TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (1992) 86, 113-114
113
(Leading The Onchocerciasis
Control Programme
G. Webbe London School of Hygiene and Tropical Medicine, Winches Farm Laboratories, St Albans, Hertfordshire, AL4 OQX, UK Extensive researchconducted in West Africa between 1950and 1965demonstratedthe importance and seriousnessof onchocerciasisas a public health problem and as an obstacle to social and eoncomic development. It was subsequently concluded that large scale Simulium control, and therefore of onchocerciasis, was feasible through aerial larviciding (WHO, 1968). SevenWest African countries, including Benin, Burkina Faso, C&e d’Ivoire, Ghana, Mali, Niger and Togo, together with bilateral donor and multilateral sponsoring agencies (WHO, IBRD, FAO, UNDP), then establishedthe OnchocerciasisControl Programme in the Volta River Basin area (known since 1986 as the OnchocerciasisControl Programme in West Africa, or OCP). The boundaries of the original seven-country programme area were determined-in 1973, on the basis of the nrevalenceof the blinding (savanna)form of the disease’,and excluded areaswheyethe non-blinding (forest) form prevailed, as the mandateof OCP was limited to the control of savanna onchocerciasis(UNDPIFAOIIBRDI WHO, 1973). The vector control operations launched in 1974-1975 were extended in 1978-1979 into the south of C&e d’Ivoire, and further expanded into the southern and western extension areas from 1986. increasing the nrogramme area to 1 235 000 km’, its total population to 30 million, and the length of rivers under control to’ about 50 000 km. The number of participating countries reached eleven, and they now include Guinea, Guinea Bissau, Senegaland Sierra Leone. The expansioninto the southern and western extension areaswas to protect the populations there and to prevent Simulium reinvading the original control area. The life-span of the femaleworm was believedto be on average11 years, with the expectation that 11 yearsof larviciding would therefore suffice to eliminate the human reservoir of Onchocerca volvulus. Epidemiological investigations in areaswhere larviciding had been conducted-since 1974, however, supported by the predictions of an enidemioloxical model (REMMEet al.. 1986). established that up to u14years of larviciding is required to eliminate the human reservoir of the onchocercalparasite. Therefore, becauseof the delay in beginning larvitiding due to resistanceproblems, the underestimation of the duration of vector control necessaryto eliminate the parasite, and in order to protect its considerableachievements, OCP will necessarily continue larviciding for transmission control bevond 1997in Dart of the extension areas,but on a gradually diminishing-scale. As the result of the interruption of transmission in most of the original programme area in the past 16 years (an area the size of France, at a cost of approximately US$l per protected person per year), the-disease has ceasedto be a nublic health oroblem and. since nrevalence of infection is insignificant, larvicidihg has been discontinued in more than 90% of the area. The community microfilarial load (CMFL, the mean number of microfilariae per skin snip for a given population) is now almost zero in most of this area, except in the reinvaded zones and a few circumscribed foci. Furthermore, epidemiological evaluation shows that no onchocercalinfection occurred in the core area among children borne since the start of vector control, except in the reinvaded zones and in the few areas where transmission control temporarily failed. It is estimated that by 1991approximately 9 million children born after OCP operations started will have been spared the risk of onchocercal
blindness, that 30 million people (including the population of the extension areas)are protected from onchocercal disease,that 1.25 million initially seriously infected are free of the parasite, and that more than 100 000 have been prevented from going blind. The OCP is also producing significant net socio-economicbenefits which can be measured(BENTON& SKINNER,1990). Applied researchwhich is operations oriented is a notable feature of OCP. and a maior contributorv factor to its success.The rotational employment of larvicides has now largely ameliorated serious interruption of operations due to blackfly resistance,and the searchfor new compounds, particularly from groups unlikely to produce cross-resistance,is being diligently pursued. The 6 larvicides available to the programme included temephos, chlorphoxim and pyraclofos (organophosphorus comnounds). Bacillus thurinpiensis. H. 