The frequency and time of occurrence of natural swine infection by Japanese encephalitis virus was demonstrated during 1965-67 by study of HI antibody and isolation of virus from blood samples collected in Gunma prefecture. Infection by JE virus occurred during July and August as evidenced by both viremia and HI antibody development in pigs.
In 1965, viremia in swine was first detected in late of July and continued about 3 weeks, and JE virus was recovered from 10 to 50% of pigs by intracerebrally inoculation into suckling mice, No virs was isolated after 100% of pigs became infected in late August, Similar results were obtained in 1966 and 1967.
Majority of human JE cases wes occurred within 2-3 weeks of demonstration of viremia in pigs. Mosquitoe infection obsrved by virus isolation was limited to the early August-late September.
Incidence of infected pigs in summer was definitely indicated by deyelopment of 2-mercaptoethanol sensitive antibodies.
