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  • The Strongest Evidence Yet That an Animal Started the Pandemic

    The Strongest Evidence Yet That an Animal Started the Pandemic

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    For three years now, the debate over the origins of the coronavirus pandemic has ping-ponged between two big ideas: that SARS-CoV-2 spilled into human populations directly from a wild-animal source, and that the pathogen leaked from a lab. Through a swirl of data obfuscation by Chinese authorities and politicalization within the United States, and rampant speculation from all corners of the world, many scientists have stood by the notion that this outbreak—like most others—had purely natural roots. But that hypothesis has been missing a key piece of proof: genetic evidence from the Huanan Seafood Wholesale Market in Wuhan, China, showing that the virus had infected creatures for sale there.

    This week, an international team of virologists, genomicists, and evolutionary biologists may have finally found crucial data to help fill that knowledge gap. A new analysis of genetic sequences collected from the market shows that raccoon dogs being illegally sold at the venue could have been carrying and possibly shedding the virus at the end of 2019. It’s some of the strongest support yet, experts told me, that the pandemic began when SARS-CoV-2 hopped from animals into humans, rather than in an accident among scientists experimenting with viruses.

    “This really strengthens the case for a natural origin,” says Seema Lakdawala, a virologist at Emory who wasn’t involved in the research. Angela Rasmussen, a virologist involved in the research, told me, “This is a really strong indication that animals at the market were infected. There’s really no other explanation that makes any sense.”

    The findings won’t fully silence the entrenched voices on either side of the origins debate. But the new analysis may offer some of the clearest and most compelling evidence that the world will ever get in support of an animal origin for the virus that, in just over three years, has killed nearly 7 million people worldwide.

    Read: The lab leak will haunt us forever

    The genetic sequences were pulled out of swabs taken in and near market stalls around the pandemic’s start. They represent the first bits of raw data that researchers outside of China’s academic institutions and their direct collaborators have had access to. Late last week, the data were quietly posted by researchers affiliated with the country’s Center for Disease Control and Prevention, on an open-access genomic database called GISAID. By almost pure happenstance, scientists in Europe, North America, and Australia spotted the sequences, downloaded them, and began an analysis.

    The samples were already known to be positive for the coronavirus, and had been scrutinized before by the same group of Chinese researchers who uploaded the data to GISAID. But that prior analysis, released as a preprint publication in February 2022, asserted that “no animal host of SARS-CoV-2 can be deduced.” Any motes of coronavirus at the market, the study suggested, had most likely been chauffeured in by infected humans, rather than wild creatures for sale.

    The new analysis, led by Kristian Andersen, Edward Holmes, and Michael Worobey—three prominent researchers who have been looking into the virus’s roots—shows that that may not be the case. Within about half a day of downloading the data from GISAID, the trio and their collaborators discovered that several market samples that tested positive for SARS-CoV-2 were also coming back chock-full of animal genetic material—much of which was a match for the common raccoon dog. Because of how the samples were gathered, and because viruses can’t persist by themselves in the environment, the scientists think that their findings could indicate the presence of a coronavirus-infected raccoon dog in the spots where the swabs were taken. Unlike many of the other points of discussion that have been volleyed about in the origins debate, the genetic data are “tangible,” Alex Crits-Christoph, a computational biologist and one of the scientists who worked on the new analysis, told me. “And this is the species that everyone has been talking about.”

    Finding the genetic material of virus and mammal so closely co-mingled—enough to be extracted out of a single swab—isn’t perfect proof, Lakdawala told me. “It’s an important step, I’m not going to diminish that,” she said. Still, the evidence falls short of, say, isolating SARS-CoV-2 from a free-ranging raccoon dog or, even better, uncovering a viral sample swabbed from a mammal for sale at Huanan from the time of the outbreak’s onset. That would be the virological equivalent of catching a culprit red-handed. But “you can never go back in time and capture those animals,” says Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security. And to researchers’ knowledge, “raccoon dogs were not tested at the market and had likely been removed prior to the authorities coming in,” Andersen wrote to me in an email. He underscored that the findings, while an important addition, are still not “direct evidence of infected raccoon dogs at the market.”

