BREAKING: Researchers Discover Malaria in Eastern Deer

The parasite that causes malaria has been discovered in white-tailed deer that live in the eastern part of the United States, with estimates of at least 25 percent of the region’s deer being infected.

Ellen Martinsen of UV  Photo by Joshua Brown

Ellen Martinsen discovered malaria parasites in white-tailed deer while studying under University of Vermont researcher Joseph Schall (rear). After two years of research, it’s believed the malaria parasite may infect as many as 25 percent of the eastern United States’ deer population. (Photo: Joshua Brown/UV)

For the last two years, researchers have been studying the parasite and how it lives within the deer. It is the first and only known native malaria parasite found in any mammal in North or South America. Research has been a collaboration among the University of Wisconsin-Milwaukee, National Park Service, American Museum of Natural History, Smithsonian Conservation Biology Institute and University of Vermont biologist and malaria expert Joseph Schall.

From a UV press release:

Two years ago, Ellen Martinsen ’00 G’09, was collecting mosquitoes at the Smithsonian’s National Zoo, looking for malaria that might infect birds—when she discovered something strange: a DNA profile, from parasites in the mosquitoes, that she couldn’t identify.

By chance, she had discovered a malaria parasite,Plasmodium odocoilei—that infects white-tailed deer. It’s the first-ever malaria parasite known to live in a deer species and the only native malaria parasite found in any mammal in North or South America. Though white-tailed deer diseases have been heavily studied—scientists hadn’t noticed that many have malaria parasites. 

Martinsen and her colleagues estimate that the parasite infects up to twenty-five percent of white-tailed deer along the East Coast of the United States. Their results were published Feb. 5 in Science Advances.

As many as 25 percent of the deer in the eastern United States are believed to be infected with the parasite that causes malaria. (Photo: Alan Clemons)

As many as 25 percent of the deer in the eastern United States are believed to be infected with the parasite that causes malaria. (Photo: Alan Clemons)

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

In 1967, a renowned malaria researcher reported he’d discovered malaria in a single deer in Texas. But the received understanding was that “malaria wasn’t supposed to be in mammals in the New World,” says Schall, who has studied malaria for decades. “It was like the guy was reporting he saw Big Foot,” and no other discoveries were made after that.

But now Martinsen and her colleagues have discovered that the deer malaria is widespread—though it’s “cryptic” she says, because the parasites occur in very low levels in many of the infected deer. “Ellen spent days and days looking through a microscope at slides that were mostly empty,” Schall says, but eventually found the parasites hiding among thousands of red blood cells. Combined with sensitive molecular PCR techniques to understand the genetics, the team confirmed a high prevalence of the disease—between eighteen and twenty-five percent—in sites ranging from New York to West Virginia to Louisiana.

Malaria is a major problem for people in many parts of the world—and for many species of wildlife too. It has been devastating bird species in Hawaii and Bermuda, among many epidemics. Whether it is hurting white-tailed deer in America is an open question. Martinsen suspects not, because she’d expect to see more obviously sick animals. But Schall wonders if, like some human malaria infections, the disease causes a low-level burden that hurts deer populations. They both agree that it is an area that calls for more research—and that the new study raises many other questions, including whether the parasite might infect dairy cows or other hoofed species.

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