Indoors man-biting mosquitoes and their implication on malaria transmission in Mpwapwa and Iringa Districts, Tanzania.

Entomological surveys were carried out in six villages at different altitudes in Mpwapwa and Iringa Districts in central Tanzania in March 2002. A total of 1291 mosquitoes were collected. Of these, 887 mosquitoes were collected by light traps and 404 by indoor pyrethrum spray catch technique. Seventy-nine percent (1026) were Anopheles gambiae s.l., 0.2% (N = 3) were An. funestus, and 20.3% (N = 262) were Culex quinquefasciatus. Other species including Cx cinereus, An. coustani and Aedes spp accounted for 0.5% of the mosquito population. In Iringa, more mosquitoes were collected by pyrethrum spray catch than light trapping technique. The light trap catch: spray catch ratio in Iringa and Mpwapwa was 1:1.15 and 2.5:1, respectively. Indoor pyrethrum spray catch gave an overall estimate of An. gambiae density of 8 and 0.6 mosquitoes per room in Iringa and Mpwapwa, respectively, whereas light trap collections gave an overall respective density of An. gambiae of 63.9 and 2.9 mosquitoes per room. The densities of house entering mosquitoes were found to range from 0 to 135 in Iringa and from 2.6 to 3.5 per room in Mpwapwa. An.funestus mosquitoes were collected in Iringa only. None of the dissected An. gambiae collected in the two districts was infected with malaria sporozoites. Despite low mosquito densities and absence of infective mosquitoes in our study, the two districts are malaria epidemic prone, thus a continuous surveillance is critical for a prompt response to any impending outbreak. Further longitudinal studies are required to determine the transmission potential of the malaria mosquitoes in the two districts.