How do people catch bird flu?Flu viruses can mutate quickly, and since 2022, H5N1 has been infecting a growing variety of mammals, including dairy cattle. That has scientists on alert because the more it circulates in animals, the better it gets at finding new hosts.
As bird flu infections rise in dairy cattle and chickens, human cases are ticking up too, leaving many people to wonder whether they might be at risk from this recently arrived virus.
Bird flu infections are rare in people. Sixty-one human cases have been confirmed in the US this year, according to the US Centers for Disease Control and Prevention, and all but three have been in people who work on poultry or dairy farms.
As the name suggests, avian influenza viruses prefer to infect birds. They break into cells by latching onto sugars that stick up from their surfaces called sialic acids. H5N1, the bird flu virus behind the ongoing outbreak in the US, has really only demonstrated an affinity for the types of sialic acid receptors that are most plentiful in the respiratory tracts of birds.
But flu viruses can also mutate quickly, and since 2022, H5N1 has been infecting a growing variety of mammals, including dairy cattle.
That has scientists on alert because the more it circulates in animals, the better it gets at finding new hosts.
A study published last week in the journal Science showed that just one key change to the virus’ genetic material would allow it to attach to the kinds of sialic acids that are most common in the nose and lungs of people. But it’s nearly impossible to predict when that could happen — or if it ever will.
Animal-to-human spillover events
When humans have become infected with bird flu, it’s almost always been through contact with infected animals. All but one of these so-called spillover infections have been mild.
The United States’ first severe case was announced this week in a person in Louisiana who remains hospitalized in critical condition. The CDC said Wednesday the person was exposed to sick and dead birds on their property, not from commercial poultry.
The two groups of people who are most at risk are farm workers who work with cows or poultry and people who keep backyard flocks, said Dr. Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota.
Birds shed the virus through their saliva, mucus and feces, and it can become airborne when their litter and feathers are churned up in barns, particularly during culling operations.
“It can be in the air,” Osterholm said. “So it’s not even just contact touching the birds but just the dander and all the dust that occurs when you’re dealing with birds.”
The virus also homes in on the udders of milking cows, and studies have found high concentrations of bird flu virus in milk that is raw or unpasteurized.
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