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Scientific American
7 hours ago
- Health
- Scientific American
The Invisible Toll of Bird Flu on Wildlife
25,669 Northern Gannets in Canada. 134 harbor and gray seals along the coast of Maine. 21 California Condors in the western U.S. These are just a tiny fraction of the wild victims of a strain of high pathogenicity avian influenza—what we colloquially call bird flu. The virus, which scientists call H5N1, has spread like wildfire around the globe in recent years, surprising and horrifying scientists at every unpredictable turn. And while most people have fretted about the rising price of eggs, the possibility of viruses in our milk and the risk of a pandemic in humans, countless wild animals are dying almost entirely out of our view—so many that even the limited tallies scientists can make are incomprehensibly large. 'It's easier to treat the numbers as numbers and not think too hard about what they really represent,' says Stephanie Avery-Gomm, a conservation scientist at Environment and Climate Change Canada. 'But if you do take that time to think about it, it's pretty sad.' On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. She lived that reality firsthand in early 2022, soon after the killer strain of bird flu arrived in North America. Northern Gannets, which span the Atlantic and spend most of their year out to sea but breed every spring at six colonies in eastern Canada, started washing up on beaches. Hundreds of their massive white bodies littered the shorelines across the region. Scientists couldn't figure out the source, so they enlisted a helicopter to fly over the largest breeding colony in the region, capturing footage that still makes Avery-Gomm emotional years later. 'It showed absolute devastation,' she says. 'Just so many dead gannets.' Extrapolating from reports of dead birds, she and her colleagues calculated that in six months avian influenza killed 25,669 of Canada's 213,704 tallied breeding Northern Gannets—literally decimating the population. Totaling across all species, her team calculated more than 40,000 wild birds died in the region's monthslong outbreak. Common Murres were the second most heavily affected species, with more than 8,000 dead. 'I don't think anything could have really prepared us for this mass mortality event,' Avery-Gomm says. But the numbers that came later were even harder to bear. Wildlife scientists knew all along they weren't seeing every bird flu casualty on land, much less at sea, where it is more difficult to monitor species. And since avian influenza's devastation began, they haven't seen nearly as many birds at the breeding colonies as previous years. At the largest Common Murre breeding site in her area, Avery-Gomm says tallies are down 9 percent from before the outbreak; Northern Gannet reductions are more like 40 percent of the Canadian population. 'We have a lot fewer gannets in North America than we did in 2021,' Avery-Gomm says quietly. A Totally New Bird Flu 7,000 Snow Geese in Idaho. 2,712 Humboldt Penguins in Chile. 9,600 Sandwich Terns in the Netherlands. Bird flu viruses have been circulating for a couple centuries, popping up in historical records as 'fowl plagues,' says Wendy Puryear, a scientist at Tufts University, who tracks influenza viruses in wildlife. Ducks and geese tend to act as reservoirs for the virus, but domestic poultry are also susceptible. In crowded modern farming operations, poultry are very susceptible. Killer strains of bird flu can wipe out 75 percent or more of a flock in just days, earning them the designation of high-pathogenicity avian influenzas—a classification that's traditionally only reflected fatality in farmed birds, not wild ones. Puryear is among a host of scientists who have been monitoring avian influenza strains in wild birds for decades now, on guard for potential spillovers into poultry and humans. How wildlife weathered the virus has historically been of little concern—wild birds and waterbirds particularly have been carrying flu strains for ages without serious issues. 'There's this huge variation of influenza viruses that circulate out there in nature, in wild birds, and most of those, as far as we're aware, really don't cause much in terms of disease,' Puryear says. 'You don't see die-offs; you don't see an impact on their migration patterns—any sort of thing that we've been able to pick up.' 'We are in uncharted territory.' —Wendy Puryear, scientist, Tufts University But influenza viruses are slippery beasts. Their genetic material is packaged on eight segments of RNA that can easily get swapped around into new arrangements when two different flu viruses infect the same animal. Sometimes this trading results in novel strains that cause more severe illness, spread more easily or survive better in particular species. Scientists trace the heritage of the H5N1 virus that decimated Northern Gannets back to a goose in southern China in 1996. In the three decades since that infection, the virus has hopped around the world, swapping genes with local influenza viruses all along the way. In 2020—while the virus that causes COVID devastated humans worldwide—a group of bird flu viruses that scientists call 2.3.4.4b emerged and spread across swaths of Africa, Asia and Europe. By the late days of 2021, a virus in that killer strain made the leap across the Atlantic Ocean, showing up first in Canada, then the U.S. And this bird flu strain is a whole new bird flu. 'We are in uncharted territory,' Puryear says. 'It's doing things that we had not observed with flu ever in the past, and it doesn't show signs yet of going away.' Within months of bird flu reaching North America, scientists began detecting the virus in wild mammals—terrestrial and marine alike—in both the U.S. and Canada, as wild birds continued to turn up dead. Next, the virus zipped down into South America, then finally breached Antarctic islands and even the mainland in early 2024. And the harsh Antarctic winter didn't clear the disease, which returned with a vengeance during this year's southern summer. 