Though it is easy to think only of how malaria impacts humans, recent research suggests that this disease also negatively affects the health of mosquitoes. Researchers from Switzerland reported evidence to suggest that nutritionally-deficient mosquitoes infected with malaria are more likely to succumb to starvation than non-infected mosquitoes. Understanding how malaria negatively affects mosquitoes may offer insights on how to reduce the overall number of infected vector populations.
Mosquitoes play an essential part of the life cycle of the parasitic protozoan that causes malaria. This parasite is often referred to by its genus name—Plamodium. Female mosquitoes infected with Plasmodium transmit the infection to humans when they feed on human blood. The parasite then travels first to the liver and then proliferates in the bloodstream. Eventually Plasmodium will sexually differentiate into male and female gametocytes (male and female forms). When another mosquito bites a human, these male and female gametocytes are sucked up with the blood meal. In this new host the sexually differentiated parasites produce “gametes”—cells which are similar to the sperm and eggs found in humans. The gametes fuse to form a new, genetically distinct generation of Plasmodium. After many rounds of further cellular division the parasite invades the salivary glands of the mosquito host and the cycle repeats.
Traditionally malaria researchers have investigated how malaria parasites affect human hosts. Comparatively little information is available on how malaria might also negatively affect mosquito hosts.
However in a study recently published in the Journal of Animal Ecology, researchers from Switzerland sought to address just this topic. They collected mosquitoes from malaria-zones and raised them either in normal environmental conditions or in conditions set to induce starvation. Over time researchers monitored the rate and raw magnitude of how many mosquitoes died. After all mosquitoes perished the researchers tested each individual bug for malaria infection.
The results of this study demonstrated that mosquitoes infected with the malaria parasite were less able to survive in a starvation scenario. This finding makes sense when one considers how taxing a malaria infection can be on a human host’s immune system. Within the mosquito, Plasmodium not only activates the energy-costly immune system, but also damages the lining of the gut and the insect’s salivary glands.
In addition it was found that mosquitoes infected with malaria did not experience reduced fertility. This is a perplexing result because other research indicates that Plasmodium infection does indeed reduce reproductive success. This disparity may indicate that there are other confounding environmental factors that have yet to be studied.
The discovery that malaria negatively affects mosquitoes may suggest that perhaps evolutionary pressure exists and/or could be manipulated in such a way that would select against malaria-infected mosquitoes. In particular one might imagine finding a method to weaken mosquitoes and starve them in such a way that they would cause them to immediately succumb to a malaria infection. Such efforts to use genetic engineering to manipulate the population ecology of mosquitoes have already been undertaken by other malaria researchers. These researchers hope to introduce sterile male mosquitoes to malaria zones as a way to curb epidemics. Such innovative efforts, though still in the developing stages, might one day offer a unique solution to resolving the world’s persistent battle against malaria.
By Sarah Takushi