Seasonal Malaria Transmission and Variation of Anopheline Density in Two Distinct Endemic Areas in Brazilian Amazônia

Abstract Studies on seasonal anopheline fauna variation were performed in two distinct settlements in the State of Rondonia, Brazil: one at the Madeira River banks (Portuchuelo) with stable native Amazonian population; the other at an inland lumber-extracting farm (Urupa) in dry land, in which adults are mostly migrants. During a 6-yr period (1994–2000), 8,638 adult anophelines were collected: 2,684 in Urupa and 5,954 in Portuchuelo. Anopheles darlingi represented >95% of total mosquitoes caught. Dissection of 4,424 A. darlingi females yielded a very low sporozoite infection index below 0.1%. Oocysts were found in both localities in ∼0.1% of dissected mosquitoes. Determination of the hour biting rates disclosed seasonal variations in both localities. However, in Portuchuelo, mosquito density peaked at the acme of the rainy season, whereas at Urupa it peaked in the dry season. The increase in mosquito density and incidence of malaria cases were coincident. The high mosquito densities observed in the riveri...