Arboviroses in the region of Nosy-Bé, Madagascar. Serologic and entomologic data

Since 1977, the Pasteur Institute of Madagascar has been studying, during six surveys, the arboviruses of Nosy-Be area, in the north-west of Madagascar. 47.2% out of 271 human sera and 11.3% out of 151 sera of Lemurs, tested for antibodies to 16 arboviruses by the haemagglutination inhibition test, are positive. The results show an important prevalence of Flaviviruses. West Nile and Dengue 1 viruses were probably circulating some years before the surveys. Antibodies against Sindbis and Rift Valley Fever viruses, were found only in few subjects. Bunyamwera and California groups of virus are absent. The rate of positive Lemurs is weak, particularly in Lemur macaco macaco. Flaviviruses are the most frequent. 12,262 haematophagous diptera (11,965 Culicidae belonging to 40 species) were caught. Aedes aegypti and Aedes albopictus are both present. Arbovirus isolation attempts from 394 mosquito pools failed; only Mengo virus was isolated from four pools of Eretmapodites quinquevittatus and one pool of Aedes (Skusea) sp.