A bird flu strain that began circulating in 2020 continues to evolve globally and locally within the United States. If you’re wondering what this means, understanding the basics — what bird flu is, how it spreads, whether foods are safe, and prevention tips — can help. More information will come in as scientists learn more, so stay tuned.

1. What is bird flu and how does it spread?

Bird flu, or avian flu, is a naturally occurring illness. Just as certain flu viruses spread among humans, Type A influenza viruses often spread among wild birds. The strain of virus circulating now is H5N1, named for two proteins on its surface.

Avian flu infections are highly contagious. Infection often spreads first among wild water birds, such as ducks, geese and gulls, and shore birds, such as plovers and sandpipers. The viruses are carried in their intestines and respiratory tract and shed in saliva, mucus, and feces. Wild birds can easily infect domestic poultry, such as chickens, turkeys and ducks.

Some bird species, including ducks, may carry and spread infection without appearing sick. Domestic flocks are more likely to sicken and possibly die from bird flus. However, not all avian flu viruses are equally harmful:

2. Can humans get bird flu?

Yes, though this doesn’t usually happen.

When flu viruses mutate, they may be able to move from their original hosts — birds in this case — to humans and other animals. As of early April 2024, only two cases of bird flu in humans had been reported in the U.S. since 2022. In May, two more cases were reported. Newer case numbers of bird flu will continue to be reported by the CDC, which offers weekly snapshots of influenza in the U.S.

The virus may be introduced into the body through the eyes, nose, or mouth. For example, a person may inhale viral particles in the air (droplets, tiny aerosolized particles, or possibly in dust). Or they might touch a surface contaminated by the virus, then touch their eyes or nose. Bird flu in humans typically causes symptoms similar to seasonal flu, such as fever, runny nose, and body aches.

3. Which animals have been affected by bird flu?

A surprisingly long list of animals affected by the current H5NI bird flu infection includes:

4. Why are experts concerned about this bird flu outbreak?

It might seem odd that there’s been so much concern and news coverage about bird flu lately. After all, bird flu has been around for many years. We’ve long known it sometimes infects nonbird animal species, including humans.

But the current outbreak is unique and worrisome for several reasons:

5. Are milk, beef, chicken, and the rest of our food supply safe?

Public health officials emphasize that the food supply is safe.

But concern has understandably run high since the discovery that this outbreak has spread from birds to dairy cows for the first time. More alarming? A study found fragments of bird flu DNA — which is not the same as live virus — in 20% of commercially available milk in the U.S.

So far, there’s been no indication that bird flu found in pasteurized milk, beef, or other common foods can cause human illness. Even if live bird flu virus got into the milk supply, studies show that routine pasteurization would kill it. Initial tests did not find the virus in ground beef.

Of course, if you are particularly concerned, you could avoid foods and beverages that come from animals affected by bird flu. For example, you could switch to oat milk or almond milk, even though there’s no convincing scientific justification to do so now.

6. What if you have pets or work with animals?

Bird flu rarely spreads to pets. While that’s good news, your pets could have exposure to animals infected with bird flu, such as through eating or playing with a dead bird. So, it’s safest to limit your pet’s opportunities to interact with potentially infected animals.

If you work with animals, especially birds or livestock, or hunt, the Centers for Disease Control and Prevention (CDC) recommends precautions to minimize your exposure to bird flu.

7. What else can you do to stay safe?

The CDC recommends everyone take steps to avoid exposure to bird flu, including:

Right now, available evidence doesn’t support more dramatic preventive measures, such as switching to an all-plant diet.

8. Is there any good news about bird flu?

Despite all the worrisome news about bird flu, this recent outbreak may wind up posing little threat to human health. Virus strains may mutate to spread less efficiently or to be less deadly. Efforts are underway to contain the spread of bird flu to humans, including removing sick or exposed animals from the food supply and increased testing of dairy cattle before transport across state lines.

And there is other encouraging news:

9. How worried should you be about bird flu?

Though there’s much we don’t know, this much seems certain: bird flu will continue to change and pose challenges for farmers and health experts to stay ahead of it. So far, public health experts believe that bird flu poses little health risk to the general public.

So, it’s not time to panic about bird flu. But it is a good idea to take common sense steps to avoid exposure and stay current on related news.

For updated information in the U.S., check the CDC website.

(Robert H. Shmerling, M.D., is a senior faculty editor at Harvard Health Publishing and an Editorial Advisory Board member, and Francesca Coltrera is an editor for the Harvard Health Blog.)

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