Single genotype of measles virus is dominant whereas several genotypes of mumps virus are co-circulating

We have reported that in Japan measles virus strains have been classified into three distinct different genotypes (C1, D3 and D5) under the new international genotype classification since 1984. Similarly, mumps virus strains have been divided into two genotypes with three subtypes (B1, B2, B3, and D) under the proposed international classification since 1976. To differentiate these genotypes we developed a restriction fragment length polymorphism assay in the hemagglutinin (H) region for measles virus and in the hemagglutinin-neuraminidase (HN) region for mumps virus to facilitate the expanded molecular epidemiology. In the Sapporo 1995/1996 measles outbreak, all 26 strains were classified as D5. Among 32 samples from patients with measles from 1994 to 1997 in Tokyo, 28 were identified as D5 and four were D3; these D3 strains were ascertained as a same hospital acquired infection. Among 45 strains obtained in the Tokyo 1999 outbreak, 38 were D3 and the remaining seven were D5. The dominant genotype of measles in Tokyo has replaced from D5 to D3 similar to the Chicago1/89 strain. We obtained 220 samples from patients with mumps from 1993 to 1997 and they were classified into one strain of B1, 14 strains of B2, 151 strains of B3, and 54 strains of D. Therefore, we suggest that two or three subtypes of mumps virus are co-circulating with a different geographic pattern in genotype distribution, whereas a single measles virus genotype is dominantly observed, showing different epidemiological patterns.