The need for evidence-based strategies and tools for onchocerciasis elimination in Africa

In a recent article we discussed the feasibility of onchocerciasis elimination in Africa by 2025. We expressed concern that elimination may be impeded by failure to build on the lessons learned in the African onchocerciasis control programmes and the introduction of strategies and tools from the Americas. Richards et al. and Cupp et al. wrote to refute our concern and described recent achievements with stopping treatment in some areas.In this response, we discuss their arguments which did not convince us. We point out several scientific flaws in the American conceptual framework of elimination which has led to longer periods of treatment than necessary, and in the use of an arbitrary threshold for stopping treatment. We show that recent achievements fall significantly short of what would be needed to achieve onchocerciasis elimination by 2025.We conclude our response by advocating for a more objective and inclusive debate on strategies and tools for onchocerciasis elimination.

Is onchocerciasis elimination in Africa feasible by 2025: a perspective based on lessons learnt from the African control programmes

BACKGROUND

Onchocerciasis is found predominantly in Africa where large scale vector control started in 1974. Registration and donation of ivermectin by Merck & Co in 1987 enabled mass treatment with ivermectin in all endemic countries in Africa and the Americas. Although elimination of onchocerciasis with ivermectin was considered feasible only in the Americas, recently it has been shown possible in Africa too, necessitating fundamental changes in technical and operational approaches and procedures.

MAIN BODY

The American programme(OEPA) operating in onchocerciasis epidemiological settings similar to the mild end of the complex epidemiology of onchocerciasis in Africa, has succeeded in eliminating onchocerciasis from 4 of its 6 endemic countries. This was achieved through biannual mass treatment with ivermectin of 85% of the eligible population, and monitoring and evaluation using serological tests in children and entomological tests. The first African programme(OCP) had a head start of nearly two decades. It employed vector control and accumulated lots of knowledge on the dynamics of onchocerciasis elimination over a wide range of epidemiological settings in the vast expanse of its core area. OCP made extensive use of modelling and operationalised elimination indicators for entomological evaluation and epidemiological evaluation using skin snip procedures. The successor African programme(APOC) employed mainly ivermectin treatment. Initially its objective was to control onchocerciasis as a public health problem but that objective was later expanded to include the elimination of onchocerciasis where feasible. Building on the experience with onchocerciasis elimination of the OCP, APOC has leveraged OCP's vast modelling experience and has developed operational procedures and indicators for evaluating progress towards elimination and stopping ivermectin mass treatment of onchocerciasis in the complex African setting.

CONCLUSIONS

Following the closure of APOC in 2015, implementation of onchocerciasis elimination in Africa appears to overlook all the experience that has been accumulated by the African programmes. It is employing predominantly American processes that were developed in a dissimilar setting from the complex African onchocerciasis setting. This is impeding progress towards decisions to stop intervention in many areas that have reached the elimination point. This article summarizes lessons learned in Africa and their importance for achieving elimination in Africa by 2025.

A model for evaluating the sustainability of community-directed treatment with ivermectin in the African Program for Onchocerciasis Control

Onchocerciasis is controlled by mass treatment of at-risk populations with ivermectin. Ivermectin is delivered through community-directed treatment (CDTI) approach. A model has been developed to evaluate the sustainability of the approach and has been tested at 35 projects in 10 countries of the African Program for Onchocerciasis Control (APOC). It incorporates quantitative and qualitative data collection and analysis, taking account of two factors identified as crucial to project sustainability. These are (i) the provision of project performance information to partners, and (ii) evidence-based support for project implementation. The model is designed to provide critical indicators of project performance of the model to implementing, coordinating, and funding partners. The model's participatory and flexible nature makes it culturally sensitive and usable by project management. This model is able to analyze the different levels involved in project implementation and arrive at a judgment for the whole project. It has inbuilt mechanisms for ensuring data reliability and validity. The model addresses the complex issue of sustainability with a cross-sectional design focusing on how and at which operational level of implementation to strengthen a CDTI project. The unique attributes and limitations of the model for evaluating the sustainability of projects were described.

The African Programme for Onchocerciasis Control: impact on onchocercal skin disease

OBJECTIVES

To assess the long-term impact of the African Programme for Onchocerciasis Control on itching and onchocercal skin disease (OSD).

