November 2001 EAST AFRICAN MEDICAL JOUR 4AL 595

East African Medical Journal Vol. 78 No. I I November 2001 LYMPHATIC FILARUSIS IN SINCE 1910, AND THE PROSPmS FOR ITS ELLMINATIOI I: A REVIEW C. N. Wamae,BSc, MSPH, PhD, Principal Research Officer, C. Mwandawiro. BSc, MSc, PhD, Senior Reva ch Officer, Centre for Microbiology Research. E. Wambayi. BE4 MSc, PhD, Senior Research Officer, Centre for Biotechnology Research and Developmat. S. Njenga BSc. MSc. Research Officer, Centre for Clinical Research. F. Kiliku, DMLT. HDMLT, Rincipal Medical Laborarory Technologist,Cenm for Microbiology Rd.Kenya Medical Research Institute, P.O. Box 54840. Nairobi. Kenya

Request for reprints to: Dr. C. N. Wamae, Centre for Microbiology Research, Kenya Medical Research Ins itute, P. 0. Box 54840. Nairobi, Kenya.

LYMPHATIC FILARIASIS IN KENYA SINCE 1910, AND THE PROSPECTS FOR ITS ELIMINATION: A REVIEW

C. N. WAMAE, C. MWANDAWIRO, E. WAMBAYI, S. NJENGA and F. KILIKU

ABSTRACT

Objectives: To provide an overview of lymphatic fhriasi in Kenya from the first time its prevalence was reported to the present day, with suggestio~nsof issues that are yet to be resolved and to present the prospects for its elimination. Ikukz sources: Published and unpublished reports on filarias s studies in Kenya. Sady selection: Field-based epidemidogical studies covering a spects of clinical, parasitology, entomology, social, economic, dingwsi and control of filarii sis. Ikukz extraction: Review of published articles in scientific jcmrnals and communications, retrieval and review of published scientific articles front the Internet and personal communications. Ikukz synthesis: Re-organisation and pooling retrieved publk hed data. Conclusions: Almost one century after the first documented report of lymphatic filariasis in Kenya, no National Control Programme has been instituted. However, important findings that have implications on its control have been made and they! hould be utilised to implement a National Control Programme. On implementation of the I iational Control Programme, research should be focussed on the remaining unresolved is! ues and conducted within the framework of the Programme. The World Health Orgaeation has targeted lymphatic fdariasis for global elimination by the year 2020. Kenya is wl :U positioned to formulate her National Plan for Elimination of Lymphatic Filariasis (NPELF) and join dher endemic countries worldwide, which have already launched their ldans, in the global efforts to eljminate lymphatic filariasis as a public Mthproblem.

INTRODUCTION clinical" hidden damage of their lymphatic and renal systems(3). Added to this disease burden, there are the Lymphatic filariasis is a major public health problem serious psycl~osocial consequences, the sexual/social throughout the tropical and sub-tropical areas of Asia, dysfunction cff men with hydroceles or other genital Africa, the Western Pacific and some parts of the abnormalities and of young women with lymphoedemaof Americas(1). Over 120 million people in 73 countries the breasts or l:enitals(4,5). Among Wuchereriubancrofti, worldwide areafflicted with lymphatic filariasis, which is Bmgia malay and B. timori, the three aetiologic agents of a leading cause of disabling morbidity. Approximately lymphatic filariasis, W. bancrofti is the only known cause one-third of people with this infection live in while of infection in Africa where an estimated 564 million another third live in countries in Africa. Most of the persons are either infected or have chronic disease(6). In remaining one-third of the infected population live in the Africa, incluc ing Kenya, the infection predominates in remaining endemic regions. Over 1.1 billion people (20% rural areas wh, :re access to health care is mostly inadequate. of the world's population) live in areas where they are at It is estimatec that all persons living in endemic areas in risk of infection(2). Thus, lymphatic filariasis has been coastal Ken! a are at risk of infection as they are recognised as an important impediment to socioeconomic continuousl~ exposed to infective mosquitoes development in many parts of Africa, Asia, the western (Mwandawirc ,personal communication). Moreover, some Pacific and certain regions of the Americas due to the of the peoplt living in the Lake Region may also be physical disabilities associated with it. A total of 44 infected (Gitf ure, personal communication). million persons currently suffer from one or more clinical Thought Ere have been some significant successes in manifestations such as lymphoedemaand elephantiasis of the control of the disease, in most endemic countries the the limbs or genitals, hydrocele, chyluria, pneumonitis or burden of lyr lphatic filariasis remains unaffected, or is recurrent infections associated with damaged lymphatics. even on the ir crease. However, the introduction in recent The remainder of the 120 million infected have "pre- years of new drugs and improved diagnostic tools to 596 EAST AFRICAN MEDICAL JOUK NAL November 2001