14 (a bioloeical con&o1agent), permethrin (a”pyrethroid), and carb&ulfan (a carbamate). Chlorphoxim has now been phased out and pyraclofos introduced operationally. The abilitv to detect resistance to larvicides has been greatly improved, thresholds of resistanceof populations of S. damnosumsensu latu have been reassessed,and a computerized cytotaxonomic data bank has been developed. The cytotaxonomic data can be correlated with known resistancepatterns, thus facilitating redefinition of the range of susceptibility of the various members of the S. damnosum complex. Larviciding operations have been improved in accuracy and consequently cost-effectiveness, and in the capability to judge when spraying may be safely discontinued, through the introduction of a computer program (PERLES).The program minimizes larvicide and application costs by embracing simultaneously all relevant larvicide, hydrological and aircraft data. Hydrological conditions (water level and discharge rates) are monitored by automatic devices in rivers and transmitted via satellite to the operational centres. Epidemiological mapping and entomological surveillance procedures are complemented by another computer model, ONCHOSIM, which predicts long-term epidemiological trends given control methods based on specific combinations of vector control and chemotherapy (REMME,1989). Sinceits inception, OCP has benefited from the advice of an independent ecological group, in conducting programme-wide aquatic monitoring to assessthe impact of larviciding in the environment. So far, no long-term adverse effect on non-target fauna has been revealed (YAMEOGO et al., 1988). A better understanding of the distribution of vector speciesis being sought, to add to knowledge of their respective roles in ,transmission. Pending the separation into blinding and non-blinding strains of infective larvae recovered from man-biting vectors, the decisions on which vectors should becomethe targets for control will depend on cross-transmissionstudies and knowledge of man-biting rates, anthropophily, survival rates, natural infection levels and associationswith blinding foci. The usefulnessof deoxyribonucleic acid probes is currently being studied, in differentiating blinding and non-blinding strains of the parasite. This approach may also be of value in distinguishing human and animal strains. Ivermectin (Mectizan@).a serendioitous windfall from veterinary medicine, after evaluationand clinical trials by the onchocerciasis chemotherapy project (OCT), has emerged as an acceptable microfilaricidal agent. The
114
major endeavour of OCT is, however, the continuing searchfor an effective and safemacrofilaricide (SMITH& STOCKING.1983). Studies of the enidemioloeical imnact of ivermectin have establishedthaithe drug aone cannot effectively control transmission of onchocerciasis (in hyper- and holo-endemic areas) using an annual treatment schedule. Further researchis under way to assess its epidemiological impact at more frequent dosageschedules (e.g., severalyearsof treatments at 3 to 4 month intervals). Epidemiological surveyshave indicated areasof high endemicity and risk of blindness in the western extension area, and studies of ocular diseasepatterns have led to a better understanding of the relationship between prevalence of severe eye lesions, onchocercal blindness and CMFL. The potential role of ivermectin in the prevention of diseasemay be much greater than was earher thought. Annual treatment has been shown, in the savannaarea, to causeregressionof iridocyclitis and sclerosing keratitis, and to arrest optic atrophy and choroi- doretmitis (D~1%1~etaZ.,1991)~ OCP will continue large-scaledistribution of ivermectin annually for morbidity control with increasing national participation. The treatment will continue for an averageof 6 years, after which vector control will ensure virtual elimination of the human reservoir of the parasite before the year 2003. With the introduction of ivermectin, ‘devolution’ and its objectives (progressivenational participation in activities to detect and suppress recrudescenceof transmission and in distribution of ivermectin to reduce morbidity) are now better understood in feasible operational terms. Implementing devolution (first articulated by the independent commission in 1981: WHO, 1981) has so far proved difficult owing to the programme’s reliance upon highly sophisticated technology and on strong vertical management.The external review of OCP (WO;LD BANK, 1995) considered that the sustainability and impact of devolution would be better assuredand amplified if it were