| Fifty-eight strains of Japanese encephalitis (JE) virus from a variety of geographic areas in Asia were examined by primer-extension sequencing of the RNA templates. Two hundred-forty nucleotides from the C and pre-M gene regions were selected for study, since this region provided sufficient information for determining genetic relationships among the virus isolates. Using 12% divergence as a cutoff point for virus relationships, the 58 isolates fell into four distinct genotypic groups. One genotypic group consisted of JE virus isolates from northern Thailand and Cambodia. A second group was comprised of isolates from southern Thailand, Malaysia, Sarawak and Indonesia. Isolates from Japan, China, Taiwan, the Philippines, Sri Lanka, India and Nepal made up a third group. Several isolates from Indonesia formed a distinct fourth genotype. Strains belonging to the second and fourth genotypic groups were from areas where JE virus infection is common but encephalitis is rare. In contrast, strains from areas in which JE epidemics have occurred fell into the first and third genotypes. In an attempt to find biological virulence markers which might correlate with these genotypic variations, in vivo and in vitro systems were tested. Although individual differences among JE virus strains in plaque morphology and mouse virulence were found, no consistent biological patterns could be demonstrated among the various genotypes. |
