STUDY OF JAPANESE ENCEPHALITIS VIRUS IN CHIANGMAI VALLEY, THAILAND

Abstract

One hundred persons living in the Chiangmai Valley of northern Thailand were hospitalized with encephalitis in 1970; 83 cases occurred in May, June and July, and 17 cases occurred in August through December. Twenty patients died. Males comprised two-thirds of cases. The peak age incidence for both sexes was 5–9 years; only 6% of cases were over age 30. Patients and deaths were distributed throughout the Valley, with case incidence rates by district similar to the overall Valley rate of 14.7 per 100,000 population. Japanese encephalitis virus (JEV) infections were serologically confirmed by hemagglutination-inhibition and complement-fixation tests in 84% of cases submitting adequate serum pairs; about three-fourths of these had a primary JEV antibody response and one-fourth a secondary group B arbovirus type response. Epidemiologic evidence supported the concept that the secondary response occurred only in people who had prior group B arbovirus experience, and that this experience was probably due to dengue infection. The finding of JEV-specific IgM antibody in serum from the majority of the secondary responders and from all primary responders tested, provides immunologic evidence for first JEV infection. It is concluded that prior infection with dengue did not guarantee protection against the development of encephalitis after subsequent JEV infection.