Enzootic activity of Rift Valley fever virus in Senegal.

In two areas of Senegal where previous evidence of Rift Valley fever (RVF) virus circulation was detected, Barkedji in the Sahelian bioclimatic zone and Kedougou in the Sudano-Guinean zone, a longitudinal study of the enzootic maintenance of RVF virus was undertaken from 1991 to 1993. Mosquitoes, sand flies, and ticks were collected and domestic ungulates were monitored with serologic surveys. Rift Valley fever virus was not isolated in Kedougou. In Barkedji, RVF virus was isolated from Aedes vexans and Ae. ochraceus mosquitoes collected in traps near ground pools and cattle droves and from one health sheep. Sand flies were not involved in the maintenance cycle. Seroconversions were recorded in three (1.9%) of 160 monitored sheep and goats. The interepizootic vectors appeared to belong to the Aedes subgenus Neomelaniconion in East Africa, and to the subgenus Aedimorphus in West Africa. Epizootics in East Africa are associated with an increase in rainfall. However, factors associated with epizootics remain unknown for West Africa.