Avian influenza, also known as bird flu, is caused by viruses that normally infect birds but can infect other animals and humans. It is a contagious disease spread through contact with infected birds or surfaces contaminated with bird droppings or secretions. The document discusses the causative agent, reservoirs, transmission, signs and symptoms, diagnosis, treatment and prevention of avian influenza. It emphasizes the importance of surveillance in poultry, culling infected birds, maintaining biosecurity, and using personal protective equipment to control the spread of this zoonotic disease at the source, transmission and host levels.