How do people get infected with bird flu?

CNN
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As avian influenza infections in dairy cows and chickens increase, so too does the number of human cases, leaving many people wondering if they are at risk from this recently arrived virus.

Bird flu rarely infects humans. sixty-one for humans The U.S. Centers for Disease Control and Prevention says all but three of the confirmed cases in the U.S. this year were contracted by people working at poultry or dairy farms.

As the name suggests, avian influenza viruses prefer to infect birds. They enter cells by attaching to sugars that protrude from the cell's surface called sialic acids. H5N1, the avian influenza virus behind the ongoing pandemic in the United States, has only an affinity for the type of sialic acid receptor most abundant in the airways of birds.

However, influenza viruses can also mutate rapidly, and since 2022, H5N1 viruses have been infecting an increasing variety of mammals, including dairy cows.

Scientists are concerned because the more the virus circulates within an animal, the better its ability to find new hosts.

the study A paper published last week in the journal Science showed that by making just one key change to the virus' genetic material, it can attach to the type of sialic acid most commonly found in people's noses and lungs. But it's nearly impossible to predict when that will happen, or if it will actually happen.

Humans are most often infected with avian influenza through contact with infected animals. All but one of these so-called spillover infections are mild.

This week, it was announced that the first seriously ill patient in the United States remains hospitalized in critical condition in Louisiana. The CDC said Wednesday that the person was exposed to sick or dead birds on his own property, not from commercially available poultry.

No one in the United States who has been infected with H5N1 is known to have passed the infection on to others. Therefore, although the CDC estimates that the current risk to the public is low, certain occupations and situations may increase the risk of contracting avian influenza.

Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said the two groups of people most at risk are farmworkers who handle cattle and poultry and people who keep herds in their backyards. That's what it means.

Birds shed the virus through saliva, mucus, and feces, and the virus can be transmitted through the air, especially when bird litter and feathers are stirred up in barns during culling operations.

“It could be up in the air,” Osterholm said. “So it's not just contact with the birds, it's just the dander and dust that comes from handling the birds.”

The virus also settles in the udders of milking cows. research has discovered Raw or unpasteurized milk contains high concentrations of avian influenza virus.

Milking parlors on dairy farms are humid environments, and workers can become infected if they get raw milk in their eyes or rub their eyes with milk on their hands. Virus-laden milk droplets from milking equipment can also become airborne.

One of the most noticeable symptoms in infected farm workers is redness, inflammation, or conjunctivitis of the eyes. That may be because human eyes share the same type of sialic acid receptors as those most common in birds.

What about drinking raw milk?

the cat has infected After drinking raw milk. There are also reports of calves becoming ill after drinking infected milk.

“We don't have the same data for humans,” Osterholm says.

Although no human infections have been reported related to the consumption of raw milk, a toddler in California recently tested positive for influenza after drinking large amounts of raw milk. CDC could not confirm if infected However, since it was bird flu, the child is listed as a suspected case.

But there are many Even in the absence of specific evidence for H5N1, data on other pathogens present in raw milk. In 2023 and 2024, Escherichia coli and Salmonella The cause of the infection was traced to raw milk. Other pathogens such as Listeria and Campylobacter may also be lurking.

Pasteurization kills all of these harmful bacteria, including the recent H5N1 outbreak. government research is shown.

However, this is not the case with freezing. a recent research A Stanford University study injected influenza virus into raw milk and tested it on cells in petri dishes, and found that the virus could infect cells for up to five days even after being refrigerated. did.

The best way to protect yourself from bird flu is to avoid the source of infection. According to CDC.

If enough of the virus gets into your eyes, nose, or mouth, or if you breathe it in, you can contract bird flu. This usually requires close proximity to the infected animal for an extended period of time.

Therefore, the CDC recommends that people stay away from sick or dead birds and other animals and avoid touching surfaces contaminated with feces or saliva, such as trash or bedding.

If you need to work with sick birds, cows, or other animals, such as on a farm or rescue site, the CDC recommends wearing appropriate personal protective equipment (PPE). This includes:

Raw milk can contain so many dangerous bacteria that experts advise avoiding raw milk and using pasteurized dairy products.

But what about raw eggs? of The US Food and Drug Administration says Because birds get sick quickly from avian influenza, eggs from infected flocks are unlikely to reach stores, and safety measures such as testing are in place to prevent contaminated eggs from reaching the market.

It's still a good idea to cook eggs and chicken at safe temperatures to prevent cross-contamination between raw and cooked foods in the kitchen.