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Trente ans de lutte contre l’onchocercose en Afrique de l’Ouest. Traitements larvicides et protection de l’environnement

Laurent Yaméogo
Christian Levêque
Jean-Marc Hougard


Boakye A. Boatin

Texte intégral

1Within the decade, sustainable development has become the leitmotiv of all development activities. It is worth noting however that sustainable development does not in any way mean blind and mindless protection of the environment. The ultmate goal is indeed to find compromises in which the primary objective of development remains the improvement of living conditions in human societies and the welfare of human beings on the one hand, and a good management of the environment and its resources on the other hand.

2To reach this goal, it is sometimes necessary to modify the natural trend of events. In fact, this rich environment which provides us with numerous goods and services (living resources, water soils, etc) can also be harmful to human beings. Many diseases are induced by the coexistence of man and his parasites, and nobody would question the urgency to bring them under control. All those who lived near the African rivers some decades ago remember numerous endemic diseases affecting natural environments which were only slightly modified by human activities. Some of these endemic diseases are still present, but there is the capacity today to control, in the majority of cases, their extension and virulence.

3The control of an endemic parasitic disease as onchocerciasis falls within the framework of sustainable development. In fact, it was unacceptable that the populations living in these fertile valleys continued to suffer from this disease, or leave for less fertile and arid zones to prevent blindness. Moreover persisting draughts imposed to re-colonize riverside irrigable lands to host migrant farmers chased out from desertified areas. All the available technological means to control the disease were therefore implemented. Control was first directed against the blackfly vector then the parasite. The initial strategy being based on vector control through applications of Chemicals In its river breeding sites, it was necessary at the same time to fight for the preservation of the aquatic environment, which supplies the communities that lived along the rivers with good quality water and biological resources. The Onchocerciasis Control Programme in West Africa (OCP) was set up to meet this challenge.

4Concerning the preservation of the environment, the OCP set up, right from the very beginning, an aquatic monitoring programme of the rivers treated with larvicides, conducted by national experts from the African participating countries, under the aegis of a group of national and international independent experts, the Ecological Group. One of the specific purposes was to preserve the fish populations, En matière de préservation de l'environnement, l'OCP a mis en place, dès l'origine, un programme de surveillance aquatique des rivières traitées aux insecticides anti-simulies, exécuté par des experts nationaux des pays africains participants du Programme, sous l’égide d'un groupe d'experts indépendants internationaux, le Groupe écologique. L’un des buts affichés était de préserver les populations de poissons qui constituent une source importante de protéines pour les populations riveraines.

5Pour cela, il a fallu utiliser les technologies les plus modernes au fur et à mesure de leur développement, tant en matière de lutte contre la maladie qu'en matière de protection de l’environnement. Ainsi, un important travail de sélection des insecticides a permis de mettre en œuvre une stratégie de rotation des larvicides tenant compte non seulement de critères de coût et d’efficacité mais aussi d’impact sur la faune aquatique non cible. Il s’agissait donc de trouver des compromis entre ce qui était techniquement disponible, écologiquement acceptable, et économiquement viable. L’utilisation des satellites pour connaître les débits des fleuves au moment précis des épandages a permis des progrès importants dans l'utilisation des insecticides en évitant aussi bien les surdosages néfastes à la faune non cible que les sous-dosages préjudiciables au contrôle efficace des simulies. Dans le domaine de l’épidémiologie, la mise au point de sondes ADN a également permis de mieux faire la part des parasites d’origine humain et animale dans les simulies infectantes et d’ajuster ainsi les opérations de lutte.

6Le programme de lutte contre l’onchocercose en Afrique de l’Ouest est indubitablement un succès en ce qui concerne le contrôle de la maladie et la protection de l'environnement. C’est un exemple unique au monde de programme de santé publique à long terme à s’être doté dès son lancement en 1974, de tous les moyens possibles pour préserver l’environnement aquatique. Il a été un précurseur avant la lettre, des principes du développement durable. Il s'est achevé avec la satisfaction de léguer aux générations futures un environnement non dégradé, des vallées libérées de l’onchocercose qui pourront accroître la production agricole des pays participant, ainsi que des connaissances nouvelles sur les fleuves africains et sur les moyens de contrôle des endémies parasitaires.

7C'est le lieu d'adresser ici nos remerciements les plus sincères à toute la communauté scientifique (Comité consultatif d'experts et Groupe écologique de l'OCR hydrobiologistes, entomologistes et épidémiologistes des pays participants et des différents instituts de recherche de par le monde qui ont collaboré avec l'OCP à cette importante mission), à la communauté des donateurs qui a fait confiance à l'OCP pendant de si longues années malgré les multiples défis à relever et au personnel du Programme dont le dévouement, la persévérance et l'esprit de suite et de sacrifice ont été salutaires.

8Notre souhait est que cette expérience unique de mobilisation de la communauté internationale en faveur d’un réel développement durable de zones « laissées pour compte » fasse école pour le plus grand bien des populations locales. which constitute a considerable source of protein for the riverside populations. Therefore, it was necessary to use the most modem technologies as they became available, to fight the disease as well as to preserve the environment. A programme of insecticides selection was launched and allowed to use larvicides on a rotational basis taking into account not only their cost/efficacy ratio, but also their impact on the non target aquatic fauna. The question was to find compromises among what was technically available, ecologically acceptable, and economically viable. Using satellites to estímate the river discharges when spraying is was applied allowed to make considerable progress in the use of insecticides, thus avoiding both the fatal overdoses on the non target fauna and under-dosages which would be ineffective against the blackfly populations. In the field of epidemiology, the development of DNA probes also provided a better knowledge of human and animal parasites in the infective females of the vector and accordingly, an adjustment of the control strategy.

9The Onchocerciasis Control Programme in West Africa is indisputably a success as regards the control of the disease and the preservation of the environment. It is a quite unique example of long-term public health programme which has made every effort possible to preserve the aquatic environment since its inception in 1974. It has been a precursor of sustainable development long before the term existed. It ended with the satisfaction of bequeathing to the coming generations a non degraded environment and valleys free from onchocerciasis which would increase the agricultural productivity of the countries, together with novel knowledge on African rivers and means of combating parasitic endemic diseases.

10We are therefore pleased to extend our sincere thanks to the whole scientific community (the Expert Advisory Committee and the Ecological Group of the OCR hydrobiologists, entomologists and epidemiologists from the participating countries and from the various research institutes throughout the world which collaborated with the OCP), to the donor community which trusted the OCP during so many years despite the multiple challenges to be met, and to the staff of the Programme for their unvaluable dedication, perseverance, consistency and spirit of total sacrifice.

11We hope that this quite unique involvement of the international community in a genuine sustainable development of "forgotten areas" becomes widespread for the benefit of the local communities.

© IRD Éditions, 2003

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