METHODS

Seven study sites in Cameroon, Sudan, Nigeria and Uganda participated. Two cross-sectional surveys were conducted of communities meso- and hyper-endemic for onchocerciasis before and after 5 or 6 years of community-directed treatment with ivermectin (CDTI). Individuals were asked about any general health symptoms including itching and underwent full cutaneous examinations. Onchocercal skin lesions were documented according to a standard classification.

RESULTS

Five thousand one hundred and ninety three people were examined in phase I and 5,180 people in phase II. The presence of onchocercal nodules was a strongly significant (P < 0·001) risk factor for all forms of onchocercal skin disease: APOD (OR 1·66); CPOD (OR 2·84); LOD (OR 2·68); reactive skin lesions (OR 2·38) and depigmentation (OR 3·36). The effect of community-directed treatment with ivermectin was profound. At phase II, there were significant (P < 0·001) reductions in the odds of itching (OR 0·32), APOD (OR 0·28); CPOD (OR 0·34); reactive skin lesions (OR 0·33); depigmentation (OR 0·31) and nodules (OR 0·37). Reduction in the odds of LOD was also significant (OR 0.54, P < 0.03).

CONCLUSIONS

This first multi-country report of the long-term impact of CDTI reveals a substantial reduction in itching and OSD. APOC operations are having a major effect in improving skin health in poor rural populations in Africa.

African Programme for Onchocerciasis Control (APOC): sociological study in three foci of central Africa before the implementation of treatments with ivermectin (Mectizan®)

The African Programme for Onchocerciasis Control (APOC) has put in place a study to assess the long-term impact of the community-directed treatments with ivermectin on various clinical and entomological indicators of onchocerciasis. As the results obtained would depend on community participation in the treatments, surveys were also conducted at the study sites to assess the people's knowledge, attitudes and practices regarding onchocerciasis and its treatment. This article presents the anthropological observations made before the implementation of the treatments in three sites: one in the Central African Republic, and two in the Democratic Republic of Congo. The information collected shows that the populations have a relatively poor knowledge of the manifestations and mode of transmission of onchocerciasis. The communities' attitudes towards those individuals afflicted with the disease vary from one site to another. Regarding treatment, the populations use both traditional and 'modern' treatments, but the beneficial effects of ivermectin are not well known. The differences recorded between the sites surveyed demonstrate that the messages to be delivered to the populations before the distributions should take into account the local epidemiological and socio-anthropological context.

Evaluation of the diethylcarbamazine patch to evaluate onchocerciasis endemicity in Central Africa

OBJECTIVE

As part of a baseline data collection for assessing the impact of the African Programme for Onchocerciasis Control, to evaluate the diethylcarbamazine (DEC) patch test in determining the endemicity of onchocerciasis.

METHOD

A total of 226 untreated children aged 3-5, living in four selected endemic foci, in Cameroon, Gabon and Central African Republic, were tested. Observed graded skin reactions to the patch were analysed and compared with the prevalence of onchocercal nodules and reactive skin disease in the corresponding community.

RESULTS

The proportion of children who tested positive ranged from 25.0% to 77.1%. The values were closely correlated with the prevalence of nodules, i.e. the level of endemicity for onchocerciasis.

CONCLUSION

The DEC patch test, which has been so far used only in West African foci of onchocerciasis, can also constitute a valuable tool to evaluate the levels of endemicity of onchocerciasis in Central Africa, and to follow-up the intensity of transmission of Onchocerca volvulus.

[African programme for onchocerciasis control (APOC): entomological aspects of Onchocerca volvulus transmission by Simulium neavei in the Basin of Sankuru (Eastern Kasai, Democratic Republic of Congo)]

As part of a study to evaluate the long-term impact of community-directed treatment with ivermectin (CDTI), baseline entomological data on the transmission of onchocerciasis in the forest zone of the Eastern Kasai Province were collected from July 1998 to January 1999. Species of the Simulium neavei complex were the only vectors found in the site during the study. Nuisance activity was low with a mean biting rate of only 32.5 bites/man/day. The mean parturity rate was 29.4%, the mean rate of infected females was 14.5% and the mean number of infective Onchocerca larvae per 1000 parous flies was 659. These findings clearly show that the S. neavei population at the study site has high vector capability and constitutes a large microfilarial reservoir. The entomological features found in the study area are consistent with a hyper-endemic zone.

