Onchocerciasis Control in the Volta River Basin Area: information paper

WORLD HEALTH ORGANIZATION ORGANISATION MONDIALE DE LA SANTE December 1977 ONCHOCERCIASIS CONTROL IN THE VOLTA RIVER BASIN AREA INTORMATION PAPER Background 0nchocerciasis, or river blindness, is a parasitic disease caused by the threadlike worm Onchocerca volvulus which affects from 20 to 40 million people in tropical Africa, the Yemen and parts of Central and South America. Man is Ehe only hosE of practical significance and onchocerciasis is transmiEted by the bites of female blackflies (Simuliidae). Among the important clinical manifestations of onchocerciasis are intense itching, rashes, wrinkling, thickening and depigmentation of Ehe skin, the characteristic skin nodules in which the adult hrorms are to be found, and as the most serious consequences of the disease, eye lesions leading to blindness. The medically most important and largest endemic areas are located in tropical Africa where the main vector is Simulium damnosum. This blackfly breeds in fast-flowing streams and rivers. As a consequence, the greaEest suffering occurs among people who live close to the river val1eys. The area affecEed The savanna area of the Volta River basin, in West Africa, is one of the worst endemic onchocerci-asis zones of the world. In Ehis area of approximately 7OO OOO km2, which includes Parts of Dahomey, Ghana, Ivory CoasE, I"Iali, Niger, Togo and Upper Volca, it is estimated that over a million people are infected and thaE, as a consequence, at least 5O OOO of these are blind while many more have serious impairment of sight. The association of proximity to the rivers and the risk of onchocerciasis was recognized by the local populations, who moved from Ehe fertile valleys to seEtle in relatively infertile lands. The disease thus constitutes for the area Ehe most important single deterrent to human sett.lement, and the subsequenE economic development of the fertile valleys which lie uninhabited and unproductive. Furthermore, the persistent and critical effects of drought in the sahel and the savanna, following the failure of the rains for six successive years, have gravely complicated the already precarious socioeconomic balance in Ehe Volta River basin area. EvenEs leading to the programlre In July L968 a technical conference held in Tunis under the joint auspices of USAID, OCCGE and WHO concluded Ehat onchocerciasis control in the West African savanna zone \^/as feasible and that the time had come to underEake large-scale action against Ehe vector Simulium damnosum i-n order to reduce the prevalence and intensity of the disease and to open up hitherto deserted fertile land to human settlement, livestock raising and crop growing. The recommendations of the Tunis meeEing were taken int.o consideration by a1l the parties concerned. In 1969 and 1970 the seven GovernmenEs involvedl confirmed their interest in such a regional onchocerciasis control programme and formulated requests in Ehis sense Eo UNDP. WHO then drew up a proposal designed to assign to the Volta River basin a PreparaEory AssisEance to Governments Mission (PAG Mission), for which the Administrator of UNDp agreed to provide the necessary funds. WHO was designated as Executing Agency, in association wiEh FAO. In July 1970 at a meeting in Geneva (organized jointly by UNDp and WHO, on the proposal of the World Bank) agreement was reached on the mandate of the Mission between UNDP, FAO, WHO, the World Bank, OCCGE and the Government of Ghana, rtConseil de ltEntenterr, FED and USAID. ocPf 7 4.1 Rev. 3 1 Benin, Ghana, Ivory Coast, Mali, Niger, Togo and Upper Vo1ta. ocPf 7 4.1 Rev.3 page 2 'Ihe PAG Mission had a major twofold objective. In the health sector, it was requeste.d to prepare a plan of work to achieve control of onchocerciasis over the entire recommended Programme area, taking into account economic development of reclaimed zones; to work out the expected costs and benefit-s of the scheme; and to analyse che possible financial resorLrces available. In the economic sector, it was called upon to identify zones within the prograrnme area 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 accepted to act as host to the PAG Mission whose head- quarters were set up in August l97I at Ouagadougou in premises placed at Ehe disposal of the Mission by the Government. Operating from Ouagadougou, the Mission benefited from che fulL collal>oration and encouragement of the Government of Upper Volta as well as of the other six countries in which it carried out rts actr-vrties. Tlrus the PAG l"lission carried out its work from mid-1971 through L972 and was extended to cover 1973 again under UNDP regional funds with l^iHO as Executing Agency and FAO asAssociate Agency. Early in 7912 the Executive heads of UNDP, FAO, the l^iorld Bank and WHO decided to establish a Steering Committee for Onchocerciasis Control comprirrng a representative from each ,rf the four agencies to coordinate action. The S[cering Committee has accordingly met regularly to monitor progress and resolve problems. The reporJ The Report of the PAG Mission, supplemented by a series of technical annexes, was submitted on 2O AugusL L913 to the Governments of the seven countries of the Volta River basin area. This report includes a