We think of COVID-19 as a human pandemic, but it is so much more than that. The virus that causes the disease, SARS-CoV-2, can infect a wide and growing range of animals, both captive and wild.
To date, the virus has been detected in more than a hundred domestic cats and dogs, as well as captive tigers and lions, gorillasnow leopards, otters and spotted hyenas, According to the US Department of Agriculture. US zoo staff recorded one positive case in a benturong monkey, coati, cougar, domestic mongoose, hunting cat, lynx, mandrill, and squirrel monkey.
In the United States, only three species of wild animal — mink, deer, and white-tailed deer — have tested positive, according to the USDA. Cases have been detected elsewhere in the world in the wild Black tailed monkeyAnd Large hairy armadilloAnd Fahad.
But wild animal testing is rare, and COVID-19 is likely to have an impact on many other species, which emerging research is beginning to show. “I think the range of wild animals is much wider than previously thought,” he says. Joseph Hoyta disease ecologist at Virginia Tech.
How does SARS-CoV-2 infect such a wide range of species, and what are the effects?
One of the main reasons lies in a complex receptor found in all mammals, called ACE-2. This receptor plays an important role in regulating blood pressure and other physiological functions.
Once the SARS-CoV-2 protein enters the body, it begins to infect host cells by binding to the ACE-2 receptor, which is circulating in the airways and sinuses of humans and many other mammals.
He says the physical structure of the ACE-2 receptor differs relatively little between vertebrate species compared to other similar proteins Craig Willen, a virologist at Yale University. However, there are small enough differences that scientists initially thought some mammals were unlikely to become infected.
But that thinking has changed because animals that were initially thought to be less sensitive have demonstrated anything but that. It now appears that many, if not most, of the ACE2 receptors are sensitive and do not represent a limiting factor for the virus.
He says “it looks good enough…even if it’s not an exact match” Rick Bushmana professor at the University of Pennsylvania School of Medicine who studies host-microbe interactions.
Instead, there are likely many other factors that determine the extent of vulnerability, the details of which remain almost completely unknown.
We already know that the virus can infect and spread within wild mink and white-tailed deer — and for both species, there is at least 1 verified instance Where the virus passed from humans to animals and Back to humans. Besides mink, domestic ferrets and golden hamsters appear to readily spread the virus to each other in captive settings.
Apart from the previously listed animals, an upcoming study Published ahead of print in BioRxiv It has identified potential cases of SARS-CoV-2 infection in wild deer mice, raccoons, opossums, gray squirrels, white-footed mice, striped skunks, and more.
Carla FinkelsteinThe research co-author, along with Hoyt and conservation biologist Amanda Goldberg, were surprised when they first found evidence of SARS-CoV-2 infection in Virginia opossums.
“We were worried,” says Finkelstein, “because that means it’s jumping” to distantly related mammals. “Opossums are very different from us biologically,” Goldberg adds.
opossums Marsupials give birth to young the size of honeybees, sucking the nipples into their mother’s pouches. The marsupials differed from the placental mammals – which include many common mammals –More than 150 million years ago.
If SARS-CoV-2 could infect opossums, they thought it could potentially infect a wide range of mammals. In fact, the team found signs of antibodies against SARS-CoV-2 in large proportions of six urban wildlife species in southwest Virginia. They also had positive PCR results — which are indicative of infection but not proof — in two of these species and in four others, including red foxes and felines.
Another recently presented paper also found signs of the pathogen It infects 17 percent of sewer rats in New York City tested. A small percentage of wild white-footed rats in Connecticut have also become infected, according to research by Rebecca Earnest, a doctoral student at Yale University.
But how are wild animals like deer exposed to the virus?
The question has not yet been answered, but there are theories. Wildlife can become infected through close contact with human litter or sewage, or by breathing in the virus when close to people. Exposure can also occur after interactions with pets such as cats and dogs — or captive deer — that can carry the virus.
But Bushman says, “I think everybody agrees… nobody knows.”
Although white-tailed deer have been exposed, it happens quite often. One Study 2021 It indicates that more than a third of the deer in the US Northeast and Midwest have been detected. Another paper found that the virus had entered deer at least four times separate from humans, however a third study found that The virus was transmitted to one human being in Canada. (Read more: Wild boar deer have been found with coronavirus antibodies.)
One reason animal infections are so important is that they represent new reservoirs for the virus, where it can persist and acquire new mutations that could theoretically help it spread better if it finds its way to humans.
“More transmission across more species is not something we want to see,” says Earnest.
An overlooked problem
SARS-CoV-2’s ability to infect wildlife amounts to a cryptic virus — an animal version of a pandemic — with effects that are virtually unknown, says Finkelstein.
Infected animals often show mild symptoms, but experts know almost nothing about how different variants of the virus affect most animals. Sometimes, the infection is fatal. The virus appears to kill a small percentage of infected mink, and three snow leopards have died of complications from COVID-19 at the Lincoln Children’s Zoo in Nebraska.
We don’t really know how sick animals can pass into the wild, Willen cautions. He cites the example of the chimpanzee immunodeficiency virus (SIVcpz), which jumped to humans and mutated into HIV-1. It was long thought that SIV caused only mild symptoms in chimpanzees, but research has finally determined that The virus can lead to a condition similar to AIDS In animals, which usually shortens their lifespan.
And Hoyt adds that it’s especially difficult to study the effects of viruses on wild animals, particularly at an ecological level.
Finkelstein agrees: “We don’t know the consequences for wildlife.” “This is another aspect that has been largely ignored.”