London, Europe Brief News – Since the pandemic began, 19 species of animals across 35 countries have contracted COVID-19.
The hamster outbreak was notable as the second-ever recorded case of animals reinfecting humans with the virus – and the first traced to the international pet trade as the animals were imported from the Netherlands.
In 2020, farmed mink in Denmark were also found to have spread the virus to humans, leading authorities to cull millions of animals, but confirmed cases of COVID-19 being transmitted from animals to humans have been few and far between.
More recently, researchers said in late February that a white-tailed Canada deer may have infected a human, according to another pre-print study, although the case has been difficult to trace.
Scientists say it remains difficult to assess the immediate risk of COVID-19 in animals, and why some animals appear more susceptible than others.
But a key risk factor can be found at the cellular level.
COVID-19 infects humans via the angiotensin-converting enzyme-2 (ACE-2) receptor on cells, which means animals with a similar ACE-2 receptor are more at risk of contracting the virus than others, according to Suresh Kuchipudi, a veterinary virologist at the University of Pennsylvania.
“Based on the similarity of ACE-2 receptors in animals to humans, we can then predict at least with reasonable certainty, which animals are likely to be infected by the virus,” Kuchipudi told Al Jazeera.
Mustelids — the animal family that includes mink, otters, badgers, weasels, and ferrets — seem to be susceptible, as well domestic cats and dogs.
Other factors, however, also play a role. Some are known, like proximity to humans, while others are yet to be identified, Kuchipudi said, which is why all members of a single species are not equally susceptible.
