Avian Influenza

close up of young broilers

Photo credit: U. S. Department of Agriculture

Avian influenza (or bird flu) is a disease of birds caused by infection with avian influenza A viruses. These viruses are excreted in the droppings, saliva, and nasal secretions of infected birds. Avian influenza A viruses usually do not infect humans; however, sporadic cases have been reported. These viruses can be transmitted to unprotected workers who have contact with infected wild birds, poultry, or contaminated materials or surfaces.

Domestic poultry may be infected with highly pathogenic avian influenza (HPAI) A viruses or low pathogenic avian influenza (LPAI) A viruses:

  • The highly pathogenic viruses spread quickly and may kill nearly an entire poultry flock within 48 hours.
  • The low pathogenic viruses may not cause symptoms or may cause only mild symptoms such as ruffled feathers or a drop in egg production.

The classification of low pathogenic or highly pathogenic avian influenza A virus refers to the ability of the virus to cause disease in chickens in the laboratory, not in humans. Human infection with low pathogenic and highly pathogenic avian influenza A viruses have resulted in a range of symptoms from mild to severe.

Avian influenza A viruses are a public and occupational health concern for several reasons, including:

  • Some of these viruses have passed sporadically from poultry to humans and caused serious illness and death.
  • They may change into a form that is highly infectious in humans and spreads easily from person to person.
  • As these viruses threaten domestic poultry throughout the world, they are also a risk to workers worldwide who have contact with poultry.
Page last reviewed: May 19, 2017