for more than two years, COVID-19 has had its way with humanity. But humans are not the only victims of the virus. The disease, which leading theories still state that it was transmitted from animals to humans at a wholesale seafood market in Wuhan, China, has now infected pets and animals from farms, labs and zoos. It has also made its way into the wild, infecting many non-domesticated species.
COVID-19 now appears to be widespread across the animal kingdom, according to a recent study in the journal Scientific data providing the first global number of animal COVID-19 cases. But there’s good news: Other research has indicated that the highly contagious Omicron variant and its multiple sub-variants may hit animals less hard than they do — transferring less easily between them and causing less serious illness.
“To my knowledge, there has been no apparent increase in SARS-CoV-2 reporting in animals after the emergence of BA.5,” said Amélie Desvars-Larrive, an assistant professor at the University of Veterinary Medicine Vienna in Austria and a co-author of the Scientific data study. “Still, the kind of active animal monitoring and surveillance that” [has been] implemented is crucial. We should not think ‘humans first’, but rather integrate knowledge about animals, humans and their shared environment and develop a holistic approach to monitoring and control of SARS-CoV-2.”
In the study, researchers collected reported incidents of COVID-19 by analyzing two animal health databases: the Program for Monitoring Emerging Diseases, a reporting system of the International Society for Infectious Diseases; and the World Animal Health Information System, to which veterinarians, conservationists and other researchers report diagnoses of COVID-19 in non-humans. From February 2020 to June 2022, there have been 704 SARS-CoV-2 ‘animal events’ – defined as a single case or multiple related cases within a particular group, herd or other animal population – in 26 different species. The outbreaks have occurred in 39 countries on five continents, with Australia and Antarctica reporting no cases. As for the total number of sick animals that represents? Only 2,058.
But that small number has big consequences. Most reports only indicate the number of animals that tested positive, not the proportion they represent of the total number of animals tested, so it is not possible to say what percentage of an animal population harbors the virus.
“Obviously we’re only seeing the tip of the iceberg,” Desvars-Larrive said, because animals are tested for SARS-CoV-2 much less than humans are. “It is impossible to answer how many animals are actually infected, but SARS-CoV-2 is a generalist coronavirus. The adaptability to new hosts is impressive.”
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Of all the species studied, the American mink, with 787 reported cases, and the white-tailed deer, with 467, lead the pack. To be fair, that’s partly due to sample bias, Desvars-Larrive says. Minks have been tested extensively as they are bred on densely populated farms. (In November 2020, the government of Denmark ordered the killing of 12 million minks on farms as the virus began to spread through the species.) Deer, meanwhile, live near people and are hunted for their meat, leading them to be sampled for COVID-19 something that is in our own interest. Next on the list are domestic cats, with 338 cases, and domestic dogs, with 208. Further down are lions (68), tigers (62) and western lowland gorillas (23). The list ties in with several other animals, including the black-tailed marmoset, Canadian lynx, ring-tailed coati, and giant anteater, with one case each.
Other animal species that did not make the list either have not been tested or may have natural immunity – or at least resistance – to SARS-CoV-2. “Some animal species are more susceptible to coronaviruses,” says Desvars-Larrive. “This could be related to molecular mechanisms for virus entry or to some genetic mutations in the host.”
One of the questions raised by the study, but not answered, is how animals are affected by Omicron and its sub-variants, including BA.5, which are so highly transmissible to humans.
However, a handful of other studies to address that question have been conducted or are currently underway, and they show that animals are quite resistant to the new strains. Prior to the emergence of the Omicron variant and its numerous subvariants, researchers at Texas A&M University studied infection rates in dogs and cats living in homes where at least one person had tested positive for COVID-19. From a sample of 600 animals, they found 100 infections – or 16% of the total tested – believed to have been transmitted from humans to pets. Some of the positive cases were symptomatic, with the animal coughing, sneezing, vomiting or behaving listlessly; others were asymptomatic.
A second phase of research is now underway, since the emergence of Omicron and BA.5, and although only 100 animals have been tested so far, the difference in results is striking. “Because Omicron and its subvariants are the dominant strains in humans, we’ve had only two positive animal infections to date,” said veterinary epidemiologist Sarah Hamer, director of the study. “So it’s definitely lower infection prevalence now.”
Hamer emphasizes that the results are preliminary and that the researchers will have many more animals to test before the second phase of the study is completed — and she has no definitive answer as to why the number of animal infections might be lower in the era of Omicron and BA .5. “Could it be that there’s something about this virus that just doesn’t infect animals that much?” she asks. “Could it be that SARS-CoV-2 has been around for a while and that these animals have developed an immune response? We don’t know yet, but hopefully the neutralizing antibody test we’re doing now will help fill these gaps.”
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Similarly, other studies show that Omicron tends to cause less severe symptoms in animals than previous variants, and researchers have ventured some theories as to why. In a study published in Nature in January 2022, researchers found that the Omicron variant was less pathogenic in laboratory mice and hamsters than previous SARS-CoV-2 strains, and that infected animals lost less weight and had less virus in their upper and lower extremities. had lower airways. tracts. The researchers haven’t determined exactly what makes Omicron less virulent in rodents, but offered some theories: With more than 30 mutations distinguishing the new variant from the original, the virus’s spike protein may interact less effectively with cell receptors in the animals. . It’s also possible that changes in other proteins can slow viral replication in rodents, or even that the variant doesn’t replicate as effectively at rodent body temperature as it does at human temperature. A study published in Nature in May yielded similar results with the BA.2 variant. This time, the researchers also noticed a reduced inflammatory response in the animals’ lungs.
Yet another study, published in April as a pre-print in bioRxiv, conducted analyzes of 28 cats, 50 dogs and one rabbit living in households with people infected with Omicron and found that just over 10% of the animals tested positive for the virus, and none showed clinical signs. Lidia Sánchez-Morales, a veterinary scientist at the University of Madrid and the study’s lead author, hypothesized what might protect the animals.
“Numerous studies have shown that animals are less susceptible than humans to SARS-CoV-2 infection, which may be due to a lower affinity between the cell receptor and the binding viral receptor,” she wrote in an email. Specifically, she says, the ACE2 receptor in human cells to which the virus attaches is found to a lesser extent in animals, and Omicron may be less effective at overcoming this hurdle than the parent virus. “We therefore conclude that the sensitivity of the companion animals to this variant appears to be much lower than for the other variants of care known to date.”
But danger remains. The seemingly infinite variability of SARS-CoV-2 means that new variants are sure to emerge. Desvars-Larrive worries that animals could serve as a kind of laboratory for the virus to try out new variants before those new strains jump to humans.
“The introduction and further spread of SARS-CoV-2 in an animal population could lead to the establishment of an animal reservoir that can further maintain, spread and stimulate the emergence of new variants,” she says. “This is of particular importance for species that are abundant, live in social groups and have close interactions with humans.”
This fact, Desvars-Larrive argues, calls for much more aggressive testing of wild, captive and domestic animals. “Active monitoring and surveillance of animals is crucial,” she says. “This is the only way to get more data and better understand the epidemiology of SARS-CoV-2, not only in animals, but also at the human-animal interface.”
It is at this interface that our own interests come into play. We often do what the animals catch. Taking care of them is one of the most important steps in taking care of ourselves.
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