Credit: Unsplash/CC0 Public Domain
Credit: Unsplash/CC0 Public Domain
New research finds that white-tailed deer across Ohio have been infected with the virus that causes COVID-19, and the results also show that viral variants evolve in deer nearly three times faster than in humans.
Scientists collected 1,522 nasal swabs from free-grazing deer in 83 of the state’s 88 counties between November 2021 and March 2022. More than 10% of the samples were positive for SARS-CoV-2, and at least one positive case was found. In 59% of the counties where the test was administered.
Genomic analysis showed that at least 30 infections in deer had been introduced by humans, a number that surprised the research team.
Associate Professor Andrew Bowman said: “We generally talk about transmission between species as a rare event, but this was not a huge sample, and we are able to document 30 knock-on effects. It seems to be transmitted between people and animals quite easily.” Doctor of Veterinary Preventive Medicine at The Ohio State University and senior co-author of the study.
“And the evidence is growing that humans can get it from deer – which is not radically surprising. It’s probably not a one-way pipeline.”
The combined results indicate that the white-tailed deer species is a reservoir for SARS-CoV-2 that enables persistence of the mutation, and that the spread of the virus in deer can lead to its spread to other wildlife and livestock. The study is published in Nature Communications.
Bowman and colleagues Previously mentioned SARS-CoV-2 infection detected in white-tailed deer at nine Ohio sites in December 2021, and we continue to monitor deer for infection with newer variants.
“We’ve been expanding all over Ohio to see if this is a local problem, and we’ve found it in a lot of places, so it’s not just a local event,” Bowman said. “Some of the ideas at the time were that maybe it’s only in urban deer because they’re in close contact with people. But in rural areas of the state, we find a lot more positive deer.”
In addition to detecting active infection, the researchers also found through blood samples that contained antibodies — indicating previous exposure to the virus — that an estimated 23.5 percent of deer in Ohio had been infected at one time or another.
The 80 whole-genome sequences obtained from the pooled samples represent combinations of viral variants: the highly pathogenic delta variant, the human strain prevalent in the US in early fall 2021 which accounts for approximately 90% of the sequences, and the alpha. , the first named variant of anxiety to circulate in humans in the spring of 2021.
The analysis revealed that the genetic makeup of the delta variants in deer matched the dominant strains present in humans at the time, indicating indirect events, and that deer-to-deer transmission followed in clusters, some spanning multiple counties.
“There’s probably a timing element to what we found,” Bowman said. “We were near the end of the peak delta in humans, and then we saw a lot of delta in deer.” “But we’re past the last detection of alpha in humans. So the idea of deer holding onto lineages that have since become extinct in humans is something that worries us.”
The study indicates that vaccination against the Corona virus is likely to help protect people from severe disease in the event that the disease spreads to humans. Analysis of the effects of deer variants on Siberian hamsters, a model animal for SARS-CoV-2 studies, showed that vaccinated hamsters did not get sick from the infection as well as unvaccinated animals.
However, the variants prevalent in deer are expected to continue to change. Investigation of the mutations found in the samples provided evidence for the rapid evolution of both alpha and delta variants in deer compared to humans.
“Not only do deer become infected and maintain SARS-CoV-2, but the rate of change in deer is accelerating — perhaps far from what has infected humans,” Bowman said.
How the virus was transmitted from humans to white-tailed deer remains a mystery. To date, even with about 30 million free-range deer in the United States, there has been no major outbreak of indigenous deer subspecies among humans.
However, spread between animals is still very likely. About 70 percent of deer grazing freely in Ohio have not been infected or exposed to the virus, Bowman noted, “so there’s a large group of gullible animals through which the virus can spread fairly unimpeded.”
“Having this host animal in play creates things we need to be wary of,” he said. “If this pathway continues for years and we have a virus that adapts to deer, does this become the pathway to other host animals, wildlife or domestic life? We just don’t know.”
Martha Nelson of the National Library of Medicine was a co-author of the study. Ohio State co-authors Dillon McBride, Stephen Overend, Devra Huey, Amanda Williams, Seth Faith, and Jacqueline Nolting worked on the study with co-authors from St. Jude Children’s Research Hospital; University of California, Los Angeles; the National Research Center in Giza, Egypt; PathAI Diagnostics; Ohio Department of Natural Resources; US Department of Agriculture; Columbus and Franklin County Metroparks; and the Riga Medical Research Institute in Belgium.
Accelerated evolution of SARS-CoV-2 in free-roaming white-tailed deer, Nature Communications (2023). doi: 10.1038/s41467-023-40706-j