A bird flu primer: What to know and do

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 after 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 tracts 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 flu. 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.

Importantly, genetic mutations can allow low pathogenic avian influenza to become highly pathogenic. These mutations may also allow it to spread more easily from one species (such as wild birds) to another (such as chickens).

2. Can humans get bird flu?

Yes, though it's not common.

When flu viruses mutate, they may be able to move from their original hosts — birds in this case — to humans and other animals. Since early 2024, 70 human cases of bird flu have been reported in the U.S. Updated U.S. case numbers of bird flu will continue to be reported by the CDC.

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 (from droplets, tiny aerosolized particles, or possibly in dust). Or they might touch a surface contaminated by the virus, then touch their eyes or nose.  The most common risk factor for human infection with bird flu is exposure to sick or dead poultry.

Bird flu in humans typically causes symptoms similar to seasonal flu, such as fever, conjunctivitis (pink eye), 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 every state in the US and in more than 100 countries
• livestock, such as dairy cows in 17 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 that it can infect birds and other animals, 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. So far, the current outbreak of H5N1 bird flu has spread to every continent except Australia.
• Many species have been infected. Previously uninfected species have been affected, including animals in our food supply.
• Economic impact. Large numbers of infected chickens may cause their death or require culling (killing them to contain the outbreak) and milk from infected dairy cows is removed from the food supply. As a result, bird flu is having a major economic impact on some farmers, agriculture businesses, and affected countries' economies. And it is already leading to higher prices at the grocery store.
• Opportunities for exposure. Though only 70 human infections in the U.S. during the current outbreak, the more exposure humans have to bird flu, the more chances the virus has to develop mutations that allow easier spread.
• Potential for fatalities. Over the last 20 years, H5N1 bird flu infection has been confirmed in more than 950 people in 24 countries worldwide; nearly half were fatal. It's likely that many more cases of bird flu in humans have occurred but people experiencing few or no symptoms or those not tested may not be counted, so lethality is likely overestimated. During the recent outbreak of bird flu in the US, one death has been reported.
• New mutations. It's possible that mutations in the virus causing the current bird flu outbreak could enable more efficient person-to-person spread. If that happens, bird flu could become the next human pandemic.

5. Is 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 2024 study found fragments of bird flu DNA in 20% of commercially available milk in the US. And while the virus has been found in milk samples from infected dairy cattle, human illness due to drinking infected milk has not been reported.

So far, there's been no indication that bird flu virus 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. Testing of commercially available ground beef has not demonstrated contamination with bird flu virus particles.

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 can infect pets but it's not common. Pets can be exposed 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.

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 too soon to know if this will be successful).
• If spread to humans does occur, antiviral treatment, such as oseltamivir, is available.
• 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, human vaccines may become available.

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's website on bird flu.