a highly contagious viral disease among domestic fowl and other birds, colloquially known as bird flu. It is usually spread by migratory birds, which can carry the virus asymptomatically. Cross-transmission to humans has been rare (requiring close contact with infected birds), but there is potential for mutation, which could lead to increased bird-to-human transmission and human-to-human transmission. In humans, typical symptoms include fever, cough, sore throat, muscle aches, eye infections, and pneumonia; it can be fatal.