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' - 111 - 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 l, -iv- 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.