Ecology of Japanese Encephalitis Virus in Nagasaki Area, Okinawa and Amami Islands

ナノ-予"/、/川川/り/'卜ん."/りぷ.\.▼山s/高'/-iノ1げ.什'小(''h、J-i-/J(高卜、▲\'".q.山"ん/卜机上i'叫、. ABSTRACT: Comparative investigations on the ecology of Japanese encephalitis (JE) virus have been made in Nagasaki area, Okinawa and Amami islands. In Nagasaki area, the virus dissemination in nature had been observed in a long duration (35 to 100 days per year) from 1964 to 1968, although it has been shortened up to two weeks after 1969 until now. In the interepidemic season, the overwintering of the virus still remains as a difficult problem. In the main island of Okinawa, the virus has disseminated about two or three months earlier in every epidemic season than in Nagasaki area. In Amami island, a peculiar evidence was found that JE virus was isolated from hibernated female mosquitoes of Culex tritaeniorhynchus caught in winter, (February), 1973, and thereafter the virus was continuously transmitted between vector mosquitoes and swine in that year. However, it was interrupted in the interepidemic season in 1974 and the virus isolation was made in the middle patrt of July, 1974. It was concluded that the localized persistence of the virus might be preserved under a suitable condition. However, when it was interrupted in winter, the virus might be carried again from elsewhere to the survey area. These findings may support the carried-in theory on the problems of overwintering of JE virus in Japan. Itis a WellNknoWn fact thatJapanese encephalitis　(JE)virusis widespreadin Asia inc1udingIndia,South China,Korea and Marianaislands.The favorable situation for the transmisSion cycle and theinterepidemic persistence ofJE virus mightvariedby area among the temperate　(mainislands ofJapan and Korea),Subtropical(Amamiand OkinaWaislandsinJapan)and tropical(South East Asia)Z0neS.Itis cosideredthat, in the temperate ZOne,there may be unique circumstances for the transmiSsion o圭JE