Neutralization and/or hemagglutination-inhibiting antibody tests of sera and plasmas from rodents collected in urban and rural areas near Tokyo, Japan failed to show evidence of frequent infection of wild rodents by JE virus during 1953–1957. Plasma from only one of 131 rodents tested in 1956 unequivocally neutralized virus and only one of 373 rodents tested by the hemagglutination-inhibition test showed antibody in heated, acetone-extracted plasma. These results strongly suggest that wild rodents play an unimportant role in the ecology of JE virus near Tokyo despite their large yearly population turnover. Perhaps their low infection rate reflects infrequent biting by Culex tritaeniorhynchus, the vector of JE virus in Japan.
Present address: Sloan-Kettering Institute for Cancer Research, New York (C. M. S.)