Covid - reverse zoonosis (and back again)19 Nov 2021 19:49
From New Scientist 20/11/21:
Recent studies suggest that SARS-CoV-2 is rife among the 30 million white-tailed deer in North America. This means there is a risk of deer infecting other species, and also of new variants emerging in other animals and jumping back to people.
It has long been clear that people with SARS-CoV-2 are occasionally infecting pets, farm and zoo animals. Such outbreaks have also led to cases in humans – in November 2020, Denmark culled millions of mink after the virus began spreading in farmed mink and these animals then infected a few farm workers. Until now, however, it was thought that outbreaks in other animals had largely died out or been eliminated.
Researchers at Pennsylvania State Uni have found an astonishingly high rate of infection among white-tailed deer in Iowa. They have been testing 5000 samples taken up to January 2021.
After a third of PCR tests on the first 300 samples came up positive, the researchers decided to make their results public. “This is the first evidence of any free-living wild animal species having widespread SARS-CoV-2 infection,” (bioRxiv, doi.org/g5x2).
The researchers think what they have found is the tip of the iceberg. It is likely that the coronavirus is common in white-tailed deer across the US and it will probably keep circulating indefinitely because deer populations have a high turnover rate. The extent of the problem may have gone unnoticed for so long because the deer show few symptoms when infected. It is quite possible that SARS-CoV-2 is also spreading unnoticed in other wild species elsewhere in the world.
SARS-CoV-2 infects a wide range of animals in addition to us. The list includes mink & ferrets, seals, some rodents, cats, dogs and other canids, cows and other ungulates, bats and perhaps even whales and dolphins.
The more animals that harbour the virus, the more risk there is of other species being infected. In some species, SARS-CoV-2 might be more lethal, which could be bad news for endangered species. Also, if there are animal reservoirs of SARS-CoV-2, there is a risk of new and potentially dangerous variants emerging and jumping back to people.
While there is some evidence that SARS-CoV-2 mutates more rapidly when it first jumps to a new species, there is no reason to think that the mutations that emerge in other animals will be more dangerous than those constantly occurring in the viruses spreading among humans. As long as SARS-CoV-2 is circulating widely in people, we will remain the most likely source of dangerous new variants such as alpha and delta.
That said, the virus will evolve differently in animal reservoirs. If it manages to circulate in more than one host, the way it changes becomes twice as complicated.
In the long run, we could end up with a situation like that of flu, which circulates in a number of species. Every now and then, an animal strain jumps to people, sparking a pandemic.
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