H5N1 Bird Flu (Avian Influenza)

Bird flu, also called avian influenza, is a viral infection that primarily affects birds but can sometimes spread to mammals, including humans. Migrating waterfowl such as wild ducks, geese, and storks are natural carriers of bird flu viruses. Scientists believe that infection can spread from wild birds to domestic poultry (chickens and turkeys) and some mammals.

Bird flu is mostly a concern for birds and does not spread easily among humans. However, a 2024 outbreak affected dairy cows and individuals working in the dairy and poultry industries in the United States.

There have been very few cases of human-to-human transmission during bird flu outbreaks. The rare instances that occurred involved very close contact, such as a mother contracting the virus while caring for her infected infant. No human-to-human transmission has been reported in the 2024 outbreak.

The most common strain of bird flu is H5N1.

Various strains of bird flu occasionally appear in U.S. poultry. When this happens, farmers must cull (remove and kill) all affected poultry flocks.

For example, in 2004, a highly pathogenic bird flu strain was detected in a Texas chicken flock. That outbreak involved an H5N2 virus, not the H5N1 strain. By April 2004, the outbreak had been controlled, and no human infections were reported.

The CDC considers bird flu to be widespread in wild birds and sporadic in poultry. They estimate that more than 125 million birds in the U.S. have been affected by bird flu.

The most recent outbreak in the U.S. began in 2022. As of December 2024, it has affected nearly 11,000 wild birds and 125 million poultry across all 50 states.

In March 2024, the virus was detected for the first time in dairy cows. The CDC reports that H5N1 bird flu has infected 876 dairy herds across 16 states. Additionally, as of December 2024, 65 confirmed cases of bird flu in humans have been reported in the U.S., primarily in California, Colorado, and Washington state.

Despite this, the CDC still considers the risk of H5N1 to be very low for the general human population. All reported cases have involved direct exposure to infected poultry or cows, with no evidence of human-to-human transmission.

Pets, such as cats and dogs, are unlikely to contract bird flu. However, they may become infected if they eat a bird that carries the virus. Rarely, bird flu has been found in cats that consumed raw milk or undercooked meat from infected cows.

Bird flu is caused by influenza A viruses. Humans contract bird flu through direct exposure to an infected animal’s fluids, such as saliva, respiratory droplets, or droppings.

Possible transmission sources include: Breathing in contaminated dust in poultry facilities, touching infected surfaces and then touching the eyes, nose, or mouth, and consuming raw or undercooked poultry, eggs, or unpasteurized milk.

Doctors cannot diagnose bird flu based on symptoms alone. They use a swab test of the throat or nose, with the highest accuracy occurring within the first few days of illness.

Early antiviral treatment can help manage symptoms. Common antiviral drugs include: Oseltamivir (Tamiflu), Peramivir (Rapivab), and Zanamivir (Relenza).

For the best results, these medications should be taken within 48 hours of symptom onset.