Avian influenza

Avian influenza, also known as avian flu, is a bird flu caused by the influenza A virus, which can infect people. It is similar to other types of animal flu in that it is caused by a virus strain that has adapted to a specific host. The type with the greatest risk is highly pathogenic avian influenza (HPAI).

Though influenza A is adapted to birds, it can also stably adapt and sustain person-to-person transmission. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted from both human and avian strains. Pigs can also be infected with human, avian, and swine influenza viruses, allowing for mixtures of genes (reassortment) to create a new virus, which can cause an antigenic shift to a new influenza A virus subtype which most people have little to no immune protection against.

Avian influenza strains are divided into two types based on their pathogenicity: high pathogenicity (HP) or low pathogenicity (LP). The most well-known HPAI strain, H5N1, was first isolated from a farmed goose in Guangdong Province, China in 1996, and also has low pathogenic strains found in North America. Companion birds in captivity are unlikely to contract the virus and there has been no report of a companion bird with avian influenza since 2003. Pigeons can contract avian strains, but rarely become ill and are incapable of transmitting the virus efficiently to humans or other animals.

Avian flu or bird flu mainly affects chickens, geese, pigeons, quail and similar domesticated birds. There is also evidence that wild bird populations serve as reservoirs for the virus. The virus can be transmitted directly from fowl to humans leading to serious illness and death. Two characteristics of "bird flu" make it potentially pandemic: (1) it represents a new strain of influenza and (2) people have no natural immune resistance to it. To date it is unproven whether the virus can be transmitted person to person or is solely contracted from direct contact with diseased fowl. The human symptoms of "bird flu" are classic for influenza; sore throat, fever and muscle ache, but can become deadly in the young, elderly or infirm.