Diversity, abundance and the vectorial capacity of anopheline mosquitoes, and the risk for malaria in Rufiji district, Tanzania.

A longitudinal entomological study was undertaken on the abundance, diversity, seasonal/spatial abundance and the transmission dynamics of malaria vectors in the Rufiji district, South-eastern Tanzania. Method used to collect mosquitoes included CDC light traps, human biting catches, pyrethrum spray catches and pit traps. Over a three year sampling period a total of 64,875 female mosquitoes were collected using light traps, and of these 46% were culex species, 28% anopheles gambiae complex, 25% An funestus Giles, 1% An pharoensis Theobald and Mansonia uniforms Theobald. Mosquito abundance and species composition varied seasonally, spatially and between years. Using PCR, three members of the Anopheles gambiae complex namely An. Gambiae s.s Giles ( 69%), An. Arabiensis Paton (23%) and An.merus Donitz ( 7 %) were confirmed to occur in the study area. Plasmodium falciparum circumsporozoite antiogen ( CSA ) rates were An. Gambiae complex ( 3.5%) and An. Fenustus ( 2.3%). The mean entomological inoculation rate ( EIR) ranged from 28-275 infective bites/person/year, the vectorial capacity ranged from 0.02 to 42.11. Transmission indices varied even over short distances, seasonally and between years, and were similar to those reported in other holoendemic areas of Tanzania. Light traps recorded significantly higher rates in mosquito density and sporozoites rates than human-biting catches. Malaria risk was significantly higher on the plateau than on the flood plain ( p < 0.05 ). Environmental factors, poor housing, low utilization of bed-nets and other protective measures, poverty and human behavior were identified as risk determinants for malaria in this study area. Intervention measures relevant to the study area are discussed.