Serological and virological studies on patients with dengue hemorrhagic fever (DHF) in Chanthaburi province, Thailand. I. Serological studies on paired sera from DHF patients by neutralization (N), hemagglutination inhibition (HI) and staining tests.

Twenty paired sera were collected from DHF patients admitted to the provincial hospital of Chanthaburi, Thailand in 1978. They were tested by the N and HI tests and a newly developed staining test against all four serotypes of dengue (DEN) virus and Japanese encephalitis (JE) virus. Four patients were demonstrated to be cases of primary DEN infection and the other 16 to be cases of secondary DEN infection. The serotypes of recent DEN infections were easily determined by the N test in cases of primary infection, but were difficult to determine in cases of secondary infection because of the strong cross reactions among DEN serotypes. These cross reactions seemed to be due to subgroup-specific antibody, which reacts with all 4 serotypes of DEN virus in the N test. However, acute phase sera from some patients with the secondary type of antibody response reacted monospecifically in the N test, indicating the serotype of the primarily infecting viruses.