Infection Patterns of Nude Mice to Japanese Encephalitis Virus : Report 2. Virus Recovery from Organs of Nude Mice during One Year Study Period After Infection and Histopathological Findings in Organs of Nude Mice at Three Weeks…

Seventy BALB/c nu/nu and 74 BALB/c nu/+ mice which were the survivors at 8 weeks after subcutaneous inoculation with JaTH 160 strain of Japanese encephalitis virus (JEV) were used in this experiment. Each of nu/nu and nu/+ mice was sacrificed at 20, 30, 40 and 53 weeks after inoculation, and superficial lymph nodes and brains of mice of both groups were assayed for virus titer and each sera was tested for neutralizing antibody. In the next experiment, total 30 of BALB/c nu/nu mice were inoculated in the same way, and virus recovery, titration of neutralizing antibody and histopathological examination were carried out. 1) In the 20― to 53― week period after inoculation, 8 of 70 nu/nu mice died. One mouse which died at 83 days showed apparent symptoms of Japanese encephalitis (JE) and in 2 cases of these 8 nu/nu mice, which died at 83 and 90 days, virus was detected from brains and superficial lymph nodes, and in one case which died at 246 days, virus was detected only from superficial lymph nodes. 2) In nu/nu mice, virus was detected from superficial lymph nodes of 2 of 10 mice at 20 weeks and from superficial lymph nodes of 3 of 10 mice at 40 weeks and from inguinal lymph node of 1 of 10 mice at 53 weeks after inoculation under the presence of high titers of neutralizing antibody. 3) In the next experiment, all survivors were sacrificed at 21 days after infection, and histopathological findings in organs of the above 15 survivors were examined. In one mouse, which showed clinical signs and from which virus was detected, very poor perivascular cell infiltration was observed in the brain, but no marked changes were recognized in the remaining 14 including 4 virus holders. It is strongly suggested by the above findings that cell mediated immunity plays important role in the onset of JE following JEV infection in miee.