Feasibility of Onchocerciasis Elimination with Ivermectin Treatment in Endemic Foci in Africa: First Evidence from Studies in Mali and Senegal

The control of onchocerciasis, or river blindness, is based on annual or six-monthly ivermectin treatment of populations at risk. This has been effective in controlling the disease as a public health problem, but it is not known whether it can also eliminate infection and transmission to the extent that treatment can be safely stopped. Many doubt that this is feasible in Africa. A study was undertaken in three hyperendemic onchocerciasis foci in Mali and Senegal where treatment has been given for 15 to 17 years. The results showed that only few infections remained in the human population and that transmission levels were everywhere below postulated thresholds for elimination. Treatment was subsequently stopped in test areas in each focus, and follow-up evaluations did not detect any recrudescence of infection or transmission. Hence, the study has provided the first evidence that onchocerciasis elimination is feasible with ivermectin treatment in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other areas in Africa, the principle of onchocerciasis elimination with ivermectin treatment has been established

Impact sur les entomocénoses aquatiques des insecticides utilisés pour contrôler les stades larvaires de Simulium damnosum Theobald (Diptera : Simuliidae), vecteur de l'onchocercose humaine en Afrique de l'Ouest

Le Téméphos ou Abate (R) était le seul insecticide utilisé depuis 1974 par le Programme de Lutte contre l'Onchocercose en Afrique de l'Ouest pour contrôler les stades aquatiques du vecteur #Simulium damnosum$ s.l. Une résistance à ce larvicide est malheureusement apparue en 1980 chez certains cytotypes forestiers du vecteur puis s'est étendue aux espèces de savane. Depuis lors, des dizaines de produits ont été testés tant sur les larves du vecteur que sur la faune aquatique non-cible pour trouver des insecticides de remplacement à l'Abate (R)... Les progrès réalisés dans la prédiction de l'impact à long terme des larvicides sur la faune entomique non-cible à partir des données de la surveillance à moyen terme ont été analysés. Les principaux facteurs qui empêchent la prévision de l'impact à long terme des larvicides sur la densité des taxons à partir de la toxicité à court terme de ces larvicides (dans le cadre du Programme) ont également été discutés. (D'après résumé d'auteur

Environmental Impact Assessment of Settlement and Development in the Upper Léraba Basin

Copyright © 1995The International Bank for Reconstructionand Development/THE WORLD BANK1818 H Street, N.W.Washington, D.C. 20433, U.S.A. All rights reservedManufactured in the United States of AmericaFirst printing November 1995 Technical Papers are published to communicate the results of the Bank’s work to the development community with the least possible delay. The typescript of this paper therefore has not been prepared in accordance with the procedures appropriate to formal printed texts,..

Laboratory Toxicity of Potential Blackfly Larvicides on Some African Fish Species in the Onchocerciasis Control Programme Area

Received June 5, 1990 The Onchocerciasis Control Programme of the World Health Organization uses larvicides to fight against the aquatic stages of the vector Simulium damnosum s.l., and thereby interrupt transmission of the disease. Since the appearance of resistance to Abate and chlorphoxim in certain cytotypes of the vector, the efficacy of many possible replacement insecticides has been tested and the impact of the best of them (permethrin, cyphenothrin, pyraclofos, and carbosulfan) on the..

Trente ans de lutte contre l’onchocercose en Afrique de l’Ouest. Traitements larvicides et protection de l’environnement : Thirty years de onchocerciasis control in West Africa. Blackfly larviciding and environmental protection