'The entire Antarctic peninsula is covered in outbreaks,' says Marcela Uhart, a wildlife veterinarian at the University of California, Davis. Today at least 406 wild bird species and 51 wild mammals globally have been infected. Australia is the only continent to remain free of the virus. As it has spread, the virus has devastated some species and regions while leaving others unaffected. 'What's emerged is just this really complex picture,' says Brian Millsap, a raptor ecologist at New Mexico State University. 'It flares up in a place kind of out of the blue and then fades away.... Then it pops up somewhere else.' The Hidden Declines 17,400 southern elephant seal pups in Argentina. 2,286 Dalmatian Pelicans in Greece. 24,463 Cape Cormorants in South Africa. Scientists have seen glimpses of the virus's devastation, but the public has been largely unaware of the death unfolding often in the far reaches of the planet. 'This is a massive event, but I think it's pretty much invisible,' Uhart says. She watched as avian influenza blazed through a massive breeding colony of southern elephant seals in Argentina in late 2023. Of the year's pups, 96 percent died—some 17,400 animals. Even a few adults died at the colony, which is an unusual occurrence. And much like Avery-Gomm's team, Uhart and her colleagues have only gotten worse news in the virus's wake. In late 2024 only one third as many adult females arrived at the colony's most densely populated beaches to breed as researchers were used to seeing. 'Instead of seeing long lines of animals, hundreds of animals and listening to their vocalizations,' says Claudio Campagna, a wildlife conservationist, 'it was a silent beach with a few animals and that's it.' The huge reduction in animals at the colony suggests that many adult elephant seals had died of avian influenza at sea, out of scientists' view, says Campagna, who worked with Uhart to model potential recovery scenarios. 'It could take a century before we get back to 2022,' he says. Fortunately, many of the mammals in the U.S. being reported ill or dead with avian influenza are of common species. Infected red foxes, coyotes and raccoons, for instance, are appearing relatively frequently—but not at nearly the scale of the marine mammal mass mortalities. And these are plentiful species, says David Drake, an urban wildlife ecologist at the University of Wisconsin-Madison, so he isn't too concerned. Other species aren't as fortunate. Bald Eagles were one of the early species to suffer from bird flu, and scattered populations continue to fall ill. Between January and June of 2022, 136 dead eagles were confirmed to have avian influenza across 24 states. Rebecca Poulson, a wildlife disease researcher at the University of Georgia, watched the outbreak unfold along the Georgia coast. 'The reports of devastation from the field were just really sobering and daunting,' she says. Bird flu has also hit Bald Eagle populations in the Great Lakes region, where Bill Bowerman, a wildlife ecologist and toxicologist at the University of Maryland, has been studying the animals for 40 years. Here, too, devastation. In Minnesota's Voyageurs National Park—dubbed 'eagle nirvana'—the iconic bird is now much harder to find than just a few years ago. Across the park, researchers found only four chicks last year. Breeding adults are scarce, too. 'Two thirds of the nesting pairs are gone,' Bowerman says. 'It may take three decades for them to recover.' The Limits of Data 5,500 Peruvian Pelicans. 600 Arctic Tern chicks in the U.K. At least one walrus, plausibly six, on the Norwegian Svalbard islands in the Arctic. The tallies of known dead animals and the calculations of missing breeders at colonies are heartbreaking, but there's a third number that's more distressing: the number of invisible deaths. 'A lot of mortality happens in wildlife and no one sees it,' Poulson says. 'These events might be happening in expanses of the country where there just aren't a lot of human eyeballs to see them and characterize them.' Much of what Bowerman knows about Bald Eagles in the Great Lakes, for example, comes from the national park and from five sites he's monitoring as part of a pollution remediation project, watching eagles as a signal for the health of the ecosystem overall. The rest of the nation doesn't have that kind of monitoring in place. And the problem isn't limited to Bald Eagles, Millsap says. Quite the opposite: Bald Eagles and Peregrine Falcons have more monitoring in place than most species he studies, after their near extinction in the 20th century. Other species—Merlins, Cooper's Hawks, Sharp-shinned Hawks—may be equally vulnerable bird flu but have never come as close to extinction. That means they don't have any dedicated surveys at all, so there's no sense of local or even regional declines. 'The bottom line is we're in a place where we don't know, and we may not have a mechanism to really know unless it's hugely catastrophic,' Millsap says. And in order to really see the real effects of avian influenza, scientists needed these programs in place before the outbreak began, says Frank Baldwin, a waterfowl biologist at the Canadian Wildlife Service who studies Snow Geese. Because hunters target these birds, the government tracks them with a program that involves putting ID bands on individuals at their nesting sites across the Arctic. When a hunter kills a banded Snow Goose, they report it to the government, allowing scientists a glimpse of that animal's story. The strategy has shortcomings: in the first few seasons of avian influenza, the team hadn't been able to band many birds as a result of the COVID pandemic, but the hunting data results looked normal. Then this spring, Baldwin began hearing more reports of dead geese, but he won't have any data until hunting season, beginning in the fall. Still, it's better than no data at all. And it's exactly the sort of program that needs to be in place long before any unusual event begins in order to offer helpful insight. 