About one-third of white-tail deer tested in northeastern Ohio earlier this year were carrying the coronavirus responsible for COVID-19, according to a newly published study.
Out of 360 animals killed and collected by researchers from January to March, 129 were positive for SARS-CoV-2 in PCR testing, reported Andrew Bowman, MS, DVM, PhD, of Ohio State University’s College of Veterinary Medicine in Columbus, and colleagues.
Viral gene sequencing indicated that the isolates obtained from these animals were closely related to SARS-CoV-2 variants circulating among humans at the time, the group noted in their paper appearing Thursday in Nature.
The report follows an earlier, similar study conducted in Iowa, posted on the bioRxiv preprint server last month. In that paper, researchers from Penn State University found that 33% of deer collected during April-December 2020 were positive for the virus — and the proportion rose to an astonishing 83% in deer harvested from Nov. 23, 2020, to Jan. 10, 2021.
While it’s unclear how the virus jumped from humans to deer, that hunters and other people will eventually catch it back from them seems inevitable.
In their paper, Bowman and colleagues acknowledged that the human-to-deer transmission route remains speculative. They suggested that deer could contract it from browsing through people’s trash or by drinking contaminated water (infected people shed live virus in feces).
Whereas nearly all human cases come from prolonged close contact with infected people, that’s not necessarily the case with deer, which seem highly susceptible to SARS-CoV-2 infection, Bowman told MedPage Today.
“The way in which humans and deer browse and consume are completely different, so there may be pathways of viral introduction to deer that are less important for humans,” he said in an email. “We have to consider all possibilities and not assume human-to-deer transmission is the same as human-to-human transmission.”
Vivek Kapur, BVSc, PhD, senior author on the Penn State preprint, agreed. He pointed out that people constantly leave half-eaten food out where deer can eat them. Also, there could be “bridging hosts” such as rodents or feral cats that carry the virus from humans to deer (and potentially back again), he told MedPage Today.
“Bottom line — we do not know [the exact transmission route]; but there are lots of ways for deer to pick up the virus without being in the same (room/spot) at the same time as an infectious human,” Kapur said.
However, virologist Benjamin tenOever, PhD, of New York University, didn’t find any of those scenarios entirely persuasive.
Browsing garbage is probably “the most likely,” he told MedPage Today, but mainly because he ruled out other routes such as an insect vector or respiratory droplets.
“In our work, we find that if you take the bedding from an infected hamster cage and add it to a cage of naive animals, they always get infected. This is also true for water bottles,” tenOever, who was not involved with the research, said in an email.
Yet while deer could rummage “a trash can full of dirty Kleenexes or maybe a contaminated straw or plate… the virus does not survive long on these surfaces (no more than a few hours under ideal conditions),” he noted. “While unlikely, this does seem possible.”
As for the reverse — transmission from deer to humans — it’s easier to imagine how that can happen, although no actual cases have been reported.
For deer killed by hunters, the butchering (which may not be done neatly or with great sanitation) is an obvious way to expose humans to infected tissue. Deer killed on roadways may be hauled away manually, again with exposure to raw tissue. And if there are bridging hosts, that could well be a two-way street.
Moreover, not only could widespread infection in deer herds mean that these animals are a reservoir for SARS-CoV-2 in North America, but they could also become incubators for new variants.
“A number of mutations were observed in white-tailed deer that are very low frequency in humans, including a mutation in the receptor binding motif,” Bowman’s group wrote in Nature. “Such mutations could potentially be amplified in a new reservoir host with high infection rates and different constraints on evolution.”
Importantly, the group found that deer in urban settings were more likely than those caught in rural areas to be infected. They cited an “urgent need to expand monitoring” of deer and other wildlife that may be hosting SARS-CoV-2.
Study authors declared they had no relevant financial interests.