豚に対する日本脳炎生ワクチン接種の野外実験

Abstract

Since 1968 to 1970, field studies in immunization of pigs have been carried out in Kyoto city, to control the transmission of Japanese encephalitis virus (JEV) into mosquito population. One or one and half months before JE epidemic season, a total of 13, 900 pigs was vaccinated with the live attenuated Japanese encephalitis vaccine (m-strain) produced by Dr Inoue, No serious side reaction due to the vaccination was reported.The result of the vaccination was followed by the determination of the hemagglutination inhibition (HI) antibody level in pigs and by the survey of the infection rate of engorged mosquitoes caught in pig pens. To determine the HI antibody level, blood in visibly engorged mosquitoes was employed. The infection rate was calculated from the JEV isolation rate of engorged mosquitoes which had been incubated for 7-10 days after collection.HI antibody titers of 1:20 or 1:40 were observed in the vaccinated pigs although the secondary sharp rises were noted at a time when the wide spread of JEV was observed in nature. The infection rates of the pig pen administered with vaccine were markedly lower than the rates of those not vaccinated; the former was less than 1/2 of the latter at the highest point of the infection rates.These results suggest that vaccination on pigs seems to be applicable in the field to reduce the density of infected mosquitoes.