Microsporidia MB in the primary malaria vector Anopheles gambiae sensu stricto is avirulent and undergoes maternal and horizontal transmission

Abstract

Background The demonstration that the recently discovered Anopheles symbiont Microsporidia MB blocks malaria transmission in Anopheles arabiensis and undergoes vertical and horizontal transmission suggests that it is a promising candidate for the development of a symbiont-based malaria transmission-blocking strategy. The infection prevalence and characteristics of Microsporidia MB in Anopheles gambiae sensu stricto (s.s.), another primary vector species of malaria in Kenya, were investigated. Methods

Field-collected females were confirmed to be Microsporidia MB-positive after oviposition. Egg counts of Microsporidia MB-infected and non-infected individuals were used to infer the effects of Microsporidia MB on fecundity. The time to pupation, adult sex ratio and survival were used to determine if Microsporidia MB infection has similar characteristics in the host mosquitoes An. gambiae and An. arabiensis. The intensity of Microsporidia MB infection in tissues of the midgut and gonads, and in carcasses, was determined by quantitative polymerase chain reaction. To investigate horizontal transmission, virgin males and females that were either Microsporidia MB-infected or non-infected were placed in standard cages for 48 h and allowed to mate; transmission was confirmed by quantitative polymerase chain reaction targeting Microsporidia MB genes.