Bird flu is an infection caused by a type of avian influenza virus. Although there are many types of bird flu, the types that now concern health workersâ€”because they are very serious and often fatalâ€”are the H5N1 and H7N9 bird flu viruses.
Symptoms of bird flu can be the same as common flu symptoms. These can include a fever, cough, sore throat, muscle aches, or eye infection (conjunctivitis). More serious symptoms of bird flu include pneumonia, a serious lung infection, or acute respiratory distress syndrome, a life-threatening lung problem.