H7N1 avian influenza in Italy (1999 to 2000) in intensively reared chickens and turkeys

From the end of March to the beginning of December 1999, an epidemic of low pathogenicity avian influenza (LPAI) affected the industrial poultry popul ation of northern Italy. The virus responsible for the epidemic was subtype d as H7N1 with an intravenous pathogenicity index (IVPI) of 0.0, and a dedu ced amino acid sequence of the region coding for the cleavage site of the h aemagglutinin molecule typical of low pathogenicity viruses. The circulatio n of the virus in a susceptible population for several months caused the em ergence of a highly pathogenic virus with an IVPI of 3.0 and the presence o f multiple basic amino acids in the deduced amino acid sequence for the cle avage site of the haemagglutinin molecule. Over 13 million birds were affec ted by the epidemic and, in the present paper, we report the results of the clinical, virological and histopathological investigations performed on af fected chickens and turkeys. Clinical, gross and microscopic lesions caused by LPAI were more severe in turkeys than in chickens, while highly pathoge nicity avian influenza (HPAI) caused similar mortality rates in both specie s. Current European legislation considers LPAI and HPAI as two completely d istinct diseases, not requiring any compulsory eradication policy for LPAI but enforcing eradication for HPAI. In the Italian 1999 to 2000 epidemic, L PAI mutated to HPAI in a densely populated area, causing great economic los ses. A reconsideration of the current European Union legislation on avian i nfluenza, including LPAI of the H5 and H7 subtypes, could possibly be an ai d to avoiding devastating epidemics for the poultry industry.