大阪府における日本脳炎(日脳)の生態学的研究

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Long-term field studies on Japanese encephalitis (JE) in Osaka Prefecture revealed the following points. 1) Though there were 71-346 human cases in the epidemic years of 1965-1967, the incidence of JE has markedly decreased since 1968. In addition, there has been a marked decrease in the number of districts with developed paddy fields and high density of swine farms since 1965. 2) The abundance of Culex tritaeniorhynchus decreased annually during the years 1968-1997. 3) In the 1990s the mosquitoes collected from many piggeries were not infected with the JE virus. In most of the districts, the mosquito populations may be far below the critical level for JE virus infection. 4) It was noted that the critical level of mosquito populations below which the JE virus could no longer be isolated varied according to such environmental conditions as the scarcity of paddy fields near a piggery and the breeding number of swine per piggery. As large-scale breeding farms having a large number of swine per piggery have recently been increasing, a rise in this critical level was observed. 5) In 1)-4), from the latter half of 1960s to the 1990s, the total absolute amount of infected mosquitoes in Osaka Prefecture markedly diminished, greatly reducing the possibility of JE virus transmission to humans. 6) Further, it seemed probable that according to the small number of swine per piggery, high enough density of swine farms might be necessary for producing a large absolute amount of infected mosquitoes, which in turn brought about the outbreaks of JE, in the 1960s because small-scale breeding farms were common. Thus, it seemed that the environmental condition for mosquito breeding such as the density of swine farms is one of the essential factors involving the epidemics of JE.
日本衛生動物学会の論文
2002-03-15

大阪府における日本脳炎(日脳)の生態学的研究

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