Avian influenza is a highly contagious disease that affects birds, particularly wild waterfowl. It is caused by viruses belonging to the Orthomyxoviridae family and is characterized by symptoms such as fever, respiratory problems, and neurological issues in infected birds. The virus can also be transmitted from bird to bird through direct contact or via contaminated environments. In some cases, avian influenza viruses have been known to mutate and spread to other species, including humans, which can lead to outbreaks of disease in these populations as well.