Bird flu should make us worried — but not panicked

By Lisa Jarvis

The bird flu keeps catching the world off guard by finding new ways to spread — this time finding an unexpected host in cows.

As of April 4, the virus had been confirmed in more than a dozen herds across six states, with Kansas, Idaho, Michigan, New Mexico, Ohio and Texas all reporting infected cows. An infected dairy farm worker in Texas is just the second person in the US to have ever contracted bird flu.

By now, the public could be getting worried. Bird flu in our dairy supply? A human infection? The situation needs careful monitoring and coordination between agencies to ensure the spread is contained. It is also a reminder that viruses excel at catching us by surprise — and we must remain vigilant when they start to do new and surprising things.

Examples of wild and domestic animals being infected with avian flu are widespread — ferrets, dogs, cats, foxes, sea lions, otters and recently even a polar bear have had confirmed infections.

But the cases in cattle worry scientists for a few reasons. The first is that cows are getting infected with bird flu at all. Despite isolated reports of other types of influenza in cattle, cows were not believed to be highly susceptible to the virus until 2011, when scientists discovered a new form of the virus, influenza D, in cows and pigs in France and the US.

As for the bird flu, researchers had shown that it was possible to infect cattle with it, but this 2024 outbreak is the first time it’s ever been detected in herds. Although the virus is highly lethal to chickens, the good news is that the cows don’t get as sick — their symptoms include decreased appetite and lower milk production. But the virus is showing up in cow’s milk, which suggests it is spreading well beyond the respiratory tract, behaving more like a regular influenza virus, says Andrew Pekosz, professor of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health. (I’ll get to how worried you should be about infected milk in a moment.)

The other troubling piece is the increasing likelihood that cows are giving the virus to one another, rather than contracting it from a bird or other wildlife. While the USDA has not come out and said cow-to-cow transmission is occurring, livestock and infectious disease experts told me it would be surprising at this stage if it weren’t happening. Several of the farms with sick cows had recently received a herd from Texas, where the infections seem to have originated.

And then there are the concerns over the human who contracted the virus, seemingly from direct contact with cattle. The patient’s only symptom is conjunctivitis, or eye inflammation, with seemingly no involvement of the respiratory system. That the infection is mild is reassuring, but also suggests some cases could easily go undetected by physicians.

All of that adds up to cause for vigilance, but not panic. The risk to the general public remains low, highlighted this week by comforting news from the Centers for Disease Control and Prevention: The viral genome from a sample collected from the patient in Texas showed no worrisome changes from samples collected from birds and cows. There were a few tiny differences, but none were in spots that would indicate the bird flu is getting better at infecting humans. Agriculture and public health authorities need to continue to swiftly sequence samples and share that information with the research community.

And experts say the food supply is not at risk. So far, the spread isn’t enough to be felt in the supply chain (in other words, no need to hoard milk). And farmers are required to destroy the milk produced by sick cows, so the public shouldn’t be exposed.

But even if that milk did end up on grocery store shelves, the bird flu is “pretty wimpy” outside of its host and would be easily killed during pasteurization process, says Stacey Schultz-Cherry, an influenza expert at St Jude Children’s Research Hospital. Enthusiasts of raw milk, which is unpasteurized, might have reason to worry, but as of now there’s no evidence the virus can be transmitted that way. (And Schultz-Cherry points out that the dangerous bacteria potentially growing in raw milk is a far bigger individual health threat than bird flu.)

But there’s a non-zero chance of this bird flu outbreak growing into a bigger problem for humans. More needs to be done to ensure the safety of workers who come into direct contact with potentially infectious material, which is anyone handling animals, manure or unpasteurized milk, says Joe Armstrong, a livestock expert at the University of Minnesota Extension.

Not only is offering workers protective gear critical to their personal health, it’s important to public health. In a 2022 study, researchers found that 21 out of 31 workers on large-herd dairy farms tested positive for influenza D (of note, they did not have symptoms or signs of diseases). The study was tiny and has limitations, but highlights the need to take steps to prevent human exposures in the environment where bird flu is spreading.

And the various government agencies protecting our food and health need to continue to be speedy and transparent with information as the situation evolves. They also should have a strategy ready for making and distribution a vaccine and antivirals in the case it worsens.

Covid showed us how quickly a virus can catch the world off guard. Vigilance is our best protection.