'You can't just build these monitoring programs in a few years, the value of them is in their long-term nature,' Baldwin says. Ecosystems in Flux A polar bear in the North Slope of Alaska. 1,621 Caspian Terns in Washington State. 3,500 northern fur seals in southeast Russia. Understanding the numerical impact on individual populations and species is only the first step of grasping the outbreak's scale. Uhart worries that the devastated southern elephant seal colony in Argentina won't be able to breed as successfully into the future because of how many animals perished and that this can have larger repercussions. Already she's seen changes to the intricate harem system that governs breeding at the colony. 'The whole reproduction system was damaged,' she says. 'There was no social structure anymore.' Large animal die-offs could also throw whole ecosystems in disarray, as deaths unfold within a network in which every species fills particular niches. The Northern Gannets of Canada, for example, act as apex predators for the ocean, Avery-Gomm says, feasting on fish such as mackerel and herring. With fewer gannets to eat them, fish populations may grow, potentially throwing off local balance. 'There's so many stressors that this is just an additional stressor that they really didn't need.' —Johanna Harvey, wildlife disease ecologist, University of Rhode Island And during breeding season, the birds are on land, depositing nutrients they gobbled from the ocean into terrestrial ecosystems through their droppings. Each changed dynamic can send ripples deeper into the ecosystem, often in ways too subtle for scientists to detect. And then there are the carcasses. Every ecosystem has ways to break down dead animals, but death at the scale of avian influenza can overwhelm that system. Indeed, scavengers such as Black Vultures and raccoons in the U.S. have been hit relatively hard by the virus, likely from trying to clean up infected corpses. 'Anything that might be feeding on infected individuals or mortalities, those are kind of sentinel species that give you an indication of how much virus is actually on the landscape that you're not detecting,' says Johanna Harvey, a wildlife disease ecologist at the University of Rhode Island. A different ecological crisis highlights the potential costs of lost scavengers. In India, a veterinarian treatment used in cows decimated local populations of vultures that feasted on bovine carcasses. In much of the nation, vultures nearly disappeared—and now scientists have estimated that human death rates increased four percent in these areas from diseases spread by carcasses that vultures were no longer scavenging. Uhart worries similar issues may develop because of bird flu—particularly in Antarctica, where Brown Skuas that eat seal carcasses, penguin chicks and seabird eggs have been hard hit. Especially in Antarctica's harsh climate, 'if nobody is removing dead carcasses because there are no cleaners, well, the virus might just stay there,' she says. 'All those carcasses will be everywhere.' Fears of Extinctions, Glimmers of Hope It's not clear yet whether avian influenza will drive any species to extinction —but it's a close prospect for some. Overall, one in six of the bird species and fully a quarter of mammals affected by avian influenza are considered near threatened or worse by conservationists, according to research from Sergio Lambertucci, an ecologist at Argentina's national science agency, CONICET, and at the National University of Comahue. Lambertucci also points to a California Condor—one of the rarest birds in the U.S.—was found dead of the virus in March 2023. Officials were so concerned that they took the unprecedented step of vaccinating condors against bird flu, but the damage was already done. Before the immunizations were ready to administer, 21 of the fewer than 600 living birds had died in the outbreak. Uhart, meanwhile, worries particularly about the continuing toll of infections in the 22 species of albatross, which is one of the most threatened groups of birds in the world—and about what could happen if the virus finds its way into the about 1,600 living endangered Hawaiian monk seals. After all, bird flu is not the only threat struggling species face. 'There are so many species that are already in decline,' Harvey says. 'There's so many stressors that this is just an additional stressor that they really didn't need.' It's not all doom, though. Many researchers are finding protective antibodies to avian influenza in wildlife and have found them in some animals. 'There's good evidence from our group and many others that these animals, if they survive, can mount an immune response,' Poulson says of the eagles and many other species as well. No one knows yet how effective that immunity is or how long it can last, but it's a promising sign that some infected animals are surviving and may be better prepared to weather another infection. 'And that's true in lots of different species,' Poulson adds. That's a small glimmer of hope as animals continue to get sick. Among the most recently reported infections of bird flu in U.S. wildlife: a round-tailed ground squirrel and a desert cottontail in Arizona. Red foxes in Colorado, New York and Massachusetts. A pair of Common Eiders in Maine. A Gambel's Quail and a Black-necked Stilt in Arizona. Five Black Vultures in South Carolina.