combat the disease prompted the International Task Force ten mile "cosstal strip", the areas along the Tana and on Disease Eradication to identify lymphatic filariasis as Sabaki Rivers and the -Nairobi road, excluding one of the six potentially eradicable diseases(7). In 1997, more inland a.eas (Figure I ). the World Health Assembly passed a resolution on the elimination of lymphatic filariasis as a public health Figure 1 problem through mass chemotherapy of affected individuals and appropriate morbidity management of Map of the Kenp coast showing the towns and villages where DEC mass treutmen was curried out (ufier Wijers und Kuleli, 1984) those presenting with clinical signs. Whilst Kenya is endemic for lymphatic filariasis, the disease remains of low priority in health circles although agood proportion of people living in the Coastal region are condemned to psychosocial, physical and reproductive disabilities due to filarial infection. This paper gives an Slyu -- overview of all the major research and control activities, Pate town on bancroftian filariasis in Kenya, from the time it was town first documented in 1910 to the present time and also Manda describes some of the on-going projects. Since there are Lamu unresolved issues still to be addressed, prospective studies in the field of lymphatic filariasis have been outlined in the last part of the paper. In recognition of Kenya's position in both lymphatic filariasis research and the focal (regional) L7 INDIAN OCEAN endemicity of the disease, the formulation of the National Plan for Elimination of Lymphatic Filariasis (NPELF) is advocated.

DOCUMENTED STUDIES

Parasitological and clinical investigations (Tables 1, 2 and 3): The only known type of lymphatic filariasis afflicting humans in Kenya is bancroftian filariasis, which is endemic along the Indian Ocean coastal districts of The rnost ex ensive work was carried out in 1977 Kwale, Kilifi, Malindi, Tana River and Lamu. About three (1 I), which coverc:d the same coastal length but extended million people live in areas where transmission occurs. deeper inland, examining only males over 14 years of age The disease causes severe morbidity, deformity and in the four district; of Kwale, KilifiMalindi, Tana River disability in infected persons. It has been known on Pate and Lamu borderiiig the sea (Figure 2). Prevalence in the () Island, where pioneering epidemiological work wet, densely pop~latedten-mile wide coastal strip was began, since 1910. Documented epidemiological work(8) generally low; it \/as much higher in the more sparsely was conducted in 1921 in and the Tana River populated, drier : nland areas. Microfilaria rates and area, during which 3 17 persons (285 males and 32 females) densities seemed t') increase with age but levelled off at inendemic villages wereexamined. Out ofthese, 97 males around the age oi 50 years. Similarly, hydrocele and and 15 females (35.33%) were microfilaraemic. This was elephantiasis incresed steadily with age. Elephantiasis followed by another survey by members of the Division of was found to be more common in the north than the south, Insect-Borne Diseases in 1946 who found eight out of 34 and occurred without the accompanying abnormalities of persons examined in to have microfilariae in their the genitals. However, the disease in males of the East blood. A human infection rate of 32 % was recorded from African coast is gen :rally characterised by a lack of severe night blood samples in another study carried out in Pate or acute signs of lyr ~phvessel inflammation compared to Island, Figure l(9). The highest parasite density was other parts of the w~rld(12). foundinsix totwenty-yearage group, with themicrofilarial Differencesin tl~eepidemiologyof lymphaticfilanasis densities being three times higher in males than in females, were observed betvfeen a small compact Moslem town despite the latter living in closer contact with the vector. () and an inland rural area (Jaribuni) where A broader survey conducted in 1962 (10) covered 36 people over one yea1 old were examined(l3). In Mambrui, villages in the entire coastline from Vanga near the microfilaria rates ar d densities were lower in the richer Tanzanian border to Pate Island on the northern coast. people living in beter quality houses and higher in the Microfilaria rates were found to vary from 25% in the poor individuals livi ]gin poor quality and less-lit houses. north to 10 % in the south. Men were more heavily infected In Jaribuni, however the type of housing did not matter as than women, with hydrocele being the commonest much as the distance from the Jaribuni River, which was complication. The study however, examined only people the main breeding sitc forAnophelesfunestus (the principal aged 15 years and above and was mainly confined to the vector in that area). November 2001 EAST AFRICAN MEDICAL .OURNAL 597