La lutte contre l'onchocercose, ou cécité des rivières, une maladie parasitaire endémique, fut entreprise en Afrique de l'Ouest dans une perspective do développement durable. Tous les moyens technologiques disponibles ont de ce fait été mobilisés pour le contrôle du vecteur, une simulie, puis du parasite responsables de cette maladie, par le Programme de Lutte contre l’Onchocercose en Afrique de l'Ouest (OCP). La lutte antivectorielle consistant en épandages d’insecticides chimiques sur les sites de développement de la simulie dans les rivières, il est apparu indispensable d’assurer la sauvegarde de l’environnement aquatique qui fournit aux communautés riveraines eau et ressources biologiques. Les technologies les plus modernes ont été mises en œuvre dès leur mise au point, pour combattre la maladie, contribuant ainsi à la protection de ce milieu. Le programme de surveillance écologique des rivières traitées par des larvicides anti-simulies a été mis en place dès le lancement d’OCP. et assuré par des spécialistes de I' hydrobiologie des pays africains participants du Programme, sous la supervision d’un groupe international d’experts indépendants, le Groupe Écologique. OCP est incontestablement un succès aussi bien pour ce qui est du contrôle de la maladie que de la protection de l'environnement. Il est l'exemple unique au monde d’un programme de santé publique de longue durée qui depuis son origine a mis en œuvre tout ce qui était possible pour harmoniser les enjeux de l’amélioration de la santé et ceux de la protection de l’environnement. Il s'est achevé avec la satisfaction de laisser aux générations montantes un environnement non dégradé et des vallées libérées de l’onchocercose, qui permettront d’accroître la productivité agricole des pays africains

Effects of larvicide treatment on invertebrate communities of Guinean rivers, West Africa

Biological and hydrological data collected from 1984 to 1998 in three Guinean rivers were analysed to evaluate adverse effects of biological and Chemical larvicides applied for the control of blackfly Simulium damnosum, vector of the parasitic digenean worm Onchocerca volvulus. Although most of the variation in invertebrate populations were flow-related, larvicide applications affect community structure reducing the abundance of the most sensible taxa. In spite of these results, in the long term the rarefaction of some invertebrate taxa (i.e. Tricorythidae) does not cause a significant reduction of total invertebrate densities because of the corresponding increase of other taxa (i.e. Hydropsychidae and Philopotamidae). The functional structure of the communities is also not affected

Stability and change in the distribution of cytospecies of the Simulium damnosum complex (Diptera: Simuliidae) in southern Ghana from 1971 to 2011.

BACKGROUND: Simulium damnosum s.l., the most important vector of onchocerciasis in Africa, is a complex of sibling species that have been described on the basis of differences in their larval polytene chromosomes. These (cyto) species differ in their geographical distributions, ecologies and epidemiological roles. In Ghana, distributional changes have been recorded as a consequence of vector control and environmental change (e.g. deforestation), with potential disease consequences. We review the distribution of cytospecies in southern Ghana and report changes observed with reference to historical data collated from 1971 to 2005 and new identifications made between 2006 and 2011. METHODS/RESULTS: Larvae were collected from riverine breeding sites, fixed in Carnoy's solution and chromosome preparations made. Cytotaxonomic identifications from 1,232 samples (including 49 new samples) were analysed. We report long-term stability in cytospecies distribution in the rivers Afram, Akrum, Pawnpawn and Pru. For the rivers Oda, Ofin and Tano we describe (for the first time) patterns of distribution. We could not detect cytospecies composition changes in the upper Pra, and the lower Pra seems to have been stable. The elimination of the Djodji form of S. sanctipauli in the Volta Region seems to have had no long-term effects on the distribution of the other cytospecies, despite an initial surge by S. yahense. There has been a recent increase in the occurrence of savannah cytospecies in the river Asukawkaw, and this might be related to continuing deforestation. CONCLUSIONS: Cytospecies' distributions have not been stable from 1971 to 2011. Although there are no obvious causes for the temporary appearance and subsequent disappearance of cytospecies in a particular location, a major influence has been vector control and migration patterns, probably explaining observed changes on the Black Volta and lower Volta rivers. Deforestation was previously implicated in an increase of savannah cytospecies in southern Ghana (1975-1997). Our data had little power to support (or refute) suggestions of a continuing increase, except in the Asukawkaw river basin

Eliminating Onchocerciasis after 14 Years of Vector Control: A Proved Strategy

From 1976 through 1989, weekly aerial spraying operations against blackflies were carried out along the rivers of a wide savanna area of West Africa (~700,000 km2) where onchocerciasis was hyperendemic. The level of endemicity began to decrease significantly after 4 years of vector control and became very low in 1989. This situation has been maintained without any vector control activity or chemotherapy, and no incidence of any new cases has been detected. An ophthalmological study carried out in 2000 has confirmed these good results, showing only cicatricial ocular lesions in the examined population. These results led to the conclusion that 14 years of vector control may achieve long-term elimination of onchocerciasis, even in the absence of chemotherapy, provided that the treated areas are not subjected to any contamination by exogenous parasites carried in infected humans or flies