[Onchocerciasis in the area of Lastourville, Gabon. Clinical and entomological aspects]

The African Programme for Onchocerciasis Control (APOC) has implemented a series of surveys aimed at evaluating the long-term impact of its activities. The region of Lastourville (Gabon) is one of the selected sites for this study. A total of 886 persons was examined for skin lesions, and 459 out of them participated in detailed ocular examinations. Blackflies were collected during one year and dissected. Although the focus was found to be hypoendemic (prevalence of nodules: 7.7%), the frequency of onchodermatitis was relatively high. The lesions of the anterior segment of the eye were rare, but the prevalence of optic nerve disease, and of choroido-retinal lesions reached 5.2 and 2.7%, respectively. The annual transmission potential (2,171 infective larvae per man) was high, when compared with the results recorded in the human population. This may be due to the presence of Onchocerca spp. of animal origin in the blackflies. These results indicate that in the area of Lastourville, though regarded as the main focus of onchocerciasis in Gabon, the disease is relatively mild.

[African Programme for Onchocerdasis Control (APOC): Onchocerca Simulium squamosum in two regions in the Republic of Cameroon]

In 1998, the African Programme for Onchocerciasis Control (APOC) decided to launch a long-term impact assessment of its operations. This paper reports the baseline entomological data collected throughout a whole year in two sites of Cameroon (Kahn and Bolo). The Simulium populations of the two study sites were characterized by parous rates of 7.2% and 33.5% respectively and infectivity by O. volvulus of 31 and 190 infective larvae per 1000 parous flies respectively The Annual Transmission Potentials (ATP) were respectively 523 and 9972 infective larvae per man and per year in Kahn and in Bolo. The Simulium populations studied in both sites, even though the ATP in Kahn is 19 times lower than that of Bolo, showed a pattern of an onchocerciasis hyperendemic zone in terms of vector capacities and entomological indices.

[Vector capacities of Similium damsnosum s.l and risk for Onchocerca volvulus transmission in Inga (Democratic Republic of Congo)]

This article analyzes the results of a one-year entomological survey conducted near the Yalala rapids in the Inga region, Democratic Republic of Congo, prior to the implementation of Community-Directed Treatment with Ivermectin (CDTI). A vector control program had been undertaken from October 1969 to December 1980, 20 kilometers upstream from the study site. The results of the present study show that during 122 collection days, 5,824 females were captured, of which 3,899 were dissected; 2,001 (51.3%) were parous while 44 (2.2%) were infected while 4 (0.2%) were infective. The crude Annual Transmission Potential (ATP) was 65 infective larvae per man and per year at the river as against 12 in Yalala village located two kilometers from the rapids. The average biting rate was 5 flies/man/day during the dry season and 90 during the rainy season. The vector capacity of similium shows that the risk of transmission of Onchocerca volvulus to the human population was not only reduced in time (2-3 months), but was also negligible all year round.

Programme africain de lutte contre l’onchocercose (APOC) : transmission d’Onchocerca volvulusparSimulium damnosumS. l. dans deux régions de la République Centrafricaine

Entomological baseline data were collected in the villages of Zinga and Boali-Falls in Central African Republic (CAR) in view of the long term impact assessment of community-directed treatment with ivermectin (CDTI). Morphological determinations revealed that flies caught in both sites belong to the sub-group Sou/Sq. In Boali, the nuisance was relatively high with biting rates averaging 243 bites/man/day, with a parous rate of 61.6% and a crude annual transmission potential (ATP) of 8,259 infective larvae/man/year; and the average number of infective larvae per 1,000 parous flies was 177. In Zinga, the mean biting rate was 191 bites/man/day, with a parous rate of 51.6%, a crude ATP of 3,422, and 86 infective larvae per 1,000 porous flies. In conclusion, the vectorial capacity and the entomological indices recorded are characteristic of high onchocerciasis transmission zones. However, some of the infective larvae found, maybe of animal origin, need identification to better determine the real level of endemicity.

Twenty-two years of blackfly control in the onchocerciasis control programme in West Africa

Twenty-two years after the launch of the Onchocerciasis Control Programme in West Africa (OCP), Jean-Marc Hougard and colleagues critically review the vector-control strategy adopted. They go on to identify the few hydrological basins where transmission of the infection remains difficult to control, to analyse the causes and to propose appropriate corrective measures on a case-by-case basis. Most of these measures, which are mainly based on ivermectin chemotherapy, will continue to be applied after the end of the OCP in 2002, under the control of the countries concerned.

