Prevention and management of avian influenza outbreaks: experiences from the United States of America.

The epidemiology and control of avian influenza (AI) are complex. The virus is transported in nature by the activities of wild birds and in commercial poultry by the activities of people. In general, all the outbreaks of AI in the United States of America (U.S.A.) have involved AI virus spread by the movement of poultry and manure and objects contaminated by poultry and manure, butthe specific cause of spread has been different for most outbreaks. The 1924 highly pathogenic AI (HPAI) outbreak was spread halfway across the U.S.A. by contaminated rail cars and poultry crates; the 1983 HPAI outbreak was spread by the movement of people between farms and transport of live and dead poultry, including depopulation efforts; whereas low pathogenicity AI (LPAI) outbreaks in different states were spread by people and equipment, partial flock removal, transport of spent hens and/or manure, and transport of dead birds for rendering. There is a dichotomy surrounding AI control methods in the USA. Large LPAI outbreaks have mainly affected turkeys in the western part of the country and have been controlled by vaccination and controlled marketing-strategies developed prior to the 1983 HPAI outbreak. By contrast, in the eastern part of the country, the AI control strategy has been modelled on the successful stamping-out programme that was used during the HPAI outbreak in 1983. The author presents a summary of the costs and control strategies in table form.