Immunologic Studies of Japanese Encephalitis Virus in Japan

Abstract

Discussion and Summary Antibodies to JE virus of maternal origin were found in pigs 2–7 months of age near Tokyo, Japan. These passively acquired antibodies were detected most frequently by the neutralization test, less often by hemagglutination-inhibition and never by complement fixation. Detectable maternal antibodies disappeared in the majority of pigs by 4–6 months of age, at which time swine became susceptible to virus. No information was sought or obtained in these studies concerning the mechanism of antibody transfer from sows to shoats although transfer via the colostrum and placenta were two recognized possibilities. HI and neutralizing antibodies developed regularly within 1–4 weeks of natural or experimental swine infection by JE virus, but CF antibodies formed in only 18 per cent of 61 pigs infected naturally at farms and in only two of four pigs after subcutaneous inoculation of virus at the laboratory. Although the neutralization test was most sensitive for detection of maternal antibody, the HI test, because of the ease and and inexpense of performance, and the promptness with which the test became positive after infection, proved best for evaluating recent swine infection near Tokyo, where no other Group B arbor virus was endemic. The lack of consistent quantitative relationships or temporal concurence in development of the different antibodies following infection supported the conclusion that HI, CF and neutralization tests measured three different antibodies to JE virus in pigs. Viremia was demonstrated following natural infection of pigs in mosquito traps. After subcutaneous inoculation of JE virus at the laboratory, virus was found in blood for 4 days and to titers of 2.5–2.6 log LD50/0.03 ml of blood.