HIGH ANNUAL AND SEASONAL-VARIATIONS IN MALARIA TRANSMISSION BY ANOPHELINES AND VECTOR SPECIES COMPOSITION IN DIELMO, A HOLOENDEMIC AREA IN SENEGAL

We conducted a three-year entomologic study in Dielmo, a village of 25 0 inhabitants in a holoendemic area for malaria in Senegal. Anopheline s were captured on human bait and by pyrethrum spray collections. The mosquitoes belonging to the Anopheles gambiae complex were identified using the polymerase chain reaction. Malaria vectors captured were An funestus, An. arabiensis, and An. gambiae. Anopheles funestus was the most abundant mosquito captured the first year, An. arabiensis in the following years. The annual entomologic inoculation rates calculated b y enzyme-linked immunosorbent assay were 238, 89, and 150 for the firs t, second, and third years, respectively. Each year there was a peak o f transmission at the end of the rainy season, but transmission occurr ed year round. The heterogeneity of transmission was found at four dif ferent levels: 1) the relative vector proportion according to the plac e and method of capture, 2) the human biting rate and relative proport ion of vectors by month and year, 3) the infection rate of each vector by year, and 4) the number of infected bites for all vectors, and for each species, for the year. Our data show that even in areas of inten se and perennial transmission, there exist large longitudinal variatio ns and strong heterogeneity in entomologic parameters of malaria trans mission. It is important to take these into account for the study of t he variations in clinical and biological parameters of human malaria, and to evaluate this relationship, a very thorough investigation of tr ansmission is necessary.