Effect of Plasmodium falciparum on the Survival of Naturally Infected Afrotropical Anopheles (Diptera: Culicidae)

Abstract

The effect of the malarial parasite, Plasmodium falciparum Welch, on the daily survival rates and longevity of Anopheles gambiae Giles sensu lato and Anopheles funestus Giles was determined for wild-caught, naturally infected females from western Kenya. Mosquitoes were collected inside houses and held in cages until death, after which they were assayed for P. falciparum circumsporozoite protein by an enzyme-linked immunosorbent assay (ELISA). Survival rates of field populations determined by parity rates were significantly higher than survival rates estimated by regression for Anopheles dying in cages. Overall, An. gambiae s.l. had a significantly higher daily mortality rate ( $\bar x$ = 17.5%) than An. funestus ( $\bar x$ = 13.2%). P. falciparum ELISA infection rates, which were higher for An. gambiae s.l. ( $\bar x$ = 19.8%; n = 1, 221) than for An. funestus ($\bar x$ = 11.9%; n = 1, 128), did not increase as a function of time for caged Anopheles. For An. gambiae s.l., there was a significant negative correlation between holding time and P. falciparum ELISA absorbance, suggesting that detectable circumsporozoite protein and perhaps the number of sporozoites may decrease with time in the vector. In western Kenya, an area where Anopheles populations often have extremely high malaria infection rates, Plasmodium infections did not reduce vector survivorship.