Scientific American
7 hours ago
- Health
- Scientific American
What Would It Take for Bird Flu to Spread among Humans?
H5N1 avian influenza has long been a concerning virus. Since its discovery in 1996 in waterfowl, bird flu has occasionally caused isolated human cases that have quite often been fatal. But last year H5N1 did something strange: it started infecting cattle. The absolute oddity of this leap may have been somewhat lost in the flood of bad news about H5N1, which by 2024 had already caused mass die-offs of seals and other marine mammals and which was simultaneously devastating chicken farms and causing periodic shortages of eggs. But infectious disease specialists were shocked. 'Flu in cows is not really a thing,' says Jenna Guthmiller, a microbiologist and immunologist at the University of Colorado Anschutz Medical Campus. 'If you would ask anybody that studies flu on their 2024 bingo card if they had, you know, mammary infection of dairy cows on there, no one would have.' Influenza hadn't previously been known to infect cattle, much less cause the kind of infections in their udders that have now begun circulating in milking parlors across the country. The continued circulation of H5N1 in cows is one of the biggest concerns experts have about this flu subtype. Though H5N1 hasn't yet spread human-to-human, people can catch the disease from cattle, mostly through close contact with infected milk. And the more it circulates in an animal that humans regularly interact with, the more chances the flu has to stumble on just the right mutation to leap to people and start adapting into something with pandemic potential. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. 'That's the main thing I worry about in terms of potential human disease,' says Jonathan Runstadler, a professor of infectious disease and global health at the Tufts University Cummings School of Veterinary Medicine. '[It's] increasing that interface and giving the virus the opportunity to establish infection in humans.' Researchers are still trying to catalogue the ways the virus has adapted to spread within cows, seals, cats and hundreds of other mammal species. They're watching for particular mutations and adaptations that might hint that a certain strain of H5N1 could start spreading from person to person. But as the surprise leap into cows shows, flu viruses sometimes do something unexpected and unpredictable. There may be unknown genetic mutations not yet on scientists' watchlists that could change H5N1's behavior overnight. The Leap to Cows The early spring day that H5N1 was first reported to be circulating in dairy cattle was a memorable one for Guthmiller and her colleagues. Guthmiller grew up on a 70-head dairy cattle farm in South Dakota, a biographical tidbit she never expected to overlap with her work as a flu researcher. Flu infecting the udders of cows was such an out-of-left-field idea that when cows started to show signs of sickness (such as poor appetite and discolored milk) in early 2024, veterinarians didn't think to test for influenza at first. It was actually the simultaneous sickening of barn cats, which then tested positive for flu, that led researchers to look for the virus in the cows. Guthmiller and her lab members were already trying to figure out the genetic sequences of the receptor-binding domain (RBD) of the H1N1 seasonal flu that regularly infects humans. The receptor-binding domain is a crucial but delicate fragment of the flu virus that allows it to dock onto and enter specific cells in the body. Mutations within the RBD can enable a virus to lock on to new receptors on new host cell surface. Different species have different types of these receptors, so a genetic switch by the virus can open up new host species for infection. Sometimes, however, a mutation can turn a functional virus into a functionally dead one that's unable to invade any host at all. Guthmiller asked her graduate student Marina Good to pull the genetic sequences for the receptor-binding domain of this bizarre cow strain of H5N1. She feared that the mutated form of RBD in this strain could unlock a cell receptor that predominates in the human respiratory tract. In general, flu viruses like to bind to tiny strings of sugars on cell surfaces called sialic acids. These sialic acids are linked together by different kinds of bonds. Avian flu tends to attach to an alpha-2,3 bond. Alpha-2,3 receptors are bountiful in the gastrointestinal tracts of waterfowl and the upper respiratory tracts of chickens. Humans have alpha-2,3 receptors, too, but mostly in the conjunctiva, or lining of the eye, and deep in our lungs. Our upper respiratory tract is largely filled with alpha-2,6, which is the preferred target of the seasonal influenzas that typically circulate in humans. The fact that humans carry alpha-2,3 receptors in the eyes and lower respiratory tract means that we can catch H5N1; currently this appears as mild pink eye or occasionally as a profoundly serious viral pneumonia. Even so, the virus doesn't easily infect the lining of our nose and throat. If it did, humans likely would have spread the disease to one another rapidly