Vectorial capacity and entomological inoculation rates of Anopheles gambiae in a high rainfall forested area of southern Sierra Leone.

We report the first study of gonotrophic cycle duration, survival rates, pre-gravid rates, vectorial capacity and chromosomal polymorphism of Anopheles gambiae s.s. in Sierra Leone. In the village of Bayama in the Southern Province, An. gambiae was the only species found to be naturally infected with Plasmodium falciparum and it constituted 99.7% of 22,541 anopheline mosquitoes caught. Chromosomal studies revealed only An. gambiae s.s. out of 66 females examined for chromosomal polymorphism, 61 (92.4%) had the 2LA inversion in the standard arrangement. Other inversions observed in low frequencies included 2Rcu and 2Ru. We estimated a gonotrophic cycle length of three days and survival rate per gonotrophic cycle of 0.59 for this species. The mean daily survival rate of An. gambiae was 0.85 and the entomological inoculation rate was 1,235 infective bites/person/year. Blood-meal ELISA tests showed that the species was very anthropophagic and that there were an estimated 35.4 daily inoculations per infective case. The epidemiological significance of these entomological parameters is discussed in the light of parasitological results for nearby villages.