Co-circulation of two genotypes of measles virus and mutual change of the prevailing genotypes every few years in Osaka, Japan.

Genotypes of 44 wild-type measles virus (MV) strains isolated in Osaka, Japan, during 1997-2001, were determined based on phylogenetic analyses of a 456-nt 3' terminal nucleoprotein gene sequence with the reference MV strains designated by the World Health Organization. The wild-type MV strains were classified into two genotypes, D3 and D5, recognized as indigenous in Japan. Six of 12 strains isolated in 1997 were classified into genotype D3 and the other 6 into D5. Eleven of 13 strains were D3, and 2 were D5 in 1998. There were no measles epidemics, and no strains were isolated in 1999. Nine of 10 strains were genotype D5, and only one was D3 in 2000, and 9 of 9 were D5 in 2001. These results indicate that the wild-type MV strains classified into genotypes D3 and D5 co-circulated without the complete change of the MV genotype in Osaka, except in 2001. Furthermore, the prevailing genotype was different between 1998 and 2000-2001. Together with a previous report about MV genotype in this area during 1993-1995, these results suggest that the mutual change of the prevailing wild-type MV genotypes between D3 and D5 occurs every few years in Osaka, Japan.