Mosquito distribution and entomological inoculation rates in three malaria-endemic areas in Gabon

Mosquitoes were collected during 3 separate periods in 3 areas of different malaria transmission rates in the province of Moyen Ogooué, Gabon, within 1 year (July 1996-May 1997). The campus of the Albert Schweitzer Hospital (HAS) and 2 villages, Bellevue and Tchad, were investigated. A total of 19,836 specimens were collected: 13,122 Mansonia, 3944 Anopheles, 2755 Culex and 15 Aedes were captured. The number of mosquitoes was 7896 and 7995 in July to August and from April to May respectively, and dropped to approximately half in November to December. The individual species showed a different distribution pattern in the 3 study areas. In Tchad we found the lowest number of mosquitoes and also the fewest Anopheles, but when we investigated the number of Plasmodium falciparum-infected Anopheles sp. we observed the highest entomological inoculation rate (EIR) there. The EIRs were 23 in HAS, 53 in Bellevue and 61 in Tchad. The method used to determine the number of infected mosquitoes was an enzyme-linked immunosorbent assay (ELISA), confirmed by a polymerase chain reaction-based approach. The ELISA alone revealed too many false-positive mosquitoes.