via coughing, sneezing and simply breathing. Less than a month after the first public report of H5N1 in a dairy cow in March 2024, Good, Guthmiller and their colleagues discovered a bit of good news that they posted on the preprint site bioRxiv: The flu hadn't made this crucial shift, meaning the circulating strain still preferred alpha-2,3 receptors. (These findings have been replicated multiple times since then, suggesting this is still the case.) What the virus had done, however, was become less choosy about the alpha-2,3-containing sugars it could bind with, Guthmiller says, likely helping enable the sudden spread within cows and other mammals. In some ways, labeling influenza types 'avian' or 'mammalian' can be a little misleading, says Daniel Perez, a professor of poultry medicine at the University of Georgia who studies how viruses leap from animals to humans. Perez and his team have been studying a modified form of H5N1 that is less deadly to animals, and they're finding that the virus's big evolutionary shift has been to replicate more easily in wild bird airways, not just in their gastrointestinal tracts. 'The changes that we're actually seeing in the virus are not necessarily mammalian-adapted mutations,' Perez says. 'What we are seeing is more of these respiratory-adapted mutations that occasionally do help it to replicate better in mammals.' The shift to mammals might have been incidental at first. But now mutations are accumulating in the cattle version of the virus. For instance, they found a mutation in the amino acids at a position in the virus strain's genome called 631, a spot where changes are known to help a virus better interact with mammalian proteins inside the cell. These proteins are involved in the translation of genetic instructions to cellular activity, including the replication of genes that the virus needs to reproduce. 'What we're starting to see are sprinklings of more of these mammalian adaptions happening in the background of this cattle strain,' says Seema Lakdawala, an associate professor of immunology and microbiology at Emory University. As this mammalian spread continues, Lakdawala and other infectious disease researchers worry about further mutations that would help this flu spread even more easily between mammals. This might happen in a slow and stepwise fashion, leading to more animal-human spillovers, followed by household transmission between close contacts and finally to community spread, Lakdawala says. Or it might be quick: another worry is reassortment, the ability of a flu virus to snag genetic material from another flu virus more adept at infecting people. A person who happened to be infected with both avian flu and seasonal flu could be ground zero for this kind of change. 'If this virus continues to circulate in cows and continues to have these sporadic spillover events, eventually it's going to gain segments through reassortment with either a human seasonal strain or a pig strain or another bird strain,' Lakdawala says. If that happens, a pandemic could take off overnight. Flu Red Flags When people are exposed to a high enough viral load of H5N1, they can become infected. There have been 70 known human cases in the U.S., including one death. But to establish itself in a human host, H5N1 would need to do three things, says Richard Webby, the director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds who studies host-microbe interactions at St. Jude Children's Research Hospital. One is to better attach to the receptors found in the human upper respiratory tract, those alpha-2,6 receptors that the virus has not yet unlocked. Fortunately, that seems to be a difficult evolutionary trick for the virus to pull off, Webby says. Perhaps multiple simultaneous evolutionary changes would be needed to make the switch successfully, or maybe receptor binding is so important to a virus's survival, that this part of its genome doesn't mutate so quickly. Whatever the reason, Webby says, 'we haven't really seen any movement there' since H5N1 was discovered. The second change the virus must make is to adapt itself to better interact with the proteins inside human cells. The virus needs these proteins to hijack host cells and replicate, and these proteins in birds and mammals are quite different from each other. There are some changes that researchers suspect would create a strain of H5N1 that is more suited to infecting humans, Webby says. A variant gene sequence in a part of the virus called the PB2-627 domain is known to enable H5N1 to better interact with the human protein ANP32A and more effectively replicate itself. 'It's a change the virus can make pretty easily when it does start to replicate in a mammal system, unlike the receptor change,' Webby says. Finally, an adapted avian flu would need to evade our innate immune system, the body's nonspecific defenses against new invaders. Human influenzas, for example, are adept at evading human antiviral proteins called Mx GTPases, while H5N1 is not. There are other considerations as well, including how long the virus can survive outside the body, which determines how easily it can transmit. The cattle strain of H5N1 is very stable in milk, Lakdawala and her team have found. For a virus to transmit between people, though, it needs to be stable in human mucus or saliva. Seasonal influenzas that infect humans are expelled into the world in tiny globules of spit or snot, and those secretions protect the virus as it travels between hosts, Lakdawala says. 