COVID-19 has been devastating for people across the world, with more than 5 million confirmed deaths globally. However, humans are not the only species that the SARS-CoV-2 virus can infect. In this Special Feature, we discuss recent research into animal populations that might harbor the virus.
Recently, scientists have documented that SARS-CoV-2 has spread to white-tailed deer in the United States.
Researchers believe that SARS-CoV-2 is a type of zoonosis — a disease that transfers from nonhuman animals to humans, often via an intermediary nonhuman animal with which humans have contact.
To date, scientists are not sure which species acted as the originator or the intermediary. However, all known human coronaviruses have their origins in nonhuman animals.
Experts believe that
the meat markets of Wuhan, China, provided an opportunity for the SARS-CoV-2 virus to transfer from nonhuman animals to humans, as was the case with the original SARS-CoV virus in meat markets in China in 2002 and 2003.
As well as emerging from nonhuman animals, there is also evidence that SARS-CoV-2 has returned to other animal species.
The Centers for Disease Control and Prevention (CDC)Trusted Source note that the virus has infected pets, animals in zoos and sanctuaries, and mink on farms.
White-tailed deer infection
Multiple recently-released reports have documented that SARS-CoV-2 has now also spread to white-tailed deer in the United States.
In a brief report in the Proceedings of the National Academy of Sciences of the United States of America, researchers tested the blood of 624 deer from four U.S. states before and during the pandemic. They found that 40% of the samples taken since the pandemic began contained SARS-CoV-2 antibodies.
In another preprint study, researchers used RT-PCR tests on lymph node samples that they had taken from 283 captive and wild deer. One-third of the samples were positive for SARS-CoV-2.
The presence of SARS-CoV-2 in animal populations is a concern for scientists, as it raises the possibility that a new variant of the disease, which could potentially be more dangerous, could cross back into human populations.
Speaking with Medical News Today, Dr. Graeme Shannon — a lecturer in zoology at the School of Natural Sciences in Bangor University, Wales — said:
“Animal reservoirs have the potential to generate mutations that the human immune system has not come into contact with before. We see this regularly with influenzas that hop readily from birds and a number of mammals back into humans.”
This could complicate our attempts to suppress the disease. Indeed, we have already seen that infected captive mink were able to reinfect farmworkers,” said Dr. Shannon.
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Origin of the infection?
Scientists are not yet sure how the deer became infected with SARS-CoV-2.
Prof. Vivek Kapur told MNT that there could be multiple ways in which the deer became infected but that direct hunting interactions were unlikely.
“While there are likely many sources with which the spillovers to deer from people may occur, including through contact with contaminated food — for example, a contaminated half-eaten apple thrown in the woods or contaminated bait or food left for deer in urban settings — [or a] contaminated environment — a discarded tissue, spit, or other bodily fluids from hunters or hikers in the forest — or even a yet undiscovered intermediary host such as deer mouse.”
Prof. Kapur is a professor of microbiology and infectious diseases and associate director of the Huck Institutes of the Life Sciences at Pennsylvania State University. He also co-authored one of the preprint studies mentioned earlier.
“We have no evidence that hunting interactions are the primary mode of transmission,” he explained. However, he also added that “hunting may contribute through the larger number of people on public lands where there are deer, and [it] also causes dispersal and mixing of deer that may enhance opportunities for transmission.”
Prof. Kapur also said that it is likely that the virus can infect other deer species.
According to Dr. Shannon, the new reports are striking because they show that SARS-CoV-2 can circulate in wild animal populations.
There are also reports of the virus in zoo animals
“I think what is really interesting about the latest studies from the U.S. is that there is now solid evidence that SARS-CoV-2 can be transmitted to and among free-ranging mammals.”
– Dr. Shannon
“This is likely further exacerbated by the prevalence of the disease in the human population, which presents multiple opportunities for SARS-CoV-2 to infect other animal species,” he added.
Other potential reservoirs?
Speaking with MNT, Dr. Eman Anis — assistant professor of pathobiology at the School of Veterinary Medicine at the University of Pennsylvania in Philadelphia — said there may be other animal species within which the virus could be circulating.
– Dr. Anis
Crucially, scientists are not yet sure whether SARS-CoV-2 circulating in deer populations can then return to humans.
Further research needed
Dr. Roderick Gagne is an assistant professor of wildlife disease ecology at the School of Veterinary Medicine at the University of Pennsylvania. He told MNT that more research was necessary to build a better understanding of the risks that come with SARS-CoV-2 circulating in white-tailed deer.
Speaking with MNT, Gail Keirn — public affairs specialist for the National Wildlife Research Center, U.S.