VARIATION IN FIELD ISOLATES OF MEASLES-VIRUS DURING AN 8-YEAR PERIOD IN JAPAN

Field isolates of measles virus (MV) during an 8-year period in four areas of Japan, i.e., Osaka, Nagoya, Tokyo and Akita, were classified into three types in regard to the electrophoretic mobility of the hemagglutinin (HA) proteins: S type with small (78 K) HA, M type with intermediate (80 K) HA and L type with large (82 K) HA. The type of field isolates was closely related with the geographical location and the year of virus isolation. The S type strain was isolated only in an outbreak from 1983 to 1984, whereas the M and L type strains were isolated between 1983 and 1990. The HA genes of the M and L type strains of MV were found to have a nucleotide substitution which introduces a new potential glycosylation site. In addition, the matrix proteins of all field strains isolated after 1977 showed slower electrophoretic mobility of 42 K than 39 K of the Edmonston and Toyoshima strains. These results indicate that MV strains of different HA types existed concomitantly and that major populations of MV currently circulating in Japan are changing from those prevalent in 1983-1984.