    Still, the findings don’t stand alone. “Do I believe there were infected animals at the market? Yes, I do,” Andersen told me. “Does this new data add to that evidence base? Yes.” The new analysis builds on extensive previous research that points to the market as the source of the earliest major outbreak of SARS-CoV-2: Many of the earliest known COVID-19 cases of the pandemic were clustered roughly in the market’s vicinity. And the virus’s genetic material was found in many samples swabbed from carts and animal processing equipment at the venue, as well as parts of nearby infrastructure, such as storehouses, sewage wells, and water drains. Raccoon dogs, creatures commonly bred for sale in China, are also already known to be one of many mammal species that can easily catch and spread the coronavirus. All of this left one main hole in the puzzle to fill: clear-cut evidence that raccoon dogs and the virus were in the exact same spot at the market, close enough that the creatures might have been infected and, possibly, infectious. That’s what the new analysis provides. Think of it as finding the DNA of an investigation’s main suspect at the scene of the crime.

    The findings don’t rule out the possibility that other animals may have been carrying SARS-CoV-2 at Huanan. Raccoon dogs, if they were infected, may not even be the creatures who passed the pathogen on to us. Which means the search for the virus’s many wild hosts will need to plod on. “Do we know the intermediate host was raccoon dogs? No,” Andersen wrote to me, using the term for an animal that can ferry a pathogen between other species. “Is it high up on my list of potential hosts? Yes, but it’s definitely not the only one.”

    On Tuesday, the researchers presented their findings at a hastily scheduled meeting of the World Health Organization’s Scientific Advisory Group for the Origins of Novel Pathogens, which was also attended by several of the Chinese researchers responsible for the original analysis, according to multiple researchers who were not present but were briefed about it before and after by multiple people who were there.

    Shortly after the meeting, the Chinese team’s preprint went into review at a Nature Research journal—suggesting that a new version was being prepared for publication. (I reached out to the WHO for comment and will update the story when I have more information.)

    At this point, it’s still unclear why the sequences were posted to GISAID last week. They also vanished from the database shortly after appearing, without explanation. When I emailed George Gao, the former China CDC director-general and the lead author on the original Chinese analysis, asking for his team’s rationale, I didn’t immediately receive a response. Given what was in the GISAID data, it does seem that raccoon dogs could have been introduced into and clarified the origins narrative far sooner—at least a year ago, and likely more.

    China has, for years, been keen on pushing the narrative that the pandemic didn’t start within its borders. In early 2020, a Chinese official suggested that the novel coronavirus may have emerged from a U.S. Army lab in Maryland. The notion that a dangerous virus sprang out from wet-market mammals echoed the beginnings of the SARS-CoV-1 epidemic two decades ago—and this time, officials immediately shut down the Huanan market, and vehemently pushed back against assertions that live animals being sold illegally in the the country were to blame; a WHO investigation in March 2021 took the same line. “No verified reports of live mammals being sold around 2019 were found,” the report stated. But just three months later, in June 2021, a team of researchers published a study documenting tens of thousands of mammals for sale in wet markets in Wuhan between 2017 and late 2019, including at Huanan. The animals were kept in largely illegal, cramped, and unhygienic settings—conditions conducive to viral transmission—and among them were more than 1,000 raccoon dogs. Holmes himself had been at the market in 2014 and snapped a photo at Stall 29, clearly showing a raccoon dog in a cage; another set of images from the venue, captured by a local in December 2019 and later shared on Weibo, caught the animals on film as well—right around the time that the first recorded SARS-CoV-2 infections in humans occurred.

    And yet, Chinese researchers maintained their stance. As Jon Cohen reported for Science magazine last year, scientists from several of China’s largest academic institutions posted a preprint in September 2021 concluding that a massive nationwide survey of bats—the likeliest original source of the coronavirus before it jumped into an intermediate host, such as raccoon dogs, and then into us—had turned up no relatives of SARS-CoV-2. The implication, the team behind the paper asserted, was that relatives of the coronavirus were “extremely rare” in the region, making it unlikely that the pandemic had started there. The findings directly contradicted others showing that cousins of SARS-CoV-2 were indeed circulating in China’s bats. (Local bats have also been found to harbor viruses related to SARS-CoV-1.)

