SARS-CoV-2 is thought to be a zoonosis, or a disease that spreads from nonhuman animals to people via an intermediary nonhuman animal with whom humans come into contact.
Scientists are unsure which animal acted as the originator or intermediate at this time. All known human coronaviruses, on the other hand, have nonhuman animal origins.
Experts believe that the meat markets of Wuhan, China, provided a chance for the SARS-CoV-2 virus to spread from nonhuman animals to humans, similar to how the initial SARS-CoV virus spread from nonhuman animals to humans in 2002 and 2003.
There is evidence that SARS-CoV-2 has returned to additional animal species, in addition to nonhuman animals.
The virus has sickened pets, animals in zoos and sanctuaries, and farm mink, according to the Centers for Disease Control and Prevention (CDC).
White-tailed deer infection
SARS-CoV-2 has now spread to white-tailed deer in the United States, according to many newly disclosed reports.
Researchers analyzed the blood of 624 deer from four states in the United States before and during the pandemic, according to a brief article published in the Proceedings of the National Academy of Sciences of the United States of America. They discovered SARS-CoV-2 antibodies in 40% of the samples taken since the pandemic began.
Researchers used a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay to discover SARS-CoV-2 in 129 out of 360 deer in northeast Ohio, according to a preprint article that has yet to be peer reviewed.
Researchers utilized RT-PCR assays on lymph node samples gathered from 283 captive and wild deer in another preprint investigation. SARS-CoV-2 was found in one-third of the samples.
A concern
Scientists are concerned about the presence of SARS-CoV-2 in animal communities because it raises the risk of a new strain of the disease, which might be more severe, spreading back into human populations.
Dr. Graeme Shannon, a lecturer in zoology at Bangor University’s School of Natural Sciences in Wales, told Medical News Today:
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.”
“However, equally, the disease may infect wildlife and mutate but become less of a threat to humans as it adapts to the biology of the current host.”
“Certainly, the presence of multiple animal reservoirs on top of the high prevalence of the disease in humans would be cause for concern. 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.
Origin of the infection?
Scientists are still unsure how the deer contracted SARS-CoV-2.
Prof. Vivek Kapur told MNT that the deer could have become infected in a variety of ways, but that direct hunting interactions were unlikely.
“While there are likely many sources through which human-to-deer spillovers may occur, including 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 — discarded tissue, spit, or other bodily fluids from hunters or hikers in the forest — or even a yet undiscovered intermediary host such as the deer mouse
Prof. Kapur is an associate director of the Huck Institutes of the Life Sciences at Pennsylvania State University and a professor of microbiology and infectious diseases. He was also a co-author on one of the previously mentioned preprint research.
“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 further stated that the virus is likely to infect other deer species.
“There is considerable evidence from natural or experimental infection with SARS-CoV-2 of many different animal species, and based on the structure of the ACE-2 receptor targeted by the viral spike protein, other cervid species are highly likely to be able to get infected.”
The new reports are noteworthy, according to Dr. Shannon, since they reveal that SARS-CoV-2 can circulate in wild animal populations.
“We are currently aware that SARS-CoV-2 can be transmitted to domestic animals such as cats and dogs, as well as captive species, particularly farmed mink. 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.”
“Another point worth considering is that although these species are all mammals, they are quite phylogenetically distinct and come from a range of taxonomic families, demonstrating that the disease is not specific to one host — or even similarly related hosts.”
– 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?
Dr. Eman Anis, an assistant professor of pathobiology at the University of Pennsylvania’s School of Veterinary Medicine in Philadelphia, told MNT that the virus could be circulating among other animal species.
“Because we don’t know the exact reservoir, or reservoirs, of SARS-CoV-2, there’s a chance there are animal reservoirs that we don’t know about.”
“Several animal species, such as civets and pangolins, have been considered potential viral reservoirs,” she noted. “Until researchers discovered the virus in deer populations across numerous states, white-tailed deer were not considered a potential reservoir of the virus.”
“What we do know, however, is that any animal species that has the capacity to maintain the virus permanently and potentially spread it to humans or other domestic or wild animals could be a potential reservoir of SARS-CoV-2.”
“We will not be able to determine exact reservoirs and the true host range of SARS-CoV-2 until we conduct extensive surveillance on both domestic and wild animals to determine which species can permanently maintain the virus and spread the infection to other animals and humans.”
– Dr. Anis
Importantly, scientists aren’t clear if SARS-CoV-2, which is circulating in deer populations, may subsequently spread to humans.
“We highly propose expanding surveillance for the virus in additional peri-domestic and free-living species to better understand the dangers associated with infection overflow to other potential reservoir species and prospects for spill back to humans,” Professor Kapur told MNT.
More investigation is required
Dr. Roderick Gagne is an assistant professor of wildlife disease ecology at the University of Pennsylvania School of Veterinary Medicine. More research is needed, he told MNT, to have a better knowledge of the hazards associated with SARS-CoV-2 circulating in white-tailed deer.
“No research has been done on the risk of the virus spreading to people because it was only recently detected in deer.” We need to learn more about how widespread the virus is in deer, what variations are circulating, and whether deer can keep the virus continuously and shed it in high titer/load.”
“More research is needed to investigate the genetic links between SARS-CoV-2 strains acquired from deer and humans at the same time.”
“Epidemiological studies would also need to assess the possibility for deer to infect humans — for example, by monitoring those who care for confined deer,” Dr. Gagne stated.
Gail Keirn, a public affairs specialist for the National Wildlife Research Center of the United States Department of Agriculture’s Animal and Plant Health Inspection Service, told MNT that more research was needed to fully comprehend the importance of these early observations.
“Research and surveillance are needed to determine 1) when and where white-tailed deer are being exposed to the virus, 2) if the virus is circulating in deer populations, 3) if new variants of the virus are emerging in deer, and 4) what is the risk, if any, to deer, other animals, and people,” said Keirn.
