The search for animals that may be carriers of the next deadly virus

Which animal is most likely to harbor the next deadly coronavirus?

With the Covid-19 pandemic fueling a sense of urgency, researchers are finding new ways to predict the answer to that question.

“We are thinking about the next one,” says Maya Wardeh of the University of Liverpool, one of the authors of an article in the journal Nature Communications that found that there are many more mammals that can be infected with multiple coronaviruses than previously known.


Several countries around the world participate in or fund programs to test wild animals that have been linked to previous outbreaks or are considered high-risk, such as bats and rodents. Samples are collected and sequenced to identify new viruses, including those that have the potential to infect humans. Efforts are also underway, including one at Ohio State University, to test domestic, wild, zoo and livestock animals to see if they can contract SARS-CoV-2, the pathogen that causes Covid-19 infections.

The Covid-19 pandemic has sparked additional strategies to better quantify risks, make more accurate predictions, and then identify which animals require closer surveillance.

“You can’t look everywhere for something dangerous all the time. That’s not sustainable and it’s expensive and hard work, especially if you don’t know what you’re looking for, ”says Barbara A. Han, a disease ecologist at the Cary Institute for Ecosystem Studies in Millbrook, New York, who is applying the existing prediction. . algorithms to novel combinations of ecological and other data to better predict animal disease risk from SARS-CoV-2. Her and her colleagues’ research combines data about the ACE2 receptors in animals, which the virus uses to infect human cells, with information about the habitats, diets, metabolism and biology of animals, to predict with which animals and specific species are likely to become infected. SARS-CoV-2 and transmit it to others.

“We wanted to make predictions that were more accurate and could be tested in the field,” says Dr. Han.


Taking the leap

Most human infectious diseases come from animals and then “spread” to humans. Viral outbreaks such as Ebola virus disease, Middle East respiratory syndrome, and severe acute respiratory syndrome have been linked to human interactions with palm civets, dromedaries, non-human primates, and rodents. Many scientists believe that SARS-CoV-2 likely originated in animals, but it is still up for debate.

Scientists are concerned not only about the animals that could have caused the initial contagion to humans, but also about the possibility of humans transmitting the coronavirus to animals. In such cases, the disease could remain in the animal population, continue to infect animals, and potentially re-infect humans. Mink-related cases have already been reported in the US and Europe that initially contracted Covid-19 from humans and then transmitted the virus to people again. Viruses often produce genetic changes as they spread between hosts. If animals eventually transmit a more lethal variant of the virus to people, it could undermine efforts to control the pandemic through vaccination, says Dr. Han.

According to the Centers for Disease Control and Prevention, a small number of domestic dogs and cats have been reported to be infected with SARS-CoV-2 around the world, including in the U.S. Studies are underway to examine which animals humans can spread the disease to. The data so far shows that dogs can become infected, but they do not appear to transmit the virus to other animals of the same species as easily as cats or ferrets do, at least in the laboratory.

Vanessa Hale of Ohio State University, which launched eScout, a surveillance program for Covid-19, is conducting tests for SARS-CoV-2 in animals and the environment. Surveillance teams are targeting cats in animal shelters and veterinary offices, pigs at agricultural fairs, and animals captured by trappers and hunters, among others. So far in Ohio, all animals tested since May 2020, including ferrets, horses, and goats, are negative. “We don’t want people to be afraid of cats and dogs in their homes,” says Dr. Hale. “At this point, animals do not play a significant role in human infections.”


An arduous process

For some scientists, the most urgent threat to public health is the potential for recombination of SARS-CoV-2 with another coronavirus in an animal, a process that can occur when two viruses infect the same animal, the viruses exchange genetic material, and then create a new disease, says Dr Marcus Blagrove of the University of Liverpool, one of the authors of the Nature Communications paper that tried to predict where new coronaviruses might emerge.

The new study identified more mammals than are currently known that may be potential sources for generating new coronaviruses. Some involve familiar names believed to be sources or intermediaries in previous coronavirus outbreaks, such as horseshoe bats, palm civets, dromedary camels, and pangolins. But there were also new suspects that emerged through the team’s analysis, including the African green monkey and the lesser Asian yellow bat. Other animals on the watch list include the common hedgehog, the European rabbit and domestic cats, the study found.

It is not easy to make predictions about future outbreaks. For one thing, pandemics are likely to occur more frequently, the researchers say, driven by human behavior that is difficult to change. Farms and markets contain domestic and wild animals that live in close proximity and increase the possibility of diseases passing from animals to people. People continue to invade wildlife habitats through deforestation and the construction of roads and cities.

“We are getting in more contact with animals and their microbes,” says Dr. Scott L. Nuismer, a professor in the department of biological sciences at the University of Idaho.

“There are so many different ways that a virus can spread to people and it’s hard to take them all into account,” says Simon Anthony, a virologist at the University of California at Davis.


Dr. Anthony says it is helpful to develop mathematical and statistical forms to discern patterns and make better predictions. But the overflow process is complex, not fully understood, and likely to involve random events that, by definition, cannot be predicted. “We need all the help we can get to make decisions. But there are many possibilities in virus outbreaks, ”he says.

In trying to create a better algorithm to predict the animals likely to harbor SARS-CoV-2, researchers often encounter challenges. Databases contain much more information about animals that people have been studying for decades because of long-standing research by scientists, or because animals make up a major industry like poultry.

For example, bats are known as important sources of coronaviruses, but data sets containing genetic sequences for those viruses are not complete, especially compared to avian influenza databases, says Maciej Boni, evolutionary biologist and associate professor. from Pennsylvania State University. Before Covid-19, there were no financial incentives for bat studies, he says, while the poultry industry is a multi-billion dollar business. Also, many bats prefer to congregate in dark and remote places that are not always easy to get to. “Bat populations die and no one knows,” says Dr. Boni. “Bats are much more difficult to sample than chickens.”

Dr. Han from the Cary Institute says that in building their prediction algorithm, the research team looked for genetic sequence data for ACE2 receptors in animals. But no database contained all the information scientists need to know. In the case of Dr. Han’s study, the genetic sequence data on the ACE2 receptors of some animals was incomplete, with information from only 142 mammals out of about 6,000. Some of the strongest data involved ray-finned fish, which were not considered critical for predicting future coronavirus pandemics, given what is known about the transmission of SARS-CoV-2.

Therefore, they also extracted information from other databases on the habitats, diets, metabolism and biology of the animals, which they then combined with the sequence and molecular data to provide information on which animals have the ability to become infected with SARS-CoV-2 and transmit it. to others.

Some animals turned out to be highly prone to transmitting SARS-CoV-2, but they are unlikely to encounter humans on a regular basis, such as the scimitar-horned oryx or the addax, says Dr. Han. Those animals went lower. on the list of animals that need closer monitoring. Higher on the list were deer mice and white-footed mice, which often harbor pathogens and thrive living among humans. It turns out that when it comes to making predictions about the animals most likely to be involved in future pandemics, Dr. Han says that “contact with humans is the most important element.”

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