carried out as part of general health systemsdevelopment in the participating countries, and that OCP can meet these needsby national training and in-service training, and through technical assistance,particularly with regard to planning, managementand operational research. It was recommendedthat OCP should create a devolution unit,, with specialist personnel to address training, epidemiological surveillance and social scienceand public health managementissues, and this has now been done. Consideration is being given to the preparation of an ‘inter-country facility’ to support intercountry co-operation and maintain a regional perspective on onchocerciasiscontrol (WHO, 1989).Thus far, devolution plans have been prepared by 7 participating countries, and external support is being sought to fund them in the face of deteriorating economics in the region, where cut-backs have been particularly damaging to health and socialservices. The external review (WORLD BANK, 1990) recommended that participating countries and interested donors, following consideration of the socio-economic reports produced by the committee of sponsoring agencies’ land settlement review, should jointly support socioeconomicdevelopment planning and programmesfor the onchocerciasis-freeareas,while ensuring the integra-
tion of such planning into the broader national development strategy of eachof the participating countries. It is estimated that 15 million hectares of riverain, tillable land have beenmade available for resettlement and cultivation, in part, as a result of OCP operations, and that this areawill come closeto 25 million hectaresbefore the end of this century. Many interdependent characteristics of the OCP can be identified as factors which have contributed to its manifest success,including (i) clearly defined objectives, (ii) a realistic and feasible time-frame, (iii) choice of the right technology, (iv) the suceptibility of onchocerciasis transmissionto the applied control strategy, (v) contracting out of highly specializedoperations (e.g., aerial larvitiding), (vi) strong emphasis on operational research; (vii) a high degreeof autonomy within WHO and its governing structures, (viii) clear delegation of authority allowing operational flexibility, (ix) medium-term planning (6 year financial phases)and sustained donor commitment, (x) unrestricted information flow maintaining a systemof internal checksand balancesand clear accountability, and (xi) strong management and high quality staff (WORLDBANK, 1990). References Benton,B. & Skinner,E. (1990).Costbenefitsof onchocerciasis control.Acra Leidensiu,59,405-411. Dadzie,K. Y., Remme,J. & De Sole,G. (1991).Changesin ocularonchocerciasis after two roundsof communitv-based ivermectin treatment in a holo-endemiconchocerciasis focus.Transactions of the Royal Society of Trooical Medicine andHygiene, 852671271:
-
Remme,J., (1989).The Eptdemiology
. and Control of Onchocer-
ciasisin WestAfrica. PhD thesis, University of Rotterdam. Remme, J., Ba, O., Dadzie, K. Y. & Karam, M. (1986). A force of infection model for onchocerciasisand its application in the epidemiological evaluation of the Onchocerciasis Control Programme in the Volta river basin area.Bulletin of the World Health Organization, 64,667-68 1. Smith, C. E. G. & Stocking, B. (1983). The Onchocerciasis Control Programme. An interaction of politics, economics, scienceand health. Interdisciplinary ScienceReviews, 8, 168 178. UNDPIFAOIIBRDNCTHO (1973). Onchocerciusis control in the Volta river basin area: report of the preparatoy
assistance
missionto the governments of Dahomey, Ghana, Ivory Coast, Mali, Niger, Togo and Upper Volta. Geneva: World Health Organization, mimeographeddocument no. OCPi731. WHO (1968). US-AIDIOCCGEIWHO Technical Meeting on the Feasibility of Onchocerciasis Control [Tunis Report/. Geneva: World Health Organization, mimeographed document WHOlOncho/69-75. WHO (1981). Independent Commission on the Lonp Term Prospecti of the Onchocerciasis Control Programme.&al Report. Geneva:World Health Organization. WHO (1989). Devolution of the OnchocerciasisControl Programme in the Framework of the Three Phase Health Development Scenario for the Africa Region. Brazzaville:WHOIAFROIOCP.
mimeographeddocument. World Bank (1990). External Review of the OnchocerciasisControl Proaram.Washineton. DC: IBRD.
Yameogo,L., Leve&e,‘C:, Traore, K. & Fairhurst, C. P.
(1988). Dix ans de surveillance de la faune aquatique des rivi&es d’ilfrique de l’ouest traitees contre les simulies (Diptera: Simuliidae), agents vecteurs de I’onchocercose humaine. Naturaliste Canadienne,115,287-298.