'Novel viruses that come in may not have that same kind of protection,' she says. On the other hand, if dairy workers continue to catch H5N1 pink eye from milking cows, there is a risk of further adaptation—in all of these ways. Being able to recognize alpha-2,3 alone seems sufficient for the virus to keep spreading in cows, Guthmiller says, so there doesn't seem to be much evolutionary pressure for the virus to recognize alpha-2,6 receptors in the cow mammary glands, Guthmiller says. But the human nose, connected to the eye lining by the tear ducts, could be fertile ground for H5N1 if it could unlock those ample receptors. Each time the virus spreads from a cow to a person, it gets another shot at this evolutionary opportunity. The virus may or may not take it. It may or may not be able to. One complication to this story, Guthmiller says, is that though the nose is probably the first place in the body that the immune system encounters most viruses, researchers know little about the immune response in the nasal tissue. It's a labyrinth of folded mucosa, and unlike blood, it's not easy to get samples of the actual tissue from a person who is sick or recovered. Guthmiller's lab is now studying internal nose samples from people who have had this tissue surgically removed for unrelated medical reasons. They're mapping the cell types found in the layers of tissue, trying to understand how the nose responds to new incursions by unfamiliar viral visitors. The Future of Flu The CDC ended its emergency response to avian flu in early July, citing a decline in animal cases and the absence of human cases since February 2025. Avian flu is somewhat seasonal, with peaks in fall and spring as wild birds migrate. But evolution happens over longer time scales. The 2009 H1N1 pandemic, known as the 'swine flu' pandemic, was caused by a new H1N1 flu strain that had emerged from a mix of several pig flus, a human flu and an avian flu. Oddly, people older than age 60 had some preexisting immunity to this new Frankenstein's monster of a virus, which turned out to be because it shared similarity with the descendants of the devastating 1918 pandemic flu. These long-ago flu lineages had been in circulation when people aged 60-plus in 2009 were kids but had been replaced by H2N2 viruses in 1957. Pig versions had persisted, however, gradually evolving and swapping bits of genes with avian and human flus. Before the 2009 virus had emerged, a handful of farm workers had been infected with these 'triple-reassorted' viruses, but these infections didn't go on to infect others. Then, 'all of a sudden, the North American pig lineage grabbed two segments from the Eurasian pig lineages, probably somewhere in [Mexico], and that virus started to spill over,' Lakdawala says. A new human pandemic, which may have killed around half a million people worldwide, was born. Fortunately, there are already approved human vaccines for H5N1, Perez says. These are based on older strains, but the vaccines would probably still protect against severe disease should the virus start spreading human-to-human. Preexisting vaccine know-how and newer technologies such as those used to create mRNA vaccines would also allow for the quick development of updated vaccines, he says. Whether H5N1 causes the next flu pandemic, it's safe to say one will come. There have been four flu pandemics since 1918, and today's high-density agricultural practices provide prime hunting ground for viruses. On poultry farms, nearly 175 million birds have been affected since 2022, according to the U.S. Department of Agriculture. Egg-laying operations have been dense for decades, but similar practices are spreading to other types of animal husbandry. Small farms with a few dozen cows, like the one Guthmiller grew up on, were once common. Now farms with at least 1,000 cows comprise more than 55 percent of the dairy herds in the U.S., according to the USDA. This density, along with the practice of moving cows between herds, means that viral spillovers that might have once died out on a small farm in South Dakota can now spread far and wide. In that sense, rather than a revolutionary understanding of influenza, Perez says, the best course of action might be a rethinking of agricultural practices. Humans are increasing the size of farms without increasing farm hygiene, which sets the stage for the emergence of new pathogens. 'Yes, we can keep making better vaccines faster,' he says. But an ounce of prevention is worth a pound of cure. 'It would be much easier if we created the conditions of raising animals in a way that actually prevents emergence of disease instead of promoting them,' Perez says. 'The best vaccine is the one we don't have to use.'
Scientific American
7 hours ago
- Health
- Scientific American
Where Did Bird Flu Go?
