The control of avian influenza in areas at risk: the Italian experience 1997-2003

Abstract

From 1997 to 2003, Italy has been affected by two epidemics of highly pathogenic avian influenza and by several outbreaks of low-pathogenic avian influenza (LPAI). In 1999-2000 a severe avian influenza (AI) epidemic affected the country. The epidemic was caused by a type-A influenza virus of the H7N1 subtype, originated from a low-pathogenic (LP) AI virus, which spread in 1999 among poultry farms in Northeastern Italy and eventually became virulent by mutation with the emergence of a highly pathogenic (HP) strain. From 17 December 1999 to 5 April 2000, a total of 413 outbreaks (178 meat-type turkey, 5 turkey breeder, 29 broiler breeder, 119 layer, 37 broiler, 9 guinea fowl, 11 game farm and 25 back-yard flocks) were identified and the last affected flock was stamped out on 5 April 2000. A total of about 16 million birds died or were stamped out on affected and at-risk premises. From August 2000 to March 2001 in two epidemic waves, the H7N1 LPAI strain infected 73 turkey farms, which housed 1 million turkeys, 4 quail farms, with about 800,000 quails, and 1 layer farm (40,000 layers) located in the southwestern part of the Veneto Region (Verona and Padua provinces). To supplement disease-control measures already in force an emergency vaccination programme was implemented based on the ‘DIVA’ (differentiating infected from vaccinated animals) strategy. After the implementation of the vaccination programme, only 3 meat-type turkey farms were infected inside the vaccination area and among these, only one vaccinated flock was affected. The last affected flock was stamped out on 26 March 2001. In October 2002, another LPAI virus of the H7N3 subtype emerged in the northern part of the country. The H7N3 LPAI strain rapidly spread among poultry flocks located in the densely populated poultry area (DPPA) which had been affected by the H7N1 epidemic in 1999-2001. Eradication measures were based on stamping out or controlled marketing of slaughterbirds on infected farms and on the prohibition of restocking of poultry farms. Restriction measures on the movement of live poultry, vehicles and staff were also imposed in the areas at risk. To supplement diseasecontrol measures already in force, an emergency vaccination programme, based once again on the ‘DIVA’ strategy was drawn, approved by the EU Commission and implemented in the area. From 10 October 2002 to 10 October 2003, the H7N3 LPAI virus was able to spread and infect a total of 387 poultry holdings, mainly meat-type turkey farms; of these 88 were vaccinated. The implementation of a vaccination programme and the enforcement of strict restriction measures did not avoid the spread of the H7N3 LPAI virus infection among meat-turkey farms located in a DPPA. Nevertheless, it was possible to prevent the massive spread of infection to poultry farms other than turkey and to neighbouring vaccinated areas.