Parasites that cause malaria can lurk in plain sight, including in deer in North America.
Researchers who analyzed blood samples from 33 farm-raised, white-tailed fawns in Florida report that about 21 percent — 7 of 33 — were infected by malaria parasites at some point during the first eight months of life. This research was published in mSphere, an open-access journal of the American Society for Microbiology, Blood samples were collected at three months, six months, and eight months of age. The researchers also found that infected baby deer were more likely to die during the first year than uninfected animals, and that correlation suggests the parasites may contribute to that increased risk.
"If you look at the fawns that were infected at the earliest timepoint, half of those die," says pediatrician and microbiologist Audrey Odom John at Washington University in St. Louis, who led the study. Odom John's lab focuses on the biology of malaria parasites, though her research usually focuses on human infections.
However, adults and children may have dramatically different responses to infection, and children infected with malaria face a much higher risk of death than adults. More than 400,000 people die every year from malaria, and the majority — about 70 percent — are five years old or younger, according to the World Health Organization. The findings by Odom John and her colleagues suggest that while many animals readily clear the infection, young animals, too, are particularly vulnerable to the parasites.
Biologists have identified more than 600 malaria parasites, or haemosporidians, but only five are known to use humans as hosts. Biting flies transmit the parasites, which infect vertebrates including rodents, bats, birds, lizards, and primates. Scientists first identified Plasmodium odoceoilei, a malaria parasite, in white-tailed deer in 1967, but until recently little followup work has been done to understand the clinical implications of infection in the animals.
Scientific interest in deer malaria has increased recently, in part due to studies that have analyzed the genome of malaria parasites and surveys that show P. odocoilei is common in North American white-tailed deer. "Deer are everywhere," says Odom John. "I have a malaria parasite in my backyard."
She and her colleagues worked with the University of Florida Cervidae Health Research Initiative, which organizes and coordinates deer research. They collected blood samples from fawns born and raised within a 500-acre preserve in Gadsden County, Florida. Studying deer, says Odom John, offers researchers a way to understand how the parasites evolve with their hosts and move from place to place.
"This study opens new opportunities to study the malaria parasite-mammal interface in North America," notes microbiologist Susan Perkins, at the American Museum of Natural History in New York City, in a commentary published concurrently in mSphere with the study.
Odom John says her lab plans to continue studying malaria in deer. Their study couldn't discern, for example, whether the fawns were infected by mosquito bites or through vertical transmission, from their mothers. "We also don't know how intense the transmission pressure is for this parasite," she says. They plan to sequence the genome of P. odocoilei and conduct further studies to understand the role of the parasite in fawn mortality.
Deer offer an easy opportunity to study parasitism in a true field population, she says. "I'm very interested in seeing if we can see the parasite DNA in deer poo," she says. "We have a whole bunch of samples waiting in the freezer."
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