113
(Leading The Onchocerciasis
Control Programme
G. Webbe London School of Hygiene and Tropical Medicine, Winches Farm Laboratories, St Albans, Hertfordshire, AL4 OQX, UK Extensive researchconducted in West Africa between 1950and 1965demonstratedthe importance and seriousnessof onchocerciasisas a public health problem and as an obstacle to social and eoncomic development. It was subsequently concluded that large scale Simulium control, and therefore of onchocerciasis, was feasible through aerial larviciding (WHO, 1968). SevenWest African countries, including Benin, Burkina Faso, C&e d’Ivoire, Ghana, Mali, Niger and Togo, together with bilateral donor and multilateral sponsoring agencies (WHO, IBRD, FAO, UNDP), then establishedthe OnchocerciasisControl Programme in the Volta River Basin area (known since 1986 as the OnchocerciasisControl Programme in West Africa, or OCP). The boundaries of the original seven-country programme area were determined-in 1973, on the basis of the nrevalenceof the blinding (savanna)form of the disease’,and excluded areaswheyethe non-blinding (forest) form prevailed, as the mandateof OCP was limited to the control of savanna onchocerciasis(UNDPIFAOIIBRDI WHO, 1973). The vector control operations launched in 1974-1975 were extended in 1978-1979 into the south of C&e d’Ivoire, and further expanded into the southern and western extension areas from 1986. increasing the nrogramme area to 1 235 000 km’, its total population to 30 million, and the length of rivers under control to’ about 50 000 km. The number of participating countries reached eleven, and they now include Guinea, Guinea Bissau, Senegaland Sierra Leone. The expansioninto the southern and western extension areaswas to protect the populations there and to prevent Simulium reinvading the original control area. The life-span of the femaleworm was believedto be on average11 years, with the expectation that 11 yearsof larviciding would therefore suffice to eliminate the human reservoir of Onchocerca volvulus. Epidemiological investigations in areaswhere larviciding had been conducted-since 1974, however, supported by the predictions of an enidemioloxical model (REMMEet al.. 1986). established that up to u14years of larviciding is required to eliminate the human reservoir of the onchocercalparasite. Therefore, becauseof the delay in beginning larvitiding due to resistanceproblems, the underestimation of the duration of vector control necessaryto eliminate the parasite, and in order to protect its considerableachievements, OCP will necessarily continue larviciding for transmission control bevond 1997in Dart of the extension areas,but on a gradually diminishing-scale. As the result of the interruption of transmission in most of the original programme area in the past 16 years (an area the size of France, at a cost of approximately US$l per protected person per year), the-disease has ceasedto be a nublic health oroblem and. since nrevalence of infection is insignificant, larvicidihg has been discontinued in more than 90% of the area. The community microfilarial load (CMFL, the mean number of microfilariae per skin snip for a given population) is now almost zero in most of this area, except in the reinvaded zones and a few circumscribed foci. Furthermore, epidemiological evaluation shows that no onchocercalinfection occurred in the core area among children borne since the start of vector control, except in the reinvaded zones and in the few areas where transmission control temporarily failed. It is estimated that by 1991approximately 9 million children born after OCP operations started will have been spared the risk of onchocercal
blindness, that 30 million people (including the population of the extension areas)are protected from onchocercal disease,that 1.25 million initially seriously infected are free of the parasite, and that more than 100 000 have been prevented from going blind. The OCP is also producing significant net socio-economicbenefits which can be measured(BENTON& SKINNER,1990). Applied researchwhich is operations oriented is a notable feature of OCP. and a maior contributorv factor to its success.The rotational employment of larvicides has now largely ameliorated serious interruption of operations due to blackfly resistance,and the searchfor new compounds, particularly from groups unlikely to produce cross-resistance,is being diligently pursued. The 6 larvicides available to the programme included temephos, chlorphoxim and pyraclofos (organophosphorus comnounds). Bacillus thurinpiensis. H. 14 (a bioloeical con&o1agent), permethrin (a”pyrethroid), and carb&ulfan (a carbamate). Chlorphoxim has now been phased out and pyraclofos introduced operationally. The abilitv to detect resistance to larvicides has been greatly improved, thresholds of resistanceof populations of S. damnosumsensu latu have been reassessed,and a computerized cytotaxonomic data bank has been developed. The cytotaxonomic data can be correlated with known resistancepatterns, thus facilitating redefinition of the range of susceptibility of the various members of the S. damnosum complex. Larviciding operations have been improved in accuracy and consequently cost-effectiveness, and in the capability to judge when spraying may be safely discontinued, through the introduction of a computer program (PERLES).The program minimizes larvicide and application costs by embracing simultaneously all relevant larvicide, hydrological and aircraft data. Hydrological conditions (water level and discharge rates) are monitored by automatic devices in rivers and transmitted via satellite to the operational centres. Epidemiological mapping and entomological surveillance procedures are complemented by another computer model, ONCHOSIM, which predicts long-term epidemiological trends given control methods based on specific combinations of vector control and chemotherapy (REMME,1989). Sinceits inception, OCP has benefited from the advice of an independent ecological group, in conducting programme-wide aquatic monitoring to assessthe impact of larviciding in the environment. So far, no long-term adverse effect on non-target fauna has been revealed (YAMEOGO et al., 1988). A better understanding of the distribution of vector speciesis being sought, to add to knowledge of their respective roles in ,transmission. Pending the separation into blinding and non-blinding strains of infective larvae recovered from man-biting vectors, the decisions on which vectors should becomethe targets for control will depend on cross-transmissionstudies and knowledge of man-biting rates, anthropophily, survival rates, natural infection levels and associationswith blinding foci. The usefulnessof deoxyribonucleic acid probes is currently being studied, in differentiating blinding and non-blinding strains of the parasite. This approach may also be of value in distinguishing human and animal strains. Ivermectin (Mectizan@).a serendioitous windfall from veterinary medicine, after evaluationand clinical trials by the onchocerciasis chemotherapy project (OCT), has emerged as an acceptable microfilaricidal agent. The
114
major endeavour of OCT is, however, the continuing searchfor an effective and safemacrofilaricide (SMITH& STOCKING.1983). Studies of the enidemioloeical imnact of ivermectin have establishedthaithe drug aone cannot effectively control transmission of onchocerciasis (in hyper- and holo-endemic areas) using an annual treatment schedule. Further researchis under way to assess its epidemiological impact at more frequent dosageschedules (e.g., severalyearsof treatments at 3 to 4 month intervals). Epidemiological surveyshave indicated areasof high endemicity and risk of blindness in the western extension area, and studies of ocular diseasepatterns have led to a better understanding of the relationship between prevalence of severe eye lesions, onchocercal blindness and CMFL. The potential role of ivermectin in the prevention of diseasemay be much greater than was earher thought. Annual treatment has been shown, in the savannaarea, to causeregressionof iridocyclitis and sclerosing keratitis, and to arrest optic atrophy and choroi- doretmitis (D~1%1~etaZ.,1991)~ OCP will continue large-scaledistribution of ivermectin annually for morbidity control with increasing national participation. The treatment will continue for an averageof 6 years, after which vector control will ensure virtual elimination of the human reservoir of the parasite before the year 2003. With the introduction of ivermectin, ‘devolution’ and its objectives (progressivenational participation in activities to detect and suppress recrudescenceof transmission and in distribution of ivermectin to reduce morbidity) are now better understood in feasible operational terms. Implementing devolution (first articulated by the independent commission in 1981: WHO, 1981) has so far proved difficult owing to the programme’s reliance upon highly sophisticated technology and on strong vertical management.The external review of OCP (WO;LD BANK, 1995) considered that the sustainability and impact of devolution would be better assuredand amplified if it were carried out as part of