Entomological investigations were conducted in 1995 in Senegal, following a yellow fever (YF) outbreak. A total of 1125 mosquitoes collected in the field, including males, females and 12-48 h old newly emerged adults reared from wild-caught larvae, were tested for YF virus. Among the 22 species captured, Aedes aegypti was the most common. 'Wild' vectors of YF were also captured, including A. furcifer, A. metallicus and A. luteocephalus. In all, 28 YF virus isolations were made: 19 from A. aegypti females, including 2 from newly emerged specimens; 5 were obtained from A. aegypti males, including one from a pool of newly emerged specimens, 2 from A. furcifer females, and one each from a female A. metallicus and a female A. luteocephalus. The true infection rates (TIRs) were much higher in adult A. aegypti than in specimens reared from larvae--8.2% and 31.4% for female and male A. aegypti captured on human volunteers, respectively (P < 0.0001). The TIRs for A. aegypti reared from larvae were 1.4% and 0.5% for females and males, respectively (P > 0.05). This outbreak was an intermediate YF epidemic, involving 4 vector species. Our data provide the first evidence of vertical transmission of YF virus in nature by A. aegypti, its main vector to humans, and strongly suggest that vertical transmission played a major role in the spread of the epidemic.

Our results demonstrate that, from Madagascar to Senegal, the epidemiologic and virologic characteristics of influenza viruses are diverse in terms of spatiotemporal circulation of the different virus types, subtypes, and strains. Our data highlight the importance of country-specific surveillance and of data and virus sharing, and they provide a rational basis to aid policy makers to develop strategies, such as vaccination at the right moment and with the right formulation, aimed at reducing the disease burden in Africa and Madagascar.

The human humoral immune response to the Plasmodium falkiparum merozoite surface antigen gpl90 was analyzed to determine the rate of reinfection by the parasite and the ability to control parasite density. The prospective study was carried out in a West African village where malaria is hyperendemic. No correlation between the antibody titers and protection against infection was observed within the group of children. Positive and negative associations of antibody specificities with protection against and/or control of parasitemia were, however, found for adolescents and adults, respectively. Thus, in adolescents, the presence of antibodies to gpl90 fragment M6 correlates with a 50%v reduced risk of P. falciparum infection and an increased ability to control parasitemia, whereas in adults, the humoral response to some of the polymorphic regions of gpl90 associates with an increased risk of infection.

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In 2005, a serological study was carried out on horses in five ecologically contrasted zones of the Senegal River basin (Senegal) to assess West Nile virus (WNV) transmission and investigate underlying environmental risk factors. In each study zone, horses were randomly selected and blood samples taken. A land-cover map of the five study areas was built using two satellite ETM+ images. Blood samples were screened by ELISA for anti-WNV IgM and IgG and positive samples were confirmed by seroneutralization. Environmental data were analysed using a principal components analysis. The overall IgG seroprevalence rate was 85% (n=367; 95% CI 0.81-0.89). The proximity to sea water, flooded banks and salted mudflats were identified as protective factors. These environmental components are unfavourable to the presence of Culex mosquitoes suggesting that in Senegal, the distribution of the vector species is more limiting for WNV transmission than for the hosts' distribution.