Avian influenza, or bird flu, is a contagious virus that largely affects birds though some humans also become sick with the infection, explains World Health Organization. There are several species of the virus though most human infections result from A(H5N1) and A(H7N9).
Symptoms of the virus include diarrhea, stomach pain, fever and respiratory problems, Flu.gov explains. Most cases of avian flu in humans result from direct contact with infected poultry or bodies of birds that died from the disease. Avian flu is not spread through properly prepared poultry products, and it is not typically spread between humans.
Bird flu may have a 100 percent mortality rate in some species of birds, according to WHO. The mortality rate is 60 percent for infected humans, according to Flu.gov though there were only 650 reported cases worldwide between 2003 and 2011.