Vertical and horizontal transmission mechanisms of a Plasmodium-blocking symbiont in Anopheles mosquitoes

Microsporidia MB, a symbiont that inhibits Plasmodium transmission in An. arabiensis, has the potential to be developed into a transformative symbiont- based malaria control strategy. It spreads naturally through vector populations via vertical (mother-to-offspring) and horizontal (sexual) transmission. However, our previous research has demonstrated inefficiencies in these transmission routes, which can limit its application as a malaria control tool. In the proposed study, the mechanistic basis of variations in vertical transmission rates will be investigated by determining symbiont infection dynamics across mosquito developmental stages. Also, horizontal transmission mechanisms will be assessed by determining how Microsporidia MB is transmitted during mating. To achieve these aims, high-resolution microscopy imaging will be applied to track Microsporidia MB’s interaction with An. arabiensis at the tissue and cellular level. Host and symbiont factors mediating or inhibiting symbiont colonization and transmission will be investigated using gene expression studies while symbiont transmission efficiencies will be assessed using experimental bioassays. Understanding vertical and horizontal transmission mechanisms and efficiencies of Microsporidia MB will establish the stability of Microsporidia MB infections, determine the specificity of host-symbiont interactions, and establish transmission bottlenecks. This knowledge will be the foundation for developing optimized Microsporidia MB-Anopheles symbioses for deployment as a novel malaria control strategy.