Malaria Found in American White-Tailed Deer

A new study from the Univ. of Vermont published in Science Advances has found that malaria infects up to 25% of white-tailed deer along the United States’ eastern seaboard. Previously, it was thought that malaria was eradicated from the U.S. in the 1950s, according to the Centers for Disease Control and Prevention.   

Named Plasmodium odocoilei, the malaria parasite represents the first of its kind to live in a deer species, and is the only parasite known to live in a mammal in North or South America, according to the Univ. of Vermont.

“You never know what you’re going to find when you’re out in nature—and you look,” said Ellen Martinsen, who is an adjunct faculty member at the university and a research associate at the Smithsonian Conservation Biology Institute. “It’s a parasite that has been hidden in the most iconic game animal in the United States. I just stumbled across it.”

This isn’t the first case of a deer being infected with malaria. In 1967, a researcher reported finding the parasite in a single white-tailed deer from Texas. However, no other reports occurred until recently.

“Our results beg the question of why diverse malaria parasites that are specialized to (white-tailed deer) remained cryptic in a large game mammal that has long been the center of study for wildlife biologists and managers,” the researchers wrote. “Most likely, the answer is the occult nature of all the infections observed for P. odocoilei, with extremely low parasite density (an estimate ~1/65,000 red blood cells infected).”

The researchers believe the species doesn’t pose a threat to humans. Of the hundreds of species of malaria, only four are known to infect humans. Usually, humans are infected by mosquitos.  

The researchers found the studied deer were actually hosts to two distinct lineages of the malaria parasite. The lineages, according to the researchers, split from one another about 2.3 to 6 million years ago. The parasite likely made its way to the Americas when the ancestor of the white-tailed deer crossed the Bering Land Bridge to North America during the Miocene, between 4.2 and 5.7 million years ago.

The researchers plan to further the study, and want to figure out whether the parasite infects other hoofed species, such as dairy cows.