Antigenic and genetic characterization of three influenza C strains isolated in the Kinki district of Japan in 1982-1983.

Three strains of influenza C virus (C/Kyoto/41/82, C/Nara/82, C/Hyogo/1/83) have been isolated from humans in the Kinki district of Japan between February 1982 and December 1983. Oligonucleotide mapping of total vRNA and antigenic analysis with anti-HE monoclonal antibodies have shown previously that they are closely similar to one another but dissimilar to any of the strains isolated in Japan before 1982. In the present study, the nucleotide sequences of the hemagglutinin-esterase (HE) genes of these three strains were determined and compared with those of the previously published strains. The results revealed that the Kinki isolates had a high nucleotide sequence homology (98.4-98.5%) with the virus isolated in 1980 in the United States (C/Mississippi/1/80). Similarity of the Kinki strains to C/Mississippi/1/80 was also confirmed by oligonucleotide mapping of total vRNA and antigenic comparison using a panel of 11 anti-HE monoclonal antibodies. The isolates from Kinki and Mississippi could be distinguished from the previously isolated strains in serological tests with heterogeneous sera, suggesting that they may have possessed epidemiological advantage in Japan around 1982-1983. These observations raise the possibility that the rapid spread of influenza C variant closely related to C/Mississippi/1/80 has occurred in Kinki in 1982-1983 presumably because this imported virus was largely different in antigenicity from the previously prevalent ones.