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:

• Low pathogenic avian influenza (LPAI) may cause no signs of illness, or signs of mild illness like fewer eggs or ruffled feathers in domestic poultry.
• Highly pathogenic avian influenza (HPAI) causes more severe illness and high rates of death in infected poultry. The current H5N1 virus is considered an HPAI.

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 US 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 US.

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:

• wild birds, chickens, ducks, geese, and other domestic and commercial poultry in 48 states and more than 500 countries
• livestock, such as dairy cows in nine states at this writing, and other farm animals
• marine animals, such as seals, sea lions, and even dolphins
• wild animals, such as foxes, skunks, and racoons, and some domestic animals, such as farm cats.

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:

• Fast, far-reaching spread. The virus has been found throughout the US, Europe, the Middle East, Southeast Asia, multiple sub-Saharan African countries, and even Antarctica.
• Many species have been infected. Previously uninfected species have been affected, including animals in our food supply.
• Economic impact. If large numbers of beef and dairy cows and chickens sicken or must be culled (killed) to contain outbreaks, this could have a major economic impact on farmers, agriculture businesses, and affected countries’ economies. This could also mean higher prices at the grocery store.
• Opportunities for exposure. Though only two human infections were reported in the US in recent years — both in people working with animals — the more exposure humans have to bird flu, the more chances the virus has to develop mutations that allow easier spread to humans.
• Potential for fatalities. Severe strains of bird flu have led to H5N1 infections in nearly 900 people in 23 countries since 2003. More than half of these reported cases were fatal. Keep in mind that the math isn’t straightforward. It’s likely that many more cases of bird flu in humans occurred, yet people experiencing few or no symptoms or those not tested weren’t counted, so lethality is likely overestimated.
• New mutations. It’s rare, but possible: If this H5N1 bird flu develops mutations that enable efficient person-to-person spread, bird flu could become the next human pandemic.

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 US.

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:

• Avoid contact with sick or dead animals and keep pets away from them.
• Avoid animal feces that may be contaminated by birds or bird droppings, as might be common on a farm.
• Do not prepare or eat raw or undercooked food.
• Do not drink raw (unpasteurized) milk or eat raw milk cheese or raw or undercooked foods from animals suspected of having bird flu infection.
• Wear personal protective equipment (PPE), such as safety goggles, gloves, and an N95 face mask, when working near sick or dead animals or their feces.

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:

• Some birds appear to be developing immunity to the virus. This could reduce the chances of continued spread between birds and other animals.
• Developing a vaccine to protect cattle from bird flu may be possible (though it’s unclear if this approach will be successful).
• If spread to humans does occur, genetic tests suggest available antiviral medicines could help treat people.
• So far, human-to-human transmission has not been detected. That makes it less likely that the H5N1 bird flu will become the next pandemic.
• And if human infections with bird flu did become more common, researchers are working on human vaccines against bird flu using virus strains that match well with those causing the current outbreak.

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 US, check the CDC website .

About the Authors

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD

Francesca Coltrera, Editor, Harvard Health Blog

Francesca Coltrera is editor of the Harvard Health Blog, and a senior content writer and editor for Harvard Health Publishing. She is an award-winning medical writer and co-author of Living Through Breast Cancer and The Breast … See Full Bio View all posts by Francesca Coltrera

About the Reviewer

John Ross, MD, FIDSA, Contributor; Editorial Advisory Board Member, Harvard Health Publishing

Dr. John Ross is an assistant professor of medicine at Harvard Medical School. He is board certified in internal medicine and infectious diseases, and practices hospital medicine at Brigham and Women’s Hospital. He is the author … See Full Bio View all posts by John Ross, MD, FIDSA