Talk about a surprise: Two years ago, scientists researching avian malaria happened to learn that two strains of the parasite are infecting white-tailed deer—possibly 25 percent of those living on the East Coast, Smithsonian reports.

Until then, no endemic malaria had been seen in North or South American mammals. "You never know what you're going to find when you're out in nature—and you look," says lead study author Ellen Martinsen, per a press release.

"It's a parasite that has been hidden in the most iconic game animal in the United States. I just stumbled across it." Her team was screening mosquitoes for avian malaria at the Smithsonian's National Zoo in Washington, DC, when they stumbled across some surprise DNA and found that the insect had fed on white-tailed deer.

Researchers then screened more than 300 white-tailed deer and found the parasite in 41 of them, in roughly half the states studied, Science reports. None were in the west, but it was common in the east, particularly in West Virginia and Virginia.

Seems the two malaria species pose little risk to deer or to people: Though humans haven't been tested for the strains yet, co-author Robert Fleischer says "if it’s getting into humans, which it probably is, it probably isn’t able to reproduce. ... This is not Zika virus." The deer's ancestors may have brought the parasite into North America by way of the Beringia land bridge millions of years ago, researchers say.

So how is it no one noticed malaria before in the much-studied deer? "This story suggests there is still much we don’t know about the natural world," says a biologist not involved in the study.

(Meanwhile, Lyme disease is spreading across US counties.)

This article originally appeared on Newser: 1st-Ever Endemic Malaria Found in US Mammals

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