北海道における日本脳炎の疫学的研究　第2編　北海道住民の日本脳炎ウイルスに対する中和抗体保有状況

A total of 2,760 persons fo varying ages born in different parts on Hokkaido and who have been residing at their places of birth were subjected to the present study. They had never travelled in endemic areas during the summer season to the best of their knowledge. The sera of these persons were titrated for neutralizing antibody against JaGAr 01 strain of JE virus to study retrospectively the virus infection in the past. The summarized data were as follows : 1. Approximately 9% of the subjects in the southern district were found to have the antibody. The sero-positive rate decreased to 1.9-2.9% in the central and eastern districts, and to 1.1% in the northern district. In other words, the sero-positive rate decreased with the increase in lattitude. 2. In the southern district the number of seropositive individuals increased progressively with the increase in age, reaching its highest level at the age 60-64. This suggests that JE virus has frequently been disseminated there for long years, although the amount of virus disseminated may have been small. In other districts, however, the antibody was detectable almost exclusively in those of 50 years of age or older. 3. The relationship was investigated between the age distribution of serum antibody, which may reflect the dissemination of JE virus in the past, and the years in which JE outbreaks occurred in man and animals. In the southern districts, the seropositive rate by age of inhabitants was well correlated with JE outbreaks in the past. However, JE epizootics which occurred recently in the central and eastern districts seemed not to influence the antibody distributions in man of the same districts. 4. The duration of neutralizing antibody in sera of the naturally infected was studied for those who had immigrated to Hokkaido after living for different periods of time in endemic areas of JE. The longer the subjects resided in an endemic area, the higher the seropositive rate was-is a trend that was apparent. The rate declined gradually with the increase in the period of living in Hokkaido after immigration, but 11.1% of those who had lived more than 50 years after immigration retained the antibody.