Malaria Parasite May Hijack Mosquitoes’ Appetite

Ever been so full that you can’t even contemplate another bite? Mosquitoes experience something similar after a hearty blood meal.

Diego Giraldo is exploring whether the Plasmodium parasites responsible for malaria hijack this sense of satiety to improve their odds of infecting human hosts.

Giraldo, PhD, a postdoc in Molecular Microbiology and Immunology, is interested in understanding these insects’ appetites. “Mosquitoes are attracted to human smell, but this attraction can vary and depends on [the insects’] internal physiological state—basically, if a mosquito has fed or not,” he says.

Preliminary evidence shows that the presence of Plasmodium in the mosquito gut may manipulate the insect’s urges to feed. It takes two weeks for parasites taken up during a blood meal to mature sufficiently for transmission—but this can only happen if the mosquito doesn’t get swatted. “The theory is that the parasite is modifying the mosquito’s behavior, essentially telling it, ‘Don’t look for humans because it’s dangerous,’” says Giraldo. “Once the parasite is ready, you see the opposite trend, and mosquitoes are very attracted to human odor.”

Limited data are available to support this theory, but he notes numerous examples of parasites influencing their insect hosts. For example, hairworms compel the crickets they infect to seek out bodies of water—and, in many cases, even drown themselves—
so that the parasite can spread.

In March, Giraldo, who works in the lab of MMI assistant professor Conor McMeniman, PhD, received a three-year fellowship from the Human Frontier Science Program to explore this theory. McMeniman, who was awarded the same fellowship in 2010, has mapped the basic neuronal circuitry of smell in mosquitoes. Giraldo now aims to trace the wiring involved in feeding and satiety in order to identify connections between these networks. To achieve this, he will adapt the arsenal of molecular tools from fruit fly research to identify neuromodulators that regulate mosquito appetite and characterize their interplay with Plasmodium parasites. “Our School has very good facilities for safely studying the behavior of infected mosquitoes,” he says.