    The original Chinese analysis of the Huanan market swabs, from February 2022, also stuck with China’s party line on the pandemic. One of the report’s graphs suggested that viral material at the market had been mixed up with genetic material of multiple animal species—a data trail that should have led to further inquiry or conclusions, but which the Chinese researchers appear to have ignored. Their report noted only humans as being linked to SARS-CoV-2, stating that its findings “highly” suggested that any viral material at the market came from people (at least one of whom, presumably, picked it up elsewhere and ferried it into the venue). The Huanan market, the study’s authors wrote, “might have acted as an amplifier” for the epidemic. But “more work involving international coordination” would be needed to suss out the “real origins of SARS-CoV-2.”

    The wording of that report baffled many scientists in Europe, North America, and Australia, several of whom had, almost exactly 24 hours after the release of the China CDC preprint, published early versions of their own studies, concluding that the Huanan market was the pandemic’s probable epicenter—and that SARS-CoV-2 might have made its hop into humans from the venue twice at the end of 2019. Itching to get their hands on China CDC’s raw data, some of the researchers took to regularly trawling GISAID, occasionally at odd hours—the only reason that Florence Débarre, an evolutionary biologist at the French National Centre for Scientific Research, spotted the sequences pinging onto the server late last Thursday night with no warning or fanfare.

    Within hours of downloading the data and starting their own analysis, the researchers found their suspicions confirmed. Several surfaces in and around one stall at the market, including a cart and a defeathering machine, produced virus-positive samples that also contained genetic material from raccoon dogs—in a couple of cases, at higher concentrations than of human genomes. It was Stall 29—the same spot where Holmes had snapped the photo of the raccoon dog, nearly a decade before.

    Slam-dunk evidence for a raccoon-dog host—or another animal—could still emerge. In the hunt for the wild source of MERS, another coronavirus that caused a deadly outbreak in 2012, researchers were eventually able to identify the pathogen in camels, which are thought to have caught their initial infection from bats—and which still harbor the virus today; a similar story has played out for Nipah virus, which hopscotched from bats to pigs to us.

    Read: Bird flu leaves the world with an existential choice

    Proof of that caliber, though, may never turn up for SARS-CoV-2. (Nailing wild origins is rarely simple: Despite a years-long search, the wild host for Ebola still has not been definitively pinpointed.) Which leaves just enough ambiguity to keep debate about the pandemic’s origins running, potentially indefinitely. Skeptics will likely be eager to poke holes in the team’s new findings—pointing out, for instance, that it’s technically possible for genetic material from viruses and animals to end up sloshed together in the environment even if an infection didn’t take place. Maybe an infected human visited the market and inadvertently deposited viral RNA near an animal’s crate.

    But an infected animal, with no third-party contamination, still seems by far the most plausible explanation for the samples’ genetic contents, several experts told me; other scenarios require contortions of logic and, more important, additional proof. Even prior to the reveal of the new data, Gronvall told me, “I think the evidence is actually more sturdy for COVID than it is for many others.” The strength of the data might even, in at least one way, best what’s available for SARS-CoV-1: Although scientists have isolated SARS-CoV-1-like viruses from a wet-market-traded mammal host, the palm civet, those samples were taken months after the outbreak began—and the viral variants found weren’t exactly identical to the ones in human patients. The versions of SARS-CoV-2 tugged out of several Huanan-market samples, meanwhile, are a dead ringer for the ones that sickened humans with COVID early on.

    The debate over SARS-CoV-2’s origins has raged for nearly as long as the pandemic itself—outlasting lockdowns, widespread masking, even the first version of the COVID vaccines. And as long as there is murkiness to cling to, it may never fully resolve. While evidence for an animal spillover has mounted over time, so too have questions about the possibility that the virus escaped from a laboratory. When President Biden asked the U.S. intelligence community to review the matter, four government agencies and the National Intelligence Council pointed to a natural origin, while two others guessed that it was a lab leak. (None of these assessments were made with high confidence; a bill passed in both the House and Senate would, 90 days after it becomes a law, require the Biden administration to declassify underlying intelligence.)

