Avian Influenza in Birds

Avian influenza refers to infection of birds with avian influenza Type A viruses. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Wild aquatic birds can be infected with avian influenza A viruses in their intestines and respiratory tract, but usually do not get sick. However, avian influenza A viruses are very contagious among birds and some of these viruses can sicken and even kill certain domesticated bird species including chickens, ducks, and turkeys.

Infected birds can shed avian influenza A viruses in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with the virus as it is shed by infected birds. They also can become infected through contact with surfaces that are contaminated with virus from infected birds.

Types of Avian Influenza

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​.

Avian Influenza in wild birds.

Avian influenza A viruses have been isolated from more than 100 different species of wild birds. Most of these viruses have been LPAI viruses. The majority of the wild birds from which these viruses have been recovered represent gulls, terns and shorebirds or waterfowl such as ducks, geese and swans. These wild birds are often viewed as reservoirs (hosts) for avian influenza A viruses.