Across the globe, several studies have been conducted on the transference of SARS-CoV-2 – the virus that causes COVID-19 – to animals, specifically companion dogs and cats. Some may think that these studies are excessive; others may be concerned. Why do scientists continue to test animals, particularly dogs and cats? The primary reasons are: dogs and cats are in close proximity to humans; to ensure they do not become potential reservoirs of the disease; viral recombination possibilities; and, decision practices for future pandemics.
With a few exceptions, the consensus around the globe is that cats, and less commonly dogs, can become infected with SARS-CoV-2, but they have not been transferring the virus back to humans. Yet, there is one documented case of a companion cat sneezing in the face of a Thai veterinarian who developed symptoms. And, one study determined that cats can spread the virus to one another in a laboratory setting. It is important to remember that a laboratory setting is not the same as the natural environment. A statistic in a study published in the Journal of the American Veterinary Medicine Association demonstrated that 94% of companion cats and dogs had exposure to a human diagnosed with COVID-19.
In summary, dogs and cats are not shown to be reservoirs of SARS-CoV-2 (COVID-19).
As a reminder, the canine coronavirus vaccine given to combat enteric canine coronavirus does not provide cross-protection for COVID-19 because enteric canine coronavirus is an alphacoronavirus. SARS-CoV-2 is a betacoronavirus. Furthermore, the American Animal Hospital Association, the World Small Animal Veterinary Association and Dr. Jean Dodds do not recommend giving the vaccine against enteric canine coronavirus.
If you or another household member is diagnosed with COVID-19, please follow the Centers for Disease Control and Prevention guidance on protecting your pet from becoming infected with the SARS-CoV-2 virus from you and other household members.
Regarding the majority of other naturally infected animals, humans have been shown to transmit the virus to them. To date, white-tailed deer and mink are of particular concern. Not only have they been able to transmit SARS-CoV-2 back to humans, they have also spread the virus amongst their respective species and the virus has become adapted in them.
We have known about mink infection practically since the start of the pandemic. This is largely due in part to mink farms. Now, many scientists want to test wild mink, which makes sense.
But, deer? How would deer become infected if they are not around humans? We do not know the specific route of infection, but it has been postulated that wastewater might be the cause. Remember, wastewater is one of the early detection methods of COVID-19 and other viruses because humans shed the virus through urine and feces. On top of that, deer are very social with each other which can add to intra-species spread.
Deer also share something else in common with humans. The ACE2 receptor part of a deer’s cell is very similar to that of humans. The spike protein of the SARS-CoV-2 virus latches onto the ACE2 receptor.
Additionally, deer seem to be circulating what we might consider “legacy” variants of the virus like Delta. This potentially enables an adaptation or resurgence of one of these variants because the deer could be reservoirs.
In fact, it has been surmised that the Omicron variant may have animal origins. Others say this is not possible. However, the premise of variant origins should always keep us on the alert we should not simply disregard animal sources.
Recombination of viruses is another reason why we need to continue surveillance in animals. Recombination is basically when two distinct parent strains of a virus merge into a new strain. For example, let’s say the Zeta variant is the primary circulating virus in humans. We’ll hypothesize that the Delta variant is still circulating in deer and that it can be passed back to humans. Then, the Zeta and Delta strains could recombine and become a new strain.
While many of us are mentally just “over” with the COVID-19 virus and are wondering when it will be labeled “endemic”, we still need to be vigilant to a certain degree. Currently in the U.S., the pandemic is officially scheduled to end on May 11, 2023. Finally, we need to protect vulnerable animal populations for the ecosystem and their lives, therefore the onus of SARS-CoV-2 transmission to animals is on us – the humans.
Additional References
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What Is One Health? US CDC and One Health Commission, https://www.onehealthcommission.org/en/why_one_health/what_is_one_health/.