Thirty-seven strains of dengue viruses were isolated during the investigation of an epidemic of dengue hemorrhagic fever with direct and delayed plaque methods in LLC-MK2 cell culture. Identification of these agents by plaque-reduction neutralization tests indicated that serotypes 1, 2, and 3 were represented. Neutralization tests indicated that strains recovered and passaged in cell culture were less readily neutralized than mouse-brain-passage strains.
A survey for dengue and chikungunya antibody was carried out in 646 children ages 2 to 11 years from the village of Ang Tong in February 1966 before an epidemic of dengue hemorrhagic fever. A second serum specimen was obtained from 336 of these children in February 1967. Dengue-antibody prevalence was found to increase rapidly with age, reaching 80% by 4 years. Chikungunya prevalence was not age-dependent, but about 50% of all ages showed antibody. During the 1-year interval between specimens, the initial attack rate for dengue was 47%. The reinfection rate was 30%, and the attack rate for chikungunya was 4%. The amount and severity of clinical illnesses observed during the epidemic was greater in the reinfection group than in the primary infection group.
Three cases of dengue shock syndrome occurring in the group under study were shown to be due to a second dengue infection.
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