Molecular and phylogenetic analysis of haemagglutinin and neuraminidase sequences from recent human influenza type A (H3N2) viral isolates in Southern Greece

Eighteen haemagglutinin (HAI) gene segments and eleven neuraminidase (NA) g enes of human influenza type A (H3N2) viruses isolated from non-vaccinated individuals presenting severe influenza-like illness at peak influenza acti vity in Southern Greece during the surveillance period 1996-1999, were subj ected to sequence and phylogenetic analyses following propagation in embryo nated hen's eggs. The HAI gene segment of the clinical isolates differed fr om the recent reference influenza type A (H3N2) vaccine strains in an Ile a t residue 186, a Val at residue 194 and a Val at residue 226 for one, two a nd thirteen isolates of the 1996-1997 and 1996-1999 periods, respectively. The analogous differences in the NA gene were confined in an Asp to Asn sub stitution at residue 198 in one A/Wuhan/359/95 (H3N2)-like isolate of the 1 996-1997 period, primarily. In addition, phylogenetic analysis revealed tha t an isolate of the 1997-1998 period was a recombinant with its HAI gene se gment being closely related to that of A/Wuhan/359/95 -like viruses and its NA to viruses of the A/Sydney/5/97 (H3N2) lineage. These findings confirme d the profound genetic instability of influenza type A (H3N2) viruses and u nderscored the importance for periodic molecular surveys of HA and NA in th e effective prevention and management of viral outbreaks. Most importantly, however, they contributed the first complete epidemiological material for influenza in Southern Greece, the archival nature of which constitutes valu able reference for future surveys.