An outbreak of influenza A (H5N1), “bird flu,” in humans started in the U.S. in March 2024, and as of March 2025, continues to be monitored by the Centers for Disease Control and Prevention (CDC). Influenza A is spread by wild birds worldwide, and is causing outbreaks in domesticated poultry and U.S. dairy cattle. The majority of human infections have been in people exposed to infected animals, such as in the dairy and poultry industries. Visit the CDC’s Avian Influenza section for the latest on the situation.

What is bird flu?

Bird flu, formally known as avian influenza A (H5N1), is a disease caused by infection with avian flu Type A viruses. These viruses naturally spread among wild aquatic birds, including ducks, geese and swans, and can infect domesticated birds like chickens and turkeys. Some bird flu viruses can infect and spread to other animals, too. While bird flu viruses do not normally infect humans, sporadic human infections with bird flu viruses, including H5N1, have occurred.

How can bird flu spread to humans?

Bird flu can infect humans if they come into contact with an infected animal’s body fluid, such as saliva, milk, respiratory droplets or feces. It can be inhaled from small dust particles in animal habitats, or get into the eyes, nose or mouth after touching body fluids.

What are symptoms of bird flu?

The following symptoms may occur at different levels of infection.

Mild Symptoms

• Eye redness and irritation — this has been the main symptom among recent U.S. cases.
• Mild fever or feeling feverish (but fever not always present)
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue

Less common symptoms include diarrhea, nausea or vomiting.

Symptoms of Moderate or Severe Disease

• High fever or other symptoms listed above that limit or prevent usual activity
• Shortness of breath or difficulty breathing
• Altered consciousness
• Seizures

When do bird flu symptoms start?

Eye redness and irritation can occur one to two days after exposure and infection. In general, the time between exposure and when symptoms occur is about three days, but it can range from two to seven days.

If I suspect I have bird flu, when should I see a doctor?

If you have been exposed to bird flu or suspect you have, and have symptoms, call or message your doctor right away.

How is bird flu diagnosed?

A throat or nose swab can be used to diagnose bird flu. A swab from the clear membrane covering your eye (conjunctiva) can also be used. If you are diagnosed with bird flu, stay away from others until you are better, to help prevent the spread of the virus.

How is bird flu different from the seasonal flu?

Bird flu and seasonal flu can cause similar symptoms and complications. Eye irritation has been more common in bird flu cases in the U.S.

How is bird flu treated?

Antiviral medicine can help stop the bird flu from spreading in your body. This medicine works best if started as soon as you have symptoms.

More severe cases may require hospitalization.

When are people with bird flu contagious?

For mild infections, the period of contagiousness is not well understood, but it may be similar to seasonal flu, which is contagious for about a week. In general, people are considered contagious during the first few days of illness.

People with severe disease who require hospitalization may be contagious for several weeks.

Some people may not have symptoms, but they may still be contagious.

How long does it take to recover from bird flu?

Bird flu symptoms can last anywhere from a few days to less than two weeks, but can vary. People who are severely ill may have symptoms for several weeks.

Are there additional complications from bird flu?

The following are some complications that may occur due to severe bird flu:

• pneumonia
• respiratory failure
• acute respiratory distress syndrome
• acute kidney injury
• multi-organ failure (respiratory and kidney failure)
• sepsis, septic shock
• inflammation of the brain (meningoencephalitis)

Although it is rare, bird flu may lead to death.

Is bird flu a concern for humans?

It’s rare for bird flu to infect humans. However, since the influenza A virus that infects birds infects many animals, including humans, and can also change to become better able to spread, health officials keep a close eye on the spread of bird flu. H5N1 is new to humans, therefore there is no built-up immunity against the virus. If H5N1 changed and gained the ability to spread from human to human, it has the potential to  spread quickly.

What can I do to avoid getting bird flu?

• Do not touch or handle dead or dying birds or other animals.
• Protect your pets: Keep cats indoors, keep dogs away from areas with migratory birds, and avoid feeding raw milk and raw meat to your pets.
• Contain backyard chickens, and change your clothes and wash your hands after visiting the coop. Consider wearing a mask when caring for chickens.
• Avoid raw milk products and raw or undercooked meat products, including eggs; consume pasteurized milk and pasteurized milk products only.

For additional information, visit The Johns Hopkins University’s Q&A: How Serious Is Bird Flu? and Baltimore City Health Department’s Avian Influenza page.

Posted 3/18/25