There are more than 100 species of malarial parasites in the world, found on every continent except Antarctica. The malaria parasites that infect birds and lizards are widely distributed, and have even been found on isolated islands, and of course, in the Americas.
Yet scientists have believed that microorganisms that infect mammals originated in the Old World, mainly Asia and Africa. So this discovery marks the first finding of a malaria parasite species of mammals that is native to the Americas, although a single specimen of white-tail deer in Texas was found to harbor a malaria parasite in 1967.
That the malaria parasite was found at all is just good luck, according to the Smithsonian Magazine. National Zoo researchers Ellen Martinsen and Rob Fleischer and their colleagues were doing a DNA survey on mosquitoes at the National Zoo when they turned up a strange malaria parasite gene sequence in two of their captured mosquitoes.
Using polymerase chain reaction (PCR) technology which makes DNA easier to study, the researchers were looking for the source of malaria parasites in birds at the zoo. They came across the genetic signature for Plasmodium odocoilei, previously unknown in the Americas.
From the mosquito’s blood-filled abdomen, researchers got enough of a specimen to trace the blood’s origin to white-tail deer. “We weren’t out there, testing a hypothesis,” Martinsen says. “We serendipitously stumbled upon this weird sequence.”
To find out how common the infections were, the team screened 300 white-tail deer with PCR. Of the 10 out of 17 states surveyed, 41 deer were harboring the parasite. No malaria parasite was found in deer populations in the west, however, in the east, the malaria parasite was widespread. Twenty-five percent of the animals tested at sites in Virginia and West Virginia carried them, the team reports today in Science Advances.
No evidence of the parasite was found in other hoofed species, including cows, gazelles, goats, elk, oryx, alpaca, donkeys, and Przewalski horses.
What is most interesting about this new study is the suggestion that the malaria parasite has a long evolutionary history in the new World, dating all the way back to when the ancestors of white-tail deer crossed the Bering Land Bridge between 2.3 million to 6 million years ago. Perhaps even more intriguing is that unless we look closely, we don’t know what we could find in our own backyard.
This study, “Hidden in plain sight: Cryptic and endemic malaria parasites in North American white-tailed deer (Odocoileus virginianus),” was published in Science Advances on February 5, 2016.