An estimated 250 million people become infected with malaria each year and nearly a million die from it, according to the World Health Organization. Now, a new study finds that most of these human infections might trace back to one infected gorilla.

The study, published in the Sept. 23 issue of the journal Nature, used a genetic analysis of the parasites that cause malaria found in primate feces to create an evolutionary family tree for the disease. The parasite most closely related to human malaria came from gorillas, the researchers found, and may have made the leap from animal to human host in a single mosquito bite.

Five types of malaria parasites infect humans, but the most common (and most deadly worldwide) is Plasmodium falciparum. Like all Plasmodium parasites, P. falciparum, as it is called, is carried from host to host by mosquitoes. When the mosquito bites someone, the parasite infects the person’s red blood cells, causing fatigue, fever and vomiting. Untreated, the infection is fatal.

The malaria family tree

For many years, researchers thought the closest relative of P. falciparum was a similar Plasmodium infection found in chimpanzees. This led to the theory that the malaria parasite originated in the common ancestor of […]