An animal sneezes, his nose runs and he seems sluggish. Could it be a normal pet illness like a cold – which can be caught by dogs and cats from human owners – or could it be COVID-19?
It’s a question that has lingered uncomfortably on the minds of many pet owners throughout the pandemic and was resurrected in January when Hong Kong authorities culled hundreds of hamsters and other small animals. following an outbreak of the Delta variant attributed to a pet store and depot.
Since the start of the pandemic, 19 species of animals in 35 countries have contracted COVID-19, ranging from domestic cats and dogs to white-tailed deer and even gorillas, according to the World Organization for Animal Health (OIE).
The hamster outbreak was notable as the second recorded case of animals re-infecting humans with the virus – and the first attributed 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 transmitted from animals to humans have been few and far between.
More recently, researchers said in late February that a white-tailed deer from Canada 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 is found at the cellular level.
COVID-19 infects humans via the angiotensin-converting enzyme-2 (ACE-2) receptor on cells, meaning animals with a similar ACE-2 receptor are at higher risk of contracting the virus. 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 and humans, we can then predict with at least reasonable certainty which animals are likely to be infected with the virus,” Kuchipudi told Al Jazeera.
Mustelids – the family of animals that includes mink, otters, badgers, weasels and ferrets – appear to be susceptible, as well as domestic cats and dogs.
However, other factors also play a role. Some are known, such as closeness to humans, while others have yet to be identified, Kuchipudi said, which is why not all members of the same species are equally susceptible.
In Hong Kong, researchers found that while Syrian hamsters contracted the Delta variant, dwarf hamsters stored next to them in the store did not. Likewise, some, but not all, of the Syrian hamsters have contracted the virus, in the same way that some members of the same family living in the same house might not contract COVID-19 even when another does.
The virus also did not spread to rabbits, chinchillas, mice and guinea pigs kept near infected hamsters.
In a domestic setting, there is so far no real risk of transmission of COVID-19 from animals to humans, said Keith Hamilton, a trained veterinarian and head of the Department of Preparedness and Resilience at the ‘GOOSE.
“We advise people to be careful with pets that have been infected and to take hygiene precautions as they would with an infected person,” he said.
Humans are the biggest risk to pets
Hamilton says the risks from pets are “not comparable” to a scenario like a mink farm, where thousands of animals are kept together in close proximity, providing the virus with the opportunity to mutate.
Pets, on the other hand, are only contagious for a period similar to humans with little chance of spreading the virus elsewhere if isolated with proper care. In the case of Hong Kong hamsters, their very small lung capacity meant they were still at very low risk even if briefly contagious, he said.
In the long term, however, there are still reasons to be vigilant, Kuchipudi said, as COVID-19 keeps mutating. Scientists have seen experimental and natural cases of spillover in zoos, managed settings like mink farms and among North American deer, but there may be other cases that have not yet been discovered. .
Hong Kong’s hamster outbreak was exceptional because the city’s ‘Zero COVID’ policies made the virus easier to trace – but the same is not happening elsewhere.
“The uncertainty is that there could be other animals in other geographic areas that could also be infected, but no one is actually monitoring them,” he said. “Just because there are no reports from other parts of the world doesn’t mean it’s not happening.”
One speculation about the so far unknown origins of the coronavirus is that it jumped from wild animals that were on sale in the now closed Huanan Market in the central city of Wuhan, China, where the virus emerged for the first time at the end of 2019.
The more transmissible Omicron variant, which was first detected in South Africa, may also have evolved within an animal population before returning to humans, Kuchipudi said.
“It’s possible that a similar scenario could play out in the future and reinfect humans even after the pandemic appears to have ‘over’,” he said.
“So the challenge is that if we don’t pay attention to the circulation of the virus in animals, we may be taken by surprise or caught off guard when a completely new variant emerges from an animal reservoir and begins to infect people again.
For now, however, humans remain the riskiest source of the virus — both to their fellow human beings and to animals — even as COVID-19 precautions are lifted around the world.