A recent study revealed that humans transmitted the virus responsible for COVID-19 to wild white-tailed deer in the United States.

In late 2021 and early 2022, over 100 instances of the virus that causes COVID-19 were transmitted from humans to wild white-tailed deer in the United States, according to a recent study by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. The research findings indicated that the infection spread widely within the deer population, and there were even suspicions that humans might have contracted the virus from deer in at least three cases.

The study also highlighted that various COVID-19 lineages, including Alpha, Delta and Omicron, continued to circulate within deer after these strains had left the human population. The discovery raised concerns among scientists about the potential for deer to become a long-term reservoir for the virus, allowing it to persist and potentially develop new, more dangerous mutations.

While the prospect of a viral reservoir in wild animals would be worrisome if the virus were under control in humans, it is important to note that the infection is still spreading among human populations. Humans remain the preferred hosts for the virus, and it is more likely to mutate within us. Nevertheless, the risk of new variants increases with the virus’s presence in multiple species and through ongoing transmission.

Scott Weese, a veterinarian and expert in zoonotic diseases at the University of Guelph in Canada, commented on the findings via CNN, saying, “The more species it’s in and the more transmission that occurs, the greater the risk of new variants. However, it’s hard to say whether deer constitute much of a risk in the grand scheme at this point.”

In response to these findings, the U.S. government has planned to expand its surveillance of animal populations to monitor the movement of the virus within them. While there is a desire to avoid additional mechanisms for variant emergence and exposure to wildlife species, the challenge lies in the limited options available to halt the spread among deer. Vaccinating wild animal populations is an expensive undertaking, similar to the challenges faced in vaccinating humans against COVID-19 transmission.

Deer are of particular interest in this study due to their strikingly similar ACE2 receptors to humans, which the virus uses to enter cells. Scientists collected thousands of respiratory swabs from wild deer across 26 U.S. states and the District of Columbia. Analysis of nearly 400 viral sequences from 34 lineages revealed close similarities between viruses found in deer and those found in humans.

Contact between deer and humans is not uncommon, with deer populations now thriving in urban environments. Deer may scavenge for food in human trash or consume contaminated wastewater, increasing the risk of exposure. Humans may encounter deer directly while feeding or hunting them, or indirectly through contact with droppings. Additionally, outdoor cats can act as potential intermediaries, contracting the virus outside and bringing it home.

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