detailed anaLysis of onchocerciasis and its socioeconomic implications in the area as well as a costed proposal for launchlng an onchocerciasis control programme i,n I974, and suggestions for the economic development of the fertile valleys and other abandoned areas of the Volta River basin. No less Ehan five years of concerted study and effort were needed to determine with the necessary precision the conditions under which an onchocerciasis ccntrol prograrmne could be launched with the best chances of success. Onchocerciasis can be controlled through a campaign against the parasite, the vecEor, or both. Presently two drugs are avallable for the chemotherapy treatment of onchocerciasis: suramin and diethylcarbamazine. However, although these drugs can be used \,rith little difficulty and risk under close medical super- vision, for individual treatment of patients suffering from onchocerciasis, their use in mass chemotherapy campaigns rai-ses problems that require further study. In the absence of an acceptable drug for mass chemotherapy, control of the insect vector offers the only means at present for interrupting transmission of the disease. The mechanical eliminati-on of S. damnosum breedi ng sites (e.g. through the construction of dams and the regularization of river beds) is not economically feasible, although in restricted areas it could be a consequence of certain river management projecEs. The possi- bility of controlling this vector with biological agents is being invesEigated under a research programme jointly supporLed by the Government of Canada and OCCGE, but the develop- ment of an effecEive biological control methodology will require many ye.ars. Insecticides constitute at present the only effective means of interrupting onchocerciasis transmission. As the flight range of the adult S. damnosum may, in favourable circumstances, exceed 3OO km, an attack on the adult fly would require the insecticide treatment of an immense area and is not considered feasible. As the vector breeding sites are restricted to fast-flowing sectors of rivers, control of S. damnosum in the Volta River basin area is being directed against the larvae and is based on weekly application of insecticide immediately upstream from the larval breeding places. oCP /74.1 Rev.3 page 3 Because of the inaccessibility by land of many of the breeding sites of Slmullum, th" only feasible method of applying Ehe insecticide is from the air. In the case of large rivers that are sufficiently sEraight, light planes can be used, buE narrow twisEing water- ways and those overhung by forest require the use of helicoprers. The selection of an insecticide was based on specific criEeria: Ehe candidate compound was required to have low toxicity for man and vertebraEes in general and, while being very effecEive against b1ackly, to have as little effect as possible on non-target fauna. Only biodegradable compounds with littte residual activity were considered Eo make sure that no contamination of the environrnent could take place. The insecticides selected were sEudied by hydrobiologists and a fishery biologisE in WesE. African laboratories and in field condi- tions to confirm their suitability. Because of the long life of the adult worm in the human host, sufferers from onchocer- ciasis may remain infective for as long as 15 years even if not reinfected. Therefore the duration of a campaign to prevent Ehe disease by eliminating its insecE vector nnist not be less than this length of time after the last new case in the prograrrne area. For this reason the Progranune is scheduled to last 2O years. The effects of the vector control campaign on the prevalence and severity of onchocer- ciasis must be continuously monitored by epidemiological evaluation teams. The onchocerciasis control Progranrne is supported by appropriately applied researchprojects' Particularly in the fi.elds of chemotherapy, vector control and protection of theenvironment. Another imPortant element of the Programme is personnel training, to ensurethe progressive take over of the Progranrne by specialists of the seven countries concerned. The repopulaEion and/or settlement of the uninhabited fertile areas freed from thedisease is a major objective of the onchocerciasis control programme. such acEion wouldalso permit development measures to be taken in areas of high population density. rn many cases the lands Eo be repopulated or colonized require infrasErucEure in Eermsof road networks, r^/ater supply and medical, educational and agriculEural extension services.rn other instances improvemenr. of such facilities is essenEial for Ehe success of repopula-tion and settlement. The required low and medium leve1 agricultural extension services in some instances, need backsEoppinB by professional officers in Ehe relevant disciplines. The main responsibility for the economic development projects remains with each of theGovernments which may however request external assistance in the rnethodology and planning ofactivities, and external funds for their financing. A series of reclamation plans based onthe development of agriculture and sEock raising were studied and costed, as examples, toassist national authorities. Launching of the prograltrrne The Prograrmne is necessarily a joint undertaking