Impact of ivermectin on onchocerciasis transmission: assessing the empirical evidence that repeated ivermectin mass treatments may lead to elimination/eradication in West-Africa

BACKGROUND: The Onchocerciasis Control Program (OCP) in West Africa has been closed down at the end of 2002. All subsequent control will be transferred to the participating countries and will almost entirely be based on periodic mass treatment with ivermectin. This makes the question whether elimination of infection or eradication of onchocerciasis can be achieved using this strategy of critical importance. This study was undertaken to explore this issue. METHODS: An empirical approach was adopted in which a comprehensive analysis was undertaken of available data on the impact of more than a decade of ivermectin treatment on onchocerciasis infection and transmission. Relevant entomological and epidemiological data from 14 river basins in the OCP and one basin in Cameroon were reviewed. Areas were distinguished by frequency of treatment (6-monthly or annually), endemicity level and additional control measures such as vector control. Assessment of results were in terms of epidemiological and entomological parameters, and as a measure of inputs, therapeutic and geographical coverage rates were used. RESULTS: In all of the river basins studied, ivermectin treatment sharply reduced prevalence and intensity of infection. Significant transmission, however, is still ongoing in some basins after 10–12 years of ivermectin treatment. In other basins, transmission may have been interrupted, but this needs to be confirmed by in-depth evaluations. In one mesoendemic basin, where 20 rounds of four-monthly treatment reduced prevalence of infection to levels as low as 2–3%, there was significant recrudescence of infection within a few years after interruption of treatment. CONCLUSIONS: Ivermectin treatment has been very successful in eliminating onchocerciasis as a public health problem. However, the results presented in this paper make it almost certain that repeated ivermectin mass treatment will not lead to the elimination of transmission of onchocerciasis from West Africa. Data on 6-monthly treatments are not sufficient to draw definitive conclusions

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

Etude de la diffusivité thermique de latérite du Bénin par la « méthode FLASH ».

La détermination des paramètres thermophysiques des matériaux locaux de construction s’avère indispensable dans le domaine scientifique et industriel. La connaissance de ces constantes physiques s’impose lorsque l’on considère le développement rapide du marché du logement et surtout la nécessité d’économiser de l’énergie tout en assurant le confort thermique de l’habitat. Cet article présente les résultats de mesures de la diffusivité thermique de la terre de barre stabilisée à différents taux de ciment à l’état sec et à l’état saturé.Mots clés : Terre de barre, ciment, stabilisation, diffusivité thermique, méthode Flash.The determination of the thermophysical parameters of local materials of construction proves to be essential in the scientific and industrialist fields. Knowledge of this physics constant is essential when we consider the fast development of the market of housing and especially the need for saving energy while ensuring the thermal comfort in the habitat. This article presents the results of measurement of the thermal diffusivity of dry clay and saturated clay, at different rates of cement.Key words: Clay, cement, stabilization, thermal diffusivity, “Flash Method”

Determination of thermal diffusivity of cement-stabilized laterite by transient thermal field and induced surface stress

Knowledge of thermo-physical properties of local building materials are necessary for thermal comfort design and construction of residential accommodation. Thermal diffusivity of cement-stabilized laterites were measured under conditions of transient thermal field and induced surface stress, assuming constant temperature within the samples. The laterites were stabilized by 4 %, 8 % and 12 % cement content, and tested at water saturated and un-saturated states. The values of thermal diffusivity of dry and saturated samples were respectively ~ 5.01 x 10-7 m2/s and ~ 5.35 x 10-7 m2/s, and the two values indicated the suitability of stabilized laterite for providing thermal comfort in buildings.Keywords: Laterite, Cement-stabilization, Thermal diffusivity, Thermal comfort, Constant temperature bat

Etude de la vitesse du vent avec la distribution de weibull : cas de la ville de cotonou au Benin

Dans le but d’améliorer la production de l’énergie électrique et surtout d’explorer des sources complémentaires aux sources d’énergies existantes, nous avons choisi d’étudier la vitesse du vent au Bénin. Cette étude a été faite avec la distribution de probabilité de Weibull dans le but de calculer la puissance éolienne récupérable à Cotonou. Notre étude nous a permis de constater que la distribution utilisée ne permet pas de caractériser la vitesse du vent à Cotonou et par conséquent la recherche d’autres outils telle que la distribution de Weibull modifiée s’est avérée nécessaire.Mots clés : Distribution de Weibull, distribution de Rayleigh, vitesse du vent, paramètres de Weibull

Determination experimentale et approches simplifies de modelisation des proprietes thermo-physiques du bois borassus (Palmier Ronier)

Le présent article donne les résultats de recherche d’une étude expérimentale sur les propriétés thermiques du bois Borassus Aéthiopum (palmier rônier) exploité au Bénin. Les propriétés telles que la masse volumique, la chaleur massique spécifique et la diffusivité thermique ont été mesurées et ont permis d’estimer la conductivité et l’effusivitéthermiquesde l’espèce de bois. La méthode dite du régime régulier est utilisée pour la mesure de la diffusivité (α) ; tandis que les valeurs de la conductivité thermique (λ)et l’effusivitéthermiques (E)sont déduites dans les trois directions à partir de corrélations théoriques. Les résultats des essais par la méthode du régime régulier ont donné les valeurs moyennesrespectives de la diffusivité thermique, suivant les axes (ο,x ), (ο,y ) et (ο,z ) : 2,54.10-7 m2/s,1,97.10-7m2/s 1,80.10-7 m2/s. Quant à la conductivité et l’effusivité thermiques, les valeurs calculées sont respectivement de 0,34 W/m.K, et 682,01J.m2.K-1.s-1/2 ; 0,27 W/m.K et 600,63J.m-2.K-1.s-1/2 ; et de 0,24 W/m.K et 557,95J.m-2.K-1.s-1/2. Les caractéristiques thermiques, physiques voire mécaniques de l’espèce de bois étudiée et la durabilité du matériau dans les constructions traditionnelles à partir du Borassus permettent d’envisager son utilisation comme armature dans le béton.Mots clés : Borassus Aethiopum (palmier rônier), transfert de chaleur, propriétésphysiques,conductivité, diffusivité

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