Genetic study of Japanese encephalitis viruses from Vietnam.

Two hundred eighty-five nucleotides from the capsid/premembrane gene region of 16 isolates of Japanese encephalitis (JE) virus from the southern and northern regions of Vietnam obtained during the period 1964-1988 were sequenced and compared with each other and with wild JE virus strains from China and Japan. The 16 Vietnamese isolates showed low rates of genetic evolution (< or = 3.2%) and were classified into one genotype with an overall similarity of > or = 95.4%, including the Japanese JaArOS982 strain taken as reference, and earlier isolated strains from Japan (Nakayama 1935) and China (Beijing-1 1949 and SA14 1954), the wild-type strains used to derive JE vaccines. The implications of the close genetic relationship among Vietnamese strains of JE virus analyzed in our study in relation to their epidemiology and evolution are discussed.