and requires Ehe fulI collaboration ofeach of the seven countries concerned. The Progranrne is governed by an operational AgreemenEsigned at Accra on 1 November 1973, which brings into association the Governments and WHo, EheExecuting Agency. The operational Agreement is supplemented by separaEe country protocols which esEablish the contributions of the participating Governments. oCP /74.1 Rev.3 page 4 It was decided tc implement the Programme by staggering the inception of operar ions over a period of three years, from L974 to L976, as it would have been unrealistic to attempt to launch the vector control operations simultaneously over such a large area. The first phase thus started at the beginning of the dry season in December L974, when the S. damnosum po pu la- tion was on Ehe decrease, and concenLrated initially on a zone of heavy infestation in the Black Volta, Como6-L6raba, Bandama, Nzi and Banifing basins as a logical extension of the old FED/OCCGE campaign. The work was extended in a second phase ro rhe Red Volra, White Volta and Dalta basins in L976, Phase three of operaLi.ons, frc,m l977 onwards, covered the basins of the Oti-Pendjari, and of the Mali, Ivory Coast, Upper Volta, l1lger and Benin tributaries of the Niger River. A large-scale inEercountry programme of this nature requires the coordination of efforts at the national level and the consistent support of each parti-cipating Government. To this end t:ach of the seven Governments concerned has set up a National Onchocerciasis Comnittee to rlsume responsibiliEy for coordinating the rechnical, social, budgetary and logistic support of the Programme at the national level. Such national committees play a key role in ensuring the provision of Government counterpart contributions, the link between the Onchocerciasis Control Programme itself, the repopulatirr;r and settlement activities anrl projects for the sub- sequent economic development of the fteed zones, and other necessary measures. Tt vras estinuted that the overall Programme would requir, funds rn the region of some $ 120 million over a 20 year period, from 1974 to L994. In t-he tj-rsl instance, detailed planning covers the six years L974-L979. The World Bank accepted L.; mobilize contributions to the Prograrmne and to act as the custodian of the Special irund for Onchocerciasis Control for the financingofactivities. The Fund Agreementwas signed on 7 Ma.r 1975 in Washington, D.C. As Execuuing Agency, WHO assumes the technical responsibility, in conjunction with the Covernments involved, for the technical and logistic management oftheProgranme. WHOappoint-ed a Prograuune Director who is assisted by four specialized Units (Simulium Control, Epidemiology and Public Health, Economic Development support "na-earr-irr-Gtrative support).The Programme headquarters is located at Ouagadougou, Upper Volta, in view of its central position in the affected area and in one of the most sorely alflicted of the seven countries invo lved. UNDP and FAO are associated with the Programme to assist Governments, at their request, in planning and implemenEing national projects and schemes in the economic field where exter- nal assistance is required to develop the zones freed of onchocerciasj-s. The Steering Co[Enittee remains as the executive organ of the Progranrne with the duty of studying and reconrnending the plans of work prepared by the Executing Agency. A Joint Coordinating Cornrnittee was set up grouping the seven participating countries, the donor nations and institutions, and the four sponsoring agencies. The CommitEee, headed by an Independent Chairman meets once every year to review the annual budget and exercise general supervision over the Progranure. Specialists from all continents are participating in the activities of the Progranune, through their contributions to and their membership of its different scienLific, technical and advisory groups. Numerous scientific bodies and inscitutes have been collaborating in Ehe activities of the Programne since it was launched in the fields i.>f research, training, ecology, hydrology and economic development. Prograrmne activities The Vector Control Unit maintains constant entomological surveillancc 1ry prospection flights and thanks to a network of 7 sectors and 22 subsectors spread all over the Progranrne area. Air operations are carried out from the two main bases at Bobo-Dioulasso and Tama16. IocPf 7 4.1 Rev. 3 page 5 The sectors and subseciors are linked to one another and to Ehe Progranune Director by 17 radio transmitting/receiving uniEs. The btackfly capture points number about 3OO. The catches are counted and examined to determine the morphology, physiological age and infesEation rate of the blackflies. The entomological situaEion is continuously evaluated. Weekly treatment of hrater courses by application of insecticide is planned on the basis of this evaluation. The rhythm of treatment is based on the biological cycle of the vector larvae. The insecticide employed at present is a biodegradable organophosphorus compound, namely a 20% emulsion concentrate of Abate. The dosages are calculated in accordance with the vrater flow of the rivers in Ehe different hydrological basins; underdosages can, in fact, be just as disastrous for the proper functioning