white-tailed deer
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Malaria detected in up to 25 percent of American white-tailed deer

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Thanks to advanced DNA technology, American researchers have detected low levels of malaria in up to a quarter of white-tailed deer.

Researchers led by Ellen Martinsen, a postdoctoral fellow at the Smithsonian National Zoo’s Center for Conservation and Evolutionary Genetics, came across the findings while searching for the source of malaria in birds.

“We stumbled across some DNA that we didn’t understand,” Martinsen told Smithsonian Magazine. “Fortunately one of the mosquitoes was full of blood, so we did a scan for vertebrate genes, and we found that this parasite had fed on white-tailed deer. And we knew that was something strange.”

Malaria, which is caused by a parasitic single-celled organism from the Plasmodium genus, depends on two hosts to complete its life cycle—a flying insect, like a mosquito, and a vertebrate animal. There are more than 200 species of the parasite worldwide, which can infect an array of reptiles, birds, and mammals. But this recent discovery marks the first time malaria has been found in a mammal native to the Americas.

Luckily, none of the infected deer involved in the study showed any signs of illness.

“There doesn’t seem to be a difference in health between animals with the parasite and without,” Robert Fleischer, co-author of the paper and head of the Centre for Conservation and Evolutionary Genetics, told Smithsonian Magazine. “It may be that this is one of those benign parasites that doesn’t impact the host much.”

Unlike species found in subtropical regions like sub-Saharan Africa and South Asia, which kill an estimated 600,000 people annually, he says these parasites aren’t likely to affect humans either.

“If it’s getting into humans, which it probably is, it probably isn’t able to reproduce,” he said. “We don’t know for sure, but it seems that this is not something that people need to worry about. This is not Zika virus.”

It does, however, highlight the importance of surveying, Martinsen told Mother Nature Network. “It shows the power of going out into nature and turning over stones and looking for things. And in the medical realm, if we study more hosts and invertebrates, are we likely to find more parasites like this hidden in plain sight?”

It’s a valid theory considering the amount of resources that have gone into studying white-tailed deer in the past. In fact, according to Smithsonian Magazine, “it’s arguably the most closely studied species of wildlife in North America,” which is one reason the finding came as such a surprise.

As a popular game species, the white-tailed deer drives the sale of hunting licences, and as part of the North American Model of Wildlife Conservation, this money provides funding for conservation programs for the animal. But despite non-profit organizations and state wildlife agencies devoting significant scientific resources to monitoring white-tailed deer populations for disease, the malaria was missed.

That’s likely because the most common methods for looking at blood samples couldn’t detect infection at the levels these types of malaria occur. To determine how common the infections are, the researchers screened more than 300 white-tailed deer with polymerase chain reaction (PCR) technology, which amplifies DNA to make it easier to study.

The parasite was found in 41 of the animals, which were from 10 of the 17 states studied. While no infected deer were found in the Western United States, the parasite was considered “widespread” in the east. In fact, the researchers estimate between 18 and 25 percent of white-tailed deer living along America’s East Coast are infected.

And though no signs of illness were detected, the subtle harm of a parasite has been seen in other hosts. “There are studies where you don’t see any major effect of a parasite on a host, like a bird, but if you look at its lifespan, it might have lower reproductive success or a shorter life,” Fleischer told Mother Nature Network.

The scientists hope to continue their research, which would involve looking for malaria in other species of deer throughout North and South America. They’d also like to examine the bones of deer that died thousands of years ago, in attempt to find genetic material that could reveal how and when malaria evolved in this part of the world.

“This story suggests there is still much we don’t know about the natural world,” David Hewitt, a wildlife biologist at Texas’ A&M University told Science magazine. And that includes what’s hanging out in our backyards.

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