V. Evaluation of Cross-Immunity against Type 1 Dengue Fever in Human Subjects Convalescent from Subclinical Natural Japanese Encephalitis Virus Infection and Vaccinated with 17D Strain Yellow Fever Vaccine
Antibodies against repetitive epitopes on Plasmodium falciparum and P. vivax circumsporozoite (CS) proteins and epitopes on the 45-kD and 185–200-kD P. falciparum merozoite surface antigens were measured by radioimmunoassay in Weheragala, a malaria-endemic site in the dry zone of Sri Lanka. Antibodies were measured in sera collected in February at the end of the main malaria transmission season and three months later in May during the low transmission period. Ninety-seven percent of the sample population had antibodies to the P. falciparum CS repeat in February and a significant proportion possessed antibodies directed against all epitopes tested. Concentrations and prevalence of antibodies to the CS repeats decreased with time after the end of malaria transmission in adults and children. Similar temporal changes were observed with antibodies to the epitopes on merozoite surface antigens. Children 7–15 years of age had lower antibody concentrations against most epitopes than adults. Antibody concentrations to two different epitopes within the same merozoite surface antigen showed significant association as did antibody levels against the P. falciparum CS repeat and the predominant P. vivax CS repeat. However, antibody concentrations did not correlate with the presence of blood-stage malaria infections.