Avian Influenza

Abstract

Avian influenza (AI), informally known as “avian flu” or “bird flu,” causes devastating economic losses to poultry industries worldwide and is a well-recognized zoonotic threat to humans with pandemic potential. The causative agent of AI, the influenza A virus, is an eight-segmented single-stranded RNA virus fitting to the family Orthomyxoviridae. Mechanisms of genetic diversity of avian influenza viral strains include reassortment (antigenic shift) and mutations (antigenic drift), which may contribute to the emergence of highly virulent and/or zoonotic viruses. AI viruses are categorized as highly pathogenic (HPAI) or lowly pathogenic (LPAI) strains. HPAI strains are usually derived from LPAI in poultry flocks and cause severe disease in poultry. The natural reservoirs of avian influenza virus are mostly wild water birds of the orders Anseriformes (geese, ducks, and swans) and Charadriiformes (gulls, terns, shorebirds, and auks). AI viruses are chiefly transmitted by feco-oral and respiratory routes, and via water soiled with feces from infected birds. Migratory birds and international poultry trade play a vital role in expanding the geographical distribution of the virus. The majority of cases of human influenza from an avian source have been associated to direct or indirect interaction with poultry. Control and prevention strategies such as vaccination programs and biosecurity measures in poultry farms, routine surveillance in domesticated and wild birds, and constant monitoring of the evolutionary patterns of the virus are of utmost importance to combat the spread of avian influenza among birds and eventual transmission events to humans.