Avian Influenza A(H5N1)

Avian influenza A(H5N1), also known as highly pathogenic avian influenza or bird flu, is a disease caused by infection with avian influenza type A viruses. The current bird flu strain is widespread in wild birds worldwide. These viruses can also infect other birds (including poultry) and mammals (like seals) and, most recently, dairy cows in the U.S. 

While avian flu viruses do not normally infect people, sporadic human infections have occurred around the world. In April 2024, an infection was identified in a U.S. dairy worker who reported conjunctivitis (eye redness) as their only symptom; a previous U.S. infection, which was also mild, occurred in 2022. 

Human illness from avian flu viruses has ranged from mild, such as eye infection and upper respiratory symptoms, to severe illness, like pneumonia, that has resulted in death in countries outside the U.S. Available data suggest that infections in people can be treated with current antiviral drugs, like oseltamivir, with activity against influenza. Vaccination against seasonal flu will not prevent infection with avian flu viruses but can reduce the risk of getting sick with human and bird flu viruses at the same time. 

While the current public health risk from avian flu to the general population is considered low in the U.S., federal agencies are investigating the current outbreak in dairy cows and working with states to look for unusual flu activity in people and to monitor people with animal exposures. Remnants of the bird flu virus that has infected cows have been detected in samples of pasteurized milk, but there is no evidence of actual infectious virus in pasteurized milk. The commercial milk supply is considered safe at this time. Drinking raw milk, which is not pasteurized, can lead to serious illness and is linked to many preventable foodborne illnesses every year.