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COVID-19 ISO Insights

The Link Between Covid-19 and White-Tailed Deer

December 13, 2021

Travis Decaminada

Key Takeaway: White-tailed deer are purportedly a major reservoir of the SARS-CoV virus, with some studies reporting that upwards of 40% of deer have tested positive for antibodies. Health experts warn that deer populations can serve as a source of new variants of Covid-19, among other issues that make combating the virus more challenging.

The transmission of Covid-19 between animals and humans has been a major point of research since the virus first appeared. The Verisk Emerging Issues team reported last year about some of the factors that influence the spread of zoonotic diseases which include:

  • Increasing demand for animal protein.
  • Unsustainable agricultural intensification.
  • Increased use and exploitation of wildlife.
  • Unsustainable utilization of natural resources accelerated by urbanization, land use changes, and extraction industries.
  • Travel and transportation.
  • Changes in food supply chains.
  • Climate change.

 Covid-19 and White-Tailed Deer

According to new research, white-tailed deer are a major reservoir of Covid-19 infections, reports The Conversation. (Full study here). Per the article, Covid-19 antibodies were found within the blood of 40% of tested deer from four different states – Michigan, Illinois, Pennsylvania, and New York. Other research reportedly found that around 80% of deer in Iowa also tested positive for Covid-19 antibodies. Per the article, these numbers likely indicate that deer are actively spreading Covid-19 to each other, and further, the presence of certain SARS-CoV variant strains within deer populations also suggests that there have been many human-to-deer infections as well. From the article:

Human-to-deer and deer-to-deer transmission are believed to be driving the rapid spread of the disease within white-tailed deer populations across the US. This is particularly apparent during the early months of 2021 when COVID infections were spiking in the human population. Previous studies have shown that SARS-CoV-2 [sic] the virus that causes COVID-19 in humans [sic] can be passed from humans to domestic and captive animals including cats, dogs, zoo animals and, most notably, farmed mink. But, until now, the disease had not been shown to spread in wildlife species.

The fact that deer and humans tend to interreact more frequently than other animals, and the fact that the U.S. has a massive deer population (30+ million), only exacerbates the problem. Allegedly, hunters in particular may be one of the leading sources of cross-species transmission, though hikers, campers, field researchers and other groups of people also appear to be at least partly responsible.

Ultimately, some health experts are concerned that “Not only could this readily infect large numbers of animals, but also, more worryingly, it could spill back to humans.”

Potential for New Variants

A related piece from NPR further discusses the issue. Per the article, because deer populations are such a large reservoir of SARS-CoV, a situation could theoretically arise wherein deer and humans keep passing the virus back and forth, effectively making it impossible to eradicate. A veterinarian from Penn State explains as such:

"If the virus has opportunities to find an alternate host besides humans, which we would call a reservoir, that will create a safe haven where the virus can continue to circulate even if the entire human population becomes immune," … "And so it becomes more and more complicated to manage or even eradicate the virus."

Moreover, the potential for the virus to mutate within deer to become more dangerous or infectious towards humans remains a serious concern. This is often the case with influenza, in particular the swine flu epidemic of 2009. At the very least, the relationship between Covid-19 and deer makes tracking the emergence of new variants more complicated.

See Also:

More information about zoonotic diseases from the Centers for Disease Control and Prevention (CDC).

More information about zoonotic diseases from the World Health Organization (WHO).

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