EPIDEMIOLOGICAL ANALYSES OF JAPANESE ENCEPHALITIS VIRUS SPREAD FROM MOSQUITOES TO PIGS THROUGH 5 YEARS

Abstract

The results from a five year survey on the antibody rise in summer against JE virus in pigs in Natori District of Miyagi Prefecture were analysed with regard to the time of antibody rise, detection rate of 2-ME sensitive antibodies, level of antibody titers, and duration of high-titered antibodies. These serological results obtained in pigs were finally correlated to the isolation rate of JE virus from mosquitoes collected in the same area and to the incidence of JE patients among 1, 750, 000 residents in Miyagi Pre-fecture. On the basis of this limited 5 year survey, one can conclude the following: 1. A hundred percent infection among pigs and positive isolation of the virus from mosquitoes have consistently been observed during these 5 years. Thus the cyclic outbreak between mosquitoes and pigs existed every year, even in the absence of the spread to humans. 2. The earlier the appearance of the initial antibody rise and the longer the duration of high-titered antibody among pigs, the higher the incidence of infection among humans. 3. The time of the initial and subsequent isolation of virus from mosquitoes coincided completely with the time of antibody rise among pigs, as was pointed out by us 5 years ago. 4. A minor pre-outbreak and minor post-outbreak of infection among pigs were noticed before and after the main outbreak among pigs. The fact was clearly illustrated by pursuing 2-ME sensitive antibodies. 5. The height of antibody titers in pig sera was assumed to be a reliable indicator to predict the amount of virus harbored by mosquitoes. The titer in pig sera was lowest in a year of the least incidence of human infection, irrespective of the fact that 100% of pigs were infected every year. 6. An assumption was proposed to predict the appearance of virus harboring mosquitoes almost 3 weeks in advance by setting the threshold number of 150 of the candidate mosquitoes trapped per night under a defined condition.