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Environmental conditions associated with the emergence of Rift Valley fever (RVF) in the Senegal River delta in 1987 Volume 4, issue 2, Mars-Avril 2005

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Authors
Laboratoire de physique de l’atmosphère Siméon Fongang, École supérieure polytechnique/université Cheikh Anta Diop (ESP/UCAD), BP 5085, Dakar-Fann, Sénégal, Institut national de la recherche agronomique (INRA), Unité Biomathématiques et épidémiologie, Laboratoire Environnement et prévision pour la santé des populations/Techniques de l’imagerie, de la modélisation et de la cognition (EPSP-TIMC), École nationale vétérinaire de Lyon, 1, avenue Bourgelat, BP 83, 69280 Marcy l’Étoile, France, Institut de recherche pour le développement (IRD), UR 34 « Maladies virales émergentes et systèmes d’information », BP 1386, Dakar, Sénégal, Centre de coopération internationale en recherche agronomique pour le développement (CIRAD), Département Élevage et médecine vétérinaire (CIRAD-Emvt), Campus International de Baillarguet, 34098 Montpellier cedex 5, France, Médias-France, Centre national d’études spatiales (CNES), 18, avenue Édouard Belin, BPI 2102 31401 Toulouse cedex 4, France, Institut sénégalais de recherches agricoles (ISRA), Laboratoire national d’élevage et de recherches vétérinaires, BP 2057, Dakar-Hann, Sénégal, Direction de la météorologie nationale, BP 8257, Dakar, Sénégal, adresse actuelle ISRA, Laboratoire national d’élevage et de recherches vétérinaires, BP 2057, Dakar-Hann, Sénégal

The Rift Valley fever (RVF) epidemic that occurred in 1987 in the Senegal River delta was associated by some experts with a rainfall above normal and with the opening of the Diama dam. Our main concern in this paper is to study the hydro-climatic conditions at the time RVF emerged along the Senegal-Mauritania border. We consider the rainfall observed at Rosso, the level of the Senegal River there and at the dam, and the river flow rate at Bakel. Analysis of the 1987 rainy season shows that there was no excess rainfall associated with the emergence of RVF. The only particularity in rainfall that year was the postponement of the seasonal peak month from August to September. The first human cases were diagnosed in October, when rainfall was below normal (-35% compared to the monthly average rainfall for 1961-1990). Moreover, the opening of the dam did not upset local hydrology at that time. Hydro-climatic conditions thus do not appear to explain - certainly not alone - the emergence of RVF in the area. The pattern observed in Southern and Eastern Africa does not explain what occurred in 1987 in the Senegal River basin. Without calling into question the influence of rainfall in RVF emergence, the rainfall in especially rainy periods or during series of rains seems more important than the cumulative rainfall over the entire season, because of the importance these shorter heavy rains play in the dynamics of mosquito vector populations in West Africa.