Effect of irradiation on the survival and susceptibility of female Anopheles arabiensis to natural isolates of Plasmodium falciparum

BackgroundThe sterile insect technique (SIT) is a vector control strategy relying on the mass release of sterile males into wild vector populations. Current sex separation techniques are not fully efficient and could lead to the release of a small proportion of females. It is therefore important to evaluate the effect of irradiation on the ability of released females to transmit pathogens. This study aimed to assess the effect of irradiation on the survival and competence of Anopheles arabiensis females for Plasmodium falciparum in laboratory conditions. MethodsPupae were irradiated at 95 Gy, a sterilizing dose of gamma-rays from Caesium-137 source, and emerging adult females were challenged with one of 14 natural isolates of P. falciparum. Seven days post-bloodmeal (dpbm), irradiated and unirradiated-control females were dissected to assess the presence of oocysts. On 14 dpbm, oocyst rupture in mosquito midguts and sporozoite dissemination in head/thoraces were also examined. Two assays were performed to gauge the effect of irradiation on An. arabiensis survival. First, the survivorship of irradiated and unirradiated-control mosquitoes exposed to each parasite isolate was monitored. Second, how parasite infection and irradiation interact to influence mosquito lifespan was also assessed by including a group of uninfected unirradiated mosquitoes. ResultsOverall, irradiation reduced the proportion of infected mosquitoes but this effect was inconsistent among parasite isolates. Second, there was no significant effect of irradiation on the number of developing oocysts. Third, the proportion of ruptured oocysts at 14 dpbm was higher in irradiated- than in control-unirradiated females, suggesting that irradiation might speed up parasite development. Fourth, irradiation had varying effects on female survival with either a negative effect (assay 1) or no effect (assay 2). ConclusionCombining these effects into an epidemiological model could help quantifying the net effect of irradiation on malaria transmission in this system. Together, our data indicate that irradiated female An. arabiensis could contribute to malaria transmission, and highlight the need for perfect sexing tools which would prevent the release of females as part of SIT programs.