Detection of Japanese encephalitis virus antibody in a pig on yonaguni island, where all pigs were slaughtered in 1997.

摘要

Japanese encephalitis virus (JEV) is distributed throughout Southeast Asia and South Asia (1). Pigs are seroconverted to JEV every year in Japan except for on Hokkaido, the northern island. JE patients are reported annually, although the number of the cases has been less than 10 since the 1990s. These facts indicate that JEV is still active in most areas of Japan (2). JEV is active on Okinawa Island as well; and pigs there are positive for JEV antibody (2). Although seroprevalence among pigs has been surveyed on the main Okinawa Island, the survey has not been performed on other islands of Okinawa Prefecture in the last 10 years. Yonaguni Island belongs to Okinawa Prefecture, and is located approximately 500 km southwest of Okinawa Island and aboutlOO km east of Taiwan (Fig. 1). When an outbreak of foot-and-mouth disease occurred among pigs in Taiwan in 1997, all pigs on Yonaguni Island were slaughtered. It is not known whether JEV was transmitted between pigs and Culex tritaeniorhynchus on Yonaguni Island before 1997. Thereafter, pigs were newly introduced to the island, and there are pig farms in two areas. In order to determine JEV activity on Yonaguni Island, we surveyed JEV antibody prevalence among pigs between July 2004 and March 2006.