New study sparks debate about whether H5N1 virus in cows is adapted to better infect humans – STAT
							July 9, 2024
							    A study published Monday provides new    evidence that the H5N1    virus currently causing an     outbreak of bird flu in U.S. dairy cattle may be adapted to    better infecting humans than other circulating strains of the    virus, a result that is already courting controversy among the    worlds leading flu researchers.  
    Across the globe, different influenza viruses are constantly    circulating in many different kinds of animals. One of the    things that determines what kind of animal a given flu virus    can infect is the type of receptors present on the outside of    tissues that virus comes in contact with. Flu viruses that    typically infect birds have an affinity for latching on to the    particular shape of a receptor commonly found in the guts of    avian species. Human influenza viruses, on the other hand,    prefer the shape of a receptor that lines our upper respiratory    tracts.  
    The new work, published in    Nature, showed that the bovine H5N1 virus could bind to    both receptors.  
    There is an ability to bind to human-type receptors, the    studys lead author, Yoshihiro Kawaoka, told STAT in an    interview. But he cautioned that its too soon to say whether    this ability means the recently emerged bovine branch of the    H5N1 evolutionary tree has increased potential to become a    significant human pathogen. Binding to human-type receptors is    not the only factor that is required for an avian flu virus to    replicate well in humans, said Kawaoka, a leading influenza    virologist at the University of Wisconsin-Madison who has    studied H5N1 for decades.  
    The work on predicted binding offers new evidence for wider    attachment, including to cells lining the human upper    respiratory tract but requires further study to understand the    underlying factors, Ian Brown, the former virology head at the    U.K.s Animal and Plant Health Agency who is now a group leader    at the Pirbright Institute, said in a statement to reporters.    Overall the study findings are not unexpected but this report    provides further science insight to an evolving situation, that    emphasizes the need for strong monitoring and surveillance in    affected or exposed populations, both animals and humans to    track future risk.  
    The result is sure to stoke fears that the H5N1 virus now    circulating in dairy cows has already adapted toward spreading    more efficiently in humans. But complicating this picture is    the fact that other scientists, who have examined these same    molecules that the bovine H5N1 virus uses to infect cells, have    gotten different results.  
    James Paulson, the Cecil H. and Ida M. Green Chair of Chemistry    in the Department of Molecular Medicine at the Scripps Research    Institute, told STAT via email that his lab, in collaboration    with two different research groups, has found no suggestion    that there is increased human type specificity in the H5N1    virus now expanding across U.S. dairy herds.  
    Scott Hensley, a professor of microbiology at the University of    Pennsylvania, whose group is one of the ones working with    Paulson, said in an email that their data suggest the bovine H5    molecule binds poorly to human receptors. It will be important    for us to determine why we are seeing different results, he    said.  
    Kawaoka acknowledged the conflicting data  which are not yet    published  and attributed the disagreement to differences in    experimental design. His own team used a method that involves    coating plastic plates with microscopic forests of synthetic    versions of the different receptor subunits, mixing them with    H5N1 virus, and then measuring how much virus sticks.  
    Its the same method his group used more than a decade ago, to    show that an H5N1 virus his lab had successfully (and controversially) altered    to be transmittable through the air among ferrets had gained    the ability to bind to human-type receptors. So theres an    association of this ferret transmissibility and binding to the    molecule that were using, Kawaoka said.  
    The other groups used not just the sub-units, but the whole    receptor molecule that naturally exists on human cells.  
    Ron Fouchier, a flu virologist at Erasmus Medical Center in the    Netherlands who was not involved in either study, told STAT via    email that the UW-Madison teams method is easy to perform and    interpret, but that there are other available methods that    would result in a clearer picture of binding specificity.  
    The dual receptor binding is interesting, but I do not find    these [results] very unsettling, Fouchier wrote. This is an    interesting initial observation that requires more work. In    particular, hed like to see analyses that probe which    mutations are driving the viruss ability to bind to different    receptors.  
    Other components of the study added to existing evidence that    the H5N1 virus is not very good at infecting mammals through    the respiratory route, but that it has     an affinity for mammary tissue and can transmit efficiently    through contaminated milk.  
    Previously, a team led by Kawaoka had shown that female lab    mice that were fed milk from H5N1-infected cows     became very ill, and that the virus spread throughout their    bodies, including into their mammary tissue, teats, and brains.    In this latest research, the scientists repeated those    experiments with smaller doses of infected milk, confirming    that mice are susceptible to infection from consuming even tiny    amounts  less than a single drop of milk.  
    They also showed for the first time that vertical transmission    is possible; female mice infected with the virus could pass it    on to their pups through their own milk.  
    Another aspect of the study involved intranasally infecting    ferrets, which is commonly used to study     transmission through the air of respiratory viruses. The    experimentally infected animals fell ill with fever and lost    weight, but they did not efficiently spread the virus to other    ferrets housed in cages close by. None of the four exposed    animals developed clinical signs of disease or produced    detectable levels of virus in their nasal passages, although    one did develop some influenza antibodies suggesting    there is some potential of spreading between ferrets via the    respiratory route, but that it does not happen easily.  
    These data are consistent with another study conducted by    researchers at the U.S. Centers for Disease Control and    Prevention in May. It found that an H5N1 virus isolated from        the first human case tied to the dairy cow outbreak  a    farmworker in Texas  spread easily between ferrets sharing the    same cage, but not between cages where the animals shared air    but had no direct contact. In that situation, only one out of    three exposed animals became infected.  
    Its not zero transmission; there is some transmission but    its very limited, Kawaoka said. That should provide some    reassurance that the virus has not yet acquired the ability to    easily spread through the air. But how long that will stay    true, with the virus expanding its footprint  and with it,    opportunities to adapt to human biology  is anybodys guess.  
    Continued surveillance is needed, Kawaoka said. We need to    be concerned.  
    Helen Branswell contributed reporting.  
The rest is here: 
New study sparks debate about whether H5N1 virus in cows is adapted to better infect humans - STAT