1974 Volume 24 Issue 1 Pages 65-70
In an attempt to explore the reason of sudden decrease in number of cases of Japanese Encephalitis observed in Gunma Prefecture as well as in all Japan since 1968, ecological fild study has been carried out. Following findings have been disclosed through the study;
1) During the period from 1959 to 1967 when the epidemics of Japanese Encephalitis were observed at the interval of every three years in Gunma Prefecture, size of epidemics tended to be possitively associated with the number of mosquitoes carrying the agent virus in the year.
2) The fact that no patient has been confirmed in the Prefecture since 1968 may be attributed largely to remarkable decrease of mosquitoes in number which resulted in decrease in quantity of the agent virus in the vectors followed by delay in time for the virus affecting the vectors.
3) In contrast with the years of epidemics before 1967 when the infection rate of the pig population, as measured by HI titers in serum against Japanese Encephalitis virus, had reached 100% by the August, in the non epidemic years after 1968, the infection rate did not rise to 100% until the end of observation period of the end of October.
