The malaria parasite is carried by 1 in 4 of all the white-tailed deer found in the eastern United States, researchers have just revealed.
The findings were presented on Friday, February 5 in the journal Science Advances, and were based on research led by two experts at the Center for Conservation and Evolutionary Genetics (a structure within the Smithsonian Conservation Biology Institute).
Center head Robert Fleischer and postdoctoral fellow Ellen Martinsen had been examining mosquitoes that had been caught close to the Bird House pertaining to the Smithsonian’s National Zoo.
The purpose had been to identify instances of avian malaria through polymerase chain reaction (PCR) techniques, but instead researchers discovered abnormal DNA, that couldn’t have pertained to birds.
When comparing the samples with those from collected from other vertebrates, it was soon determined that the genetic sequences had actually come from white-tailed deer.
That came as a complete surprise, given the fact that never before had a malaria parasite been proven to be endemic among mammals inhabiting North America or South America.
In addition, it was also exceptional to find the pathogen in a white-tailed deer population, since no such cases had been reported in the past, although the species had always been carefully monitored due to the crucial role it plays for the hunting business.
Approximately 200 serotypes of the malaria parasite called Plasmodium have been identified throughout the world so far. In all these cases a flying insect such as the Anopheles mosquito first becomes infected with the disease, and then transmits it to vertebrates, such as reptiles, birds, primates and even human beings.
As study authors explain, in this recent research two strains of the malaria pathogen called Plasmodium odocoilei have been found, that require Anopheles punctipennis mosquitoes as a vector for transmission, and white-tailed deer as the secondary host.
According to David Samuel, professor of wildlife biology and ecology at West Virginia University, it’s unlikely that the malaria parasite causes any significant health problems to white-tailed deer, given that it’s usually found in overly low concentrations, which aren’t considered hazardous in any way.
In fact, the pathogen is virtually undetectable in the blood when using an optical microscope, which is why study authors had to employ much more advanced techniques in order to prove its presence conclusively.
Eventually, the malaria parasite was identified in blood samples from deer studied by the Smithsonian Conservation Biology Institute, and in tissue samples made available through the Southeastern Cooperative Wildlife Disease Study (SCWDS).
From 300 white-tailed deer included in the research, a total of 41 animals were proven to be hosts for the pathogen. Surprisingly, just deer from the eastern part of the United States were tested positive for the malaria parasite.
Also, other related hooved species such as mule deer, elk, oryx, goats, pronghorn, alpaca, gazelles, donkeys, cows and blacktail deer were proven not to be susceptible to this disease.
The infected hosts never exhibited any symptoms commonly associated with malaria, which suggests once again that in their case the parasite is actually benign, without resulting in any debilitating health effects.
Given the incredibly low doses at which the malaria parasite was found in white-tailed deer, study authors emphasize that this discovery shouldn’t raise any concerns among people who may encounter deer near their homes, since this particular strain isn’t believed to be transmissible to humans as well.
Researchers have also been speculating regarding the ways in which the malaria strains reached the United States in the first place. As they explain, it appears the two serotypes became distinct around 1 and a half million years ago, and are similar to a kind of malaria that normally affects Asian bats.
Consequently, the most convincing theory is that the disease probably arrived here when bygone predecessors of the white-tailed deer crossed the Bering land bridge that used to connect Asia and North America more than 2.3 million years ago.
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