Table 1

Parasitologiral nnd clinictrl surveys cfl bnncrcfrian~luriusisrn hmuand Tar.cr River disrrrcts in cocrsrul Kenyu. 1921-1984

Area Mf (8) Mf den Hc ate El rate Ref. - No.*

Pate Island 40.0 - - - 8 Pate Island 32.0 9.4 - 11.0 9 Larnu area 23.9 24 0 - - I0 Fau 15.1 7.6 - 11.8 11 Faza 5.9 - - 3 1 20 6 l 7.3 - 0.0 I I Pate 10 9 - - I I Siyu 9.9 - - - 11 Ndau 16.4 - - I I Kipint and Witu 16.4 17.1 - 10 Tana Rrver 14.7 10.9 - 10 Mororo 2.3 13.0 0.0 I I Bura 0.0 0.0 0.0 I I Nola 10.8 1.5 0.0 I I Wenje 189 10.0 1 .b 1 I Werna 4.6 2.7 - 3.1 I I Garsen 4.5 3.5 18.1 120 I I ldsowe 8.7 17.0 30 7 5.9 I I Ngao 13.7 9.3 30.9 18.4 I I Semikaro 0.0 0.0 - 0.0 I I Kipni 28.1 27.7 - I9 I I Pandanguo 15.9 4.8 0.0 I I Mapeoya 4.8 18.0 - 0.0 I I Bargoni 8.6 2.0 - 0.0 I I Hola I1 O - 28 .0 - 14 Wenje 19.0 - 15.0 14 Werna 5.0 - 27.0 - 14 Garsen 4.0 - 22.0 - 14 ldsowe 12.0 - 38.0 - 14 Ngao 13 0 - 34.0 - 14 emikaro 0.0 - 10.0 - 14

Mf (&) = percentage of the population with ~nicrofiluiae:Mf den = rn~crofilarialdensity (no.rn'/rnl) Hc rate = hydrocele rate; El rate =elephantiasis sate: *numbers correspond to references cited ill Lext

Table 2

Parasitological and clinrctrl srrrvqvs of berncrc~flianfilariasisin Kilt$ rind Mulindi d rtricts in cotrstcri Kenya. 1962.1984

