Why are animals less vulnerable to Omicrons than humans?

FOver two years, COVID-19 has been present to mankind. But humans are not the only victims of the virus. Illnesses leading theories still point out An animal-to-human spill at a seafood wholesale market in Wuhan, China, has now infected livestock and animals from farms, laboratories and zoos. It has also found its way into the wild, infecting many untamed species.

COVID-19 now appears to be widespread throughout the animal kingdom, according to a recent study in the magazine Scientific Data provides the first global number of COVID-19 cases in animals. But there’s good news: another study has found that the Omicron variant is highly infectious and its many sub-variants can attack animals less often than they hit us — transmitting less easily. between them and cause less severe disease.

Amélie Desvars-Larrive, an assistant professor at the Vienna University of Veterinary Medicine in Austria and co-author of Scientific Data research. “However, this type of active tracking and monitoring of animals [has been] being carried out is very important. We should not think “human first”, but should integrate our knowledge of animals, humans and their common environment and develop a holistic approach to SARS surveillance and control- CoV-2. “

For the study, researchers compiled reported incidents of COVID-19 by analyzing two animal health databases: Emerging Diseases Surveillance Program, a reporting system of the International Society for Infectious Diseases; and World Animal Health Information System, veterinarians, wildlife conservationists, and other researchers report a diagnosis of COVID-19 in non-humans. Between February 2020 and June 2022, there were 704 SARS-CoV-2 “animal events” — identified as a single case or related cases in a group, herd, or population of animals. certain animals — in 26 different species. Outbreaks have occurred in 39 countries across five continents, with Australia and Antarctica not reporting any cases. What about the total number of sick animals represented? Only 2,058.

But that small number has big consequences. Most reports only indicate the number of animals tested positive, not the percentage they represent the total tested, so it is not possible to say what percentage of any animal population contains a virus.

“Obviously we’re only seeing the tip of the iceberg,” says Desvars-Larrive, because far fewer animals have been tested for SARS-CoV-2 than humans. “It is impossible to answer how many animals are actually infected, but SARS-CoV-2 is a generalized coronavirus. Its adaptability to new hosts is impressive. “

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Of all the species studied, the American mink, with 787 reported cases, and white tailed deer, with 467, leading the pack. To be fair, that’s partly down to sample bias, says Desvars-Larrive. Minks have been extensively tested because they are raised on densely populated farms. (In November 2020, the Danish government ordered to kill 12 million mink Meanwhile, it’s on farms when the virus starts to spread across species.) Deer, meanwhile, live near humans and are hunted for their meat, so it’s up to them to sample them for COVID-19 I care. Next on the list are domestic cats, with 338 cases, and domestic dog, at 208. Further down are lions (68), tigers (62) and western gorillas (23). The list ends with a variety of other animals including the black-tailed marmoset, the Canadian lynx, the ring-tailed coati, and the giant anteater, each with a case.

Other animal species are not on the list or have not been tested or may have natural immunity — or at least resistance — to SARS-CoV-2. “Some animals are more susceptible to coronavirus,” says Desvars-Larrive. “This may be related to molecular mechanisms for viral entry or some genetic mutation in the host.”

One question raised – but unanswered – by the study is how animals are affected by Omicron and its sub-variants, including BA.5very easily transmitted between people.

However, several other studies to address that question have been conducted or are currently underway, and they show that the animals are doing well with the new strains. Prior to the emergence of the Omicron variant and its many sub-variants, researchers at Texas A&M University studied infection rates in indoor dogs and cats in which at least one person had had positive test result for COVID-19. Of the 600 sample animals, they found 100 infections — or 16% of all animals tested — presumably transmitted from person to person. Some positive cases are symptomatic, the animal coughs, sneezes, vomits or is comatose; Others have no symptoms.

The second phase of the study is currently underway, since its appearance Omicron and BA.5, and while only 100 animals have been tested to date, the difference in results is remarkable. “With Omicron and its sub-variants being dominant strains in humans, so far we have had only two positive infections in animals,” said veterinary epidemiologist Sarah Hamer, director of the study. animals,” said veterinary epidemiologist Sarah Hamer, research director. “So it’s definitely a lower infection rate now.”

Hamer stresses that the results are preliminary, and that the researchers have many other animals to test before the second phase of the study is complete — and she doesn’t have a definite answer as to why. Infection rates in animals may have been lower in the eras of Omicron and BA .5. “Could it be that there is something about this virus that doesn’t infect animals that much?: she asked. “Is it possible that SARS-CoV-2 has been around for a while and these animals have developed an immune response? We don’t know yet, but hopefully the neutralizing antibody-finding test we’re doing now will help fill in these gaps.”

Read more: Why don’t we have a Pi variant – Even after so many Omicrons

Similarly, other studies have shown that Omicron tends to cause less severe symptoms in animals than previous variants, and the researchers have ventured into several hypotheses as to why. star. In a study published in the journal Nature In January 2022, investigators found that the Omicron variant was less pathogenic to lab rats and hamsters than previous strains of SARS-CoV-2, and the infected animals lost weight. and contained less virus in their upper and lower respiratory tracts. The researchers did not determine exactly what made Omicron less virulent in rodents, but suggested several hypotheses: with more than 30 mutations distinguishing the new variant from the original, the mutant protein Viruses may engage less effectively with cellular receptors in animals. It is also possible that changes in other proteins may slow viral replication in rodents, or even that this variant does not multiply as efficiently at the rodents’ body temperature as at the rodents’ body temperature. People. A published study In Nature in May yielded similar results with variant BA.2. This time, the researchers also found a reduced inflammatory response in the animals’ lungs.

Yet another study, published in April as a preprint bioRxiv, conducted an analysis of 28 cats, 50 dogs and one rabbit living in households where someone was infected with Omicron and found that just over 10% of the animals tested positive for the virus and did not have any symptoms. any clinical symptoms. Lidia Sánchez-Morales, a veterinary scientist at the University of Madrid and lead author of the study, hypothesized what might protect the animals.

She wrote in an email: “Many studies have shown that animals are less susceptible than humans to SARS-CoV-2 infection, which may be due to the affinity between the cellular receptor and the associated viral receptor. lower end. Specifically, she said, the ACE2 receptor in human cells to which the virus attaches was found to be at lower levels in animals, and Omicrons may be less effective at crossing this barrier than the original virus. “This is why we conclude that the susceptibility of companion animals to this variant appears to be much lower than that of other variants of interest to date.”

But the danger remains. The seemingly limitless mutability of SARS-CoV-2 means that new variants are bound to emerge. Desvars-Larrive is concerned that animals could serve as a kind of laboratory for the virus to try out new variants, before those novel strains transfer to humans.

“Further introduction and spread of SARS-CoV-2 in animal populations could lead to the establishment of an animal reservoir that can sustain, disseminate and promote the emergence of pathogens,” she said. new variant. “This is of particular concern 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 animal monitoring and surveillance is very important,” she said. “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 that interface that our self-interest comes into play. What animals catch, we often do too. Finding them is one of the important steps to finding ourselves.

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