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 population of northern Italy. The virus responsible for the epidemic was subtyped as H7N1 with an intravenous pathogenicity index (IVPI) of 0.0, and a deduced amino acid sequence of the region coding for the cleavage site of the haemagglutinin molecule typical of low pathogenicity viruses. The circulation of the virus in a susceptible population for several months caused the emergence of a highly pathogenic virus with an IVPI of 3.0 and the presence of multiple basic amino acids in the deduced amino acid sequence for the cleavage site of the haemagglutinin molecule. Over 13 million birds were affected by the epidemic and, in the present paper, we report the results of the clinical, virological and histopathological investigations performed on affected chickens and turkeys. Clinical, gross and microscopic lesions caused by LPAI were more severe in turkeys than in chickens, while highly pathogenicity avian influenza (HPAI) caused similar mortality rates in both species. Current European legislation considers LPAI and HPAI as two completely distinct diseases, not requiring any compulsory eradication policy for LPAI but enforcing eradication for HPAI. In the Italian 1999 to 2000 epidemic, LPAI mutated to HPAI in a densely populated area, causing great economic losses. A reconsideration of the current European Union legislation on avian influenza, including LPAI of the H5 and H7 subtypes, could possibly be an aid to avoiding devastating epidemics for the poultry industry.