Characterization of antigenically unique influenza C virus strains isolated in Yamagata and Sendai cities, Japan, during 1992-1993.

Three influenza C virus strains (C/Yamagata/1/92, C/Yamagata/1/93 and C/Miyagi/5/93) isolated in Yamagata and Sendai Cities, Japan, between June 1992 and May 1993 were found to possess haemagglutinin-esterase glycoproteins that were antigenically indistinguishable from one another but were clearly different from any previous Japanese isolates. To investigate the origin of the 1992/1993 strains, their antigenic and genetic properties were compared with those of eight strains isolated outside Japan between 1967 and 1982. The results showed that the 1992/1993 isolates were closely related to a virus isolated in Brazil in 1982 (C/SaoPaulo/378/82) and that these viruses (including C/SaoPaulo/378/82) are reassortants that had obtained PB1 and NP genes from a C/Yamagata/26/81-like parent and the other genes from another as yet unidentified parent.