GENOTYPING OF PLASMODIUM-FALCIPARUM ISOLATES BY THE POLYMERASE CHAIN-REACTION AND POTENTIAL USES IN EPIDEMIOLOGIC STUDIES

The epidemiology of malaria results from the interactions of three gen e pools-parasite, human, and mosquito vector-with one another and with their environment. Methods are being developed for characterizing the genetics of human populations at risk and of potential vectors. The c haracterization of natural populations of Plasmodium and knowledge of their distribution within the human and insect hosts in any given area under study would also greatly enhance understanding of the epidemiol ogy, pathology and biology of this parasite, particularly when combine d with simultaneous human and vector studies. This paper describes a p olymerase chain reaction (PCR)-based assay which provides a sensitive, reproducible and practical method by which parasite populations withi n species can be characterized In order to illustrate the suitability of the PCR assay, four polymorphic domains on the genes of three P. fa lciparum proteins (MSPI blocks 2 and 4, MSP2, and GLURP) and one large ly conserved region (MSPI block 17) were chosen for amplification by P CR. DNA derived from 15 in-vitro cultured lines of P. falciparum (7 of which were cloned) and from blood samples obtained from infected pati ents in Thailand were used as templates for PCR amplification. The amp lification products were analysed by gel electrophoresis for length po lymorphisms. Seven allelic variants of GLURP, five of MSPI block 2, th ree of MSPI block 4, and nine of MSP2 were detected. This high degree of polymorphism can be used to characterize the genetic composition of any parasite population, at a given time. The paper discusses the app licability of this type of genotyping to epidemiology and urges the ad option of international standards for its use so that data from differ ent areas and different times can be compared.