The coronavirus has taken root in animals. Why it increases the risk for people

The COVID-19 pandemic is rapidly receding in our collective memory. But the virus that caused it lives in our sewers, in our backyards, and may even have curled up in a sunny spot on the living room floor.

The coronavirus that prompted over 750 million infections among humans, and almost 7 million deaths also spread to creatures large and small. He was caught by lions and tigers. So there are domestic dogs and cats. Scientists even SARS-CoV-2 detected among armadillos, anteaters, otters and manatees.

At least 32 kinds of animals Coronavirus infections have been confirmed in 39 countries. In most cases, animals do not get very sick. However, some of them are able to transmit the virus to other members of their species, like asymptomatic individuals who have become “silent spreaders”.

The ability of the coronavirus to infect so many different animals and spread among some of those populations is worrisome, meaning there is virtually no chance the world will ever be rid of this particularly devastating coronavirus, scientists said.

And that’s not the worst: while SARS-CoV-2 is spreading among animals, the virus has the opportunity to acquire new mutations that can make it more dangerous to humans. If the circumstances match, the result will be pandemic 2.0.

Scientists do not say that such a scenario is likely. But it’s not so contrived.

In fact, this sequence of events – a virus that jumps from animals to humans and capitalizes on gaps in our immunity – is how most “zoonotic” outbreaks start. It remains most likely explanation about how the coronavirus circulating in horseshoe bats in China first infected humans.

When the virus that made people sick recedes but continues to circulate in the animal population, these creatures become what scientists call storage tank. Within a herd, flock, cloudder, flock or flock, it imperceptibly maintains its potential to re-infect humans and restart outbreaks.

A virus can adapt to its animal host by flipping several genetic switches. The result could be a pathogen that the person’s immune system no longer recognizes, or that causes more severe disease than it did last time.

To cause real damage, tank animals must be in constant contact with humans. It could be livestock on farms, pets, or wildlife neighbors who leave their saliva or droppings in our yards or on hiking trails.

Whether any particular species can be said to serve as a reservoir for SARS-CoV-2 is a hotly debated issue among scientists, he said. Dr. Angela Bosco-Lautveterinarian at Colorado State University who studies zoonotic diseases.

So far, no species has answered all questions, “which doesn’t mean we should stop looking,” she said. “It’s hard to predict. But we know that if we don’t look, we won’t find it.”

Virologists, immunologists and wildlife experts have shown that some species have some of the abilities necessary to become a reservoir.

One animal population white-tailed deer – continues to transmit SARS-CoV-2 among themselves. Another – american mink – maybe not only be infected but re-infected with a pandemic virus, raising the possibility that it could live indefinitely. In both cases, studies have shown that the coronavirus actively mutates to adapt to a new host species.

There are also documented phenomenon cultivated mink in Denmark and a pet shop hamsters in Hong Kong are transmitting the virus back to humans.

The number of species of wild animals that can carry the virus is significant. A group of geneticists at the University of California at Davis found that, in addition to humans, 46 species of mammals have receptors on their cells that suggest they are vulnerable to SARS-CoV-2 infection.

The World Health Organization is so worried that animals will become a safe haven for a pandemic virus that called on all member countries actively monitor their wildlife. cervids the family of animals that includes deer exist in various forms around the world and are considered prime candidates for the coronavirus reservoir. Other leading contenders are the great apes and “Old World primates” – macaques, baboons, gorillas and chimpanzees – that are genetically similar to humans. makes them susceptible to infection, and whose human contact worldwide is significant.

The only species in which scientists have documented the continued spread of the pandemic virus is the white-tailed deer, the most numerous large mammal in North America and inhabiting backyards and woodlands across much of the country. In places in the US where the animals are densely concentrated, at least a third are believed to have been infected with the virus at some point during the pandemic. (mule deerwhich are more common in the West also support and transmit coronavirus infections.)

A study published in January found that white-tailed deer continued to carry the alpha, delta, and gamma variants of the coronavirus long after they stopped circulating in the US population. The fact that deer populations can keep these variants alive and thriving even after they have left humans is seen as a strong indication that deer could well serve as reservoirs for a pandemic virus.

Deer hunted by hunters across New York State also provided other surprises: as the virus passed through the herds, it adopted new mutationsincluding several in a spike protein that it uses as a key to enter and infect cells.

Jeff Bowmana scientist from Ontario, Canada, is a senior author research the discovery in wild deer of not only a virus with a record 76 mutations, but also a “return” transmission of another strain from deer to humans was documented. However, he acknowledged that deer have become a reservoir of the SARS-CoV-2 virus. “remains an open question for now.”

In human populations, the pandemic virus often flipped genetic switches, mostly in a neutral way or making it less dangerous. But as it settles among new host populations, it may well develop differently.

“When they get inside, they are invisible,” said a molecular virologist at Washington State University. Mikhail Letko, who studied how members of the coronavirus family adapt to new hosts. “They evade immune responses and try to survive.”

This puts tremendous pressure on the fixing mechanism of the virus – its spike protein – to accept any mutations that will help it do its job. Whether these mutations make the virus more virulent is “just luck,” Letko said. “The suspense makes it quite challenging.”

The Canadian government has kept track of accounts virus in deer and other wildlife populations by combining observations with an existing program to detect chronic debilitating diseases and rabies. Hunters and trappers have been hired to bring their prey to explorers for testing, and wildlife crews collect animal carcasses in the forest and collect dead on the roads to complete the picture.

In the United States Department of Agriculture Animal and Plant Health Surveillance Services has been collecting white-tailed deer from the wild since November 2021 and is expected to publish new results soon.

So far, there is no evidence that the mutations found after the virus was found among white-tailed deer in New York made it more dangerous in any way. But the effect of any change may not be seen until the infected deer passes it on to humans.

Finley Maguirea genomic infectious disease epidemiologist at Dalhousie University in Halifax, Nova Scotia, is one of the Canadian researchers. monitoring spread of SARS-CoV-2 in white-tailed deer there, and he hasn’t found any alarming genetic changes – so far.

“We have not seen signs of strong electoral pressure that would force [the virus] better for people,” he said.

There are other encouraging studies: the researchers found no reason to believe that birds can become infected with the coronavirus. This is important because birds flock, fly and migrate, and are also bred as livestock. All these qualities make them exceptionally active carriers of pathogens capable of infecting humans. (Point to point: flu.)

The researchers also ruled out the ability of pigs, cattle, sheep, goats, alpacas, rabbits and horses to carry SARS-CoV-2 infection – a relief given that these pets are in constant contact with the people caring for them.

Bosco-Laut of Colorado said the animals that live closest to humans – dogs and cats – can become infected but are unlikely to be effective reservoirs for the virus. Dogs can lick our faces, and cats sneeze into them with pleasure. But none of them have shown to be able to effectively transmit the virus to their housemates or other members of their species.

She added that researchers have yet to find a species that sheds a lot of live virus in their feces when infected. Much has been done in connection with the opening infected rats lives near the sewers of New York. But if they cannot transmit the pathogen through their droppings, rats and other wild animals are unlikely to effectively infect humans.

“There are not many species of wild animals that I really care about,” Bosco-Laut said.

However, there is one species that continues to cause concern among scientists: homo sapiens.

“COVID-19 is still circulating among people, and people are repeatedly infected and re-infected,” the report said. Graham Belsham, a virologist at the University of Copenhagen who has studied the spread of the pandemic virus in farm-raised minks in Denmark. “The virus has not gone away, so humans are likely to be the biggest threat to other humans for years to come.”