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Published: 21 hours ago
Comment, Op/Ed
At some point during the pandemic, Sars-CoV-2, the virus that causes COVID-19, spread from humans to white-tailed deer in North America.
In 2021, scientists revealed that 40 per cent of white-tailed deer sampled in Michigan, Pennsylvania, Illinois and New York state in the U.S. had antibodies for the virus.
Surveillance of these deer continues, and a new study by researchers at Ohio State University found that the virus is still spreading among the animals and back to humans, and it is evolving rapidly.
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The researchers looked at the prevalence of the virus in a small sample of white-tailed deer in northeastern Ohio. The samples were taken between November 2021 and March 2022.
From 1,522 nasal swabs, 163 tested positive for alpha and delta variants of COVID-19. The researchers also found the virus had bounced many times back and forth between humans and deer.
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Coronaviruses are covered in spikes, and it is these spikes that latch onto our cells to gain entry and begin replicating. The particular part of our cells that the spikes latch to is called the ACE2 receptor. This receptor is similar in deer and humans, and coronaviruses have lost little time in exploiting this.
Human contact with deer is common in parts of the U.S. and Canada, where many millions of white-tailed deer live as wild, urbanized or farmed animals. In these habitats, deer may be exposed to human waste. They can carry bacteria with similar antimicrobial resistance patterns to local humans.
The Ohio researchers found that COVID-19 multiplied and spread in deer over several months, causing no obvious illness or deaths in the animals. Migrating deer, males in particular, spread the virus as they moved across the landscape.
It is not known if other potential hosts (such as skunks, squirrels or rodents) contracted the virus too, but spread from deer back to humans was seen. How this exchange happened is unclear.
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Deer sampled on Staten Island, New York, over the same period showed evidence of spillover infection from humans by another COVID-19 variant, omicron.
By measuring changes in the COVID-19 genomes in the deer, through use of a new statistical method, the researchers in Ohio estimated that the rate of viral mutation was three times greater than in humans.
The types of genetic changes were not the same as those in human COVID-19. The mutations appeared to be adaptive responses that might have increased viral spread in its new deer hosts.
The pathogen showed early increases in its diversity in humans, too, which was perhaps more rapid in the first years after 2019.
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Crucially, the viral spillover from deer to humans has not caused new human outbreaks that are making doctors lose sleep. Evolutionary changes in COVID-19 in deer populations have not resulted in a virus that can evade our antibodies, so there is no current public health risk linked to this increased mutation rate.
As with humans, some deer are “super-spreaders.” Social network analysis shows this process in the animals’ use of scraping sites, where males leave their scents to set up breeding groups. Human-made feeding or bait stations (for hunting) exacerbate the rate of viral spread, too.
White-tailed deer could be referred to as a new reservoir of COVID viruses. Animal reservoirs encompass a continuous process of viral division and change.
Hosts impose selective pressures on viruses that influence the rate at which a virus’s genome changes. For example, influenza A evolves more rapidly in populations of birds or pigs than in people.
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Probably, the lifespan of an infected animal, metabolic processes within its cells, immune actions, damage to viral RNA from host enzymes or other pathogens all force viral mutation. Whatever the reasons, these observations from Ohio raise the possibility that COVID viruses might develop into a new strain or variant capable of spreading significant illness to humans within those millions of North American white-tailed deer.
Blood tests of U.K. deer in 2020-21, in contrast, found no evidence of COVID-19.
This could be because British deer species have distinctive ecological niches and COVID susceptibilities.
It is clear that ongoing surveillance provides valuable intelligence.
Colin Michie is deputy lead in the School of Medicine at the University of Central Lancashire in Preston, England. Iain Richards is a senior lecturer in animal life at UCL. This article first appeared in The Conversation.
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