarities of the age compositlon 't of the sanples on which were based the estimates of the prevalence of infection' and blindness; use of different diagnostic criteria for recording blindness in the various areas; and the existence of blinding diseases other than onchocerciasis that could have contributed to the overall prevalence of blindness in these areas. Special epidemiological features Age and sex patterns Onchocerciasis is a cumulative parasitic infection. In endemic areas the age structure of the population reflects this time element in three ways. First, aging the of the persons; second, the length of exposure to infectlve bites by the blackflies; and third the natural course taken by the disease once a person is infected. While it is impossible to separate these three independent dynamic deveJ-opmental changes from one another if only data from cross-sectional prevarence surveys are avairable, nevertheress certain inferences can be drawn. some of the histopathological changes of the skin caused by onchocerciasis resembre those found normally in o1d persons of non-endemic areas. It thus appears that onchocerciasis accelerates the aging process of the skin. In a hyperendemic area of onchocerciasis the following age patterns are characterlstic. Depending on the degree of trans_ mission, infections in young children are usually first recognized in the second year of life. Thereafter, the prevalence increases rapidly reaching a ceiling of nearly L@% in the second decade of life. After prevalence has reached its maximum, the intensity of infection sti1l continues to rise until a saturation 1eveI, with high microfilaria counts in skin biopsies, is reached. There are considerable variations in these saturation 1evels between individuars and also between communities of similar endemicity but the reasons for these discrepancies have yet to be elucidated. Usually, there are also differences between the two sexes. In males, infections are more intense than among females of corresponding age-groups. Likewise, the prevalence of eye lesions and blindness is higher in males than females. Examples axe given in Tables 3 and 4. The age-adjusted percentages were calculated from a standard population comprising both sexes. Table 5 also 7 -31 - shows that serious eye lesions manifest themselves after a period of inapparent disease lasting for 10 years or more. Although detection and registration of btindness is usually made for bilateral vislon only, a separate presentation of visual impairment in the left and right eye is shown in Fig. 45. Both eyes are affected with equal frequency but severe eye lesions are found more often in males than in females. Large differences in endemicity leveLs, in infection intensity and frequency of blindness can be found even between villages that are located only a few kilometres apart. These micro-epidemiological gradients are directly related to the relative proximity of human settlements to fast flowing rivers and streams in which the blackfly vector breeds. Swarms of adult female flies usually seek the nearest source of human blood. Villages that are in the front-Iine of attack by the vectors serve at the same time as effective barriers, thereby reducing the number of infections in communities located at greater distances from the breeding sites of Simulium. Based on these observations, communitles have been classlfied as either "Ist", "2nd" or "3rd" line vi1Iages. As can be seen from Fig. 46, the most striking differences between the three types of communities are in the age patterns of the prevalence of infection in children and teenagers and in the frequency of eye lesions and blindness in adults. The striking association between endemicity Ievels of onchocerciasis and prevalence of severe eye lesions is further illustrated by detailed ophthalmological investigations. An exampte listing the most important types of ocular manifestations as discussed in Chapter II is given in Table 5. For each of the three categories of eye lesions, there is a rapid increase from a low level due to miscellaneous causes found in non-endemic areas to the highest frequency in a hyperendemic region. The relationship between crude prevalence of infection with ryfvulug and percentage of total blindness was analysed for aII of the 291 villages ln the programme area for whlch sufflclent baseltne data were available. Ttre results are shown in Fig. 47. They tndicate that the assoclation ls not linear but that blindness rates lncrease exponentially. Onchocerciasis, blindness and viLlage size The impact of onchocerciasis on economic development has been a major concern of governments, economists and public health officials in the countries of the programme area. It appears that many previously inhabited and fertile areas along rivers and streams in whlch Simulium is breeding have been abandoned for fear of "river blindness". An analysis of the avallabIe epidemiological data provides indirect quantitative evidence lending support to the hypothesis that onchocerciasis -32- has been the main reason for the economi-cally unfavourable trend of population movements away from the fertile valleys. Figure 48 shows the relationship between blindness rates and population ,rsizes of viltages for the endemic area of Tumu District, Northern Ghana. There.ls an exponential, negative association between village population and prevalence of ' blindness'(correlation coefficient r = -O.523). An analysis, presented in Fig. 49 shows the association between village sizes and prevalence of O. volvulus infection in 1757 communities from which basic data were available. Villages were grouped into three categories, namely those having between 40 to I99 inhabitants, those with a population of 2OO to 699 persons and the remainder exceeding 7OO residents. The graph demonstrates that of the smallest comnunities 22% rlad prevalence rates in excess of 5O%, as compared to 10% of the nedium sized villages and only 2% of the targer towns. Although this striking association supports the hypothesis of a causal relationship between onchocerciasis and emigration, it is also compatible with the assumption