Malaria load affects the activity of mosquito salivary apyrase

Mosquitoes infected by sporozoites, the infectious stage of malaria, bite more frequently than uninfected mosquitoes. One of the mechanisms underlying this behavioural change appears to be that the sporozoites decrease the activity of apyrase, an ADP-degrading enzyme that helps the mosquitoes to locate blood. Using the parasite Plasmodium berghei and the mosquito Anopheles gambiae, we confirmed that sporozoite infection alters the host-seeking behaviour of mosquitoes by making them more likely to refeed after a first blood meal, and that apyrase activity is one of the mechanisms of the increased biting persistence and motivation of infectious mosquitoes. We further showed that apyrase activity decreases as the sporozoite load increases, and that mosquitoes with lower apyrase activity take up less blood, making it more likely that they would return to top up their blood meal. Finally, by comparing full-sib families of mosquitoes, we showed that there was genetic variation for apyrase activity, but not for the resistance of parasites to be manipulated. Our results give new insights in understanding how malaria parasites change their hosts to affect their own transmission.