How does avian flu affect the body?

Avian flu, like other types of influenza, is caused by a virus that infects the respiratory system. As a result, effects on the body often focus on the throat, nose, and lungs. The nose may become congested, the throat may become sore, and a cough or sore throat may occur. A fever and muscle aches may occur. Difficulty breathing is common. In addition, some strains of bird flu cause eye infections.