Although the endemic season of Japanese encephalitis lasts from May through October, sporadic cases occur in other months of the year. To appreciate the real situation of Japanese encephalitis virus (JEV) activity throughout the year, a survey was conducted using hemagglutination-inhibition test to detect the presence of anti-JEV antibodies in pigs' sera, which were collected from 4 regions of Taiwan between January 2000 and January 2001. Results indicate that (1) JEV-infected pigs were found throughout the year; (2) the prevalence rates of JEV in the 4 regions in descending order were 70% in Miaoli, 59% in Hualien, 52% in Pingtung, and 49% in Nantou; (3) similar to that in 1990, the peak endemic months appeared 1 month after the date of 50% seroconversion (May 21, 2000); (4) infected pigs were present during the period from December through April as a reservoir for over-wintering of JEV; and (5) there was a suggestive evidence for the occurrence of sporadic cases of JEV during the December-April period. In conclusion, JEV propagates and is active indigenously in the winter as well as other seasons of the year.
J Microbiol Immunol Infect 2002;35:12-16.