According to an American study, more than 80% of deer tested between December 2020 and January 2021 in the state of Iowa in the United States are positive for the virus. Scientists who did not expect such a proportion fear that this species could become a reservoir for the virus. Especially since the phenomenon has been observed in other wild animals in zoos and even in pets such as dogs and cats.
“Many animal species are susceptible to SARS-CoV-2 and can serve as reservoirs. So write the scientific authors of a study published in preprint in early November. white-tailed gazelle (Odocoileus virginianus), the predominant deer in North America, is susceptible to SARS-CoV-2 infection, and experimentally infected calves transmit the virus to other deer in captivity.
After bats and mink, can the white-tailed deer, one of the most common large mammals in North America, become the new Covid-19 reservoir, a “walking bomb” capable of transmitting Covid? 19 to the man? For now this is not the case. But veterinarians at the University of Pennsylvania are concerned, as the presence of the virus is strong in these deer that have also been introduced in many countries such as Finland, former Czechoslovakia or even New Zealand.
The white-tailed deer could, according to these scientists, become a “reservoir” for the virus. Clearly, it could proliferate and evolve into new forms within this species before, in theory, becoming transmissible to humans again in a way not considered by vaccines. This is the first direct evidence of the SARS-CoV-2 virus in a free-living species, and our findings have important implications for the ecology and long-term persistence of the virus. Suresh Kuchipudi, study co-author and clinical professor of veterinary and biomedical sciences at the University of Pennsylvania.
The presence of Covid in the deer population on the other side of the Atlantic is nothing new. Two studies, published in the spring and summer by the American Wildlife Research Center (NWRC), showed that these animals were heavily contaminated and transmitted the virus to each other. But what surprised and worried the researchers in this new study was the high proportion of infected deer. “We were very surprised to see such a large number of positive samples”, summarizes one of the authors.
In fact, if between April and December 2020, only a third of the deer were positive, that share jumped to 80% for those analyzed between November 2020 and January 2021. And to make these results a little more anxious, the deer two veterinarians discovered the presence of numerous variants that corresponded to those also identifiable in humans. All the deer studied lived freely in public spaces or in peri-urban areas, or in the middle of nature, or finally in captivity in areas reserved for hunting.
Boomerang effect in humans
Concerned with these results, the researchers say they fear, in addition to contamination from other species, a boomerang effect in humans, as was seen at the time with cultivated mink. Other mutations in the virus can also occur. For the scientists, the implementation of “numerous urgent measures” is necessary “to monitor the spread of the virus in deer and, in return, prevent further contamination in humans. »
Meanwhile, three snow leopards housed at Lincoln Children’s Zoo in Nebraska recently died from complications from Covid-19. Two tigers at the zoo also contracted the virus in October but recovered. A comparable phenomenon occurred at the Smithsonian National Zoo in Washington D.C. in September, with six African lions, one Sumatran tiger and two Siberian tigers testing positive for SARS-CoV-2. Zoo staff were unable to determine the source of these infections.
Scientists therefore advocate greater vigilance and anticipate the appearance of variants as much as possible. And they consider it “urgent” to continue to monitor the evolution of the virus in wildlife, “especially in animals that can serve as a reservoir, such as deer. »
Worry about pets or livestock
It also remains to be determined how these white-tailed deer are contaminated by humans. So far, and although the cause is sometimes unknown, it seems that more humans are infecting animals. So, according to Angela Bosco-Lauth (Assistant Professor of Biomedical Sciences at Colorado State University, Fort Collins) quoted by Medscape’s website, humans are the supposed vector of infection in deer. On the other hand, “the probability of a human contracting the disease from a deer they have just killed is quite minimal, although it cannot be completely ruled out. “And to add, underlining the sheer number of infections in the world, that ‘what we’re seeing is unprecedented in history. What is even more worrisome is the possibility of a new variant appearing, particularly in domestic or farm animals. We saw in particular with the delta variant that mutations appear quite easily and adapt to the host. »
Angela Bosco-Lauth and her colleagues recently performed experiments on cats, dogs, hamsters and ferrets. They found rapid evolution of SARS-CoV-2, mostly in dogs and cats. In their study, published in early November in the journal Proceedings of the National Academy of Sciencesthe authors suggest closely monitoring the evolution of SARS-CoV-2 in pets and other potential animal hosts.
Given that cats seem particularly susceptible to infection by this virus and that they live very close to humans, we would be in the presence of “a more likely context of bidirectional transmission, between humans and animals, which could give rise to variants” worries Angela Bosco-Lauth.