Avian influenza, also known as bird flu, is a disease caused by infection with avian (bird) influenza (flu) Type A viruses. These viruses naturally spread among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Bird flu viruses do not normally infect humans, but sporadic human infections with bird flu viruses have occurred. The Highly Pathogenic Avian Influenza Virus (HPAIV) caused by subtypes (H5 and H7) of type A, causes serious illness in birds that can spread rapidly, resulting in high death rates in different species of birds. The Low Pathogenic Avian Influenza Virus (LPAIV) can cause a mild illness, often unnoticed or without any symptoms. Avian influenza A viruses are a public and occupational health concern for several reasons, including the fact that some of these viruses have passed sporadically from poultry to humans and caused serious illness and death. The disease can be transmitted to unprotected workers who have contact with infected wild birds, poultry, or contaminated materials or surfaces. Symptoms in people can range from mild upper respiratory tract symptoms to severe illness and death). There is no clear evidence that the virus can be transmitted from human to human, but this may have happened in rare cases.