MOLECULAR ANALYSIS OF PLASMODIUM-VIVAX RELAPSES USING THE MSP1 MOLECULE AS A GENETIC-MARKER

Plasmodium vivax has hepatocytic dormant stages, hypnozoites, that cau se relapses. This work compared paired isolates from primary attacks a nd relapses obtained from 10 individuals in Brazil using the merozoite surface protein 1 gene, PvMSP1, as a genetic marker. Four samples fro m primary attacks contained genetically mixed parasites harboring the 2 major PvMSP1 allelic forms. PCR revealed the presence of these 2 for ms in the relapse parasites of 2 patients, demonstrating that the acti vation of hypnozoites is not clonal. DNA sequences from paired primacy /relapse samples demonstrated that the parasites from the primary atta ck are identical to those in relapse samples in which the same allele forms were detected in both infections. Studies on the naturally acqui red humoral immune responses of these patients against a recombinant p rotein expressing the C-terminus PvMSP1 demonstrated an increase in th e titers, affinity maturation, and predominance of the IgG1 subclass d uring the relapse.