福岡地方における日本脳炎媒介カの出現消長と保毒状況, 1964 年と 1965 年の成績

Abstract

Since 1962, a long run project of the studies on the seasonal prevalence and JEV infection of the vector mosquito, Culex tritaeniorhynchus-vishnui complex, has been performed at a farm village near Fukuoka City, Uchihashi, Kasuyagun, Fukuoka Prefecture. In the present paper the results obtained in 1964 and 1965 are fully presented. The results and logical conclusions are summarized as follows : 1) Seasonal prevalence of the vector mosquito population : The abundant season of the vector mosquito was in the period from mid-July to mid-August in 1964 and in the period from late July to late August in 1965. 2) Natural infection of vector mosquitoes : The mosquito infections of the two years were very similar in the time of infection, the length of infection period and the isolation rate. Main period of the mosquito infection did not exceed four to five weeks, despite the fact that the vector mosquito population remained satisfactory for about eight weeks. This strongly suggests that the natural decrease of the infected mosquitoes may be due to the scarcity of amplifying hosts but not to the decline of the total population of vector mosquitoes. 3) Correlation between the mosquito infection and the epidemic of human encephalitis : Aside from the scattered occurrence of reported cases, the regular outbreak of confirmed cases yearly followed on the onset of the mosquito infection with the time lag of about two weeks, and the length of the epidemic corresponded approximately with that of the mosquito infection. A special attention should be paid to the difference between the mosquito infection in 1963 and those in 1964 and 1965 as of the epidemiological importance, because the epidemic of human encephalitis was far larger in the former year than in the latter years. The time of the mosquito infection was distinctly later in 1963 than in the subsequent two years. The significance of this problem will be elucidated in further studies.