Anopheles coluzzii infection by the microsporidian, Vavraia culicis: the effect of host age.

Host age at infection has important implications for disease development. In mosquitoes, infections with microsporidia and later concurrent infections with malaria parasites, leads to a suppression in the development of malaria parasites. Host age at infection with microsporidia could have implications for disease outcomes when infection occurs subsequently with malaria parasites. Mosquito larvae can take between five to seven days or more depending on the temperature to reach the adult stage, giving the microsporidian Vavraia culicis, a theoretical head start in establishing and developing within larvae and possibly resulting in different levels of infection in emergent adult mosquitoes. To determine the effects of early or late infection with V. culicis, equal numbers of Anopheles coluzzii larvae were infected individually with a high or low dose of V. culicis, at different ages post hatching. Significantly fewer spores were produced from mosquitoes infected later, than ones infected earlier with microsporidia and there was an initial delay in the production of spores from later infected mosquitoes. In early infected larvae, there was no such initial delay and spore production took off unchecked. The infectious dose of V. culicis did not affect the total spore count per mosquito. Male mosquitoes produced fewer spores than females. Daily mosquito longevity and pupation was not affected significantly by infection, the infectious dose of V. culicis given or by the sex of the mosquito. Considering hourly deaths, early infected hosts died 17 to 18 hours earlier than later infected larvae. The number of V. culicis spores rose with increasing duration of infection. When equal duration of infection was considered, the findings remained the same. Host age at infection influences disease outcomes and virulence.