Why cats are at a higher risk of Covid-19 than dogs, but bears don’t face a threat

NEW DELHI: Your cat is at a higher risk of catching Covid-19 than your dog, monkeys and chimpanzees are “highly susceptible” to the infection while bears run a “low” risk. A genomic analysis of 410 different species by an international team of researchers published in the Proceedings of the National Academy of Sciences journal last week has revealed species that are potentially vulnerable to catching SARS-CoV-2.
Talking to TOI from the US, first author of the paper and a postdoctoral research associate at University of California, Davis, Joana Damas, said the team studied the ACE2 protein — found on cells and tissues — to predict a species’ risk to Covid-19. In humans, 25 amino acids of the ACE2 protein are important for the virus to bind and gain entry into cells. The researchers evaluated how many of these amino acids are found in the ACE2 protein of different species through studying their DNA material combined with computational modelling.
“Animals with all 25 amino acid residues matching the human protein are predicted to be at the highest risk for contracting SARS-CoV-2 via ACE2,” said Damas. The researchers used genetic material from zoos to generate the sequence of the ACE2 gene. “The availability of DNA samples from zoos allowed us to study such a large set of species,” she said.
Cats, leopards, cheetah, Siberian tigers, cattle and sheep were found to have a medium risk while dogs, horses and pigs were found to have low risk. Pandas, grizzly bears and polar bears were also in the low risk category while animals flagged as high risk included marine mammals such as gray whales and bottlenose dolphins as well as the giant anteater. Several critically endangered primate species, such as the Sumatran orangutan, Western lowland gorilla and Northern white-cheeked gibbon were predicted to be at very high risk of infection from the virus.
Of the 410 species studied, 40% of the species potentially susceptible to SARS-CoV-2 are those classified as “threatened” by International Union for Conservation of Nature (IUCN) and may be especially vulnerable to human-to-animal transmission. “A large-scale transmission in these populations could make them even more vulnerable. Transmission in wild populations would be very difficult (if not impossible) to control,” said Damas.
Damas admitted that the virus spillover to animal species has been very limited and the aim of the study was to help “keep it that way”. “We need to understand which species are at higher risk of infection of SARS-CoV-2 so surveillance measures can be put in place. This is specially important for primate species that we predicted to have a very high risk of infection, many of which are already endangered, such as chimpanzees.”
The researcher said the current study only accounts for the risk of the virus to enter cells of animals so further assessment is required to determine the actual pathological outcome among species which would depend on factors such as immune response.
And with the jury still out on which species, if any, could have served as the intermediate host for SARS-CoV-2 — helping it jump from bats to humans — Damas said the study might give clues in that direction as well. “Potentially, any species predicted as very high or high risk, or even medium risk, could have served as an intermediate host, and our results can be used to prioritise which species should be more closely monitored for SARS-CoV-2 presence,” she said.
The study also included researchers from Broad Institute of MIT and Harvard (US), Max Planck Institute of Molecular Cell Biology and Genetics (Germany), Wuhan University (China) and University College Dublin (Ireland) among several others.