It is no longer a mystery that the virus responsible for covid-19, SARS-CoV-2, has its origins in bats, a species in which very similar coronaviruses have been found.
The question of its spread to humans, however, is not resolved: was it transmitted directly by these winged mammals, whose habitat is constantly nibbled in Southeast Asia? Did an intermediate host make the virus more adaptable to humans? Is this the less likely consequence of laboratory manipulation?
Humans, animals and their environment are at the heart of another big question about Covid-19: the risk of seeing mammals infected by humans composing a viral reservoir large enough to allow the coronavirus to mutate and create possibly more dangerous variants.
Some contaminations in zoos
If SARS-Cov-2 is able to infect wild and domestic animals, it is because “this virus took as a gateway into our cells, a receptor that is extremely widespread in mammals, and which is not subject to strong genetic variations”, recalls Alexis. Lécu, veterinarian and scientific director of the Paris Zoological Park.
“Obviously, it gave the flank that different species can be affected, even if this virus is particularly adapted to human receptors,” he continues.
Some contaminations were thus recorded in French zoos, undoubtedly from the trainer to the animal. Some cats had mild symptoms. Dogs and cats were also carriers of the virus, without a massive spread having been observed.
On the other hand, the passage of SARS-CoV-2 in mink seemed much more problematic: “This is a species in which there is a good match between the virus molecules and the cellular receptor”, explains Thierry Lefrançois, veterinarian and member of the Board. Scientific Covid-19.
The strong promiscuity between congeners on farms and with humans made this animal even more susceptible to the disease. The risk ? “If the circulation there continues intense, we can imagine that this generates mutations that can modify the virus in its effect on humans, in terms of immune escape or severity of symptoms”, adds Thierry Lefrançois, also a specialist. CIRAD
At least two “probable” cases of contamination from mink to humans have been recorded. As a result, millions of specimens were slaughtered, mostly in Denmark. But farms are still running at full speed in China and Finland, which plans to vaccinate all of its mink.
Did Omicron appear in mice?
These aren’t the only animals in sight of health: in North America, there is an increase in infections in deer. There, too, its environment plays an important role: “In the United States, the white-tailed deer has become a peri-urban animal that frequents the same areas as humans. In Europe, deer do not have this proximity and there are no cases of covid-19”, observes Alexis Lécu.
The Omicron variant itself may have “matured” in animals before returning to humans. This is suggested by a highly publicized Chinese study earlier this year, which evokes the rat trail.
“By experimentally passing the virus through rodents, the authors of this work were able to reproduce a panel of mutations close to Omicron. They conclude that this variant could therefore come from the rat or mouse. It is true that they show that it is possible, but it is not evidence”, nuance Thierry Lefrançois.
Stronger elements could be provided if stronger surveillance of domestic and wild fauna were in place, experts believe. Thierry Lefrançois defends, in this regard, a “OneHealth” approach: “It is a concept that aims at an integrated approach to all aspects of human health, animal health and ecosystem management”.
This month, the Scientific Council also issued an opinion proposing the application of this doctrine, without delay: for the next health crises, including pandemic crises”, he implores.
But, from experience, Thierry Lefrançois observed that between two health crises, “it is very difficult to make politicians understand that it is necessary to invest in animal surveillance systems even if there is no circulation of this pathogen, proven clinical cases and people who die”. And this member of the Scientific Council fears that, coming out of the current crisis, “there may be other funding priorities besides this one”.
* Center for International Cooperation in Agricultural Research for Development.