Why Animals Are Less Vulnerable to Omicron Than Humans
FCOVID-19 has been ravaging humanity for more than 2 years. The virus has not only affected humans. Leading theories suggest that the virus spread to humans from a Wuhan, China, seafood wholesaler market. The disease has infected many species that are not domesticated and also made its way to the wild.
According to recent research in The Journal, COVID-19 appears to have spread to the entire animal kingdom. Scientific Data This is the first ever global COVID-19 case report in animal models. But there’s good news: other research has found that the highly infectious Omicron variant and its multiple subvariants might hit animals less hard than they hit us—transmitting less easily among them and causing less severe disease.
“To my knowledge, there is no obvious increase in reporting SARS-CoV-2 in animals after the emergence of BA.5,” says 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 monitoring and surveillance of animals that [has been]It is essential to conduct research. We should not think ‘human first,’ but rather integrate the knowledge about animals, humans, and their shared environment and develop a holistic approach for surveillance and control of SARS-CoV-2.”
In this study researchers collected reported COVID-19 cases by analysing two animal health databases. The Program for Monitoring Emerging Diseases is a system that reports on the International Society for Infectious Diseases. And the World Animal Health Information System allows veterinarians to report COVID-19 diagnosis in nonhumans. 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 given group, herd, or other population of animals—in 26 different species. There have been outbreaks in 39 countries on five continents. Australia and Antarctica did not report any cases. What is the number of animals infected? There are only 2,058.
This small amount can have huge implications. The majority of reports only indicate the percentage of positive animals, and not how many of the total tested. It is therefore impossible to determine what proportion of an animal’s population has the virus.
“Obviously we see only the tip of the iceberg,” Desvars-Larrive says, because animals are tested for SARS-CoV-2 vastly less than humans are. “It’s impossible to answer how many animals are actually infected, but SARS-CoV-2 is a generalist coronavirus. Its capacity of adaptation to new hosts is impressive.”
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The American mink with 787 reported cases and the white-tailed Deer with 467 lead all species. To be fair, that’s partly due to sample bias, Desvars-Larrive says. Because mink are raised on heavily populated farms, they have undergone extensive testing. When the virus started spreading through the species, Denmark’s government ordered that 12 million mink be killed. The COVID-19 sampling of deer is necessary because they live close to humans, and their meat can be eaten by hunters. The next on the list is domestic cats (338) and domestic dogs (208). There are also tigers (62) and lions (68). This list is incomplete without mentioning a number of animals, including the Canada Lynx, black-tailed marmoset and ring-tailed coati. Each case contains one giant anteater.
Other species of animals that didn’t make the list either have not been tested or may have a natural immunity—or at least resistance—to SARS-CoV-2. “Some animal species are more susceptible to coronaviruses,” Desvars-Larrive says. “This may be related to molecular mechanisms for virus entry or to some genetic mutations in the host.”
One question raised—but not answered—by the study is how animals are affected by Omicron and its subvariants, including BA.5, which are so highly transmissible among humans.
The results of a handful of studies that have addressed this issue are available or in progress. These shows that the animals are able to withstand new strains. Prior to the emergence of the Omicron variant and its numerous subvariants, researchers at Texas A&M University studied infection rates among dogs and cats living in homes in which at least one person had tested positive for COVID-19. Out of a sample group of 600 animals, they found 100 infections—or 16% of the total tested—presumably transmitted from the human to the pet. Some cases of positive were symptoms, such as the animal acting lethargic, coughing or vomiting. Other cases were unsymptomatic.
Omicron, BA.5, and its subvariants have now been introduced to the market. A new phase is currently underway. Although only 100 animals were tested, there is a striking difference in the results. “With Omicron and its subvariants being the dominant strains in humans, we’ve had only two positive animal infections so far,” says veterinary epidemiologist Sarah Hamer, director of the study. “So it’s definitely a lower infection prevalence now.”
Hamer stresses that the results are preliminary and the researchers have many more animals to test before the second phase of the research is completed—and she does not have a definitive answer as to why animal infection rates might be lower in the era of Omicron and BA.5. “Could it be that there’s something about this virus that’s just not infecting animals as much?She asks. “Could it be that SARS-CoV-2 has been around for a while, and these animals have developed an immune response? We don’t yet know, but hopefully the test for neutralizing antibodies that we are doing now will help fill in these gaps.”
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Similar results have been reported in other studies. Researchers speculate as to the reasons for Omicron’s less severe effects on animals than with past versions. Investigators discovered that Omicron was less harmful in laboratory mice, hamsters and rats than other strains of SARS-2. Infected animals also lost more weight and had less virus in the upper and lower respiratory tracts. The researchers did not determine exactly what makes Omicron less virulent among rodents, but offered some theories: with more than 30 mutations distinguishing the new variant from the original, the virus’s spike protein may engage less effectively with cell receptors in the animals. It’s also possible that changes in other proteins could slow viral replication in rodents, or even that the variant doesn’t multiply as effectively at a rodent’s body temperature as it does at human temperature. In a study, NatureSimilar results were obtained with the BA.2 variation in May. The researchers noticed an improvement in the animals’ lung function.
A second study has been published, this time as a preprint. bioRxivAnalyses of 28 cats, 50 dogs, and one rabbit in homes with Omicron infected people were conducted. The results showed that less than 10% of animals tested positive. No clinical symptoms were observed in any of them. Lidia Sánchez-Morales, a veterinary scientist at the University of Madrid and the lead author of the study, hypothesized about what could be protecting the animals.
“Numerous studies have shown that animals are less sensitive 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. In particular, Omicron is less efficient at overcoming the hurdle of the virus attachment in animal cells than it is in human cells. “This is why we conclude that the susceptibility of the companion animals to this variant seems to be much lower than in the other variants of concern known so far.”
But danger remains. SARS-CoV-2’s seemingly inexhaustible mutability means there will always be new strains. Desvars Larrive fears that the virus may use animals as a laboratory to test new strains before they reach humans.
“The introduction and further spread of SARS-CoV-2 in an animal population might result in establishing an animal reservoir that can further maintain, disseminate, and drive the emergence of novel variants,” she says. “This is of particular concern for species that are abundant, live in social groups, and have close interactions with humans.”
Desvars Larrive believes this fact calls for more rigorous testing of domestic, wild and captive animals. “Active monitoring and surveillance of animals is crucial,” she says. “This is the only way to get more data and to better understand the epidemiology of SARS-CoV-2, not only in animals but also at the human-animal interface.”
It’s at that interface that our own self-interest comes into play. We often catch what the animals catch. One of the most important steps in looking after ourselves is to look out for them.
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