Area Mf den t4c rat : El rate Ref. NO*

Marnbrul 17.8 11.4 - 10 Kakoneni 26.3 24.9 - - 10 Krlifi area 13.1 23.9 - - !O Mariakani >30.0 >40.0 - - 12 Ganze >30.0 >40.0 - - 12 Kakonent >30.0 >40.0 - - 12 Mambrui 21.7 - 15 4 - 13 Janbuni-Magogoni 22.0 - 17.0 - 13 Malindl area 10.0 - 17.0 - 14 Takaungu 8.0 - 15.0 - 14 Rabar 6.0 - 19.0 - 14 Chakama 40.0 18.7 51 0 - 14 Jartbur~i 40.0 17 0 48.0 - 14 Jomvu 38.0 10.6 50.0 14 Kadungun~ 44.0 26.1 37.0 - 14 Nas~bu 56.0 20.4 42.0 - 14 Ndigiria 39.0 19.9 30.0 - 14 Mabuani 2.0 - 16.0 - 14 Mulsara 35.0 22.1 24 0 - 14 Mambrui 21.1 - - - 31

Jaribun~ 22.0 - - - 3 1 Mwangatini 27 8 - - - 32 Masheheni 15.9 - - - 32

Mf (%) = percentage of the populatton with microfilariae: Mf den = mtcrofilarial density (no.rnWrnl);~ic rate = hydrocele rate El rate =elephantiasis rate; *numbers correspond to references cited in text 598 EAST AFRlCAN MFlDICAL JOUR.JAL Nuvember 2001

Figure 2 therefore, mcre intensive than extensive in approach compared to he earlier ones. One of such studies(l5) B~mcrr~ftiunfiluriui.~endemic rrrecls. COCLYIProvince, Kenya examined 1 12 9 persons in Vanga (Lunga-Lunga location), Kwale District and found elephantiasis and hydrocele to increase with age. Another study(l6) was conducted in Maili Nane ill Mwachinga village of Kinango location (Kwale), seru n samples from all microfilaraemic persons were positive for circulating filarial antigen, as were 15% of samples from amicrofilaraemic and asymptomatic persons. Later in Muhakavillagealsoin KwaleDistrict(l7), it was shown that prevalence increased with age and was focal as both r Ucrofilaraemiaprevalence and density were significantly Irigher in Kilore thanMvumoni, twoadjacent villages. The final survey(l8) covered Gandini, Dzivani and Lutsangitni villages in Kinango division in which microfilarial iensities were significantly higher in males than femalr:~but surprisingly elephantiasis was significantlyltigherin females than males, possibly because the main clinical manifestation in males is hydrocele. In this study( la), it was also shown that the infection was generally hip her in males than females. However, when this observation was re-evaluated by age groups, it was shown that th~:significance remainedonly in mencompared I. Lurnu/Tuw River 2. KilijldMulincli 3. KwuIefMombLlsu to women of childbearing age as previously reported in Bargoni Chakama Chwake Muhaka(l7) Bura Ganze Dzivani Entomo~ogical investigations (Table 4): Initially, Faza Jaribuni Gandini Ganen Jomvu Gazi Aedes pernb,lensis was erroneously incriminated as an Hola Kadunguni Kinango important ve :tor transmitting bancroftian filariasis in Pate Idsowe Kakoneni Lunga-Lunga Island due to its abundance. This was compounded by the Kipini Kilifi Lutsangani fact that the : pecies had infection rates of six per cent and Lnmu Mabuani Mailinane Mapenya Malindi Mariakani 6.3%, from ~:ollectionsmade in the houses and the bush Mororo Mambrui Milafeny i respectively. carrying unidentified filariae larvae that were Ndau Mashekeni Mobasa presumed tc be bancroftian(l9). Other species in the , Ngao Mariakani Mri ma houses wen: Aedes aegypti and Culex fatigans with Pandanguo Mu~sara Msambweni 1 Pale Mwangatini Muhaka infection ratc :sof seven and fourteen per cent, respectively. Semikaro Nasibu Mwena Thus, it was :oncluded that the epidemiological pattern of 1 siyu Ndigiria Nguluku bancroftian 1 ilariasis for the coastal regions of Takwa Rabai Shinzi was quite c ifferent from that on the islands in Lake Wema Takaungu Vanga Wenje Victoria whe re Anopheles gambiaeand Anophelesfunestus Witu were the pri lcipal vectors(l9). In a late :survey, Ae. pembaensis was found to feed on One of the studies by Wijers (14) indicated that in domestic a~idwild animals as well as man without some rural areas on the Kenyan coast, where Anopheles discrimination(9) but seemed not to transmit human transmitted filariasis occurred, transmission levels filariasis. Tl is is because after DEC treatment, infection tremendously increased during and immediately after the rate fell onl! in Culex quinquefasciatus (from 25 to6.6%) rains but declined considerably during the drier months, butremainel the same in other mosquito species including resulting in interrupted transmission. This led to the Ae. pembat,nsis. It was therefore confirmed that Cx. hypothesis that interrupted transmission tends to promote quinquefasriatus was the chief vector transmitting the development of microfilaraemia while a more bancroftian filariasis in Pate and that Ae. pembaensis continuous transmission leads more readily to the transmitted i m animal filarial worm, Brugiapatei, recovered development of the clinical signs, in areas with equal in cats, dogs and genet cats in Pate Island(20). The yearly transmission. Before this observation, it had earlier presence of B. patei in Pate Island has been reported in been suggested that continuous transmission is necessary other epide niological studies(9, 10) and in if a high incidence of W. bancrofti infection is to be found during a screening of domestic cats(2 1 ). However, an in man(10). attempt to ~indthe infection in humans and mosquitoes Other epidemiological studies in the later years were was unsucc:ssful(22). even more localised, covering very small areas, some of Anoth1:r extensive survey(l0) documented Cx. which were conducted for academic purposes by students quinquefas~:iatus,An. gambiae and An. finestus as the pursuing higher-degree courses. These studies were, main vectol s of bancroftian filariasis in Kenya, suggesting November 2001 EAST AFRICAN MEDICAL JC IURNAL 5W