For months, bird flu was seemingly everywhere in the U.S.: news headlines reported the highly pathogenic H5N1 avian influenza virus was rapidly sweeping through hundreds of herds of dairy cattle and leading to massive culls of poultry flocks, concerning infections in humans and grocery store aisles where nary an egg could be found. But nearly as quickly as bird flu took hold in daily conversations, it disappeared from them and most people's thoughts—making it easy for the public to think avian influenza's threat had waned. Far from it, experts say. 'The flu is still there, and we just don't know enough about it,' says Angela Rasmussen, a virologist at the University of Saskatchewan. What made the virus apparently fade away—and what does that mean for the future of bird flu? On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. One scenario experts have definitively ruled out is that the currently circulating bird flu virus—a member of a subtype of influenza called H5N1 for the proteins on its surface—is simply vanishing on its own, says Jennifer Nuzzo, an epidemiologist at Brown University. 'There has been this wishful thinking that it's just going to wipe through and be gone, and we've just not seen that, and that's just not how flu viruses work,' Nuzzo says. 'This isn't going away.' Experts are still monitoring for H5N1 avian influenza in a variety of animals: wild birds, commercial poultry animals, wild mammals, dairy cattle and humans—and finding it, albeit at lower rates. But the virus is tricky, behaving somewhat differently in each host. Here's what we know about the current state of the virus. The most reliable data on bird flu prevalence come from poultry operations. That's because the virus is so devastating in chickens and turkeys that farmers must cull flocks as soon as they detect an infection to reduce spread. They are also able to report outbreaks to the federal government to receive partial compensation. There's no way to ignore a sick flock or any incentive to hide one. And right now poultry tolls to avian influenza are relatively low. Farmers reported just three million poultry birds killed by the virus or culled to stop it in March and April combined compared with 23 million and 12 million in January and February, respectively. May saw more than five million birds dead after the virus infiltrated several massive egg-laying facilities in Maricopa County, Arizona. But June rates fell far below one million birds, and July cases to date remain very low, with just one commercial facility affected so far. These lower rates of bird flu aren't particularly surprising, given the virus's past behavior in poultry to date, says Mike Persia, a poultry specialist at Virginia Tech. 'We generally see a reduction in infections over the summer,' he says. Since the current outbreak began in early 2022, U.S. Department of Agriculture data show that, each year, the monthly count of affected poultry birds has tended to dip to under five million in June, July and August. Two factors seem to contribute to the apparent seasonal trend, Persia says. The virus appears to falter in higher ambient temperatures, and the migratory wild birds that typically introduce the virus into poultry flocks aren't traveling as widely now that breeding season is in full swing. But the outbreak's history tells a cautionary tale: each autumn, the number of affected poultry birds rises again—so it would be premature to assume H5N1 is done with us. 'I'm optimistic that maybe this was the last of it, and it goes away forever. I wouldn't take the lull as proof of that, though,' says Jada Thompson, an agricultural economist at the University of Arkansas. 'We need to maintain vigilance.' Evaluating the outbreak in U.S. dairy cattle has been more difficult. Cows that are sick with bird flu eat less and produce thick and discolored milk. But the infection isn't nearly as fatal in cattle as it is in poultry, making the virus harder to see in the former. And there's no recompense for lost milk to encourage farmers to report being hit. In addition, the virus's jump into dairy cattle in late 2023 was wildly unexpected and not publicly confirmed until March 2024, giving dairy farmers and virologists little time to understand bird flu's tendencies in the species. Last year cases continued throughout the summer, particularly in the hard-hit state of Colorado. Spread proved to be difficult to contain, in part because of the movement of animals required by the dairy industry. And although the virus can be monitored through milk, officials only began mandating such testing last December, after a full year of viral circulation. This year reported infections have trailed off, with only two herds confirmed to have the virus in all of June. But it's unclear how to interpret the trend—dairy farmers, too, are left poised between caution and optimism. Throughout the outbreak, bird flu risk to humans has been low, although dairy and poultry workers with exposure to infected animals have been more vulnerable. The first detected human infection in 2024 came shortly after confirmation that dairy cattle had become sick with H5N1. Additional human cases came in flurries throughout the intervening months, totaling 70 confirmed infections, including one death, by mid-February. Since then, infection tallies at the Centers for Disease Control and Prevention have stalled. Experts doubt that's a good thing. 