    If this new level of scientific evidence does conclusively tip the origins debate toward the animal route, it will be, in one way, a major letdown. It will mean that SARS-CoV-2 breached our borders because we once again mismanaged our relationship with wildlife—that we failed to prevent this epidemic for the same reason we failed, and could fail again, to prevent so many of the rest.

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    Katherine J. Wu

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  • We Have a Mink Problem

    We Have a Mink Problem

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    Bird flu, at this point, is somewhat of a misnomer. The virus, which primarily infects birds, is circulating uncontrolled around much of the world, devastating not just birds but wide swaths of the animal kingdom. Foxes, bobcats, and pigs have fallen ill. Grizzly bears have gone blind. Sea creatures, including seals and sea lions, have died in great numbers.

    But none of the sickened animals has raised as much concern as mink. In October, a bird-flu outbreak erupted at a Spanish mink farm, killing thousands of the animals before the rest were culled. It later became clear that the virus had spread between the animals, picking up a mutation that helped it thrive in mammals. It was likely the first time that mammal-to-mammal spread drove a huge outbreak of bird flu. Because mink are known to spread certain viruses to humans, the fear was that the disease could jump from mink to people. No humans got sick from the outbreak in Spain, but other infections have spread from mink to humans before: In 2020, COVID outbreaks on Danish mink farms led to new mink-related variants that spread to a small number of humans.

    As mammals ourselves, we have good reason to be concerned. Outbreaks on crowded mink farms are an ideal scenario for bird flu to mutate. If, in doing so, it picks up the ability to spread between humans, it could potentially start another global pandemic. “There are many reasons to be concerned about mink,” Tom Peacock, a flu researcher at Imperial College London, told me. Right now, mink are a problem we can’t afford to ignore.

    For two animals with very different body types, mink and humans have some unusual similarities. Research suggests that we share similar receptors for COVID, bird flu, and human flu, through which these viruses can gain entry into our bodies. The numerous COVID outbreaks on mink farms during the early pandemic, and the bird-flu outbreak in Spain, gravely illustrate this point. It’s “not surprising” that mink can get these respiratory diseases, James Lowe, a veterinary-medicine professor at the University of Illinois at Urbana-Champaign, told me. Mink are closely related to ferrets, which are so well known for their susceptibility to human flu that they’re the go-to model for flu research.

    Mink wouldn’t get sick as often, and wouldn’t be as big an issue for humans, if we didn’t keep farming them for fur in the perfect conditions for outbreaks. Many barns used to raise mink are partially open-air, making it easy for infected wild birds to come in contact with the animals, sharing not only air but potentially food. Mink farms are also notoriously cramped: The Spanish farm, for example, kept tens of thousands of mink in about 30 barns. Viral transmission would be all but guaranteed in those conditions, but the animals are especially vulnerable. Because mink are normally solitary creatures, they face significant stress in packed barns, which may further predispose them to disease, Angela Bosco-Lauth, a biomedical-sciences professor at Colorado State University, told me. And because they’re often inbred so their coats look alike, an entire population may share a similar genetic susceptibility to disease. The frequency of outbreaks among mink, Bosco-Lauth said, “may actually have less to do with the animals and more to do with the fact that we raise them in the same way … we would an intensive cattle farm or chickens.”

    So far, there’s no evidence that mink from the Spanish farm spread bird flu to humans: None of the workers tested positive for the virus, and since then, no other mink farms have reported outbreaks. “We’re just not very susceptible” to bird flu, Lowe said. Our bird-flu receptors are tucked deep in our lungs, but when we’re exposed, most of the virus gets caught in the nose, throat, and other parts of the upper respiratory tract. This is why bird-flu infection is less common in people but is often pneumonia-level severe when it does happen. Indeed, a few humans have gotten sick and died from bird flu in the 27 years that the current strain of bird flu, known as H5N1, has circulated. This month, a girl in Cambodia died from the virus after potentially encountering a sick bird. The more virus circulating in an environment, the higher the chances a person will get infected. “It’s a dose thing,” Lowe said.