that vitlages with high frequenci-es of onchocer- ciasis are located "at the end of the road" where difficult subsistence is coinci- dental with high exposure to infected blackflies. Nevertheless, further evidence is provided to show that of the two hypotheses mentioned, the effect of onchocer- ciasis appears to be the major determinant and that the smal1 sizes of the front- line villages have resulted from emigration. Census data from Tumu District, Northern Ghana, in which onchocercal blindness prevails, have furni.shed information on the population changes that have taken place in the L'l-year period between 1931 and 1948. Figure 50 shows that there is a negative associ.atj-on between population growth and blindness rates. Whether the differences in population growth are related to migration or differential mortality and fertility rates or to all three factors cannot be decided due to the lack of specific data. Onchoqerciasis and population effects Population movement Studies of population movement in localized sectors within the programme area reveal a pattern of heavy migration loss related to the situation of an area within the river basin.. For example, calculations of trends in the onchocerciasj-s hyperendemic area of north-east Ghana (districts of Bawku, Bolgatanga and Navrongo) in the last decade show an overall net migrati-on loss per district up to 2.9% per annum - highest in the Sissili area - but with the pattern of heaviest decline quite clearly in riverine locations and movements of people to upland, watershed areas (see Fig. 51). This recent and continuing retreat is part of a much longer movement pattern, wlth considerable evldence from aerlar photographs (see Fig. s2), ground surveys of vegetation patterns and oral history, of retreat from traditional -33- stat€s slnce 1910-15 and progresslv€ abandonm€nt of the vaIleys slncc the turn of the century. Flgure 53 shows the pattern of retreat ln the Zeblla area of north- east Ghana in the last three decades. Infectivity gradients of onchocerciasis and prevalence of nodules reveal the disease to be probably the prime cause of retreat and, in addition, geographic patterns of onchocerciasis and blindness strongly correlate with the patterns of abandonment. A similar pattern of emigration and movement back from riverine areas is shown in studies from Upper Volta (Fig. 54) where the process of starving out of villages "at the end of the road" is graphically demonstrated. The pattern of retreat, which can be seen to have occurred in many other parts of the prograrnme area, is shown to cover a number of stages starting with the retreat from perj-pheral compounds, the slow movement off-river to the interior territory of the village and then gradual abandoirment and movement to upland areas. As a result there is a seri.ous concentration of population in the upland, watershed areas and, contem- poraneously, considerable movement away from the district entirely of the younger members of the family. This movement, which is a feature of the entire programme area, is directed southwards towards conurbations and agricultural plantations. It is partly seasonal or medium term (up to 5 years), but a significant part of it amounts to the permanent emigration of a considerable proportion of the most active components in the community, particularly the 15-20 age-group. Age and sex ratios Calculation of sex ratios from the most economically active age-group (75-44 years ) can provide an accurate index of migration trends and confirm the serious implications to family and compound stability. In the hyperendemic and densely populated area of north-east Ghana, for example, the ratio averages 65 males per lOO females, and falls to 55-60 per 1OO in some districts, in comparison with a ratio of 93 per 1OO for the whole of Ghana. The 1ow ratio reflects the emigration of young males when faced with insufficient land with which to support a family at subsistence level let alone provide any surplus for sale. As a result the proportion of the population within the active working age range fal1s below national levels. For example in the rural areas of Ouagadougou and Koudougou in Upper Volta the proportion of actives falls to 40-45% in comparison with the national leve1 of 50-52%. Thus not only is the productivity capacity of the family seriously reduced but there is a relative aging of the population and the proportion of work undertaken by men of over 60 has to increase signi ficant 1y. -34- Population density Population density maps highlight the relative desertion of the riverine areas and concentration of people on the uplands at relatively high but not necessari-.ly * dangerous levels. However, if population maps are redrawn at the enumeration* district level, excluding land which is completely deserted, the serj.ous overloading of the agrarian resource base can be seen. In north-east Ghana, the areas '.. adjoining the larger river systems have densities below 2O per km2, extensive. areas only 2-6 per km2, and large areas are unoccupied. On the other hand, towards the watershed densities increase sharply up to cormonly 6O_L2O per km2 and sometimes as much as 160 p." kr2 (fig. 5S). A similar pattern can be seen in other territories in the progranme area (see Figs 10 to 12 in Chapter I). Resultant socio-economic effects Maldistribution of population The retreat from the river valleys places on the plateau lands a burden of human occupati"on that they cannot support. rn the west of Upper volta, for example, in the Dissin area east of Di6bougou, land with an inherent capacity of 2 2 2o-3o peopre p", k has been at roo per k for many years. As a resurt, relatively stable traditional agricultural systems relying on a quasi-shifting principle of land rotation have been changed to a system of continual cropping with a resultant degradation of soils. Similar examples can be seen in other densely populated upland areas in Northern Ghana, the Dapango and Lama-Kara areas of Togo and the Korhogo regi-on of Ivory Coast. Soil degradation and declining yields lead to an exhaustion of the family's limited capitar reserves and creation of a vicious