Covid-19 has been found to spread repeatedly between humans and deer, raising concerns about the potential for animal reservoirs of the virus, according to a new study conducted by the US Department of Agriculture’s Animal and Plant Health Inspection Service. The study revealed that in late 2021 and early 2022, people transmitted the virus to wild white-tailed deer in the United States more than 100 times. The infection spread widely among the deer population, and researchers suspect that humans may have even contracted the virus from the deer on at least three occasions.
The study also discovered that various coronavirus lineages, including Alpha, Delta, and Omicron, continued to circulate within the deer population after leaving the human population. This raises concerns that if the virus persists in deer as it does in humans, it could serve as a long-term reservoir, allowing the virus to hide and potentially develop new and more dangerous mutations. Scientists fear that these mutated viruses could then leap back into the human population, causing another severe wave of infections, similar to the sudden emergence of the Omicron variant. However, experts consider this scenario largely theoretical at this point.
The discovery of a reservoir in wild animals would be significant if we had successfully controlled the virus in humans. However, since the infection is still spreading among humans, and humans are the preferred hosts for the virus, the risk associated with deer reservoirs may be limited for now. Scott Weese, a veterinarian specializing in diseases transmitted between animals and humans at the University of Guelph in Canada, explains that the greater the transmission among species, the higher the risk of new variants emerging. However, it remains uncertain whether deer pose a significant risk in the grand scheme of things.
To monitor the movement of the virus through animal populations, the US government plans to continue and expand its survey of animals. The study results were published in the journal Nature Communications. Weese, who was not involved in the study, expresses concern over deer acting as a potential mechanism for variant emergence and further exposure to wildlife species. However, he notes that there is little that can be done to prevent the spread of the virus among deer at this stage. Vaccinating wild animal populations can be costly, and there is currently no inoculation available to prevent transmission in animals, just as no vaccine can entirely eradicate Covid-19 transmission between humans.
So why are deer particularly susceptible to Covid-19? It turns out that deer and humans have similar ACE2 receptors, which the virus uses to enter cells. Scientists collected nearly 9,000 respiratory swabs from wild deer in 26 US states and the District of Columbia for the study. These swabs resulted in almost 400 viral sequences belonging to 34 lineages of the virus. By closely comparing these sequences, researchers identified viruses in deer that were highly similar to those found in humans. In 109 instances, the study managed to demonstrate that deer had been infected by human viruses.
Contact between deer and humans occurs frequently, especially as deer populations have expanded into urban areas. With an estimated 30 million deer in the US, they often scavenge for food in human trash or drink from contaminated wastewater. Humans can come into direct contact with deer while feeding or hunting them, or indirectly through contact with their droppings. Even house cats spending time outdoors could act as intermediaries, potentially catching the virus outside and bringing it home with them. Other species, such as mink on farms or animals in zoos, are also susceptible to the virus.
According to the US Centers for Disease Control and Prevention, the risk of catching Covid-19 from domestic or wild animals remains low. However, certain groups, like hunters, are advised to take special precautions to further minimize their risk. Although the presence of the virus in deer poses concerns, it is essential to prioritize controlling Covid-19 transmission among humans before addressing the potential risks associated with animal reservoirs.
In conclusion, the study’s findings highlight the repeated transmission of Covid-19 between humans and deer, raising concerns about the virus finding a long-term reservoir in animal populations. While the risk of mutated variants emerging from these reservoirs exists, it is currently difficult to determine the extent of the risk posed by deer in particular. The US government plans to continue monitoring the virus’s movement among animal populations to better understand and mitigate potential threats. As we strive to control the virus’s spread among humans, it is crucial to explore all avenues to prevent new variants from surfacing. However, in the meantime, the focus remains on protecting human health and containing the virus.
