How worried you should be about H5N1, the bird flu virus spreading on dairy farms in the United States, depends on who you are.
The Centers for Disease Control and Prevention has described the current H5N1 risk to the general public as low. The risk that the virus poses is tempered by the fact that it doesn’t spread easily among people — yet.
Right now public health experts have the difficult task of urging authorities who can do something about H5N1 to take action while maintaining public trust. Americans have just been through a pandemic that resulted in over one million U.S. lives lost. They may feel weary of more bad news or fear-based messaging. It is not easy but is important to communicate that the threat level for most people is low but that if nothing is done, it could become quite high.
Experts need to be clear that currently the levers of action are squarely in the hands of government leaders and agricultural interests, not in the hands of the general public. But public attention is crucial to ensuring that authorities find the will to act.
No one knows whether H5N1, if left unchecked, will become the deadly pandemic that public health experts like me worry it could. Many of us have been watching H5N1 with alarm for more than 20 years.
As an epidemiologist, I join those who are concerned that as H5N1 continues to infect animals and people exposed to them, it could become a greater threat. The virus could mutate to gain the ability to infect people more easily. Because we don’t have immunity to this virus, a version that becomes highly contagious would probably cause a new pandemic. Influenza viruses change more rapidly than others and have created four pandemics since the start of the 20th century.
H5N1 shouldn’t have to start a pandemic to be considered a public threat. Among the nearly 900 people known to have contracted the virus worldwide since 2003, about half have died. This means that H5N1 is typically more deadly than the viruses that cause seasonal flu and Covid-19.
The small number of human H5N1 infections that have been reported so far in the United States have not been deadly, but that does not mean future infections will be similarly mild. In a recent study, ferrets — which are considered proxies for how influenza viruses affect humans — were able to spread the virus and died from it. This warns us that the virus retains the potential to be quite dangerous.
Nearly all the people known to have been infected by H5N1 have had contact with infected animals. As the virus spreads, it has shown that it’s capable of infecting more and more species of animals, which could increase the risk that humans will come in contact with it.
Agricultural workers who work closely with animals like chickens and cows are the most at risk for infection. Less is known about the threat to agricultural workers who don’t work closely with cows and chickens. Or people who may come into contact with infected animals in other ways, like veterinarians and people who work at zoos or county fairs. The virus has been found at a slaughterhouse and in a range of other animals on farms, including goats, alpacas and cats.
Milk drinkers and meat eaters probably have little to worry about if they follow recommendations. Tests conducted by the U.S. Department of Agriculture and the Food and Drug Administration have so far confirmed that pasteurized milk and beef cooked to at least medium is unlikely to make anyone sick. (Though a recent experiment showed that milk may retain infectious virus after pasteurization if it is contaminated with high levels of H5N1, it seems unlikely that this will occur with pasteurized milk produced under real-world conditions.)
It’s riskier to consume raw milk or undercooked meat, both of which may carry infectious H5N1 virus and have caused outbreaks of other pathogens. Though we don’t yet know of anyone who got H5N1 from consuming milk or meat in the United States, cats that drank raw milk on H5N1-infected dairy farms have died.
Even if the food supply is largely safe, H5N1 threatens our economy. The virus is lethal to birds and has caused hundreds of millions of dollars in losses to the poultry industry and left consumers with skyrocketing egg prices last year. The response to H5N1 and other avian flu viruses on poultry farms has prompted swift containment actions that continue. The U.S.D.A. requires farmers to kill entire flocks if just one infection is identified.
In comparison, the response to H5N1 on dairy farms has been sluggish. Though cows are less likely to die from H5N1, the virus can make cows quite sick and decrease their milk production. Farmers in multiple states have killed infected cows that have not recovered from H5N1 infections.
Of great concern is that surveillance and response to infections on dairy farms is largely voluntary. Testing on farms is not systematic or fast enough to protect workers before they are exposed to infected cattle. In some states, health officials have been unable to get access to farms to monitor workers and investigate how the virus is spreading. This is why if anyone is kept up at night over bird flu, it should be those leading our agriculture and health organizations, who can protect farm workers and prevent a pandemic.
H5N1 is enough of a risk now to warrant action, before the virus becomes a pandemic threat to America. By that point, everyone will have to worry.
Jennifer Nuzzo is an epidemiologist and the director of the Pandemic Center at the Brown University School of Public Health.
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