Covid-19 is caused by a zoonotic virus, or one that can hop between animals and humans. The precise path it took to people is unclear, and scientists say it may have included a stopover in an intermediary species such as the pangolin, an endangered and highly trafficked mammal. But the virus, SARS-CoV-2, has shown an ability to be passed from humans to animals, including dogs, cats and, most recently, a Malayan tiger at the Bronx Zoo.

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Experts say the chance of the coronavirus hopping from people to North American bats is low. If it did, though, it could further threaten bat species already under pressure from white-nose syndrome, a fungal disease that has been decimating North American bat populations for more than a decade.

And because bats can fly long distances, such a spillover could allow the virus to spread widely among bats and also potentially cause a “spill-back of SARS-CoV-2 from bats back into humans … which would make eradication of SARS-CoV-2 unlikely,” U.S. Fish and Wildlife Service veterinarian Samantha Gibbs wrote in a notice to researchers.

“We know that many mammals are susceptible to infection by a diversity of coronaviruses,” a Fish and Wildlife spokesperson said in a statement. “What is not known is whether the novel coronavirus SARS-CoV-2 has the potential to infect, or cause illness in, North American wildlife, including bats.”

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Thirteen of North America’s 47 bat species are affected by white-nose syndrome, a disease that has killed more than 5.5 million bats since 2006. Most of the species roost in smaller groups, in natural caves and human-made subterranean structures or alone in trees. And most species are insectivorous, with some bats able to mow down their body weight in insects every night. That makes them highly valuable pest-controllers.

Although bats may have been the original host of the new coronavirus, the Fish and Wildlife spokesperson said, there is no evidence the flying mammals are responsible for its spread in the pandemic. Experts stress that bats, left undisturbed in the wild, pose little risk to human health.

Hundreds of coronaviruses have been identified in bats, and coronaviruses also circulate in camels, pigs, cats and birds. But bats’ amped-up immune systems allow them to carry many pathogens without being affected by them.

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Even so, wildlife experts say, the fear for North American bats is that infection with SARS-CoV-2 could cause irreparable harm to fragile populations. Bats already weakened by white-nose syndrome could be more susceptible, said Kevin Olival, an ecologist and vice president for research for the nonprofit environmental health organization EcoHealth Alliance.

Geography and epochal time have separated bat species for long enough that certain types of bat coronaviruses exist only in particular areas of the world. Whether bats here could be infected with a virus that originated across the world is unknown, scientists say.

Researcher Bruce Patterson, a curator of mammals at the Field Museum of Natural History in Chicago, said that horseshoe bats and vesper bats — the most common family of bats in North America — last shared a common ancestor approximately 50 million years ago. “They are about as different as bats get from one another,” he wrote via email.

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The Fish and Wildlife directive to suspend research comes at a problematic time, said Winifred Frick, chief scientist for Bat Conservation International. Late winter and early spring are important seasons for white-nose research, which involves going underground for population counts and pathogen surveillance. In areas where the spread of white-nose syndrome is fairly recent, as is the case in many Western states, these seasonal checkups are crucial to scientists’ ability to assess the progression of the fungal disease.

Last week, biologists and other experts from government agencies, wildlife organizations and research groups met to “quickly assess the risk SARS-CoV-2 may pose to bat populations,” the Fish and Wildlife spokesperson said.

This month, the group will issue updated recommendations on interactions with bats, according to a bulletin published April 1 by the National Wildlife Health Center, part of the U.S. Geological Survey. Although researchers who handle bats typically wear gloves, the bulletin suggests that they consider using heavier-duty masks and coveralls as standard protective gear going forward. The group will also consider protocols for sanitizing and disinfecting gear to reduce the likelihood of human-to-bat viral transmission.

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The center will conduct surveillance in other wild animals and run experiments to test North American bats’ susceptibility to the virus, according the bulletin.

One longer-term question, said Olival, who is participating in the review, is whether the human-carried coronavirus has the potential to bind with receptor cells in bats — a requirement for infection.

“Unfortunately, there will be a risk for a long time to come, and until we get a handle on this, we don’t know where the true risk will come from,” Olival said. “There’s a human health goal down the line. But the intermediate goal is that we don’t infect other species that we come in contact with.”

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Bryan Hamilton, a National Park Service biologist who works with bats and reptiles in Great Basin National Park in eastern Nevada, said that although he appreciates the concern for wildlife and human health, he’s worried about what the delay in research will mean for graduate students who need field data to advance their careers.

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“I have a big bat project that involves a lot of handling of bats, but my projects aren’t super time-sensitive, and missing a year won’t destroy the project,” Hamilton said. “But graduate students need their three years of data, and that could set them back a year or more.”

Olival’s work has been affected by the risk assessment, too. He was scheduled to leave soon to sample bats in the field — to look for coronaviruses.

“Even coronavirus research in bats is coming to a standstill,” he said.