Gender issues in the community-directed treatment with ivermectin (CDTI) of the African Programme for Onchocerciasis Control (APOC)

This paper reviews the issues relating to compliance and participation among the men and women of three countries within the remit of the African Programme for the Control of Onchocerciasis (APOC): Cameroon, Nigeria and Tanzania. Project-monitoring data from 109 focus-group discussions, 6069 household-survey respondents and 89 interviews with ivermectin distributors were analysed to gain an insight into the attitudes and behaviours of men and women in relation to ivermectin treatment and their participation in the programme. Although there are no statistically significant gender differences in coverages for ivermectin treatment, culturally prescribed gender relationships influence the ways in which men and women express and experience treatment-related behaviours. Gender roles also affect participation in the programme. Decision-making in communities on the selection of distributors tends to follow socio-cultural hierarchies based upon patriarchy and gerontocracy. Relatively few ivermectin distributors (21%) are women. Although they receive less support than their male counterparts, the female distributors are just as willing to continue ivermectin distribution in the community, and they perform as well or better than men in this regard. The terms 'community-directed', 'community participation' and even 'compliance' obfuscate important gender differences that are inherent in the implementation of onchocerciasis control. Development of strategies that recognize these gender differences will have important implications for long-term adherence to treatment and for the overall quality and sustainability of the programme.

APOC's strategy of community-directed treatment with ivermectin (CDTI) and its potential for providing additional health services to the poorest populations. African Programme for Onchocerciasis Control

Since its inauguration in 1995, the African Programme for Onchocerciasis Control (APOC) has made significant progress towards achieving its main objective: to establish sustainable community-directed treatment with ivermectin (CDTI) in onchocerciasis-endemic areas outside of the remit of the Onchocerciasis Control Programme in West Africa (OCP). In the year 2000, the programme, in partnership with governments, non-governmental organizations and the endemic communities themselves, succeeded in treating 20,298,138 individuals in 49,654 communities in 63 projects in 14 countries. Besides the distribution of ivermectin, the programme has strengthened primary healthcare (PHC) through capacity-building, mobilization of resources and empowerment of communities. The community-directed-treatment approach is a model that can be adopted in developing other community-based health programmes. The approach has also made it possible to bring to the poor some measure of intervention in some other healthcare programmes, such as those for malaria control, eye care, maternal and child health, nutrition and immunization. CDTI presents, at all stages of its implementation, a unique window of opportunity for promoting the functional integration of healthcare activities. For this to be done successfully and in a co-ordinated manner, adequate funding of CDTI within PHC is as important as an effective sensitization of the relevant policy-makers, healthworkers and communities on the value of integration (accompanied by appropriate training at all levels). Evaluation of the experiences in integration of health services, particularly at community level, is crucial to the success of the integration.

The challenges of community-directed treatment with ivermectin (CDTI) within the African Programme for Onchocerciasis Control (APOC)

The principal strategy adopted by the African Programme for Onchocerciasis Control (APOC), for the control of onchocerciasis in the 19 countries of Africa that now fall within the programme's remit, is that of community-directed treatment with ivermectin (CDTI). Halfway through its 12-year mandate, APOC has gathered enough information on the main challenges to guide its activities in Phase 2. An analysis of reports and other documents, emanating from consultants, scientists, monitors and national and project-level implementers, indicates that there are three broad categories of challenge: managerial; technical; and socio-political. Under these three categories, this review identifies the most pertinent concerns that APOC must address, during Phase 2, to enhance the prospects of establishing sustainable systems for ivermectin distribution. The major challenges include: (1) maintaining timely drug-collection mechanisms; (2) integrating CDTI with existing primary-healthcare services; (3) strengthening local health infrastructure; (4) achieving and maintaining an optimal treatment coverage; (5) establishing and up-scaling community self-monitoring; (6) designing and implementing operations research locally; (7) ensuring the adequacy of community-directed distributors; (8) increasing the involvement of local non-govemmental develop organizations in the programme; (9) achieving financial sustainability; (10) implementing equitable cost-recovery systems; and (11) engaging in effective advocacy. The implications of the challenges and suggestions about how they are being (or could be) addressed are also highlighted in this brief review, which should be of value to other programmes and agencies that may be contemplating the adoption of this unique strategy.

