This month has brought some of the most worrying bird flu news yet: Six people working on a Colorado poultry farm have tested positive for the virus, the largest confirmed human infection to date in the U.S. The number of cases in the country has reached 11 since 2022, but is almost certainly a gross undercount given the lack of regular testing.
Since the current strain of bird flu, known as “highly pathogenic avian influenza H5N1,” began spreading around the world in 2010, Late 2021Influenza expert Richard Webby of St. Jude Children’s Research Hospital in Memphis said the virus has become something of a “super virus” spreading among animals. Wild birds have been devastated, as have poultry farms. The virus has been detected in more than 100 million birds in 48 states. H5N1 has been around for more than 25 years but has only recently begun to periodically infect mammals, infecting cats, sea lions and bears. In March, the virus was detected in Newfoundland, Australia. A first for American cattle Since then, it has already spread to 163 herds in 13 states.
That’s worrying enough, even without any reports of human infections. Everyone who’s tested positive in the U.S. has worked closely with livestock, and with each new case, the possibility of a human pandemic becomes more real. “That’s definitely a worst-case scenario,” Webby says. It’s possible, but not impossible. For now, it looks likely the virus will continue on its current trajectory of circulating among wild birds, wreaking havoc on chicken farms, and spreading to cattle herds. The outcome would be less dire than a pandemic, but it’s still not something to look forward to.
Despite the recent spate of farm worker infections, the threat of avian flu to humans is currently considered low, and researchers are keeping an eye on two warning signs. The bigger one is the virus’ ability to spread. while All of the people who have tested positive in the United States were infected through contact with sick cattle or poultry and do not appear to have transmitted the virus to others. Generally mildSeveral people have developed severe cases, including respiratory problems. Conjunctivitis, or pink eye(No one has died from this H5N1 variant in the United States or anywhere in the world.) “At this time there is no evidence that this virus can be transmitted from person to person and therefore does not pose a threat to public health,” Jenna Guthmiller, an immunologist at the University of Colorado Anschutz School of Medicine, told me.
The second warning sign is that the virus itself is changing. So far, H5N1 has had little ability to enter and replicate in human cells, which allows the virus to spread between humans. But this may be changing. Laboratory ResearchVirus particles from infected cows showed signs of being able to bind to human receptors in the upper respiratory tract.
The current H5N1 strain has already mutated and is infecting mammals, and a small genetic change could allow the virus to spread more efficiently to humans, or even worse, between humans. Webby said, “We’re at the highest risk from this virus” since another strain of H5N1 caused a number of deadly human infections in East and Southeast Asia in the early 2000s. That’s not necessarily because the virus itself is more infectious, but because it’s spread to so many different animals, especially mammals, it has more opportunities than ever before to find a way to replicate in humans. But again, despite all this transmissibility — despite the chances the virus has to mutate into something that can certainly make humans sick — it hasn’t done so yet. David Topham, an influenza expert at the University of Rochester Medical Center, said it “absolutely” could become the norm going forward.
The current situation remains quite worrying, with new cases of avian flu continuing to appear in flocks across the country. May not be eradicated It is transmitted from cattle. Webby says the “most likely” scenario is that the virus becomes endemic in birds and dairy cows, where it’s always there and periodically causes infections. Currently, poultry infections tend to coincide with wild bird movements, but if cattle are constantly infected, chicken infections could become more frequent as well.
Endemic diseases have no benefit to humans. Their impact will be reduced, but not eliminated. Farmworkers may still get sick periodically, Guthmiller said. The costs of periodic animal epidemics would be prohibitive. The USDA has already Over $2 billion Dealing with the sudden increase in infections in poultry and livestock, including compensating farmers for animals killed and eggs discarded to contain the spread of infection.
“If the virus continues to periodically infect cows, it has more opportunities to mutate in a way that makes it more susceptible to infecting humans. In infected cows, the virus particles are primarily found in the udder, and the virus is thought to spread between cows through contaminated milking equipment.” the study A paper published last week, which has not yet been peer-reviewed, suggested that cows could become infected with aerosolized virus, if they could spread it through their mouths. Exhalation and sneezingYou can get infected just by breathing the same air.
H5N1 is restless, and will keep trying to infect new hosts. If given enough opportunity to mutate, the virus will. “It’s like buying a lottery ticket,” Topham says. “We’re giving this virus a lot of tickets.” H5N1 can also mix with influenza viruses from different animals. If cows, chickens and other animals, such as pigs that are not affected by the current epidemic, each have different influenza viruses on the same farm, “that becomes a mixing vessel,” Topham says. H1N1 virus For example, the virus that caused the 2009 swine flu epidemic was a mix of swine, human, and avian influenza viruses.
There’s another future, which is the best-case scenario but unfortunately the least likely: the virus “may just disappear,” Webby says. This depends in part on eradicating it from cattle, which Webby believes could be done with human intervention and herd immunity. But eradicating the virus from birds, the main animals that infect and spread avian flu, is beyond humans’ control. H5N1 is particularly deadly to birds, with mortality rates of Up to 100 percent While that’s true for some species, if enough of them die off somehow, they could well disappear, Guthmiller said. As Webby put it, “dumb luck” might still prevail.
But avian influenza viruses that infect mammals are not something that should be left to chance. As far as we know, only 11 farm workers have been infected, which is lucky. There are tools available to limit the spread of avian influenza, but they are not being used or are not being used properly. Personal protective equipment can help if worn correctly, but doing so is impractical if you have to wear respirators and Tyvek suits. Temperatures reach 104 degrees FahrenheitUnlike many other countries, the United States doesn’t vaccinate chickens against H5N1, in part because it’s expensive. And because of the cost, only 60 farmworkers have been tested for avian flu, meaning they can’t get a full picture of the virus’s spread. “It would be much more expensive to deal with a new pandemic than it would be to vaccinate farms,” Topham said.
The American response has been painfully shortsighted, and the country is paying the price. If avian flu had been contained sooner, it might never have made its way into cattle, or mutated in a way that brought it so close to human-to-human transmission. At this point, there are no good options for the future of avian flu; there are only bad options, dire options, and options that rely solely on luck.
