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. During the current U.S. outbreak in cattle, several infections have been reported in dairy farm workers with exposure to infected cows and in poultry workers. A previous U.S. infection occurred in 2022. The latest data on cases in people in the U.S. is available from the Centers for Disease Control and Prevention.
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.
Useful Information and Resources
For the Public
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- CDC: Information on Bird Flu
- CDC: Information for Farm Workers Exposed to H5N1 Bird Flu in U.S. Dairy Cows or Other Animals
- CDC: Reducing Risk for People Working With or Exposed to Animals
- CDC: Information for Specific Groups of People Who May Be Exposed to Infected Animals
- CDC: Information for Fair Exhibitors to Help Prevent Influenza
- CDC: Information for Fair Organizers to Help Prevent Influenza
- CDC: Tips for Staying Healthy at Animal Exhibits
- CDC: Influenza and Zoonoses Education Among Youth in Agriculture
- FDA: Questions and Answers Regarding Milk Safety During Highly Pathogenic Avian Influenza (HPAI) Outbreaks
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NIH: High H5N1 Influenza Levels Found in Mice Given Raw Milk From Infected Dairy Cows
For Clinicians
Centers for Disease Control and Prevention
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- CDC: H5N1 Bird Flu: Current Situation Summary
- CDC: H5N1 Indicator Monitoring and Influenza Surveillance
- CDC: Monitoring for Influenza in Wastewater
- CDC COCA Call (July 16, 2024): Update on Highly Pathogenic Avian Influenza A(H5N1) Virus for Clinicians and Healthcare Centers
- CDC MMWR (May 24, 2024): Outbreak of Highly Pathogenic Avian Influenza A(H5N1) Viruses in U.S. Dairy Cattle and Detection of Two Human Cases — United States, 2024
- CDC HAN Advisory (April 5, 2024): Highly Pathogenic Avian Influenza A(H5N1) Virus: Identification of Human Infection and Recommendations for Investigations and Response
Food and Drug Administration
U.S. Department of Agriculture
Department of Health and Human Services
Public Policy, Advocacy and Action