Taxonomic name: Avian influenza virus
Common names: bird flu (English), fowl plague (English), HPAI (English), LPAI (English)
Organism type: micro-organism
Asian Influenza is a highly contagious disease caused by type A influenza virus. Waterfowl are natural hosts of the disease and are usually asymptomatic. There are two forms of AI: Highly Pathogenic Avian Influenza (HPAI), which causes rapid mortality particularly in domestic poultry, and Low Pathogenic Avian Influenza (LPAI), which is a milder form. AI can be transmitted through the respiratory secretions or faeces of infected birds and also through contact with contaminated materials or items such as clothing, equipement and vehicles (Horimoto and Kawaoka, 2001).
AI viruses have a similar structure and consist of two glycoprotein spikes, hemagglutinin (HA) and neuraminidase (NA) and a limited number of M2 proteins that project from the viral surface (NIAID, 2004). The virus is highly pleomorphic, roughly spherical, and filamentous (NIAID, 2004). Inside the virion are eight single-stranded RNA segments waiting to be copied by a host (NIAID, 2004).
Acute Fowl Cholera, Chronic Respiratory Disease (CRD), Infectious laryngotracheitis (ILT), Newcastle disease virus (NDV)
agricultural areas, host
Waterbirds, especially Anatidae are natural reservoirs for AI which needs a host to reproduce (Horimoto and Kawaoka, 2001).
The effects of AI are felt worldwide. The virus has had a significant impact on the economy, trade industry, chicken and animal health, and human health ( APHIS, 2004). For instance, in 1983 and 1984 the the United States government destroyed more than 17 million birds at a cost of 65 million dollars due to an outbreak of AI (APHIS, 2004). In 1997, 6 out of 18 people in Hong Kong infected with H5N1 (a subtype, see Avian Influenza Virus for more details on different types) died (CDC, 2004).
LPAI can rapidly mutate into HPAI (Perdue et al. 1998) and its ability to cause fatal infections in humans (Horimoto and Kawaoka 2001; Guan et al. 2004) is of serious concern. If a human is simulataneously infected with human and AI viruses it is possible a new virus may emerge which could be transmitted from human to human. This has not occurred and the risks of this taking place are small, but the implications would be extremely serious (pandemic)
The virus was first noted in chickens in 1878, in Italy, and later isolated in 1902. HPAI occurrences have been recorded worldwide and have been found periodically in Australia, England, South Africa, Scotland, Ireland, Mexico, Pakistan, and the United States. Asia is a major source of outbreaks.
Regular updates on outbreaks of AI and control measures undertaken can be accessed from the following links:
Center for Disease Control - Avian Influenza.
OIE, an intergovernmental organisation for animal health.
Animal Production and Health Commission for Asia and the Pacific.
World Health Organisation.
Introduction pathways to new locations
Agriculture: The virus has the potential to spread through agriculture industry, such as the poultry industry and live poultry markets.
Live food trade: The virus has the potential to be spread through the food trade.
Other: The virus is spread from one continent to another by migratory birds that are natural hosts for the disease.
Local dispersal methods
Agriculture (local): The virus has the potential to spread through agriculture industry, such as the poultry industry and live poultry markets (APHIS, 2004).
Consumption/excretion: The most common transmission of the virus is from infectious nasal secretions and feces of infected birds (APHIS, 2004).
Off-road vehicles: The virus can be transmitted by any type of vehicle if the vehicle is allowed to become contaminated (APHIS, 2004).
On animals: The virus can be transmitted from bird-to-bird and bird-to-pig. A pig can act as an intermediary and transfer the virus to humans (APHIS, 2004).
Other (local): The virus can be transmitted through contaminated clothing and shoes (APHIS, 2004).
People sharing resources (local): The virus can be transmitted by mechanical means through the sharing of contaminated equipment (APHIS, 2004).
Road vehicles: The virus can be carried on the tires and other parts of vehicles and transmitted from farm to farm or farm to market when contaminated (APHIS, 2004).
Transportation of habitat material (local): The virus can transported in contaminated poultry and poultry products such as eggs and items containing down or feathers (APHIS, 2004).
Control measures include trade restrictions, and biocontrol security measures on farms and at live markets (APHIS , 2004), quarantine (Butcher, G. et al. 2004), surveillance and vaccines. Swift action following an outbreak of HPAI involves depopulation.
AI, like most viruses, has no metabolism. Therefore, the virus does not require any nutrition (Horimoto and Kawaoka, 2001).
AI needs a host to reproduce. Once inside, the virus uses the hosts DNA to replicate itself (Horimoto and Kawaoka, 2001).
The virus replicates itself once inside a host cell. AI uses the genetic material of the host for energy and for the replication process. After viral components are made inside the host cell, the components are released (Sander, 2004).
Reviewed by: John Tracey, NSW Department of Primary Industries, Orange New South Wales, Australia
Compiled by: Elizabeth Lishka, supervised by Dr. Deborah Rudnick University of Washington, Tacoma.
Last Modified: Friday, 30 December 2005