北海道における日本脳炎の疫学的研究

Abstract

Sero-epizootiological studies were performed on Japanese encephalitis (JE) in wild and domestic animals in Hokkaido. The relation of climatic factors to JE outbreaks was also investigated.1. Hemagglutination-inhibiting (HI) antibodies against both Nakayama and JaGAr-01 strains were found in 9 (1.5%) of 593 swine sera collected in different parts of Hokkaido in 1970. All the 9 sera were among those collected in the southern part (Hiyama district) of Hokkaido. Two of them were senitive to 2-ME.2. A total of 12 pools of mosquitoes belonging to Aedes vexans nipponii, Culex pipiens pallens, and Anopheles sinensis were collected in the the Hiyama district. No virus was isolated from any of them.3. Neutralizing antibody to the JaGAr-01 strain was detected from 48 (7.8%) of 604 bovine sera collected in different parts of Hokkaido by means of the microtiter method. The positive rate decreased gradually northward and became higher in accordance with the advance in age.4. Sera were collected from 35 wild birds, 87 rodents, and 28 bats in Hokkaido in 1970. All of them were negative for the microneutralization test with the JaGAr-01 strain.5. Climatic conditions for effect were investigated on the outbreak of JE in domestic animals by using the ten-day records of air temperature and precipitation over a period from April to October. An epizootic of JE occurred in a year when the mean ten-day temperature was 20°C or higher in summer, although it varied in size with the duration of the mean temperature. Precipitation was also found to affect JE infection of pigs in Hon shu, but such was not clearly demonstrated in Hokkaido.