Coronaviruses are just one of many viruses that bats carry. Why don’t they get sick?

Bunergy was a bat man. He had the expertise to isolate dangerous pathogens. And he studied how bats interact with viruses such as those that cause the Middle East respiratory syndrome. CoronavirusThat mammals can hide.

Bats are newly infamous for storing deadly viruses. In addition to hosting recurrent ancestral versions of MERS in people, bats also have very close relatives of the virus that caused the severe acute respiratory syndrome outbreak in 2003 and today’s new coronavirus pandemic. I am. These are suspected reservoirs of Ebola virus and natural hosts for Hendra, Nipah and Marburg viruses.

Today, many suspect to be a special function of the bat’s immune system. What stimulates the reaction to the invasion of the virus is very different from what is done in humans.

“It’s very interesting,” says Banerjee. “I wake up thinking about it every day. Why do bats have this immune response that is different from ours and quite different from other mammals?”

Of course, many viruses exist in wildlife, do little harm to their natural hosts, and only cause problems when they jump to humans and other creatures who do not share a long evolutionary history. Ducks and other waterbirds play around while carrying myriad influenza A strains. Pigs are not distracted by hosting hepatitis E.

But bats seem special only if they have a limited number of high-profile viruses that they possess and appear to tolerate. With a few exceptions, including rabies and the less noticeable Tacaribe virus, bats don’t appear sick when they get the virus.

“They can stay healthy and may not show any discernible signs of disease,” says Reina Plowright, an infectious disease ecologist and wildlife veterinarian at Montana State University in Bozeman.

Before the advent of covid-19, scientists summarized some of the features of the bat-virus relationship. The research has new urgency and has interesting potential. With a good understanding of how bats allow viral passengers, Can alleviate human infectious diseases..

“Rather than trying to reinvent the wheel, the result is not sick, and we can learn from what evolution happened in bats that allow survival when infected with a particular virus,” McGill Judith Mundre, a cell immunologist at the university, said. Montreal. “Once we understand that, we can probably apply the same principles to regulate the human immune response.”

When a host is infected with a pathogen, whether a bat or a human, the subsequent interaction is often described as a battle. But there is growing awareness of its importance Disease resistant, “calm and run” approach By the immune system, which limits the damage to the host, but does not worry about removing all traces of the pathogen.

Although many details are missing, there are about 1,300 bat species, and studies usually focus on one or a few, but recent studies have shown that such resistance is associated with many of the viruses bats carry. It suggests that you are catching a way to interact.

First of all, bats mount a speedy yet subtle attack that prevents the virus from being left behind and multiplying. Second, and perhaps more importantly, to dial down immune infantry activity that could otherwise cause a massive inflammatory response that would do more damage than the virus itself.

The main person in the two-part bat immune response is interferon, a small signaling molecule named for its ability to interfere with viral replication. They are generally the first line of defense in mammals. When a cell becomes infected with a virus, it releases various interferons as warning signals, as do some immune system cells.

But one bat seems to work better. First, some species carry so many genes to make interferon. For example, an Egyptian fruit bat (Rousettus aegyptiacusThe natural host for the Marburg virus) has 46 such genes (about 20 in humans).

Second, the black flying fox (Pteropus alecto) It carries several genes that keep interferon activated even in the absence of viral invaders. One of the things these “always on” interferons do is kickstart the production of enzymes that cleave the genetic material of the virus.

Bats also seem to be able to tame the inflammation, which is essential for combating infections, but can be catastrophic.

Uncontrolled inflammation Common themes of serious illness From viruses that have emerged from other species: For example, in people infected with deadly filoviruses such as Ebola, bombardment of inflammatory molecules causes multiple organ damage and septic shock-like syndrome.

And several new influenza strains, including those that caused the deadly 1918 pandemic, are particularly adept at causing a barrage of inflammatory molecules. This long-term blitz-this is the so-called Cytokine storm — It’s also seen in people who have gone wrong with SARS, killing many of the most ill patients in covid-19.

“If you’re infected with something, the immune response is always on this tightrope,” Mundle said. “It’s a balance between making sure the response is vigorous enough-but for example, you’ll end up with lungs filled with fluid and a lot of inflammatory cells.”

Bats skillfully walk this tightrope. They seem to have several ways to avoid dangerous hyperinflammatory reactions.

For example, research on immune cells of bats with large mouse ears (Myotitis) Found Interleukin-10 dial-up production, A protein known to suppress the body’s inflammatory response.

Bats also suppress the activity of large protein clusters called inflammasomes that regulate the release of all types of proinflammatory molecules.

And some bat species no longer make specific proteins that sense damaged genetic material and initiate an inflammatory response. For example, at least 10 species of bats have lost the entire family of such proteins.

In summary, bats “really seem to control inflammation,” says university co-founder Emma Tearing, an evolutionary biologist at the University of Dublin. Major efforts to explore the bat genome..

Researchers are analyzing how bats co-exist with many viruses, as well as asking why creatures exist this way. The answer may seem surprising: tolerance may be related to the fact that bats fly.

Bats are the only mammals capable of sustained power flight (not just gliding) and are a feat that requires metabolic changes. Flight is the main training — Quote suggests Bat’s Metabolic rate Once in the air, it can increase up to 34 times the resting level. This increased metabolism in flight produces harmful chemicals called reactive oxygen species that cause inflammation and are responsible for all kinds of diseases in mammals.

Therefore, scientists postulate that bats can escape the dangerous inflammation caused by viral infections by evolving to reduce flight-related inflammation.

Bat research also has more direct goals. “It’s very important to study bats in nature, to understand where the viruses are and to understand why they are from the population and kill people,” says New Zealand. Massey University Epidemiologist David Hayman Bats and viruses overview With an annual review of virology.

Recent studies suggest that stressful conditions such as food shortages and habitat loss may be major predictors of bat shedding of large amounts of virus. Plowrites have spent years capturing giant bats and sampling blood, urine and feces. Bat virus infection found to be inconsistent Beyond time and space.

Aside from stress, there is a problem with increasing contact itself. “The simple facts of more people, more habitat destruction, means more potential contact, which may simply increase the likelihood of infection,” Hayman says. ..

Trying to eliminate such encounters by eliminating bats is not the answer. “It will be a disaster,” Plowright says. “They offer huge ecosystem services.” Important pollinators of hundreds of plants, They help disperse seeds and many phagocytose insects.

Scientists know that they are just beginning to analyze the relationship between bats and the viruses they carry, and to understand the occasional crossover of catastrophic viral species to species. While the covid-19 pandemic swirls, they Recent end of funding Research on some bats and coronaviruses by the National Institutes of Health.

But they are doing their job. Mr. Banazy, who now belongs to McMaster University in Toronto, is refitting himself into a protective modality. He spent his time growing bat kidney cell petri dishes, growing a garden of viral flasks, and then combining the two to carry out infection experiments.

“I thought graduate school was busy,” he says. “But this is extremely busy.”