general health systemsdevelopment in the participating countries, and that OCP can meet these needsby national training and in-service training, and through technical assistance,particularly with regard to planning, managementand operational research. It was recommendedthat OCP should create a devolution unit,, with specialist personnel to address training, epidemiological surveillance and social scienceand public health managementissues, and this has now been done. Consideration is being given to the preparation of an ‘inter-country facility’ to support intercountry co-operation and maintain a regional perspective on onchocerciasiscontrol (WHO, 1989).Thus far, devolution plans have been prepared by 7 participating countries, and external support is being sought to fund them in the face of deteriorating economics in the region, where cut-backs have been particularly damaging to health and socialservices. The external review (WORLD BANK, 1990) recommended that participating countries and interested donors, following consideration of the socio-economic reports produced by the committee of sponsoring agencies’ land settlement review, should jointly support socioeconomicdevelopment planning and programmesfor the onchocerciasis-freeareas,while ensuring the integra-
tion of such planning into the broader national development strategy of eachof the participating countries. It is estimated that 15 million hectares of riverain, tillable land have beenmade available for resettlement and cultivation, in part, as a result of OCP operations, and that this areawill come closeto 25 million hectaresbefore the end of this century. Many interdependent characteristics of the OCP can be identified as factors which have contributed to its manifest success,including (i) clearly defined objectives, (ii) a realistic and feasible time-frame, (iii) choice of the right technology, (iv) the suceptibility of onchocerciasis transmissionto the applied control strategy, (v) contracting out of highly specializedoperations (e.g., aerial larvitiding), (vi) strong emphasis on operational research; (vii) a high degreeof autonomy within WHO and its governing structures, (viii) clear delegation of authority allowing operational flexibility, (ix) medium-term planning (6 year financial phases)and sustained donor commitment, (x) unrestricted information flow maintaining a systemof internal checksand balancesand clear accountability, and (xi) strong management and high quality staff (WORLDBANK, 1990). References Benton,B. & Skinner,E. (1990).Costbenefitsof onchocerciasis control.Acra Leidensiu,59,405-411. Dadzie,K. Y., Remme,J. & De Sole,G. (1991).Changesin ocularonchocerciasis after two roundsof communitv-based ivermectin treatment in a holo-endemiconchocerciasis focus.Transactions of the Royal Society of Trooical Medicine andHygiene, 852671271:
-
Remme,J., (1989).The Eptdemiology
. and Control of Onchocer-
ciasisin WestAfrica. PhD thesis, University of Rotterdam. Remme, J., Ba, O., Dadzie, K. Y. & Karam, M. (1986). A force of infection model for onchocerciasisand its application in the epidemiological evaluation of the Onchocerciasis Control Programme in the Volta river basin area.Bulletin of the World Health Organization, 64,667-68 1. Smith, C. E. G. & Stocking, B. (1983). The Onchocerciasis Control Programme. An interaction of politics, economics, scienceand health. Interdisciplinary ScienceReviews, 8, 168 178. UNDPIFAOIIBRDNCTHO (1973). Onchocerciusis control in the Volta river basin area: report of the preparatoy
assistance
missionto the governments of Dahomey, Ghana, Ivory Coast, Mali, Niger, Togo and Upper Volta. Geneva: World Health Organization, mimeographeddocument no. OCPi731. WHO (1968). US-AIDIOCCGEIWHO Technical Meeting on the Feasibility of Onchocerciasis Control [Tunis Report/. Geneva: World Health Organization, mimeographed document WHOlOncho/69-75. WHO (1981). Independent Commission on the Lonp Term Prospecti of the Onchocerciasis Control Programme.&al Report. Geneva:World Health Organization. WHO (1989). Devolution of the OnchocerciasisControl Programme in the Framework of the Three Phase Health Development Scenario for the Africa Region. Brazzaville:WHOIAFROIOCP.
mimeographeddocument. World Bank (1990). External Review of the OnchocerciasisControl Proaram.Washineton. DC: IBRD.
Yameogo,L., Leve&e,‘C:, Traore, K. & Fairhurst, C. P.
(1988). Dix ans de surveillance de la faune aquatique des rivi&es d’ilfrique de l’ouest traitees contre les simulies (Diptera: Simuliidae), agents vecteurs de I’onchocercose humaine. Naturaliste Canadienne,115,287-298.
