The findings are based on an analysis of ACE2 — the enzyme on our cell surface that allows SARS-CoV-2 to infect human cells. (Express photo: Javed Raja)

Since the Covid-19 pandemic began, there have been widely reported instances of a few animals — cats, dogs, tigers — being infected with the novel coronavirus, usually transmitted by humans. Now, researchers have published a comprehensive analysis of the relative potential risks faced by 410 animal species. The findings, drawn from a genomic study, are published in the Proceedings of the National Academy of Sciences of the United States.

So, which ones are at high risk?

The 410 species analysed are vertebrates — birds, fish, amphibians, reptiles and mammals.

At the highest level of risk of infection with SARS-CoV-2, the virus that causes Covid-19, are several primate species. Some are critically endangered species — such as the Western lowland gorilla, and Sumatran orangutan. Other species at “very high risk” of infection include the chimpanzee and rhesus macaque.

At “high risk” are species such as blue-eyed black lemur and common bottlenose dolphin.

What about domestic animals?

Previous studies have indicated that cats and dogs can contract the virus from humans, and that cats face a greater risk than dogs. In the new study, cats, along with other domestic animals such as cattle and sheep, were found to have a medium risk. Dogs, along with horses and pigs, were found to have a low risk.

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How does the study figure all this out?

The findings are based on an analysis of ACE2 — the enzyme on our cell surface that allows SARS-CoV-2 to infect human cells. In humans, 25 amino acids of ACE2 are important for the virus to bind with the cell. The researchers used modelling to evaluate how many of these amino acids are found in the ACE2 enzyme of other species. If a species showed a match with all these 25 amino acid residues, it was predicted to be carrying the highest risk. The fewer the matches with the human ACE2, the lower the risk of infection.

How significant are these findings?

The risk was assessed for ACE2 binding, not for actual infection. In a statement issued by the University of California—Davis, the authors have urged caution against over-interpreting the predicted risks based on computational results; the actual risks can only be confirmed with additional experimental data. They noted, however, that in the cats, dogs and tigers that have been infected, the virus may be using ACE2 receptors, or receptors other than ACE2.

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