A technique for the separation of schizonts of Plasmodium falciparum is described. The different stages of the asexual cell cycle of the parasite were positioned according to their density in a continuous gradient of Percoll. Young trophozoites coincided with erythrocytes in a broad band corresponding to densities from 1.075 to 1.100 g/ml, whereas schizonts were concentrated at a density approximating 1.062 g/ml. The viability of the parasites was unimpaired by this procedure. Young trophozoites and schizonts continued their normal life cycle when cultured after the separation procedure. The percentage of recovery was high, reaching 80% of the initial quantity. Possible applications of the technique are discussed.
Colombian field isolates of Plasmodium falciparum were analyzed for genetic diversity. Fifty-three samples were collected as thick smears from patients living in Panguí, an isolated area with low migration. While the samples were being collected, Panguí was experiencing an epidemic outbreak of malaria. The samples were typified using nested polymerase chain reaction (PCR) amplification of block 2 of the merozoite surface protein 1 (MSP1) gene and nested PCR with mutation-specific primers for position 108 of the dihydrofolate reductase enzyme gene. The results for the circulating population of parasites in Panguí show low diversity-four allelic forms-using MSP1 as a marker, a fact that contrasts with data reported for certain Asian and African zones. A high percentage of mixed infections was observed, as was high complexity of the infection. No differential distributions were found for any allelic type.
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