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 P lasmodium vivax malaria in the Republic of Korea (ROK), using an indirect e nzyme-linked immunosorbent assay (ELISA) method. Asymptomatic 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 isoty pe and 1.33 +/- 1.33 of IgM isotype) were markedly higher than those of uni nfected, 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 aft er successful treatment. Analysis of serum collected from 40 healthy, asymp tomatic soldiers who had a P. vivax malaria attack within 3 months after ou r sampling, revealed 11 antibody-positive samples (27.5%), compared to 5 po sitive samples (12.5%) collected from a random selection of 40 soldiers. Am ong 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 sample s (0.4%) were parasite positive, as determined by nested PCR. Our results s how that anti-Pv200 antibody levels can provide useful information in the l ate diagnosis of P. vivax malaria infection in a previously naive populatio n and also in large seroepidemiologic studies. Furthermore, our results sug gest that asymptomatic P. vivax carriers could be important in the current outbreak of malaria in Korea.