Avian influenza is caused by the Type “A” influenza virus. This virus can affect several species of food-producing birds (chickens, turkeys, quails, guinea fowl, etc.), as well as pet and wild birds. Avian influenza viruses are divided by subtypes based on two proteins found in the viruses: hemagglutinin, or “H” protein, and neuraminidase, or “N” protein. The H5 and H7 subtypes of the virus are of particular concern, given the ability of these two H-types to mutate from low pathogenic to highly pathogenic after they infect domestic birds.