| In areas with Plasmodium vivax transmission, malaria cases may represent primary infections or recurrent infections. Recurrent infections may be due to relapse (from hypnozoites), recrudescence (from persistent blood stages), or reinfection (from additional infectious mosquito bites). Because there are no clinical or parasitological criteria to distinguish among recurrent infections, a molecular strategy based on genetic polymorphic markers and the polymerase chain reaction (PCR) was developed to distinguish relapse from reinfection. Four sets of primers were designed and used in nested PCR to amplify polymorphic regions of P. vivax genes, including the fragments between Blocks 5 and 6, and Blocks 8 and 9 of the merozoite surface protein 1 (MSP1), the fragment between Regions I and II of the circumsporozoite protein (CSP), and a fragment between two conserved regions of the gametocyte blocking antigen 1 (GAM1). The combination of these four markers provided a sensitive system to characterize P. vivax and P. cynomolgi parasite types based on the pattern of their amplification products on agarose gel electrophoresis or amplicon length polymorphisms (ALPs).;The hypothesis that parasites which cause relapse are indistinguishable from those that caused the initial bloodstream infection was examined using the P. cynomolgi/rhesus monkey model of human P. vivax infection. Two rhesus monkeys were infected with sporozoites of P. c. bastianellii. PCR amplification products obtained from relapses were indistinguishable from each other and from the initial bloodstream infections in terms of size (MSP1 5/6 and 8/9, and CSP markers) and DNA sequence (MSP1 5/6 and CSP markers). Therefore, demonstrating the same parasite type in the initial infection and subsequent relapses.;Field studies were carried out in Colombia, South America, in collaboration with Corporacion CIDEIM (Centro Internacional de Entrenamiento e Investigaciones Medicas) located in Cali. The distribution of P. vivax parasite types was examined in endemic communities (Tumaco, Buenaventura, and the Oriental Plains) in order to estimate the probability of reinfection with the same parasite type. During the study period (March 1994 to October 1996), 339 filter paper blood samples from P. vivax infected patients were analyzed by PCR, including paired blood samples (initial bloodstream infection and subsequent recurrence) obtained from ten persons with recurrent infections. (Abstract shortened by UMI.)... |
