Field experiences in the control of avian influenza outbreaks in densely populated poultry areas.

From 1997 to 2003, Italy has been affected by two epidemics of highly pathogenic avian influenza (HPAI) and by several outbreaks of low pathogenic avian influenza (LPAI). In 1999-2000 a severe HPAI epidemic affected the country, causing 413 outbreaks: a total of about 16 million birds died or were stamped out. From August 2000 to March 2001, a H7N1 LPAI strain infected 78 poultry farms. The last affected flock was stamped out on the 26th of March 2001. In October 2002, another LPAI virus of the H7N3 subtype emerged and infected a total of 388 poultry holdings. Eradication measures were based on stamping out or controlled marketing of slaughtered birds on infected farms and on the prohibition of restocking. Restriction measures on the movement of live poultry, vehicles and staff were also imposed. To supplement these disease control measures, two emergency vaccination programmes, based on the "DIVA" (Differentiating Infected from Vaccinated Animals) strategy were implemented. The two vaccination campaigns (2000-2002 and 2002-2003) both resulted in the eradication of infection. However, the first campaign appeared to be more successful that the second and possible explanations are discussed.