    But our susceptibility to bird flu could change. Another mink outbreak would give the virus more opportunities to keep mutating. The worry is that this could create a new variant that’s better at binding to the human flu receptors in our upper respiratory tract, Stephanie Seifert, a professor at Washington State University who studies zoonotic pathogens, told me. If the virus gains the ability to infect the nose and throat, Peacock, at Imperial College London, said, it would be better at spreading. Those mutations “would worry us the most.” Fortunately, the mutations that arose on the Spanish mink farm “were not as bad as many of us worried about,” he added, “but that doesn’t mean that the next time this happens, this will also be the case.”

    Because mink carry the receptors for both bird flu and human flu, they could serve as “mixing vessels” for the viruses to combine, researchers wrote in 2021. (Ferrets, pigs, and humans share this quality too.) Through a process called reassortment, flu viruses can swap segments of their genome, resulting in a kind of Frankenstein pathogen. Although viruses remixed in this way aren’t necessarily more dangerous, they could be, and that’s not a risk worth taking. “The previous three influenza pandemics all arose due to mixing between avian and human influenza viruses,” Peacock said.

    While there are good reasons to be concerned about mink, it is hard to gauge just how concerned we should be—especially given what we still don’t know about this changing virus. After the death of the young girl in Cambodia, the World Health Organization called the global bird flu situation “worrying,” while the CDC maintains that the risk to the public is low. Lowe said “it’s certainly not very risky” that bird flu will spill over into humans, but is worth keeping an eye on. H5N1 bird flu is not new, he added, and it hasn’t affected people en masse yet. But the virus has already changed in ways that make it better at infecting wild birds, and as it spreads in the wild, it may continue to change to better infect mammals, including humans. “We don’t understand enough to make strong predictions of public-health risk,” Jonathan Runstadler, an infectious-diseases professor at Tufts University, told me.

    As bird flu continues to spread among birds and in domestic and wild animal populations, it will only become harder to control. The virus, formally seasonal, is already present year-round in parts of Europe and Asia, and it is poised to do the same in the Americas. Breaking the chain of transmission is vital to preventing another pandemic. An important step is to avoid situations where humans, mink, or any other animal could be infected with both human and bird flu at the same time.

    Since the COVID outbreaks, mink farms have generally beefed up their biosecurity: Farm workers are often required to wear masks and protective gear, such as disposable overalls. To limit the risk to mink—and other susceptible hosts—farms need to reduce their size and density, reduce contact between mink and wild birds, and monitor the virus, Runstadler said. Some nations, including Mexico, Ecuador, have recently embraced bird-flu vaccines for poultry in light of the outbreaks. H5N1 vaccines are also available for humans, though they aren’t readily available.  Still, one of the most obvious options is to shut mink farms down. “We probably should have done that after SARS-CoV-2,” Bosco-Lauth, at Colorado State, said. Doing so is controversial, however, because the global mink industry is valuable, with a huge market in China. Denmark, which produces up to 40 percent of the world’s mink pelts, temporarily banned mink breeding in 2020 after a spate of COVID outbreaks, but the ban expired last month, and farms are returning, albeit in a limited capacity.

    But mink  are far from the only animal that poses a bird-flu risk to humans. “Frankly, with what we’re seeing with other wildlife species, there really aren’t any mammals that I would discount at this point in time,” Bosco-Lauth said. Any mammal species repeatedly infected by the virus is a potential risk, including marine mammals, such as seals. But we should be most concerned about the ones humans frequently come into close contact with, especially animals that are raised in high density, such as pigs, Runstadler said. This doesn’t pose just a human public-health concern, he said, but the potential for “ecological disruption.” Bird flu can be a devastating disease for wildlife, killing animals swiftly and without mercy.

