Covid-19: worrying boomerang effect that could restart the epidemic

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It is a threat that could be at the origin of a resurgence of the Covid-19 epidemic. The transmission of Sars-CoV-2 from humans to animals could allow the virus to acquire potentially dangerous mutations for humans, according to some specialists.

In December 2020, the Covid-19 epidemic began in Wuhan, China. While there are still doubts about the exact origin of the pandemic, transmission of the virus to humans by an intermediate animal remains the most likely hypothesis according to the World Health Organization (WHO). Since then, 185 million Covid-19 cases have been identified worldwide and the epidemic has killed more than 4 million.

According to some specialists, a threat could further aggravate the situation: the transmission of the virus from humans to animals. "There is now a lot of evidence that Sars-CoV-2 can pass from humans to other animals. This is called spillback. The virus is capable of infecting a variety of animals." Species, from hamsters to gorillas, "explains Sarah L Caddy, clinical researcher in viral immunology and veterinary surgeon at the University of Cambridge (UK) in The Conversation, a phenomenon that could allow Sars-CoV-2 to acquire new mutations that can later contaminate humans.

Covid-19: the threat of contamination from humans to animals

This risk is of particular concern to Dr. Anna Fagre, a veterinary microbiologist at Colorado State University (United States), as she explains in an article in the American magazine Wired detected by Futura Sciences. This specialist usually works on the pathogens present in animals to prevent their transmission to humans. Since the emergence of Sars-CoV-2, she has been trying to fight the opposite problem: contamination from humans to animals.

And this is not without reason: she recalls that such a phenomenon has been observed during previous epidemics such as Ebola, since the virus had been transmitted from humans to great apes. The H1N1 flu had infected seals and sea lions.

At the moment, the work carried out on the subject has focused mainly on cats and dogs, because the latter have close contact with humans. According to a British study published on the scientific pre-publication site Biorxiv and carried out in 377 dogs and cats, only six of them had specific antibodies against Sars-CoV-2.

Potentially dangerous virus mutations in animals

However, the risk of transmission of the virus from humans to animals could become problematic with respect to non-domestic animals, because "we have seen in the past that it is much more difficult to eradicate a pathogen when it has a reservoir in wildlife" says the Dra. Anna Fagre.

If fighting a virus is more difficult in this context, it is in particular due to potentially dangerous mutations in the virus. To find out, Dr. Anna Fagre carried out laboratory experiments with animals and, in particular, with deer mice. "Almost the entire viral population has acquired a new mutation within a few transmission cycles," she explains.

Mutations of the same type were observed in mink: Sars-CoV-2 was detected in 400 farms located in eight countries of the European Union between March 2020 and January 2021. In Denmark, the animals transmitted a new variant of the virus to crops agricultural. workers, according to the European Center for Disease Prevention and Control (ECDC).

Greater vigilance to avoid the creation of an animal reservoir

To prevent such mutations from contaminating humans and risking restarting the Covid-19 epidemic, increased surveillance of animals is essential. "Special attention should be paid to animals that live most closely with humans" and "to wildlife known to be susceptible to infection," says Sarah L Caddy.

This last category is of particular concern to Dr. Anna Fagre, as she believes that "if the virus can spread in wildlife and continue to be transmitted within that species, then this is something that we cannot control in the same way as in wildlife. domestic animals " .

Scientists are conducting research on wildlife: In the United States, 673 wild animals have been tested. "They have all tested negative so far, but if we find positive tests, we immediately report them to state and federal authorities," said Kaitlin Sawatzki, a virologist at Tufts University.

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