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Pets: An Unexpected Reservoir for CoV-2?

Wednesday, researchers at the University of Wisconsin-Madison reported in the New England Journal of Medicine that domestic cats can spread the coronavirus between themselves. But, they did not show any illness, which is troubling. Without testing how do you know that Fluffy did not consort last night with an infected ne’er-do-well in the neighborhood, or even sniffed some infected bat poop in your back yard or on a walk?

Perhaps that news is not too surprising since we have known for a while the virus seems to easily pass between species. After all, we are pretty sure that the SARS coronavirus that infected humans came from a bat by way of a civet, and that MERS went from a bat to a camel to humans. Then there are the recent reports of 7 large cats in the Bronx zoo catching the virus from a human and showed symptoms of illness. Also, at least two pet cats and one pet dog were given the virus from their human owners.

Is this important? Well, it does suggest that animals that are in very close contact with humans might become a growing reservoir for the virus. Not too many of us have camels that sit on our laps while we binge on Netflix or have a tiger that shares our bed and cuddles with us. Many of us do have dogs and cats with which we enjoy close contact like that.

As the stay at home restrictions seem to have slowed the virus spread and we are beginning to open up, we will likely do so without sufficient “herd immunity” to quell a second or third wave of the pandemic. That means we will approach a semblance of normal activities while the virus remains with us. In turn, relaxed restrictions will likely spread more virus, including to pets and hence back to humans. It is one thing to have a coronavirus reservoir in bats that few of us directly encounter; it is another thing to have a reservoir of the virus in our animal companions.

Another concern is that as viruses pass between animal species, they often acquire new behaviors. We have found about 500 different coronaviruses in bats alone. Other animals often carry other coronaviruses typical to their species. When a coronavirus from one species enters a cell from another species that has its own endogenous coronavirus, the viruses can shuffle their genes creating new strains with new capabilities. And when we are talking about viruses infecting an animal, we are talking about billions of virions being produced that are capable of shuffling genomes with endogenous viruses. All it takes is one particularly nasty and overly competitive virion to emerge and find a new host that has not seen it before.

So, there potentially is a “perfect storm” arising consisting of having poor human herd immunity, a ready reservoir of virus, and a lot of friendly furry factories making viral variants that could prove even more virulent. Yes, this scenario is speculative, but we have seen it happen before and all the pieces seem to be in place. Time will tell.

In a separate statement, the authors of the research paper mentioned above recommended keeping pets away from other animals and even isolating them if someone in the home becomes positive for the virus.

This blogger fully expects a second wave of the pandemic.


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