Rapid epidemiological mapping of onchocerciasis (REMO): its application by the African Programme for Onchocerciasis Control (APOC)

One of the fundamental challenges that the African Programme for Onchocerciasis Control (APOC) has had to face is how to identify the endemic communities where its mass ivermectin-treatment operations are to be carried out in conformity with its stated objective of targetting the most highly endemic, affected and at-risk populations. This it has done by adopting a technique, known as the rapid epidemiological mapping of onchocerciasis (REMO), that provides data on the distribution and prevalence of onchocerciasis. Integration of the REMO data into a geographical information system (GIS) enables delineation of zones of various levels of endemicity, and this is an important step in the planning process for onchocerciasis control. Zones are included in (or excluded from) the APOC-funded programme of community-directed treatment with ivermectin (CDTI), depending on whether or not their levels of onchocercal endemicity reach the threshold set by APOC. This review describes the application of the REMO/GIS technique by APOC in its operations, and identifies the remaining related challenges.

Monitoring community-directed treatment programmes for sustainability: lessons from the African Programme for Onchocerciasis Control (APOC)

Community-directed treatment is a relatively new strategy that was adopted in 1997 by the African Programme for Onchocerciasis Control (APOC), for large-scale distribution of ivermectin (Mectizan). Participatory monitoring of 39 of the control projects based on community-directed treatment with ivermectin (CDTI) was undertaken from 1998-2000, with a focus on process implementation of the strategy and the predictors of sustainability. Data from 14,925 household interviews in 2314 villages, 183 complete treatment records, 382 focus-group discussions, and the results of interviews with 669 community leaders, 757 trained community-directed drug distributors (CDD) and 146 health personnel (in 26 projects in four countries) were analysed. The data show that CDD dispensed ivermectin to 65.4% of the total population (71.2% of the eligible population), with no significant gender differences in coverage (P > 0.05). Treatment coverage ranged from 60.2% of the eligible subjects in Cameroon to 76.9% in Uganda. There was no significant relationship between the provision of incentives to CDD and treatment coverage (P > 0.05). The frequency of treatment refusal was highest in Cameroon (29.2%). Although most (72.1%) of the communities investigated selected their CDD on the basis of a community decision at a village meeting, only 37.9% chose their distribution period in the same way. There is clearly a need to improve communication strategies, to address the issues of absentees and refusals, to emphasise community ownership and to de-emphasise incentives for CDD. The investigation of the 'predictor indicators' of sustainability should enable APOC to understand the determinants of project performance and to initiate any appropriate changes in the programme.

The achievements and challenges of the African Programme for Onchocerciasis Control (APOC)

The main strategy of APOC, of community-directed treatment with ivermectin (CDTI), has enabled the programme to reach, empower and bring relief to remote and under-served, onchocerciasis-endemic communities. With CDTI, geographical and therapeutic coverages have increased substantially, in most areas, to the levels required to eliminate onchocerciasis as a public-health problem. Over 20 million people received treatment in 2000. APOC has also made effective use of the combination of the rapid epidemiological mapping of onchocerciasis (REMO) and geographical information systems (GIS), to provide information on the geographical distribution and prevalence of the disease. This has led to improvements in the identification of CDTI-priority areas, and in the estimates of the numbers of people to be treated. A unique public-private-sector partnership has been at the heart of APOC's relative success. Through efficient capacity-building, the programme's operations have positively influenced and strengthened the health services of participating countries. These laudable achievements notwithstanding, APOC faces many challenges during the second phase of its operations, when the full impact of the programme is expected to be felt. Notable among these challenges are the sustainability of CDTI, the strategy's effective integration into the healthcare system, and the full exploitation of its potential as an entry point for other health programmes. The channels created for CDTI, could, for example, help efforts to eliminate lymphatic filariasis (which will feature on the agenda of many participating countries during APOC's Phase 2). However, these other programmes need to be executed without compromising the onchocerciasis-control programme itself. Success in meeting these challenges will depend on the continued, wholehearted commitment of all the partners involved, particularly that of the governments of the participating countries.

