Of all the creatures (foxes, bears, eagles, ducks, chickens, and many other birds) affected by this new and deadly H5N1 flu, dairy cows are some of the animals we are closest to. More than 9 million dairy cows live on farms in the United States, where people grind their feces, help give birth to calves, care for the sick, and milk them every day. It is this proximity that gives viruses countless opportunities to encounter humans, and then evolve from viruses that are only for animals to viruses that also cause nuisance to humans.
But while the current spread of H5N1 infections in cattle may be alarming, “I would be more concerned if this happened in pigs,” says the World Health Organization Collaborating Center for Influenza Ecology. Director Richard Webby says: Animals and birds taught me. Like cows, pigs also share a lot of space with us. They also have a terrible track record with influenza.The pig’s respiratory tract playground of evolution Where bird-loving influenza viruses can transform —and converted— to things that like to infect us. For example, the influenza virus that spread from pigs to humans is catalyzed 2009 H1N1 pandemic. If there was a list of animals most at risk of catching avian influenza, “pigs are clearly at the top,” Webby said.
To successfully spread to a new species, the influenza virus must invade the cells of that organism, reproduce within the cells, and reach the next host. The H5N1 virus has accomplished the feat in some animals, but so far “we’re really still dealing with very avian viruses,” said virologist Michelle Ville of the University of Melbourne. said. Scientists believe that for the virus to spread widely among humans, it needs to spread. Several new characteristics; so far, only one such modification has been detected that increased the ability of the virus to replicate inside mammalian cells.
In particular, the virus doesn’t seem to have acquired what Webby thinks is the most important modification, one that helps it efficiently invade human airway cells in the first place. This requires adjusting the ability of H5N1 to adsorb to specific sugars on the cell surface, which effectively act as a lock into the cell interior. But for decades, viruses have favored, and still seem to prefer, versions of the sugar most commonly found in birds’ gastrointestinal tracts. Webby said experts would really start to worry if it started glowing very strongly, which is not what is most commonly seen in the human respiratory tract.
However, the differences between these sugars are structurally very small. Scientists may colloquially refer to some things as bird receptor others human receptormammals can produce avian receptors, vice versa. (For example, humans have avian receptors in their eyes, which probably explains why farm workers seem to have contracted H5N1 from dairy cows. Only developed conjunctivitis.) A suitable animal host could prompt the virus to switch its preference from birds to humans, and pigs fit that requirement.They happened to be at the port. Both receptors in birds and in the human respiratory tractgiving the infectious influenza virus ample opportunity to change.
Just by hanging around inside a pig for a while, H5N1 may increase its ability to enter cells. Or, perhaps even more worryingly, we could encounter influenza that has already evolved to infect humans. Swap bits of the genome With that virus.pig catch our virus everytime. And if one of these pathogens hybridizes with this H5N1, adapts to humans and spreads among people, but still manages to adapt to birds and evade the human immune system, a large-scale epidemic could begin. There is sex.inside Late 1970s, it took just a few years for the H1N1 avian influenza virus to jump from wild waterfowl to European pig populations and begin infecting people in Europe and Asia. Ultimately, the same virus contributed to the birth of his 2009 pandemic swine flu.
Experts said swine influenza surveillance needs to be stepped up at this time. Protections for farm workers who handle animals should also be strengthened. Seema Lakdawala, a virologist at Emory University, told me that she wants milk on farms to be better contained and more quickly heat-treated so that other nearby animals are not exposed to the milk’s raw liquid. Told. shape. (For example, some farm cats I got caught You can become infected with H5N1 by drinking raw milk from a farm. )
For now, concerns about the virus evolving dramatically in pigs remain theoretical. H5N1 has not yet been detected in pigs on the farm. experimental Infection Researchers found that although the virus is capable of infecting and multiplying in pigs, it does not appear to be easily transmitted between pigs. Even if that changes, pigs may not be the ideal place for the many other genetic gymnastics that help this virus adapt to us.
That said, “we don’t fully understand all the mutations and genetic requirements” needed to transform avian viruses, said Louise Moncla, a virologist at the University of Pennsylvania. Viruses sometimes surprise us. For example, the 2009 H1N1 flu caused a pandemic without the genetic changes that would have helped this new H5N1. This means that the fact that H5N1 is not yet widespread among pigs is not completely reassuring, especially when so many cows are sick. now.
Scientists know little about bovine influenza. Although it has been known for some time that cattle can be infected with certain types of influenza, this outbreak marks the first time that influenza A, the group to which H5N1 belongs, has been detected. .Researchers are just beginning to understand the susceptibility of animals to these pathogens, and have recently preprint The research Webby contributed to showed that cows have human-like influenza receptors in several parts of their bodies, including some in birds. This finding suggests that the risk posed by continued infestation in cattle is higher than previously thought. Webby said he’s not panicking yet, but the results mainly show that cow udders, which have been shown to be rich in avian receptors, are ideal nests for H5N1. He said it would help explain why the findings were made. And since cows are likely spreading the virus to each other via milking equipment, essentially being free riders for pathogens, there may be little pressure to change the virus’s MO.
The greater the risk, the easier it is. “The species that I’m most nervous about are the ones that we’re in regular contact with all the time,” Moncla told me. The more cows that get the virus, the more exposure we have, and the more opportunities the virus has to explore and adapt to our airways. Commercial milking is a tedious job; processing machines spray or mist the liquid into the air. Lakdawala imagines that milking an infected cow without protective gear might be “like me blowing 10,000 or 100,000 virus particles into someone’s nose.” Only one of those particles needs to carry the right genetic change for this flu to become human flu.