Table 3

Parasitological and cliniccll surveys ~fbancroftianfilariasis in Kwale and M )mbasu districts in cocrsr~11Kenyu. IWZ-ZWO

Area Mf (%) Mf den H : rate El rate Ref No.'

Mombasa Mombasa-Mariakani Mombasa-Gazi Msambweni-Vanga Lunga-Lunga Kinango Milafenyi Nguluku Chwake Mwena Shirazi Mrima Muhaka Vanga Mailinane Muhaka-Mvumoni Muhaka-Kilore Gandini Dzivani Lutsangani

Mf (%) = percentage of the population with microfilariae Mf den = microfilarial density (no.mf/ml) Hc rate = hydrocele rate El rate = elephantiasis rate *numbers correspond to references cited in text

Table 4

Entomolo~icolsurveys on vectors ofbuncroftianfilariu~ is in cou~tulKenya. 1959-1997 - - Area Culex yuinyueff~rsciatus Awphel ?s gambiae Anopheles funestus Ref. a b a b a b No.*

PateiFaza Island 154 ll (7.1) - - - - 9 Kenyan Coast 2.800 47 1,020 6 925 9 9 Lamu area 3,695 56 (1.5) 56 0 0 0 10 Kipini and Witu 3,772 32 (0.8) 483 1 (0.2) 0 0 10 Tana River 129 - 738 0 0 0 10 Malindi and Mambmi 1,404 10 (0.7) 0 0 0 0 10 Malindi-Kakoneni 367 3 (0.8) 3,510 28 (0.8) 2,304 27 (1.2) 10 Kilifi area 449 0 79 1 2 (0.3) 178 1 (0.6) 10 Mombasa I ,57 1 0 0 0 0 0 10 Mombasa-Mariakani 1,770 5 (0.3) 55 2 (3.6) 49 1 (2.0) 10 Mombasa-Gazi 333 I (0.3) 469 2 (0.4) 134 0 10 Msambweni-Vanga 663 4 (0.6) 1.466 4 (0.3) 264 0 10 Mambml 3,823 37 (0.97) 0 0 0 0 24 Jaribuni 0 0 629 7 (1.1) 1 1.603 104 (0.99) 24 Spray-catch: Lutsangani 236 0 20 1 4 (2.0) 358 0 23 Dzivani 157 0 139 2 ( 1.4) 13 0 23 Gandini 98 0 369 3 (0.8) 32 l(3.1) 23 Human bait: Lutsangani 163 1 (0.6) 165 2(1.2) 176 2(1.1) 23 Dzivani 25 1 3 ( 1.2) 19 0 3 0 23 Gandini 98 0 12 0 I 0 23