Partnership and promise: evolution of the African river-blindness campaigns

This article describes the evolution of the partnership, between various health and developmental agencies, that has sustained the campaign against river blindness in Africa. The international community was oblivious to the devastating public-health and socio-economic consequences of onchocerciasis until towards the end of the 1960s and the beginning of the 1970s. Then a 'Mission to West Africa', supported by the United Nations Development Programme, and a visit to the sub-region by the president of the World Bank culminated, in 1974, in the inauguration of the Onchocerciasis Control Programme in West Africa (OCP). OCP was a landmark event for the World Bank as it represented its first ever direct investment in a public-health initiative. The resounding success of the OCP is a testimony to the power of the partnership which, with the advent of the Mectizan Donation Programme, was emboldened to extend the scope of its activities to encompass the remaining endemic regions of Africa outside the OCP area. The progress that has been made in consolidating the partnership is discussed in this article. The prospects of adapting the various strategies of the African Programme for Onchocerciasis Control, to entrench an integrated approach that couples strong regional co-ordination with empowerment of local communities and thereby address many other health problems, are also explored.

Blackfly control: what choices after onchocerciasis?

Blackflies are reappearing in areas of West Africa where they used to be controlled with insecticides because they were vectors of the parasite Onchocerca volvulus. Even though they no longer transmit onchocerciasis in these areas they can hinder optimal land use through their biting behaviour. The authors discuss the problems associated with resuming the use of insecticides to control the blackfly and recommend that ground treatment be restricted to areas where it is likely to be effective on a continuing basis. In communities lacking technical and financial resources the only alternative consists of individual protection through the use of repellents or protective clothing.

The impact of Mectizan on the transmission of onchocerciasis

For many years there was no suitable drug available for the control of onchocerciasis. The advent of Mectizan (ivermectin, MSD; an effective microfilaricide), its registration in October 1987 for the treatment of human onchocerciasis, and its suitability for large-scale application were major break-throughs in the control of human onchocerciasis via chemotherapy. Several studies, both fly-feeding experiments and community trials, have established that Mectizan treatment causes a significant reduction in the transmission of infection. Although long-term treatment in some isolated foci (such as occur in the New World and in some hypo- and meso-endemic areas elsewhere) appears to interrupt transmission, more prolonged treatment is required to prove if transmission can be stopped. Advantage could be taken of the significant impact of Mectizan on transmission by giving treatment while or just before transmission by blackflies is most intense.

Delivery systems and cost recovery in Mectizan treatment for onchocerciasis

The efficiency of on-going delivery systems and cost recovery in Mectizan (ivermectin, MSD) treatment for onchocerciasis are reviewed. The search is on for an effective system of Mectizan delivery, involving drug procurement, delivery from port to districts and distribution to eligible persons, which can be sustained by the endemic countries for many years. The mechanisms for procuring and clearing the drug at the ports, and the drug's integration into the existing delivery systems of each national health service, need to be improved. Although large-scale treatments by mobile teams or community-based methods evidently achieve high and satisfactory rates of coverage, they also incur high recurrent costs which have to be covered by external partners and are not sustainable by national health services. Cost-sharing is considered an important factor in a sustainable delivery system and community-directed treatment, in which the community shares the cost and ownership of local distribution and is empowered to design and implement it, is likely to be more cost-effective and sustainable.

Impact of combined large-scale ivermectin distribution and vector control on transmission of Onchocerca volvulus in the Niger basin, Guinea

As part of the WHO Onchocerciasis Control Programme in West Africa (OCP), the attack phase of operations in the Niger basin in Guinea began in 1989 with the simultaneous use of ivermectin and vector control. Larvicide applications coupled with annual large-scale ivermectin distribution have greatly reduced blackfly infectivity (by 78.8% for the number of infective larvae per 1000 parous flies). The combination of vector control and ivermectin has permitted excellent control of transmission. In the original OCP area, it took 6-8 years of vector control alone to obtain an equivalent decrease in blackfly infectivity. For the same number of flies caught, transmission was much higher in areas where ivermectin had not been distributed. The combined use of ivermectin and vector control has opened up new prospects for carrying out OCP operations with, notably, the possibility of reducing larviciding operations.

