Résumé
Current views about the impact of Wolbachia on Plasmodium infections are
almost entirely based on data regarding artificially transfected
mosquitoes. This work has shown that Wolbachia reduces the intensity of
Plasmodium infections in mosquitoes, raising the exciting possibility of
using Wolbachia to control or limit the spread of malaria. Whether natural
Wolbachia infections have the same parasite-inhibiting properties is not
yet clear. Wolbachia–mosquito combinations with a long evolutionary
history are, however, key for understanding what may happen with
Wolbachia-transfected mosquitoes after several generations of coevolution.
We investigate this issue using an entirely natural
mosquito–Wolbachia–Plasmodium combination. In contrast to most previous
studies, which have been centred on the quantification of the midgut
stages of Plasmodium, we obtain a measurement of parasitaemia that relates
directly to transmission by following infections to the salivary gland
stages. We show that Wolbachia increases the susceptibility of Culex
pipiens mosquitoes to Plasmodium relictum, significantly increasing the
prevalence of salivary gland stage infections. This effect is independent
of the density of Wolbachia in the mosquito. These results suggest that
naturally Wolbachia-infected mosquitoes may, in fact, be better vectors of
malaria than Wolbachia-free ones.