Characterization of H5N2 influenza viruses from Italian poultry

From October 1997 to January 1998, highly pathogenic H5N2 avian influenza v iruses caused eight outbreaks of avian influenza in northern Italy. A nonpa thogenic H5N9 influenza virus was also isolated during the outbreaks as a r esult of virological and epidemiological surveillance to control the spread of avian influenza to neighbouring regions. Antigenic analysis showed that the Italian H5N2 isolates were antigenically similar to, although distingu ishable from, A/HK/156/97, a human influenza H5N1 virus isolated ire Hong K ong in 1997, Phylogenetic analysis of the haemagglutinin (HA) genes showed that the highly pathogenic Italian viruses clustered with the Hong Kong str ains, whereas the nonpathogenic H5N9 virus, despite its epidemiological ass ociation with the highly pathogenic Italian isolates, was most closely rela ted to the highly pathogenic A/Turkey/England/91 (H5N1) strain. Like the HA phylogenetic tree, the nonstructural (NS) phylogenetic tree showed that th e H5N2 Italian virus genes are clearly separate from those of the H5N9 stra in. In contrast, results of the phylogenetic analysis of nucleoprotein (NF) genes indicated a closer genetic relationship between the two Italian viru s groups, a finding suggesting a common progenitor. Comparison of the HA, M S and NP genes of the Italian H5 strains with those of the H5N1 viruses sim ultaneously circulating in Hong Kong revealed that the two groups of viruse s do not share a recent common ancestor. No virological and: serological ev idence of bird-to-human transmission of the Italian H5N2 influenza viruses was found.