[Importance and role of spreading larvicides on the soil in river beds for the control program against onchocerciasis in west Africa]

The control of blackfly is based on larvicide spraying in rivers where the insects breed and their larval stages are vulnerable. The first technique for large-scale operations, consists of using aircraft in the same way as for mosquito control and crop protection operations. The second technique, which will be discussed in this paper, consists of ground treatment of rivers, either directly with a container or with a spraying pump or by boat spraying insecticide in cross strip. In areas of West Africa where onchocerciasis is still prevalent, ground treatment is done to support aerial operations and to a lesser extent to control nuisance in areas where the endemicity of the disease is low. In onchocerciasis-freed zones, control of blackfly aims only at suppressing the nuisance in order to enhance the socio-economic development in areas at unfair disadvantage. This distinction is important for determining the responsibilities of various groups. Vector control to interrupt the transmission of onchocerciasis is the mandate of OCP while the control of nuisance is the responsibility, depending on the circumstances, of the private sector, the government and/or village communities. In this paper, we have attempted to highlight the objectives of such treatments, the responsibilities of various groups and the prospects in West African countries located in the Onchocerciasis Control Programme area. We also present the situation of ground larviciding in countries outside the Programme, in temperate as well as tropical conditions, in order to provide some basis for the development of ground treatment strategies in the OCP area.

[National entomological teams of the western extension zone of the Onchocerciasis Control Program (OCP) in west Africa from 1986 to 1990]

The western extension area of the Onchocerciasis Control Programme in West Africa (OCP) covers five countries: Guinea, Guinea-Bissau, Mali (western part), Senegal and Sierra Leone. From 1986 to 1990, national teams employed by the respective governments have been regularly collecting entomological data on the vectors of onchocerciasis in these countries. As in the initial programme area of the OCP, the entomological surveillance network was composed of entomological sectors and subsectors (the latter are called "operational bases" in the western extension). In 1990, 308 staff in 47 capture teams were employed for the entomological surveillance activities in seven sectors and twenty-five operational bases. They included a national coordinator as head of the teams for each country, a wide range of technicians, and administrative support staff to assist the national coordinator in the overall management of available resources. The national teams worked under the technical responsibility and supervision of WHO/OCP but with no employee/employer relationship between them and WHO, since they were employed and their salaries were paid by their governments. The OCP, however, paid additional lump sum allowances to each worker, as well as daily subsistence allowances when away from their duty station. Vehicles, entomological equipment, office supplies and furniture, fuel and lubricants were provided by WHO/OCP. Despite the difficulties encountered in the field, which were often great, and their lower salaries (compared with colleagues paid by WHO/OCP), the technical workers in the national teams performed well by OCP standards, with results as satisfactory as those obtained by the WHO/OCP teams in the rest of the programme area. The main reasons for the efficiency and dynamism of the national entomological teams are described. The future of these teams after OCP has ceased its activities is also discussed.

The WHO Onchocerciasis Control Programme: retrospect and prospects

The history of onchocerciasis control in Africa and the genesis of the WHO Onchocerciasis Control Programme in West Africa (OCP) are briefly reviewed. The importance of experience gained in anti-locust campaigns in helping to plan the OCP is stressed. Members of the Simulium damnosum species complex are the vectors of onchocerciasis, which OCP is controlling with insecticide treatments on the stretches of rivers where the Simulium breed. Migrations of flies have been responsible for reinfestations of controlled areas and the spread of insecticide resistance. The management of these problems and related research are described, but it is emphasized that despite setbacks OCP is achieving its aims. A strategy for the future is outlined: vector control supplemented by chemotherapy is expected to continue until the year 2004.

Progress in controlling the reinvasion of windborne vectors into the western area of the Onchocerciasis Control Programme in West Africa

Since vector control began in 1975, waves of Simulium sirbanum and S. damnosum s.str., the principal vectors of severe blinding onchocerciasis in the West African savannas, have reinvaded treated rivers inside the original boundaries of the Onchocerciasis Control Programme in West Africa. Larviciding of potential source breeding sites has shown that these 'savanna' species are capable of travelling and carrying Onchocerca infection for at least 500 km northeastwards with the monsoon winds in the early rainy season. Vector control has, therefore, been extended progressively westwards. In 1984 the Programme embarked on a major western extension into Guinea, Sierra Leone, western Mali, Senegal and Guinea-Bissau. The transmission resulting from the reinvasion of northern Côte d'Ivoire and Burkina Faso has been reduced by over 95%, but eastern Mali has proved more difficult to protect because of sources in both Guinea and Sierra Leone. Rivers in Sierra Leone were treated for the first time in 1989 and biting and transmission rates in Sierra Leone and Guinea fell by over 90%. Because of treatment problems in some complex rapids and mountainous areas, flies still reinvaded Mali, though biting rates were approximately 70% lower than those recorded before anti-reinvasion treatments started. It was concluded that transmission in eastern Mali has now been reduced to the levels required to control onchocerciasis.

