Genotyping of Plasmodium falciparum isolates by the polymerase chain reaction and potential uses in epidemiological studies

Abstract

The epidemiology of malaria results from the interactions of three gene 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 characterization 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 epidemiology, pathology and biology of this parasite, particularly when combined with simultaneous human and vector studies. This paper describes a polymerase chain reaction (PCR)-based assay which provides a sensitive, reproducible and practical method by which parasite populations within species can be characterized. In order to illustrate the suitability of the PCR assay, four polymorphic domains on the genes of three P. falciparum proteins (MSP1 blocks 2 and 4, MSP2, and GLURP) and one largely conserved region (MSP1 block 17) were chosen for amplification by PCR. DNA derived from 15 in-vitro cultured lines of P. falciparum (7 of which were cloned) and from blood samples obtained from infected patients in Thailand were used as templates for PCR amplification. The amplification products were analysed by gel electrophoresis for length polymorphisms. Seven allelic variants of GLURP, five of MSP1 block 2, three of MSP1 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 applicability of this type of genotyping to epidemiology and urges the adoption of international standards for its use so that data from different areas and different times can be compared.