Serologic responses of Korean soldiers serving in malaria-endemic areas during a recent outbreak of Plasmodium vivax.

Anti-Pv200 antibody levels were assessed in samples from endemic areas of Plasmodium vivaxmalaria in the Republic of Korea (ROK), using an indirect enzyme-linked immunosorbent assay (ELISA) method. Asymp- tomatic carriers of P. vivax were detected using nested polymerase chain reaction (PCR) of blood samples. Anti- Pv200 antibody levels in 20 vivax malaria patients (optical density standard deviation (OD SD) values 1.85 0.29 of IgG isotype and 1.33 1.33 of IgM isotype) were markedly higher than those of uninfected, malaria-naive controls (0.08 0.16 of IgG isotype and 0.04 0.04 of IgM isotype). Antibody levels for 7 out of 8 soldiers with a recent malaria infection were sustained above the cut-off values for 4 months after successful treatment. Analysis of serum collected from 40 healthy, asymptomatic soldiers who had a P. vivax malaria attack within 3 months after our sampling, revealed 11 antibody-positive samples (27.5%), compared to 5 positive samples (12.5%) collected from a random selection of 40 soldiers. Among a larger pool of 1,713 soldiers who had served in high-risk areas for P. vivax transmission, 15% were antibody positive. Among 1,000 blood samples from asymptomatic soldiers who had served in the high-risk areas, 4 samples (0.4%) were parasite positive, as determined by nested PCR. Our results show that anti-Pv200 antibody levels can provide useful information in the late diagnosis of P. vivax malaria infection in a previously naive population and also in large seroepidemiologic studies. Furthermore, our results suggest that asymptomatic P. vivax carriers could be important in the current outbreak of malaria in Korea.