a = number of mosquitoes examined; b = number of mosquitoes infective (96);* nl mbers correspond to references cited in text

that Cx. quinquefasciatus was the main vector in the vecto :s of lymphatic filariasis but their importance varies coastal towns and villages, but in inland villages the from place to place(9,23,24) depending on the local anophelines were more important. However, Cx. ecolagical conditions. Forexample, it was shown that Cx. qiiiquefaciatils wasalsoseen toplay an equally important quinc uefasciatus wastheonly vector in Mambrui,acoastal role in some rural settings(23). The three species are all town with wet pit latrines for breeding, whi1eAn.fwrestu.s 600 EAST AFRICA!V MEDICAL JOURNAL November 2001

was the main vector in Jaribuni, an inland village with a area(31) during which the local people distributed the river serving as the breeding site(24). Peak transmission in drug and alsotreated the jideeffects. DEC was administered Mambrui was from June to July whereas in Jaribuni it was for 13 days to all persms above one year in Mambrui, from December to January, just after the short rains. Jaribuni and the vi1laj.e~off the north coast of Kenya Immunological studies: Immunological studies have (Lamu, Pate, Siyu, Faza and Ndau) with a population of been carried out only in Kwale District where it has been 20,000. Two years later, microfilariarates in Mambrui had shown that filarial specific IgG4 was significantly higher dropped by 75%. In Jaribuni, a reduction of 75% was in microfilaraemic groups than in amicrofilaraemic recordedin men, but in vlomen it wasonly 48%. Spectacular ones(17,25,26).These studies also showed that the mean reductions were also ;.thieved in Island villages to the level of filarial specific IgGI was significantly higher in north. It was conclude11that it was possible and cheap to amicrofilaraemic, symptomatic cases than in control bancroftian filsriasis on the East African coast by microfilaraemic, symptomatic ones. Use of antifilarial mass treatment camp; .igns(31). Moreover, prophylaxis IgG4 or circulating filarial antigen (Og4C3) has been trials in Burangi, Mwangatini and Masheheni in Kilifi shown to be useful in identifying persons with District(32) suggestec that DEC could be used as a filariasis(l6,17). In one of the studies(l7), antigenaemia prophylaxis against bai~croftianfilariasis if given annually increased gradually, peaking in the age group 21 - 40 years. or bi-annually . Individuals from an endemic area had higher levels of the Mass treatment w ~thDEC(3 1) was speculated to be total and filarial-specific IgE than in persons from a non- the main factorresultin ,J in the low infection rates obtained endemic area(26). However, the concentration of total 1gE in five villages of Lan u and Pate Island(21). Out of 814 was tugher in individuals who had microfilaraemia than in persons examined, on1 ,24 (17 males and 7 females) were those that did not, while the reverse was the case with infected, majority of lvhom (19 out of 183) came from filarial-specific IgE. A new method for diagnosis of Ndau where mass tr1:atment campaign had not been filariasis using detection of circulating filarial antigen is effectively carried out :3 1). now available. A multi-country study was conducted in Social- economic studies: In an effort to investigate Kenya to validate the ImmunochromatographicCard Test community perceptions regarding chronic disease (ICT).When comparing ICTsensitivity to thoseof standard manifestations, Amuy unzu(5) conducted a study among parasitological detection of microfilariae it was found to the Duruma community in Lutsangani village in Kwale be more sensitive than microfilaria detection, simple, District. Interviews with patients with chronic filariasis rapid and convenient in field settings(27). revealed that deformit:(was reported as the worst outcome Recent studies in the samedistrict have shown that the of the disease. The pitients also identified intermittent human foetus developscy tokine production patterns similar pain with chronic mimifestations as a major problem. to those observed in adults and that prenatal exposure to These episodic pains caused patients to become bed- helminthes (schistosomiasislfilariasis) may not lead to ridden and dependent ,n members of their households for tolerance or altered foetal immunity(28). It has further cure and care. The COI nmunity reactions towards victims been demonstrated that helminth-specific immune of chronic filariasis w~:revaried. People who had patients responses acquiredduring gestation persist intochildhood. in their households expressed sympathy and understanding, This prenatal sensitisationbiases T- cell immunity induced whereas those who ha11norelationship with victims joked by BCG vaccination away from type 1 T- cell EN-?I and laughed about it. 3ut of the 65 patients interviewed, responses associated with protection againstmycobacterial only one reported that mosquitoes were associated with

