Application of genetic markers to the identification of recrudescent Plasmodium falciparum infections on the northwestern border of Thailand

Parasite genotyping by the polymerase chain reaction was used to distinguis h recrudescent from newly acquired Plasmodium falciparum infections in a Ka ren population resident on the northwestern border of Thailand where malari a transmission is low (one infection/person/year). Plasmodium falciparium i nfections were genotyped for allelic variation in three polymorphic antigen loci, merozoite surface proteins-1 and -2 (MSP-1 and -2) and glutamate-ric h protein (GLURP), before and after antimalarial drug treatment. Population genotype frequencies were measured to provide the baseline information to calculate the probability of a new infection with a different or the same g enotype to the initial pretreatment isolate. Overall, 38% of the infections detected following treatment had an identical genotype before and up to 12 1 days after treatment. These post-treatment genotypes were considered recr udescent because of the low (< 5%) probability of repeated occurrence by ch ance in the same patient, This approach allows studies of antimalarial drug treatment to be conducted in areas of low transmission since recrudescence s can be distinguished confidently from newly acquired infections.