Changes in the hemagglutinins and neuraminidases of human influenza B viruses isolated in Italy during the 2001-02, 2002-03, and 2003-04 seasons.

Throughout most of the last decade, B/Yamagata/16/88-lineage influenza viruses were predominant among the B isolates circulating worldwide, whereas B/Victoria/2/87-lineage viruses were isolated infrequently and restricted geographically to eastern Asia. During the 2001-02 influenza season, B/Victoria/2/87-lineage viruses re-emerged in North America and Europe and spread worldwide. Virological surveillance in Italy during that season showed wide circulation of influenza B viruses, of which most were antigenically related to the B/Sichuan/379/99 (Yamagata-lineage) vaccine strain, together with a smaller number of B viruses antigenically similar to B/HongKong/330/01, a recent B/Victoria/2/87-lineage antigenic variant. In the subsequent 2002-03 epidemic season, B viruses with a Victoria-lineage hemagglutinin (HA), more closely related to that of B/Shandong/7/97, were isolated exclusively. Similar strains have continued to predominate among the few B viruses isolated in Italy during last season (2003-04), although most influenza B viruses, isolated sporadically elsewhere in Europe, again belong to the Yamagata-lineage. In the present study, phylogenetic analyses of the HA and neuraminidase (NA) genes of representative B strains, isolated throughout Italy during 2001-04, showed that during the first influenza season the NA genes, as well as the HA genes, separated into the two distinct clades, the Yamagata- and Victoria-lineages, and showed no evidence of genetic reassortment. On the contrary, all the B viruses isolated in the 2002-03 and most of those isolated in the 2003-04 epidemic season were "Victoria HA-Yamagata NA" reassortants similar to those isolated in other parts of the world, showing that these reassortants became established in the human population. The frequency of reassortment between HA and NA of distinct lineages and sublineages highlights again the importance of detailed molecular analyses of both surface glycoproteins in understanding the evolution of influenza B viruses.

Interspecies transmission of an H7N3 influenza virus from wild birds to intensively reared domestic poultry in Italy.

Since the "bird flu" incident in Hong Kong SAR in 1997, several studies have highlighted the substantial role of domestic birds, such as turkeys and chickens, in the ecology of influenza A viruses. Even if recent evidence suggests that chickens can maintain several influenza serotypes, avian influenza viruses (AIVs) circulating in domestic species are believed to be introduced each time from the wild bird reservoir. However, so far the direct precursor of influenza viruses from domestic birds has never been identified. In this report, we describe the antigenic and genetic characterization of the surface proteins of H7N3 viruses isolated from wild ducks in Italy in 2001 in comparison to H7N3 strains that circulated in Italian turkeys in 2002-2003. The wild and domestic avian strains appeared strictly related at both phenotypic and genetic level: homology percentages in seven of their genes were comprised between 99.8% (for PB2) and 99.1% (for M), and their NA genes differed mainly because of a 23-aminoacid deletion in the NA stalk. Outside this region of the molecule, the NAs of the two virus groups showed 99% similarity. These findings indicate that turkey H7N3 viruses were derived "in toto" from avian influenza strains circulating in wild waterfowl 1 year earlier, and represent an important step towards the comprehension of the mechanisms leading to interspecies transmission and emergence of potentially pandemic influenza viruses.