infection(29). Furthermore, the human foetus of helminth- filariasis. The majorit: I of the patients said that the disease infected mothers can be sensitised in-utero to produce was caused by witchcraft, sexual transgression and helminth-specific B cells and that neonatal B cells are consumption of bad fc od.Most (over 90%) of the patients intrinsically capable of IgE and IgG production (30). believed the disease \/as incurable. Control efforts (chemotherapy using diethylcar- In a study confin:d to Msambweni Hospital, Kwale bamazine): Although prevalence surveys have been carried District, Mwobobiaet, z1(33), revealedthathydrocelectomy out in Kenya, very little has been done to control the accounted for 9.7% ar rd 7.6% of major surgery operation disease as a public health problem. As early as the 1950s time and bed-days, respectively. The corresponding diethy lcarbarnazine (DEC) has been used to treat lymphatic proportions of the costs of supplies used in theatre and of filariasis cases in Kenya despite the side effects some recuperative drugs WI :re 9.4% and 11.2%, respectively. patients present with. Initially mass chemotherapy was Rapid assessmer !t studies: Hydrocele, a common, conducted in the late 1950s in Pate Island where adults chronic condition associated with lymphatic filariasis received 2.2g, children above five years 1. lg and those causes physical, ps) chological, social and economic below five years 0.55g of DEC spread over six days. A distress. In Kenya, hyc lrocelectomy is very common and is fortnight later, human infection rates fell from 32% to 25% a leading cause of elt ctive surgery in Kinango Hospital, and microfilarial densities from 10.3 to 1.5 mU20mm1. Kwale District (MOH, unpublished data). A study to Eight months later, infection rates fell to 16% and assess the value of t ~ydrocelectomyas a proxy for the microfilarial densities to 1. I mfl20mmY9). prevalence of lymphiaic filariasis was conducted in five The second mass treatment covered a much larger hospitals in coastal Ke nya(33). The age distribution pattern November 2001 EAST AFRICAN MEDICAL JOURNAL 60 1

