Avian influenza is an acute infectious disease of birds caused by infection with avian influenza viruses, and is most severely affected in poultry such as chickens, turkeys, and ducks. According to the degree of pathogenicity of AI viruses in chickens, it is largely divided into low-pathogenic and highly pathogenic avian influenza. HPAI is designated as a disease to be managed by WOAH due to its high risk, and it is mandatory to report to WOAH when it occurs. In Korea, it is also classified as a Class 1 livestock epidemic and is one of the major livestock epidemics for national prevention.

It is a viral disease that causes severe immunocompromise, stunting, and acute and chronic tumors in chickens, turkeys, and ducks, and is caused by reticuloendotheliosis virus, which belongs to the retrovirus family.

It is a productivity-lowering disease caused by EDS '76 virus, whose main symptom is a decrease in egg production accompanied by deformed eggs, soft eggs, discolored eggs, and no eggs, and is characterized by a slow transmission rate. EDS '76 virus, a type of Adeno virus, is the causative agent and is widespread in wild waterfowl, ducks, and geese.