Although avian influenza doesn’t spread easily to humans, health experts worldwide are worried that the pathogen is mutating in ways that could make human spread more likely. That’s worrisome in part because H5N1 infection, the designation for bird flu, can be deadly.

The Centers for Disease Control and Prevention said the risk to humans is “currently low.” But health officials want to make certain it stays that way.

So far, just two cases of bird flu in people have been detected in the U.S.: one mild case in Texas this year marked by red, miserably itchy eyes and another in Colorado in 2022. But there are outbreaks in wild birds, poultry flocks and now cattle in at least eight states. Recently, health officials told people not to drink raw milk, after a French news agency reported the pathogen was found in some.

The World Health Organization said that since 2003, 889 human cases have been detected worldwide, and 463 of them were fatal.

According to CNN, “This flu strain was first detected in birds in 1996 and has primarily been a threat to farmed and wild fowl, but in the past two years, an increasing number of mammals have tested positive with the virus, indicating that the virus is looking for new hosts and moving closer to people.”

During a 2020 outbreak in poultry, tens of millions of birds were killed, per The Guardian. The virus was detected in both dairy cows and goats this year. Before that, officials noted an outbreak among mink in Spain. As Deseret News reported, a year ago officials were considering vaccinating chickens and turkeys against avian influenza.

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The big worry is that as the infection moves through ducks and chickens “but now increasingly mammals — that that virus now evolves and develops the ability to infect humans. And then critically, the ability to go from human-to-human transmission,” Dr. Jeremy Farrar, chief scientist at WHO, said in a media briefing Thursday when he was asked about avian flu.

The CDC said bird flu doesn’t easily spread to humans, but those who come in close contact with infected animals can get it. What’s reassuring amid the worry is that while the pathogen is very active right now, it doesn’t seem to be changing fast in ways that promote spread to humans. But public health officials see the possibility that could change.

The public health agency also noted that samples of the virus taken in the recent human case “found it is susceptible to flu antiviral drugs. CDC has already made a candidate vaccine virus that could be used to make a vaccine if needed.”

How does bird flu spread among cattle?

“It is still unclear how the cows were infected — whether by contact with birds, or via feed made from litter waste — but litter has been associated with previous outbreaks of disease, including botulism,” the Los Angeles Times reported. The article added, “Poultry litter causing the bovine cases of avian flu is considered ‘very unlikely, though not impossible,’” quoting Veronika Pfaeffle in a joint statement from the U.S. Department of Agriculture and the U.S. Food and Drug Administration.

PBS reported that agriculture officials in at least 17 states have restricted dairy cattle importation from states where the virus has been detected. “Officials believe cows likely have been infected by exposure to wild birds,” the article said, but “cow-to-cow spread ‘cannot be ruled out.’”

The article noted that cows showing signs of infection, such as reduced milk production and lethargy, are being tested for avian flu and are separated from other animals. “The animals appear to recover within two weeks,” PBS reported.

Food supply worries?

In an advisory in late March, the USDA, CDC and FDA jointly said that contamination of the pasteurized milk supply is not a concern, as “dairies are required to send only milk from healthy animals into processing for human consumption; milk from impacted animals is being diverted or destroyed so that it does not enter the human food supply.” The notice added that “pasteurization has continually proven to inactivate bacteria and viruses like influenza in milk.”

Any milk in interstate commerce for human consumption must be pasteurized. “FDA’s longstanding position is that unpasteurized, raw milk can harbor dangerous microorganisms that can pose serious health risks to consumers, and FDA is reminding consumers of the risks associated with raw milk consumption,” the agencies wrote. Bird flu is far from the only concern.

Bird flu in humans has only been found with close contact to infected animals. Symptoms range from mild — eye redness or mild flu-like upper respiratory symptoms — to severe, such as pneumonia, per CDC. People with bird flu can have symptoms similar to other respiratory illnesses, including cough, fever, sore throat, runny or stuffy nose, muscle aches, headaches, fatigue and trouble breathing. Diarrhea, nausea or seizures are much less common.

Only lab testing can confirm bird flu in humans.