of hydrocelectomy patients paralleled that of hydrocele Annual Infective Biting Rate and Annual Transmission cases observed by Wijers(1 I) in the sur,ounding area. Potential (ABR, AIBR, ATP), indicating that it was the This study also showed that hydrocelec.omies form a main vector, followed by An. gambiae with Cx. significantly high proportion of major opera!ionsperformed quinquefasciatus playing a minor role. It has also been in Kwale District than in Kilifi District(incl1 ding Malindi). indicated that infectivity rates of bancroftian filariasis The foregoing section has briefly res~iewedalready vectors vary significantly between the wet and published work, which is also sumn.arised in the dry season (39). accompanying Tables and Figures. A lot of studies in the field of lymphatic filariasis, results of which are yet to be UNRESOLVED ISSUES published, have been going on from the I:~te1990s to the present time, and these are outlined in the following While Kenya is well positioned to formulate its section. National Plan for Elimination of Lymphatic Filariasis (NPELF), there are several research issues in the field of ON-GOING STUDIES filariasis that need to be addressed alongside the elimination activities. Such issues, in order of importance, include the Clinical trials: Aclinical study comparing theefficacy following: of single dose DEC, albendazole a one and their - Presence of bancroftian filariasis has recently been combination is nearing the conclusior of its second detected by PCR around Lake Victoria (Githure. year(34). The study is being conducted in Muhaka, Kwale personal communication). Entomological and District and has shown that a combillation of DECl parasitological surveys to establish the current filarial albendazole is significantly more effec ive in reducing situation in that area and all other suspect areas pre-treatment microfilaraemia prevalenc- (82.5%) than a should beconducted. Suchactivities wouldcontribute singledrug of DEC (54.5%),twelve monti s after treatment. to mapping of filariasis as a pre-requisite for up- Use of DECIalbendazole was also us:ful in clearing scaling the NPELF. intestinal helminths (hookworm, Asca-is lurnbricoides - Tools for certification of lymphatic filariasis and Trichuris trichiura). Although data a 124 months have elimination need to be established. Entomological not been analysed, this study appears 10 suggest that a investigations are very important in filariasis surveys combination of DEC/albendazole sholld be used for and seem to be more acceptable to the communities integratedcontrol of bancroftian filariasis ~ndgeohelminths than the rather invasive parasitological and clinical in areas with multiple helminthic infeclions. Because of examinations. the high concurrent endemicity c,f Schistosorna Studies are currently underway to evaluate the haernatobiurn with bancroftian filariasis ind geohelminths usefulness of testing the vector as a tool for and the high priority given by the affected communities in monitoring transmission trends during mass places similar to Muhaka, the possibility of including a treatment to eliminate filariasis. schistosomacidal drug to the DIIC/albendazole While mass treatment targets the parasites, it offers combination should be explored(35). very little help to alleviate morbidity of patients Control studies: use of impregnrzted bed-nets: A suffering lymphoedema and adenolymphangitis study conductedin Kwaledistrict(36)shc ,wed that although (ADL). Studies to show the most effective metl~ods permethrin impregnated bed-nets only arginally reduced n for management of lymphoedema and ADL are the mosquito hiting densities, they exerted a very strong urgently required. The issue of non-filarial suppressive effect on the actual transmi ision of lymphatic elephantiasis, or podoconiosis also known variously filariasis. as "Nyeri legmor"Meru1eg"according to geographical Mass drug administratiotl (co~vnunity-directed locality, should be addressed with a view to defining treatment): In a multi-country study .hat has just been its prevention and management. completed(37), treatment coverage b:~two methods of Whereas female genital filariasis has been reported mass drug administration of ivermecti I using the regular in other parts of the world, it is not documented in health service (HST) and the commun ty (Com-DT) was Kenya. Investigations on hidden pathology (kidney compared in Malindi and Kilifi Dijtricts. Treatment and lymphatic vessels) as well as female genital coverage by thecommunity was signific antly higher(88%) filariasis and their clinical management are necessary. than by the health service (46.5%), p :0.001. The Com- DT arm attained a coverage level comllatible with what is There is new evidence to support the speculation that recommended (80% and above) for the global elimination infection takes place very early in small children. In of lymphatic filariasis. a paediatric population at Kilifi District Hospital, Entomological studies: A study to determine the circulating filarial antigen was detected and filarial individual contribution of the three v~:ctorsof lymphatic infection was thought to be responsible for fevers that filariasis was conducted in Kwale Disc rict(38). Anopheles could not be explained by malaria (Peshu, personal funestus overwhelmingly dominated tlle other two vectors communication). In this regard, more intensive studies in the main indices of transmission !.nnual Biting Rate, in youngchildren, with a view to putting intervention 602 EA,;T AFRICAN MEDICAL JOURNAL November 2001

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