Why dangerous bird flu is spreading faster and farther than first thought in U.S. cattle – CBC.ca
							May 1, 2024
							    Health Second    Opinion  
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        Lauren Pelley, Amina Zafar - CBC News      
    Posted: April 27, 2024  
    This story is part of CBC Health's Second Opinion,    a weeklyanalysis of health and medical science news    emailed to subscribers on Saturday mornings. If you haven't    subscribed yet, you can do that by clicking    here .  
    A dangerous type of bird flu virus discovered     in the lung of a U.S. dairy cow that didn't show    symptoms. Viral particles identified in     processed, pasteurized milk. Genetic sequences    showing     distinct changes in this H5N1 strain that's been    rapidly spreading throughout American cattle.  
    Those were just a handful of the rapid-fire developments this    week as an unprecedented H5N1 outbreak among U.S. dairy cattle    continued to evolve.  
    Scientists now warn this form of avian influenza is likely more    widespread in cows, and was transmitting for longerthan    official reports suggest. And while American officials are    ramping up testing  all in an effort to keep sick cows from    being moved between states  others say we're already several    steps behind the spread of a disease that could pose a major    threat to human health.  
    Michael Worobey, a researcher from B.C. who's now head of the    department of ecology and evolutionary biology at the    University of Arizona, said these cattle infections may have    been "flying under our radar for months," providing ongoing    opportunities for this virus to acquire adaptations that could    lead to a flu pandemic.  
    "I think, in many ways, this is the biggest news story in the    world right now."  
    After the U.S. Department of Agriculture posted more than 230    genetic sequences from the country's growing H5N1 outbreak last    Sunday, Worobey was among the scientists racing to analyze the    complex set of data.  
    The sequences were from cattle  amid anoutbreak    impacting more than two-dozen herds across nine U.S. states     but also several bird species, cats, skunksand raccoons.  
    It's possible that local birds passed the virus to local farms,    in different states, and they're all spreading a genetically    similar lineage, he said. But Worobey believes what's far more    likely is that the cattle outbreak has a single origin point.  
    In an interview with CBC News, he outlined H5N1's evolutionary    tree, with a distinct branch of sequences linked to cattle. All    those sequences share the same mutations, Worobey added.  
    "This is the hallmark of a single jump, that's at the root of    this outbreak," he said.  
    And that jump likely occurred earlier than the     first known cattle infections reported in late    March.  
    A single introduction could have happened as far back as    November or December, with a distinct lineage of H5N1 then    spreading undetected for months, Worobey said. He added missing    details in the initial U.S. data dump  including exact cattle    locations and dates  madeit tough to know for sure.  
    The cattle sequences also contain "at least two distinct    mutations" that are known for increasing the risk of a flu    virus infecting and transmitting in humans, Worobey added.  
    "We just are producing more and more [opportunities] for    evolution to arrive at something that can transmit in humans,    and potentially kill a large proportion of them," he said.  
    What's not yet clear is how, exactly, the virus is spreading    among cattle, though several scientists told CBC News that    possibilities include close contact between cows being    transported between states or contaminated milking equipment.  
    "If the cattle indeed have [infection] in the udders, then    transmission could be through milking equipment," said Michelle    Wille, a senior research fellow with the University of    Melbourne's Centre for Pathogen Genomics andthe    department of microbiology and immunology.  
    "A number of infected states have indicated that [avian flu]    was detected in dairy herds that recently received cattle from    Texas so transport of cattle is likely playing a role in    spread."  
    At this point, it's still unclear how the virus is "sustaining    transmission" in cattle populations, added virologist Angela    Rasmussen, from the University of Saskatchewan's Vaccine and    Infectious Disease Organization.  
    It's also likely the virus is being transmitted even when cows    aren't showing symptoms  which have so far been mild,    including low appetite and reduced milk production  several    scientists agreed.  
    WATCH | Bird flu spreads in U.S.    cows:  
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    This week, officials announced dual discoveries of H5N1 in the    lung of an asymptomatic cow in North Carolina, along with viral    particles in pasteurized milk, suggesting infected cows almost    slipped into the food supply chain.  
