Bird flu is a disease caused by influenza Type A viruses that naturally spread among wild birds. These viruses occasionally jump to domestic poultry, other animals, and, rarely, humans. Most people will never encounter bird flu, and the CDC considers the current risk to the general public low. But the virus has drawn increasing attention since 2024, when it was detected in U.S. dairy cows for the first time, expanding the list of animals that can carry it and potentially expose farmworkers.
How Bird Flu Viruses Work
Bird flu viruses are classified by two proteins on their surface, labeled H and N. The subtypes known to infect humans include H5, H6, H7, H9, and H10. Among these, H5N1 has caused the most concern. Between January 2003 and December 2024, 954 confirmed human cases of H5N1 were reported across 24 countries, and 464 of those were fatal, a case fatality rate of roughly 49%. That number sounds alarming, but it reflects a relatively small number of confirmed cases over more than two decades, and severe cases are more likely to be tested and counted.
Bird flu viruses also fall into two categories based on how deadly they are in poultry. Low-pathogenic strains cause mild or no illness in birds, while highly pathogenic strains, like the H5N1 circulating today, can kill entire flocks rapidly. The distinction matters because highly pathogenic viruses tend to produce more severe disease when they do cross into humans.
How It Spreads
Among birds, the virus travels through saliva, mucous, and droppings. Infected flocks contaminate the air, surfaces, water, and soil around them. Wild birds, especially waterfowl, carry the virus across vast distances during migration, seeding it into new poultry populations and environments along the way.
Humans almost always catch bird flu through direct, close contact with infected animals or contaminated environments. That includes handling sick or dead poultry, visiting live bird markets, or working on dairy farms with infected cows. The virus can enter through your eyes, nose, or mouth after you touch a contaminated surface, breathe in droplets or dust near infected animals, or come into contact with raw milk or animal byproducts containing live virus. The closer and longer your contact with an infected animal or its environment, the higher the risk.
Sustained person-to-person spread has not been documented. Rare clusters among family members have occurred, but these likely involved shared exposure to the same animal source or very close, prolonged contact with a sick relative. This is the key reason bird flu has not caused a pandemic: it does not yet spread efficiently between people.
The 2024 Dairy Cow Outbreak
On March 25, 2024, a multistate outbreak of highly pathogenic H5N1 in dairy cows was first reported in the United States. This was unprecedented. Bird flu had never been found in cattle before. The discovery expanded concerns because dairy farming involves frequent close contact between workers and animals, and raw milk from infected cows can contain live virus.
People who work with infected birds, poultry, or cows face greater risk than the general public. The wide geographic spread of H5N1 in wild birds, poultry, and now mammals means more opportunities for human exposure, even though the virus itself hasn’t become better at infecting people. Farmworkers, veterinarians, and anyone involved in culling infected flocks are the primary groups at risk.
Symptoms and How Quickly They Appear
After exposure, respiratory symptoms typically begin in about three days, though the window ranges from two to seven days. Eye redness and irritation can show up sooner, within one to two days. In mild cases, bird flu looks a lot like seasonal flu: fever (100°F or higher), cough, sore throat, runny nose, body aches, headaches, and fatigue. Some people also experience diarrhea, nausea, or vomiting.
Severe cases escalate to high fever, shortness of breath, difficulty breathing, altered consciousness, and seizures. Complications can be life-threatening and include pneumonia, respiratory failure, acute kidney injury, multi-organ failure, sepsis, and inflammation of the brain. The speed of treatment matters enormously: studies of H5N1 patients found that starting antiviral medication within two days of symptom onset was significantly associated with survival, while delays of five or six days corresponded with much higher mortality.
How Bird Flu Is Diagnosed
Standard flu tests at a doctor’s office or hospital can confirm you have influenza A, but they cannot tell the difference between seasonal flu and bird flu. If a test comes back positive for influenza A but negative for the usual seasonal subtypes (H1 and H3), that raises a flag. The sample is then sent to a public health laboratory, where specialized genetic testing can identify whether it’s an H5 virus. Positive or inconclusive results are forwarded to the CDC for final confirmation. This layered process means a definitive bird flu diagnosis takes longer than a typical flu test.
Treatment With Antivirals
Bird flu is treated with antiviral medications, the same class of drugs used for severe seasonal flu. Treatment is most effective when started as early as possible, ideally within 48 hours of the first symptoms. In studies of hospitalized H5N1 patients across multiple countries, those who received antiviral treatment had significantly better survival rates than those who went untreated. Even patients who started treatment later than 48 hours still benefited compared to no treatment at all, which is why antivirals are recommended regardless of how many days have passed since symptoms began.
For hospitalized patients or those with weakened immune systems, doctors may use a combination of two antiviral drugs to reduce the chance the virus develops resistance during treatment. Most circulating bird flu strains respond well to the currently available antivirals, though an older class of flu drugs (adamantanes) does not work against them and is not recommended.
Food Safety
Cooking poultry and eggs to an internal temperature of 165°F kills bird flu viruses along with other pathogens. Properly cooked chicken, turkey, and eggs pose no risk. The concern centers on raw or undercooked products, particularly unpasteurized (raw) milk from potentially infected cows. Pasteurization destroys the virus, so commercially pasteurized dairy products are considered safe.
Vaccines and Preparedness
An H5N1 vaccine for humans exists but is not available to the general public. Manufactured by Sanofi Pasteur, it is approved for adults ages 18 through 64 who face increased risk of exposure, and it is held in the U.S. national stockpile for use in a pandemic scenario. The vaccine is a preparedness tool, not a routine immunization. If the virus were to mutate in a way that allowed efficient human-to-human spread, these stockpiled doses could be deployed while manufacturers scaled up production of an updated vaccine.
Reducing Your Risk
For most people, the practical steps are straightforward. Avoid touching wild birds, sick or dead poultry, and surfaces contaminated with bird droppings. If you raise backyard chickens or work with poultry or dairy cattle, wear gloves, eye protection, and a well-fitting respirator when handling animals or cleaning enclosures. Wash your hands thoroughly afterward. Don’t drink raw milk, and cook poultry and eggs to 165°F.
If you develop flu-like symptoms after close contact with birds, poultry, or dairy cows, especially if the animals were sick, contact your local health department. Early testing and early antiviral treatment are the two factors most closely linked to better outcomes in confirmed bird flu cases.