Avian influenza is first and foremost a question of animal health. Much media attention has been directed towards its potential to affect humans and from there acquire the capacity for human-human transmission and thus launch a pandemic. However, the thrust of attention, and the issue that lies at the heart of FAO's mandate, is the nature of the disease in birds and the veterinary, epidemiological and virological challenge that the disease poses for the international scientific community.
Avian influenza has been recognised as a highly lethal generalised viral disease of poultry since 1901. In 1955, a specific type of influenza virus was identified as the causal agent of what was then called fowl plague. It has since been found that avian influenza viruses cause a wide range of disease syndromes, ranging from severe to mild, in domestic poultry.
Domestic fowl, ducks, geese, turkeys, guinea fowl, quail and pheasants are susceptible to avian influenza, with disease outbreaks occurring most frequently in domestic fowl and turkeys. It is usually difficult to pinpoint the immediate source of infection for domestic poultry, but most outbreaks probably start with direct or indirect contact of domestic poultry with waterbirds. Many of the strains that circulate in wild birds are either non-pathogenic or midly pathogenic for poultry. However, a virulent strain may emerge either by genetic mutation or by reassortment of less virulent strains.
Once avian influenza is established in domestic poultry, it is a highly contagious disease and wild birds are no longer an essential ingredient for spread. Infected birds excrete virus in high concentration in their faeces and also in nasal and ocular discharges. Once introduced into a flock, the virus is spread from flock to flock through the movement of infected birds, contaminated equipment, egg flats, feed trucks, and service crews, to mention a few. The disease generally spreads rapidly in a flock by direct contact, but on occasions spread is erratic. Airborne transmission may occur if birds are in close proximity and with appropriate air movement.
The fact that avian influenza has been around in waves for such a lengthy period of time indicates its resilience to attempts to eradicate, weaken, control or prevent it. FAO, along with the World Organisation for Animal Health (OIE) and other international partners, is concentrating its efforts on understanding the disease and its capacity for transmission and mutation, and advising affected, at-risk and unaffected countries on the most appropriate measures to take. Behind its global strategy to control avian influenza, FAO is committed to ensuring the health of the world's animals as the essential prerequisite for protecting the world's people from animal-borne disease.