Like tiny nomads, malaria parasites move from human to mosquito and back again. But how do they know when to pack up and move? New research from HHMI Senior International Research Scholar Alan F. Cowman suggests that when it’s time to leave their human hosts, the parasites, a type of protozoa, send each other dispatches saying it’s time to head out.
A mosquito transmits the malaria parasite to a human host when it plunges its proboscis through the skin for a sip of blood. The protozoa travel through the bloodstream to the host’s liver, where they reproduce asexually and infect red blood cells. When it’s time to go, the protozoa develop into gametes that are taken up during a second mosquito’s bite. Inside the mosquito’s gut, the protozoa reproduce sexually and the process begins again.
Cowman’s postdoctoral fellow Neta Regev-Rudzki discovered that the protozoa were talking to each other inside their human hosts, passing vesicles between the red blood cells they had infected. As the researchers reported in Cell on May 23, 2013, vesicle production increased when the protozoa were stressed—for example, when they were exposed to an antimalarial drug—and seemed to signal to the parasites to mature into their sexual form. The communication mechanism made sense: the protozoa need a way to broadcast environmental conditions and let the community know when it’s time to catch a ride with the next mosquito.
Although Cowman and his team at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, have yet to determine the exact content of the vesicles, once they do, they could have some potential drug targets. “A big aim among malaria researchers is not only to develop ways to treat the disease but also to make compounds that inhibit transmission,” says Cowman. “Blocking the passage of the parasites into the form that can spread to mosquitoes is one way to do that.”