Researchers believe SARS-CoV-2 is a type of zoonosis – a disease that spreads from non-human animals to humans, often via an intermediate non-human animal that humans come in contact with.
To date, scientists are not sure which species played the role of initiator or intermediary. However, all known human coronaviruses originate from non-human animals.
Experts believe that the meat markets in Wuhan, China, allowed the SARS-CoV-2 virus to pass from non-human animals to humans, as was the case with the original SARS-CoV virus on Chinese meat markets in 2002 and 2003.
In addition to emerging from non-human animals, there is also evidence that SARS-CoV-2 has returned to other animal species.
The reliable source from the Centers for Disease Control and Prevention (CDC) notes that the virus has infected pets, animals in zoos and sanctuaries, and minks on farms.
White-tailed deer infection
Several recently published reports have documented that SARS-CoV-2 has now also spread to white-tailed deer in the United States.
In a brief report published in the Proceedings of the National Academy of Sciences of the United States of America, researchers tested the blood of 624 deer from four US states before and during the pandemic. They found that 40% of samples taken since the start of the pandemic contained SARS-CoV-2 antibodies.
The presence of SARS-CoV-2 in animal populations is of concern to scientists, as it raises the possibility that a new variant of the disease, which could be potentially more dangerous, could return to human populations.
Speaking to Medical News Today, Dr Graeme Shannon, professor of zoology at the School of Natural Sciences at Bangor University, Wales, said:
“Animal reservoirs have the potential to generate mutations that the human immune system has never come into contact with before. We see this regularly with influenza which easily passes from birds and a number of mammals to humans. ”
“However, in the same way, the disease can infect wildlife and mutate, but become less threatening to humans as it adapts to the biology of the current host.”
“Certainly, the presence of multiple animal reservoirs in addition to the high prevalence of the disease in humans would be of concern. This could complicate our attempts to suppress the disease. Indeed, we have already seen that infected captive mink were able to re-infect farm workers, ”said Dr Shannon.
Origin of infection?
Scientists do not yet know how the deer became infected with SARS-CoV-2.
Professor Vivek Kapur told MNT that there could be more than one way to infect deer, but direct interactions with hunting were unlikely.
“While there are probably many sources with which human fallout on deer can occur, including through contact with contaminated food – for example, a half-eaten contaminated apple thrown in the woods or bait or fish. contaminated food left for deer in an urban setting – [or a] contaminated environment – discarded tissue, saliva or other bodily fluids from hunters or hikers in the forest – or even an as yet undiscovered intermediate host such as the deer mouse.
Professor Kapur is Professor of Microbiology and Infectious Diseases and Associate Director of the Huck Institutes of the Life Sciences at Pennsylvania State University. He is also a co-author of one of the pre-publication studies mentioned above.
“We have no evidence that hunting interactions are the primary mode of transmission,” he explained. However, he also added that “hunting can contribute through the greater number of people on public lands where deer are found, and [it] also causes the dispersal and mixing of deer which can improve the opportunities for transmission. . ”
Professor Kapur also said it is likely that the virus could infect other species of deer.
“There is considerable evidence for natural or experimental infection with SARS-CoV-2 from many different animal species, and based on the structure of the ACE-2 receptor targeted by the viral spike protein, other species deer are very susceptible to infection. ”
According to Dr Shannon, the new reports are striking because they show that SARS-CoV-2 can circulate in populations of wild animals.
“We currently know that SARS-CoV-2 can be transmitted to domestic animals such as cats and dogs, as well as to captive species, especially farmed mink. There are also reports of the virus in zoo animals. ”
Other potential reservoirs?
Speaking to 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 circulate.
“We don’t know the exact reservoir (s) for SARS-CoV-2, so yes, it is possible that there are animal reservoirs that we may not be aware of. ”
“To date, several animal species have been considered as potential reservoirs of the virus, such as civets and pangolins,” she explained. “White-tailed deer were not considered a potential reservoir for the virus until researchers detected the virus in deer populations in several states.”
“What we do know, however, is that any animal species that has the ability to maintain the virus permanently and potentially spread it to humans or other domestic or wild animals could be a potential reservoir for SARS-CoV-2.”
“We will not be able to determine the exact reservoirs and true host range of SARS-CoV-2 until we conduct extensive surveillance on domestic and wild animals to determine which species can maintain the virus.” permanently and spread the infection to other animals and humans. . ”
– Dr Anis
Importantly, scientists are not yet sure whether SARS-CoV-2 circulating in deer populations can then return to humans.
Professor Kapur told MNT that “we strongly recommend expanding surveillance for the virus in other peridomestic and free-living species to better understand the risks associated with the spread of infections to other potential reservoir species and the opportunities for repression towards man ”.
More research is needed
Dr. Roderick Gagné is Assistant Professor of Wildlife Disease Ecology in the School of Veterinary Medicine at the University of Pennsylvania. He told the MNT that more research was needed to better understand the risks from circulating SARS-CoV-2 in white-tailed deer.
“Because the virus was only recently discovered in deer, no research has been conducted on the risk of spread to humans. We first need to better understand how common the virus is in deer, what variants are circulating in deer, and whether deer can hold the virus indefinitely and excrete it at a high titer / load. ”
“More research is needed to compare the genetic relationships between SARS-CoV-2 recovered from deer and those recovered from humans at the same time.”
“In addition, epidemiological studies should assess the potential of deer to infect humans – for example, by monitoring those who care for deer in captivity,” said Dr Gagné.
Speaking to MNT, Gail Keirn – public affairs specialist for the National Wildlife Research Center, US Department of Agriculture Animal and Plant Health Inspection Service – also suggested that further research was essential to understand the importance of these initial reports.
“Research and surveillance is needed to determine 1) when and where white-tailed deer are exposed to the virus, 2) whether the virus is circulating in deer populations, 3) whether new variants of the virus are emerging in deer, and 4) What is the risk, if any, to deer, other animals and people, ”Keirn said.