[Breeding sites of Glossina palpalis s.1. pupae in a transitional woodland area in Ivory Coast]

Search for pupae of G. palpalis s.1. was conducted from February to December 1981 in the Bouaflé area, Ivory Coast. 1909 pupae were collected from 70 breeding sites after 518 hours of search. Pupae were found both in the dry and the rainy seasons. The vegetation and the nature of the soil seem to be two inseparable factors for the creation and the maintenance of Glossina breeding sites in the study area. In localities with high pig population density, a greater number of pupae were found either at the edge of the village or at a distance not exceeding 500 m from the houses. This observation confirms peridomestic behaviour of G. palpalis s.1. in these localities. On the contrary, in localities with low pig population density or without pigs, peridomestic breeding was not observed; all the pupae were found at a distance 500 m to 3 km away from the houses, in coffee and cocoa plantations and in woodlands. The epidemiological significance of the distribution of G. palpalis s.1. breeding sites in the study area is discussed.

Large river treatment with Bacillus thuringiensis (H-14) for the control of Simulium damnosum s.l. in the Onchocerciasis Control Programme

Complete mortality of Simulium damnosum Theobald s.l. larvae was obtained along a 19 km stretch of the Marahoué River including and downstream of the Danangoro rapids complex in the Bandama Basin of Ivory Coast after treatment with 1.5 ppm/10 min of the Sandoz 402-1-WDC formulation of Bacillus thuringiensis Berliner serotype H-14. Partial control was observed for an additional 15 km. The level of control was especially encouraging considering the low concentration (.8%) of active ingredient in the Sandoz formulation. Additionally, the treated population has demonstrated resistance to temephos (Abate), the larvicide currently utilized in the Onchocerciasis Control Programme. Other species of Simulium were somewhat less affected by the treatment; living larvae were found 4 km downstream of the treatment point. Reinvasion of the Danangoro complex, ostensibly by drifting larvae of Simulium spp., was detected the day after treatment. Non-target organisms, including Ephemeroptera and Chironomid midges, were observed before and after treatment and were apparently not affected. In a second test, 0.8 ppm/10 min of the Sandoz formulation was tested, 0.8 pm/10 min of the Sandoz formulation was tested against S. damnosum s.l. and three other Simulium species in the N'Zi River in Ivory coast utilizing a gutter bioassay apparatus. Six hours after treatment 91% of the S. damnosum s.l. larvae had died. The other species responded with 91--100% mortality.

Studies on biting Simulium damnosum s.l. at a breeding site in the Onchocerciasis Control Programme area during and after an interruption of insecticidal treatments

The increase of population of biting S. damnosum s.l. at a breeding site situated within the Onchocerciasis Control Programme area of West Africa following a temporary cessation of insecticidal treatments was studied by making every day collections on human bait at five catching sites and for 2--3 days per week at seven others, between 17 January and 9 April 1977. Observations on pupal and larval densities, water and air temperatures, relative humidity and water level were also made. The results showed that there was an interval of 23 days between the last application of insecticide and the appearance of the first nulliparous biting flies. This coincided with the finding of the first S. damnosum larvae. Subsequently, the biting densities increased following a geometric progression from about 10 flies per day to a maximum of 188 per day, giving a daily rate of increase of 1.07. Ten days after the re-application of insecticide, biting densities had fallen to about 5% of the pre-control level giving a daily rate of decrease of 0.74. Very little dispersion was observed with biting rates falling to 5% at 3000 m. perpendicular to the river. At these sites nullipars predominated. Conversely along the axis of the river densities at 1000 m away had to only 68% and were composed mainly of parous flies. Studies on diel activity showed the greatest biting activity between 15.00 h and 18.00 h with a lesser period of activity between 07.00 and 10.00 h. The significance of these observations in future planning of control strategy is discussed.