        Ohio State University researchers also    saidthey recently did their own independent    sleuthing, collecting 150 commercial milk products from dairy    processing plants across 10 states. The team found fragments of    viral RNA in close to 60 samples  nearly 40 per cent of the    products, all of it available on store shelves.  
    Rasmussen stressed that the discovery of viral RNA in milk    doesn't necessarily mean it can make people sickif    it'sfragments of a virus, not something infectious. Dairy    products also go through     pasteurization, a heating process meant to eliminate    a variety of pathogens.  
        But in a Thursday update, the U.S. Food and Drug    Administration (FDA) said additional testing is still needed    "to determine whether intact pathogen is still present and if    it remains infectious, which would help inform a determination    of whether there is any risk of illness associated with    consuming the product.  
    The FDA added retail milk studies so far have shown no results    that would change its assessment that the commercial milk    supply in the U.S. is safe.  
    What's more concerning, Rasmussen said, is that these    developments suggest the cattle outbreak is "much larger than    originally thought."  
    To better understand the scope of H5N1's spread among cattle,    increased testing of dairy cows is now a key facet of the    American response.  
    The U.S.will require dairy cattle moving between states    for commerce to be tested for bird flu, Secretary of    Agriculture Tom Vilsack told reporters this week. All labs and    states must also report positive tests for any form of    influenza.  
    The concern from both officials and scientists alike stems from    the potential impacts on animal health and the food supply    chain, and the possibility that this virus is inching closer to    a pandemic-level threat to humans as well.While the    reported cattle infections haven't been serious, scientists    warn they could fuel adaptations that could make it easier to    infect more mammals.  
    Since 2022, only two human infections have been reported in the    U.S., with the latest one tied to these recent cattle    outbreaks. Both were mild. But sporadic human cases linked to    contact with infected animals in previous outbreaks have been    happening around the world, with many causing serious symptoms,    severe pneumonia, or even death.  
    Based on available human case data to date, the death rate of    this form of bird flu is     thought to be a staggering 52 per cent, though    scientists say there are likely far more mild cases going    underreported and skewing that data.  
    Even so, with so many cattle being infected and coming into    contact with farm workers every day, the number of human    exposures is going up, Worobey warned. "It's kind of like    buying more and more lottery tickets in the lottery of, 'Can a    new pandemic virus actually evolve?'"  
    Infectious disease physicians in Canada are keeping a close eye    on the places where livestock, wildlife and humans intersect.  
    Officials at the Canadian Food Inspection Agency have not yet    responded to a series of questions fromCBC News, but said    online it has not detected this type of avian influenza in    Canadian cattle, so it's not currently testing raw or    pasteurized milk.  
    "[Highly pathogenic avian influenza] is not a food safety    concern as pasteurization kills harmful bacteria and viruses,"    the agency said on X, formerly Twitter.  
    Dr. Samira Mubareka, a clinician scientist at Sunnybrook    Research Institute and the University of Toronto, is watching    for any signs of the virus becoming more adept at transmitting    between mammals, including humans.  
    "From the virus's perspective, the more transmission there is,    the more opportunities to adapt," Mubareka said. "That is    concerning."  
    Mubareka said any enhanced change in transmission among mammals    would also signal an enhanced ability to transmit among humans,    which is why it's so important to find out whether those in    close contact with cattle or wildlife are at higher risk.  
    She said even if this H5N1 virus doesn't infect more people,    the virus has already hit animal health significantly and could    affect food prices, food security and livelihoods.  
    Rasmussen agreed, and said the impacts could be grim if    human-to-human transmission begins.  
    "It would have a devastating impact on human and animal health,    on the economy, on the food supply," she said. "It would be a    worst case scenario."  
        Lauren Pelley        Senior Health & Medical        Reporter      
      Lauren Pelley covers health and medical science for CBC News,      including the global spread of infectious diseases, Canadian      health policy, pandemic preparedness, and the crucial      intersection between human health and climate change.      Two-time RNAO Media Award winner for in-depth health      reporting in 2020 and 2022. Contact her at:      lauren.pelley@cbc.ca    
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Why dangerous bird flu is spreading faster and farther than first thought in U.S. cattle - CBC.ca