Avian Influenza

Avian Influenza (Bird Flu)

Avian Influenza (Bird Flu)

Avian (bird) influenza (flu) viruses occur naturally in birds. Wild birds worldwide carry the viruses in their intestines and usually do not get sick from them. However, avian flu can infect domesticated birds, including chickens,ducks and turkeys.

In domestic poultry, there are two main forms of the avian influenza virus. The less severe of the two (“low pathogenic,” LPAI H5N1) commonly causes only mild symptoms (ruffled feathers, a drop in egg production) and may easily go undetected. The more severe form (highly pathogenic, HPAI H5N1, H5N2, H5N8, and H7N9) spreads very rapidly through poultry flocks, causes disease affecting multiple internal organs, and has a mortality rate that can approach 100%, often within 48 hours.

On rare occasions, bird flu viruses can infect humans. The risk is generally low to most people. However, confirmed cases of human infection have been reported since 1997.


As of December 2014, avian influenza, H5Nx, has been reported in wild birds, domestic poultry, and commercial flocks. The detections, made by the USDA, continued onto June 2015 until it affected 21 states, mostly in the Midwest and northern West Coast. Surveillance among birds is ongoing. The potential public health risk is low and USDA workers handling the infected poultry are being monitored for symptoms. There have been no human infections reported. For more information on the North American avian influenza viruses, visit the CDC webpage.