'I can't rule out that part of why we're not finding infections is: we're just simply not looking for them,' Nuzzo says. Throughout the outbreak, the CDC has kept a running tally of the testing it is conducting, and those numbers paint a clear picture. As of July 1, the CDC noted that more than 880 people had been subject to targeted testing after exposure to infected animals. On March 1 that number had been more than 840; in contrast, the February 1 number was more than 660. The CDC tested more than four times as many people in February as in March, April, May and June combined. Another way experts have kept tabs on bird flu has been through existing national flu surveillance—but because normal flu infections are in a seasonal lull, so are tests through that network. The result is a lot of question marks. 'We are in sort of a perfect storm of no testing,' Rasmussen says. Even wastewater monitoring, which has proven helpful in understanding levels of the virus that causes COVID as testing rates have fallen, is of limited help. The approach looks for the presence of viruses in community water processing plants, but H5N1 is spread so broadly across species that it is nearly impossible to use these detections to definitively trace sources. 'You don't know how it got there,' Nuzzo says of the virus in wastewater. 'You don't know if people are infected; you don't know if [the virus is present] because birds were hanging out in the wastewater.' In some cases, spikes in wastewater levels of H5N1 have even been linked to farmers dumping milk from their infected cows. Nuzzo suspects that there have certainly been more human cases of avian influenza than the 70 confirmed to date but that the virus is not spreading widely. 'I don't think there's some huge iceberg of infections that we're missing,' Nuzzo says. Nuzzo and Rasmussen find that cold comfort, however. Instead they emphasize how vital it is to have as much intel as possible about what H5N1 is doing. Choosing not to seek out evidence of the virus's behavior means passing up on the opportunity to catch any early signs of a pandemic in the making. 'No news in my world is not good news,' Rasmussen says. 'We're just not collecting any data, and those are two very, very different things.' The U.S.'s current approach is simply further shrouding a situation that is already difficult to parse—given the complexity of a multispecies outbreak and the unpredictable nature of rapidly changing influenza viruses. 'This is the kind of thing that could become a pandemic tomorrow, [or] it could never become a pandemic. And I don't know which one is going to happen,' Rasmussen says. 'This is a huge risk, but it's also a risk that may never come to pass,' she says. 'But we won't know if we just stop looking for it.'
Time of India
a day ago
- Health
- Time of India
H5N1 avian influenza detected in Odisha's Puri dist; govt culls over 6,700 birds
Bhubaneswar: A bird flu outbreak has been confirmed in a poultry farm in Odisha's Puri district, prompting the state government to launch emergency containment measures, including mass culling of over 6,700 birds, a senior official said on Sunday. The state government resorted to mass culling of the birds after the National Institute of High Security Animal Diseases (NIHSAD), Bhopal, confirmed that samples collected from Bada Ankula village in Delanga block of the district tested positive for the H5N1 avian influenza virus, he added. Over 6,700 birds were culled on Saturday and Sunday following standard operating procedure (SOP) lay down by the Centre, he said. Sarat Kumar Behera, chief district veterinary officer (CDVO), Puri, informed that five rapid response teams (RRTs) along with health teams have been deployed in the area where bird flu cases were detected. "We have completely restricted the movement of live birds in and out of the infected zone," he said. After completing culling within a 1-km radius of the village, samples from another five villages have been collected to test for the virus, Behera said. Sources said the village had witnessed unusual poultry deaths over the past week, but the outbreak was officially confirmed only after villagers raised concerns and officials collected samples on July 9. Meanwhile, Fisheries and Animal Resources Development Minister Gokulananda Mallik visited the bird flu infected area to take stock of containment measures taken to prevent further spread of the virus.
Hans India
a day ago
- Health
- Hans India
Bird flu detected in Puri dist
Bhubaneswar: A bird flu outbreak has been confirmed in a poultry farm in Puri district, prompting the State government to launch emergency containment measures, including mass culling of over 6,700 birds, a senior official said on Sunday. The State government resorted to mass culling of the birds after the National Institute of High Security Animal Diseases (NIHSAD), Bhopal, confirmed that samples collected from Bada Ankula village in Delanga block of the district tested positive for the H5N1 avian influenza virus, he added. Over 6,700 birds were culled on Saturday and Sunday following standard operating procedure (SOP) laid down by the Centre, he Kumar Behera, Chief District Veterinary Officer (CDVO), Puri, said five rapid response teams (RRTs) along with health teams have been deployed in the area where bird flu cases were detected. 'We have completely restricted the movement of live birds in and out of the infected zone,' he said. After completing culling within a 1-km radius of the village, samples from another five villages have been collected to test for the virus, Behera said. Sources said the village had witnessed unusual poultry deaths over the past week, but the outbreak was officially confirmed only after villagers raised concerns and officials collected samples on July 9. Meanwhile, Fisheries and Animal Resources Development Minister Gokulananda Mallik visited the bird flu infected area to take stock of containment measures to prevent further spread of the virus.