circle of overcropping which it is almost impossible to break without increasing the area of land available to the family. Plateau soils are generally poor, often lateritic, and almost always highly susceptibre to erosion. Many of the areas now being farmed intensivery shourd, for the prese'rvation of the land in general, be strictly maintained as forest reserves. Soir erosion can occur with dramatic speed in any upland area where grass is burned and vegetation is cleared for farming. This is not a static state of affairs. It is proceeding, with variabre speed but not srowry, all over the programme area. Uprand farming is arso excessively dependent on regular rainfall throughout the season, sj.nce the soils do not retain water. The failure of the rains in the last three to five years has exacerbated (though it dld not create) the progresslve inabllity of the savanna lands of l'tlest Africa to support thelr ever growing popula- tlon' Ttrls ls by far the most lmportant aspect of the probrems under conslderatlon. .i1to:.2': -35- Agricultural production The concentration of people on the upland soils in the savanna zone where conditions are inherently unfavourable has had specific and direct effects on production: reduction in farm area per family; reduction in work capacity and aging of the family through emigration of young people; lowering of yields due to overcropping. a) Fam size The average size of far:n - cultivated land only - in the densely populated zones is much smaller than where a more favourable land:man ratio exists. For example in the Korhogo region of the Ivory Coast 56% of the farms are of less than three hectares and in Navrongo Bolgatanga, north-east Ghana, average farm size fal1s to 1.28 heetares for a family of 6.8 people, or O.2 hectares cultivated per person. Similarly, in Upper Volta farm size in the densely populated Zorg]no area near the White Volta south of Ouagadougou averages 2.8 hectares for a family of 5.7 peopfe, and in the r,ama-Kara region (north Togo) a famiry of si.x farm r.o5 hectares. These levels represent O.Z-O.45 hectare per person active or only some 20-45% of the capacity of the individuar under traditional systems. b) Labour productivity The productive capacity of the family is seriously reduced by the shortage of land and declining yields wtrich follow overcropping. At the same time, emigration of the young presents a serious reduction in potential productivity with the consequential aging in effective labour force. The rate of emigration is such that it is often difficult for the remaining members of the family to make an adequate input for their needs. Furthermore, the remaining work force j.n onchocerciasis-infected areas is severely debilitated by the effects of the disease and, in riverine areas, the high incidence of blindness. c) Crop yields overcropping of upland soils has led to considerable yield reductions and, combined with the severe drought conditions due to shortfall in the rains for several years in succession, has resulted in serious food deficits in many areas. Even in a nomal series of years the inherent variability in the commencement of the rains resu}ts in considerabre yierd fructuation with, for example, a coefficient of variation of + 45% for sorghum in eastern upper vorta. Reoccupation and cultivation of the valley soils, on the other hand, wi-11 provide an opportunity to lift the average yield and, on some va1ley soils, reduce the degree of variation from year to year. In the meantime, under present systems _36_ oJ1 the uprands upper volta is now facing a food grains deficit of So ooo tons per annum and consumption in the area is falling well below minimum subsj.stende requiremen{s; in the *""a oi ouagadougou annual consumption of graj-ns is estimated at r32 kg per head in comparison with a minimum standard of 2oo kg. ,. The retreat from the valleys and the uneven distribution of population resu1ts in neglect of the basic infrastructural amenities in the less favoured areas. Road networks and health services are not developed or, if developed in earlier years' deteriorate often to a state of complete uselessness. ftnigration of the young men leads to increasing difficulty in maintaining subsistence levers in agrj-culture. Marketing activities faIl off from even their traditional levels (which were never very high), and the markets lose the interest of traders from outside. This in its turn removes the stimulus for producing cash crops and thus the affected community loses entirely its motives and eventually its will for normal socio-economic development. Rural income The decline of agriculture, and especially of the motivation and energy required to stimulate the production of cash crops, is reflected in a very low level of income in the whole programme area. There are marked differences in production potential in the more humid southern zones of Ghana, fvory Coast, Togo and Dahomey, but in alr these there is the possibility to produce valuable export (cocoa, crops palm oil, copra etc.). In contrast, incomes in the savanna zone are extremely low and are not increasing. The figures given in ?able 6, it must be remembered, include the most favoured as well as the more depressed rural areas. Conclusion Desertion of river va11eys, overcrowding and erosion of uplands, and inability of some West African countries to grow sufficient food even for subsistence are not static conditions. In the progranme area and elsewhere throughout the West African savanna they are progressing, and not very slowly. Repeated failure of the rains in the last 3 to 5 years has not created but only exacerbated the agricultural inadequacy. The presence of onchocerciasis and its vector may not always have been the sole factor leading to depopulation of valleys; it is hoped that this Report has made elear the belief of everyone with experience of the programme area, that the removal of onchocerciasis and S. damnosum is the first and most indj-spensable preeondition for reversing the spiral of descent. -37- o .,.{ 15troq)O 15 oocEh +J .r{ 0) o!o>O O) (o .'.{EOtrtr oi o o H o @ Q. 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