Experimental reduction of host Plasmodium infection load affects mosquito survival

Plasmodium  transmission success depends upon the trade-off between the use of host resources to favour parasite reproduction and the negative effects on host health, which can be mediated by infection intensity. Despite its potential influence on parasite dynamics, the effects of infection intensity on both, birds and vectors, and on Plasmodium  transmission success are still poorly understood. Here, we experimentally reduced the Plasmodium  load in naturally infected wild house sparrows with the antimalarial primaquine to assess the effects of intensity of infection in the vertebrate hosts on Plasmodium  transmission to and by mosquitoes. We monitored the survival of Culex pipiens mosquitoes throughout the development of the parasite and the infection status of the mosquitoes by analysing the head-thorax and saliva at 13 days post-exposure to birds. The proportion of mosquitoes infected by Plasmodium  and the presence of Plasmodium  in saliva were not associated with the medication treatment of birds. However, the experimental treatment affected vector survival with mosquitoes fed on medicated birds showing a higher survival rate than those fed on control individuals. These results provide strong experimental evidence of the impact of parasite load of vertebrate hosts on the survival probability of malaria vectors.