    Whether bird flu makes the jump into humans, it isn’t the last virus that will threaten us—or mink. The era we live in has become known as the “Pandemicene,” as my colleague Ed Yong has called it, one defined by the regular spillover of viruses into humans, caused by our disruption of the normal trajectories of viral movement in nature. Mink may never pass bird flu to us. But that doesn’t mean they won’t be a risk the next time a novel influenza or coronavirus comes around. Doing nothing about mink essentially means choosing luck as a public-health strategy. Sooner or later, it will run out.

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    Yasmin Tayag

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  • Consider Armadillo COVID

    Consider Armadillo COVID

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    This past spring, Amanda Goldberg crouched in the leafy undergrowth of a southwestern Virginia forest and attempted to swab a mouse for COVID. No luck; its nose was too tiny for her tools. “You never think about nostrils until you start having to swab an animal,” Goldberg, a conservation biologist at Virginia Tech University, told me. Larger-nosed creatures that she and her team had trapped, such as raccoons and foxes, had no issue with nose swabs—but for mice, throat samples had to do. The swabs fit reasonably well into their mouths, she said, though they endured a fair bit of munching.

    Goldberg’s throat-swabbing endeavors were part of a study she and her colleagues devised to answer an unexplored question: How common is COVID in wildlife? Of the 333 forest animals her team swabbed around Blacksburg, Virginia, spanning 18 species, one—an opossum—tested positive. This was to be expected, Goldberg said; catching a wild animal that happened to have an active infection right when it was swabbed was like finding Waldo. But the researchers also collected blood samples, and those were more telling about whether the animals had experienced previous bouts with COVID. Analysis by the Molecular Diagnostics Lab and the Fralin Biomedical Research Institute at Virginia Tech revealed antibodies across 24 animals spanning six species, including the opossum, the Eastern gray squirrel, and two types of mice. “Our minds were blown,” Goldberg said. “It was basically every species we sent” to the lab.

    That animals can get COVID is one of the earliest things we learned about the virus. Despite the endless debate over its origins, SARS-CoV-2 most likely jumped from an animal through an intermediate host to humans in Wuhan. Since then, it has since spread back to a range of animals. People have passed it to household pets, such as dogs and cats, and to a Disney movie’s worth of beasts, including lions, hippos, hyenas, tigers, mink, and hamsters. Three years into the pandemic, animals are still falling sick with COVID, just as we are. COVID is likely circulating more widely in animals than we are aware of, Edward Holmes, a biologist at the University of Sydney, told me. “In all my 30-plus years of doing work on this subject, I have never seen a virus that can infect so many animal species,” he said. More than 500 other mammal species are predicted to be highly susceptible to infection.

    Given that most people nowadays aren’t fretting too much about human-to-human spread, it makes sense that animal-to-human spread has largely been forgotten. But even when there are so many other pandemic concerns, animal COVID can’t be ignored. The consequences of sustained animal transmission are exactly the same as they are in people: The more COVID spreads, the more opportunities the virus has to evolve into new variants. What’s most alarming is the chance that one of those variants could spill back into humans. As we’ve known since the pandemic started, SARS-CoV-2 is not a human virus, but one that can infect multiple animals, including humans. As long as animals are still getting COVID, we’re not out of the doghouse either.

    Perhaps part of the reason COVID in animals has been overlooked—apart from the fact that they’re not people—is that most species don’t seem to get very sick. Animals that have gotten infected generally exhibit mild symptoms—typically some coughing and sluggishness, as in pumas and lions. But our research has gone only fur-deep. “We certainly can’t ask them, ‘Are you feeling headaches, or sluggish?’” said Goldberg, who worries about long-term or invisible symptoms going undiagnosed in species. And so animal COVID has lingered unchecked, increasing the chances that it could mean something bad for us.

    The good news is that the overall risk of getting COVID from animals is considered low, according to the CDC. This is partly explained by evolutionary theory, which predicts that most variants that emerge in an animal population will have adapted to become better at infecting the host animal—not us. But some of them, strictly by chance, “could be highly transmissible or virulent in humans,” Holmes said. “It’s an unpredictable process.” His concern is not that animals will start infecting people en masse—your neighbors are far likelier to do that than raccoons—but that in animals, SARS-CoV-2 could form new variants that can spill over into people. Some scientists believe that Omicron emerged this way in mice, though evidence remains scant.

