Avian influenza A viruses are classified into the following two categories: low pathogenic avian influenza (LPAI) A viruses, and highly pathogenic avian influenza (HPAI) A viruses. The categories refer to molecular characteristics of a virus and the virus’ ability to cause disease and mortality in chickens in a laboratory setting. Infection of poultry with LPAI viruses may cause no disease or mild illness (such as ruffled feathers and a drop in egg production) and may not be detected. Infection of poultry with HPAI viruses can cause severe disease with high mortality. Both HPAI and LPAI viruses can spread rapidly through poultry flocks. However, some ducks can be infected without any signs of illness.
In December 2014, the United States Department of Agriculture (USDA) confirmed the presence of highly pathogenic avian influenza (HPAI) H5 viruses in both domestic and wild birds in the United States. No human infections with these viruses have been detected in the United States, Canada or internationally at this time, however, similar viruses have infected people. It’s possible that human infections with these viruses may occur. While human infections are possible, infection with avian influenza viruses in general are rare and – when they occur – these viruses have not spread easily to other people. CDC considers the risk to people from these HPAI H5 infections in U.S. birds and poultry to be low at this time, but has developed interim guidance on testing and prophylaxis. More information about detections of HPAI in U.S. birds is available through a link on the USDA website.