Advances in the development of a Microsporidia MB endosymbiont-based Plasmodium transmission blocking strategy

A possible malaria control approach involves the dissemination in mosquitoes of inherited symbiotic microbes to block Plasmodium transmission. However, in the Anopheles gambiae complex, the primary African vectors of malaria, there are limited reports of inherited symbionts that impair transmission. We have established the SYMBIOVECTOR project to investigate the prospect of deploying a recently discovered Anopheles symbiont, Microsporidia MB, as a Plasmodium transmission blocking tool. The ability of Microsporidia MB to block Plasmodium transmission together with vertical transmission and avirulence makes it an excellent candidate for symbiont-based transmission blocking. We show that a vertically transmitted microsporidian symbiont (Microsporidia MB) in the An. gambiae complex can impair Plasmodium transmission. Microsporidia MB is present at moderate prevalence in geographically dispersed populations of An. arabiensis in Kenya, localized to the mosquito midgut and ovaries, and is not associated with significant reductions in adult host fecundity or survival. We investigated the mechanistic basis and efficiencies of Microsporidia MB transmission between Anopheles arabiensis mosquitoes. We show that Microsporidia can be transmitted both vertically (mother to offspring) and sexually between adult mosquitoes. The dynamics of spread and optimal dissemination strategies have been investigated under semi-field conditions and used to determine the likely outcomes of releasing Microsporidia MB in the field.