Avian Influenza (AI) or 'bird flu' is a viral disease caused by influenza type A viruses and is divided into two categories, Low Pathogenic (LPAI) and Highly Pathogenic (HPAI), referring to the severity of infection in birds. HPAI is of concern because it can cause widespread, severe illness among bird populations. There are several types of HPAI, including the most well-known, H5N1. These viruses spread naturally among wild bird populations but can also infect domestic poultry and other animals.

Human cases of bird flu are not common, but occasional cases have occurred.