Covid variants can evolve 3 times faster in deer than in humans: Study

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Covid-19 viral variants can evolve about three times faster in deer than in humans, according to a study that documented at least 30 Covid infections in white-tailed deer in the US that were introduced by humans.

The study, published in the Nature Communications, showed that white-tailed deer across Ohio, US, have increasingly been infected with SARS-CoV-2, the virus that causes Covid-19.

Scientists collected 1,522 nasal swabs from free-ranging deer in 83 of the state's 88 counties between November 2021 and March 2022.

More than 10 per cent of the samples were positive for the SARS-CoV-2 virus, and at least one positive case was found in 59 per cent of the counties in which testing took place.

"We generally talk about interspecies transmission as a rare event, but this wasn't a huge sampling, and we're able to document 30 spillovers. It seems to be moving between people and animals quite easily," said Andrew Bowman, associate professor of veterinary preventive medicine at The Ohio State University.

"And the evidence is growing that humans can get it from deer -- which isn't radically surprising. It's probably not a one-way pipeline," he added. However, no substantial outbreaks of deer-origin strains have occurred in humans.

How the virus is transmitted from humans to white-tailed deer remains a mystery. Yet the combined findings suggest that the white-tailed deer species is a reservoir for SARS-CoV-2 that enables continuing mutation, and that the virus' circulation in deer could lead to its spread to other wildlife and livestock.

Beyond the detection of active infections, researchers also found through blood samples containing antibodies -- indicating previous exposure to the virus -- that an estimated 23.5 per cent of deer in Ohio had been infected at one time or another.

The 80 whole-genome sequences obtained from the collected samples represented groups of viral variants: the highly contagious delta variant and alpha.

The analysis revealed that the genetic composition of delta variants in deer matched dominant lineages found in humans at the time, pointing to the spillover events, and that deer-to-deer transmission followed in clusters, some spanning multiple counties.

The study also suggested that Covid-19 vaccination is likely to help protect people against severe disease in the event of a spillover back to humans. An analysis of the effects of deer variants on Siberian hamsters, an animal model for SARS-CoV-2 studies, showed that vaccinated hamsters did not get as sick from infection as unvaccinated animals.

Thus, the variants circulating in deer are expected to continue to change. An investigation of the mutations found in the samples provided evidence of more rapid evolution of both alpha and delta variants in deer compared to humans.

"Not only are deer getting infected with and maintaining SARS-CoV-2, but the rate of change is accelerated in deer --potentially away from what has infected humans," Bowman said.

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