of the Prograrune as overdosages for non- target fauna. The insecticide is applied from the air. The Epidemiological Evaluation Unit carries out parasitological and ophthalmological examinations of the populations of a certain number of villages selecEed in advance so as Eo determine the prevalence of onchocerciasis, as well as the endemicity and the blindness rates. Epidemiological evaluation cakes place at t\^/o levels: (I) ln all the villages selected, a basic study is conducted so as to determine the prevalence of the infection and of serious clinical symptoms, by age and sex. The following examinations are carried out: skin snips, external search for nodules and specific skin lesions, measurement of visual acuity by means of the "hand tesE'r for Ehose who cannot read. This study is termed the "simpletr survey. (2) In about Lo% of the villages chosen, thorough epidemiological and clinical studies, termed "detailed" surveys are made, comprising eye examinations using the slit 1amp, examination of the fundus of the eye, multiple skin snips, search for microfilariae in the urine, etc. The basic epidemiological evaluation is practically complete. A second evaluation of the same villages will begin in 1978, in places where vector control has been continuing for threeyears. Three years of vector control are regarded as the minimal period for epidemiological evaluation of the trend of the disease. The Economic Development Unit collects all available data on developmenE projects underwayor being prepared, aE the national level and the regional 1eve1, in the sevenparticiPating counEries. It gives assistance to the mi-ssions concerned by this development by making the necessary contacts and supplying the basic daEa at its disposal. IE takes the necessary action vis-i-vis the executing bodies and sources of finance. Research is also one of Ehe important acEivities of the Programme. In the fields of entomology and environmental protection it deals with Ehe ecology of the vectors (rearing of a single generation and establishment of a laboratory colony of S damno sum, cytoEaxonomic and morphological studies of the s damnosum complex, sampling of S. damnosum larvae and adults, dispersion and migration of S. damnosum adult females), with vector control (evaluation of the susceptibility of blackflies to insecEicides, evaluation of new insecticides and formulations, biodegradability of insecticides, insecticide toxicity, equipment for insecti- cide application), and with protecEion of the environment (acute and long-Eerm effects of insecticides on nontargeE organisms). LonS-term hydrobiological studies are being made on characteristic stretches of the watercourses treated to ensure that the biological equilibrium of the rivers is not seriouslydisturbed by control operations. The effects of the insecticide on the number and distri- buEion of S damnosum are continuously observed so as Eo restrict treatment to larva1 breeding places actually colonized by the vector. Surveillance of these important aspects of the Progranrne takes place with the participation of the Ecological Group atEached to the prograune, which gives its views on the measures t.o be taken in order to ensure satisfactory environ- mental protection. ocPf74.1 Rev.3 page 6 Research in the medical field covers: the epidemiology of onchocerciasis (studies on thb dynamics of transmission of the disease and histological examination of skin lesions caused by onchocerciasis)1 parasitology (improvemenE of skin snips technique, research on other human filariases); inrnunology of onchocerciasis (isolation of a purified specific O. volvulus ant igen, evaluation of a fluorescent antibody test); and onchocerciasis chemo- therapy (fieta tests of existing and new drugs, creation of a Chemotherapeutic Research Centre in the Progranme area). Research is also proceeding on the distribution of animal onchocerciasis and the in vitro culture of microfilariae. The Programme, with in training activities. held for entomologists, provided for physicians or ophthalmology. the assistance of specialized institutes and bodies, is also engaged Ttreoretical and practical training and refresher courses have been enEomological assistants and technicians. Fellowships are also intending to specialize in public health, onchocerciasis epidemiology Initial results The Programme is now four years old, four years during which its establishment and its various activities have proceeded jointly, with 1994 as the target date. An evaluation of the work done should employ two different approaches. One is the entomological approach which is concerned with results in relation to the densiLy of blackflies, as well as their localization and their infection rates. Entomological evaluation is continucus and provides immediate and uP-to-date information on the effectiveness of vector control activities. The other is the epidemiological approach, based on examination every three years of thepopulations of selected villages in the zones treated. Entomological evaluation shows that apart from one or thTo pockets of reinvasion during t.he rainy season the vector control operations are giving excellent results, Subsequent epidemiological surveys will enable a definitive appralsal of these results to be made.