The illness commonly known as avian influenza is a disease caused by an alternative of the Influenza A virus. It can affect almost all wild and domestic birds. It is considered highly contagious - especially among chickens and turkeys – and may cause extremely high mortality. Avian influenza viruses were first identified during an epidemic more than a hundred years ago. Since then, the disease has regularly reappeared all over the world, though only in a relatively benign way.