    A troubling sign is that there’s already some evidence that COVID has made its way from humans to animals, where it mutated, and then made its way back into humans. Take white-tailed deer, by now a well-known COVID host. Every fall, hunters take to the golden meadows and reddening forests of southwestern Ontario to shoot the deer, giving researchers an opportunity to test some of the hunted animals for COVID. The species has been infected with the same variants circulating widely in humans—a handful of Staten Island deer caught Omicron last winter, for example—which suggests that people are infecting them. How the deer get infected still isn’t clear: Extended face time with humans, nosing around in trash, or slurping up our wastewater are all possibilities.

    The researchers in Canada found not only that some of the animals tested positive, but also that the variant they carried had never before been seen in humans, indicating that the virus had been spreading and mutating within the population for a long time, Brad Pickering, a research scientist for the Canadian government who studied the deer, told me. In fact, the new variant is among the most evolutionarily divergent ones identified so far. But despite its differences, it appeared to have infected at least one person who had interacted with deer the week before falling ill. “We can’t make a direct link between them,” Pickering said, but the fact that such a highly diverged deer variant was detected in a human is very suggestive of how that person got sick.

    This research adds to the small but growing body of evidence that the COVID we spread to animals could come back to bite us. Fortunately, this particular spillback does not appear to have had serious consequences for humans; rogue deer variants don’t seem to be circulating in southern Canada. But this is not the sole documented instance of animal-to-human spread: People have been infected by mink in the Netherlands, hamsters in Hong Kong, and a cat in Thailand. Other spillbacks have probably occurred and gone unnoticed. So far, no data show that the animal variants that have spread to humans are more dangerous for us. Even if a potential animal variant isn’t the next Omicron, it could still be better at dodging our existing treatments and vaccines, Pickering said.

    But there is also, frankly, a lack of data. Local wildlife-surveillance efforts led by researchers like Goldberg and Pickering are ongoing, but they do not exist in most countries, Holmes said. An international database of known animal infections, maintained by Complexity Science Hub Vienna, is a promising start. An interactive map shows the locations of previously infected animals, including large hairy armadillos (Argentina), manatees (Brazil), and cats (everywhere). At the very least, with animal COVID, “we need to know what species it’s in, in what abundance, and genetically, what those variants look like,” Holmes said. “It’s absolutely critical to know where [the virus] is going.” Without this, there is no way of knowing how often spillback occurs and whether it puts humans at risk. And we can’t tell whether new COVID variants are also putting animals in danger, Goldberg said; a devastating Omicron-like variant could emerge in their populations too.

    The steps we need to take to mitigate the animal-COVID problem—and prevent other zoonotic diseases from jumping into humans—are clear, even if they don’t seem to be happening. Eliminating wet markets where wild animals are sold is an obvious preventive measure, but it has been difficult to implement because the livelihoods and diets of many people, especially in the global South, depend on them. As climate change and land development decimate even more habitats, wildlife will be forced into ever-closer quarters with us, fostering an even more efficient exchange of viruses between species. Unlike mask wearing and other straightforward options for curbing the human spread of COVID, preventing its transmission to, from, and among animals will require major upheavals to the way our societies run, likely far greater than we are willing to commit to.

    Humans tend to act like COVID ends up afflicting us after traveling through a long chain of species. But to think so is like living in the Middle Ages, Holmes said, when the Earth was considered the center of the universe. As we learned then, we are not that important: Humans are but a node in an immense network of species that viruses move through in many directions. Just as animal viruses infect us, human viruses can spread to animals (measles, for example, kills a variety of great apes). There are definitely bigger problems than animal COVID—no one needs to hunker down for fear of sneezing deer—but as long as animals keep getting infected, we can’t overlook what that means for us. Paying attention to animal COVID often starts with a single swab—and a snout to stick it in.

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    Yasmin Tayag

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