Recent changes in prevalence pattern of Japanese encephalitis virus in Hyogo Prefecture, Japan, using a two-dimensional distribution of IgG and IgM class antibody levels in swine sera.

Surveillance of antibody to Japanese encephalitis (JE) virus in swine sera was performed during the epidemic season from July to September, 1978 to 1983, in Hyogo Prefecture, Japan, using enzyme-linked immunosorbent assay (ELISA). Two-dimensional distribution analyses of ELISA values for IgG and IgM class antibodies indicated recent changes in the prevalence pattern. Time courses of antibody levels observed from 1978 to 1980 were similar to those in the 1960s of major epidemics, indicating a synchronous infection during the second wave of infection. In 1982 and 1983, however, the JE prevalence pattern implies an incessant infection cycle between vector mosquitoes and pigs during the latter half of the epidemic season. The delay of the occurrence of JE in patients confirms the longer period of exposure to infectious vectors.