Bird flu: The latest on U.S. spread, the safety of milk and new federal funding to prevent outbreaks

Cattle on a dairy farm, with a farmer raking hay.
Bird flu has spread to cattle on dairy farms, including one where a worker became infected, but it has not spread between people. (Getty Images)

As bird flu continues to spread among dairy cattle herds in nine U.S. states, the federal government is providing $200 million to help stem transmission, Reuters reported on Friday. The Centers for Disease Control and Prevention has also asked states to prepare for more bird flu cases. On Monday, the agency requested that states provide personal protective equipment (PPE) to dairy farm workers who might be at risk, according to an emailed statement. Previously, the CDC had asked states to gear up to test at-risk people for the virus, Reuters reported, and now the federal funding will provide each affected farm with up to $28,000 a day toward measures to slow the spread among animals and prevent transmission to humans. Health agencies will also get $101 million for continued food safety monitoring. But U.S. officials have consistently assured Americans that the risk to the general public remains low.

So far the only person to be infected is a dairy worker who contracted bird flu in Texas, where the virus has been spreading among cattle. The worker tested positive after developing pink eye, which was their only symptom, according to a New England Journal of Medicine (NEJM) report published on May 3. Dairy cattle herds have also been infected in Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio and South Dakota. Bird flu hasn’t spread to any other people so far, but it has been detected in wild birds, including several geese, in New York City parks and green spaces, according to a new study, and there are renewed fears about other mammals being infected.

How concerned should you be about bird flu, and what might this mean for the food supply? Here’s what you need to know.

Bird flu — clinically known as influenza A (H5N1) — is a variation of flu virus that spreads primarily among birds and poultry and can be highly contagious and even fatal among birds, according to the CDC. Occasionally, the virus will jump to other animals if they eat infected birds or drink water contaminated by the feces of infected birds, the CDC says. That has become more common in recent years. Viruses are constantly mutating, and the more they spread, the more they mutate. A recent family of variants may be particularly adept at infecting other animals, including cattle, according to the World Health Organization.

It’s rare for the virus to infect humans, and when it does happen, it’s usually confined to one person who was in close contact with an infected animal and doesn’t spread to others. Bird flu may cause mild to severe sickness in humans, and it has the potential to cause pneumonia and severe, sometimes fatal lung inflammation. Since 2020, there have been 26 cases in humans confirmed by the WHO, seven of which have been fatal.

The CDC continues to call for calm and considers the risk to the general public low, but, on April 5, the agency requested that state health departments begin gearing up in case additional people are infected.

So far the U.S. Department of Agriculture (USDA) has confirmed that there are 12 infected dairy cattle herds in Texas, 10 in Michigan, four in Kansas, eight in New Mexico, three in Idaho, two in Colorado and one each in North Carolina, Ohio and South Dakota. Cases in birds in New York City parks and green spaces have also been confirmed by Icahn School of Medicine at Mount Sinai researchers.

The infected person in Texas was diagnosed after developing conjunctivitis, or pink eye. It’s only the second-ever human case of bird flu in the U.S.; the first was a poultry farmworker who was infected in 2022 while culling infected birds and recovered after experiencing only mild fatigue. Eye inflammation was the only symptom the Texas dairy worker experienced; they never developed any respiratory symptoms that health officials might have expected with bird flu, according to the NEJM report.

Other dairy and poultry farmworkers are the CDC's main concern now. On May 6, the agency asked state health and agriculture departments to provide PPE to dairy farm workers at risk of contracting bird flu in an effort to prevent any additional cases, the agency said in an emailed statement. So far, the CDC has tested at least 30 people for bird flu and monitored at least 220 for symptoms. The agency has also asked state health officials to take other steps like making sure they have bird flu tests available to confirm possible infections. It also said health officials should stay in close contact with veterinarians and agriculture department officials and asked to be notified of any "challenges" states encounter.

While farmworkers are at the greatest risk because of their close and frequent proximity to potentially infected animals, the Icahn School of Medicine study authors warned that it's not impossible for city dwellers to be exposed. "Our work highlights that the interface between animals and humans that may give rise to zoonotic infections" — germs that spread between animals and people — "or even pandemics is not limited to rural environments and commercial poultry operations but extends into the heart of our urban centers," the researchers wrote.

For the general public, the risk remains low, the CDC says. Bird flu has never been very good at spreading from person to person, so it’s unlikely to become widespread. The virus would have to mutate in some specific, key ways to make that possible. The good news is that it hasn’t, according to preliminary testing of a sample of virus from the infected person, who has only mild symptoms.

After particles of the bird flu virus were discovered in about 1 in 5 samples of grocery store milk, further Food and Drug Administration testing has confirmed that the virus was inactivated by pasteurization, a sterilizing process used on more than 99% of the commercial milk supply. The U.S. Department of Agriculture also tested ground beef for bird flu, and all the samples came back negative.

Bird flu has also been found in unpasteurized milk, but you shouldn’t consume unpasteurized milk or cheese regardless, the CDC warns, because they carry risk of infections like listeria. The CDC also says that the risk of being infected from eating eggs is low, and properly cooking them would kill any virus anyway.

Farms are prohibited from selling products — including milk and eggs — from sick animals, so it’s unlikely that contaminated food would wind up on grocery store shelves. The most likely impact of the bird flu outbreak in animals on the food supply is rising prices. Egg prices have shot up as chickens have been culled or died, limiting the supply of eggs. Milk prices could see increases but are stable so far.

On April 15, Colombia became the first country to restrict the importation of beef and beef products from U.S. states with infected herds, Reuters reported.

Two candidate vaccines — drafts of what would become the shots — seem to be good matches for the current strain of bird flu, the Washington Post reports. The federal government has a stockpile of enough doses to vaccinate a fifth of the American population, officials told Barron's. However, the vaccines are undergoing clinical testing, so it's unclear how effective they will be. Antiviral drugs can also be used to treat bird flu, although the CDC says that some variations of bird flu first found in Asia aren’t as responsive to these treatments.

Dr. Arnold Monto, a professor emeritus of epidemiology at the University of Michigan and member of the FDA’s vaccine committee, tells Yahoo Life that the U.S.’s bird flu vaccines require adjuvants, ingredients that improve human’s immune responses. An official with the Department of Health and Human Services also told the Washington Post that components for the vaccines are being tested, and it would likely take weeks to months for them to be ready for widespread distribution. Monto adds that the vaccine would also likely be given to only those at high risk — poultry and dairy farmworkers — since there’s no evidence that bird flu spreads among humans.

Avoid close or prolonged contact with wild birds, cattle or any other animal suspected of being infected. The CDC also recommends steering clear of surfaces that may be contaminated with raw milk, animal feces, litter or anything else that might have crossed paths with an infected animal.

Cooking poultry and eggs to an internal temperature of 165˚F will kill off any virus. It's also recommended for milk drinkers to consume only pasteurized milk to prevent contracting bird flu or other viruses or bacteria from raw foods, and to avoid raw or undercooked foods sourced from animals that may be infected with bird flu.

This article was originally published on April 4, 2024. It has since been updated.