Genetic diversity and population structure of plasmodium falciparum from four epidemiological locations in Malawi

In malaria-endemic regions, Plasmodium falciparum (P. falciparum) infection is characterized by extensive genetic/antigenic diversity. Describing this diversity provides important information about the local molecular epidemiology of infecting P. falciparum parasites. Intriguingly, one of the major obstacles to the development of an effective malaria vaccine has been the genetic polymorphisms exhibited by P. falciparum genes encoding targets of human immune system. This situation has necessitated the development of polyvalent vaccines with wide antigenic coverage that would increase the likelihood of vaccine efficacy that covers wide geographical areas of malaria endemic countries. Limited reports are available on the population genetic diversity and structure of P. falciparum in Malawi, and this is of particular concern as the country has put in place several interventions to combat the disease. The primary aim of the research project was to determine the genetic diversity and population structure of P. falciparum isolates and comparing complexity from four different epidemiological settings in Malawi using msp-2 gene polymorphisms. Samples were collected from four epidemiological locations in the north, centre and southern regions of Malawi. The diversity and genetic differentiation of P. falciparum populations were analyzed based on the highly polymorphic block 3 msp-2 gene. One hundred and twenty patient samples who presented with signs and symptoms of malaria and who had microscopically confirmed P. falciparum infection were enrolled in the study after they had satisfied the inclusion criteria. Parasite DNA was extracted from the blood spot on to filter paper and analyzed by genotyping the msp-2 gene using allele-specific nested PCR. A total of 28 msp-2 block 3 fragments, defined by the size and the allelic types were detected in the 102 patients. The length variants of the PCR product ranged from 240basepairs (bp) to 450bp for the K1/FC and 410bp to 780bp for the 3D7/IC allelic families. Isolates of the 3D7 alleles were predominant in the population (59 percent), compared to isolates of the K1/ FC27 alleles (41 percent) and for 3D7 and K1 most of the isolates were monoclonal infections. In comparisons between the sites, we observed the highest prevalence of mixed infection in Mwanza (46.7 percent) followed by Dwangwa (23.3 percent) compared to Bolero (16.7 percent) and Mitundu (16.7 percent). The difference in prevalence of mixed infections between Mwanza and the other sites was statistically significant (p=0.041). There was also a non-significant trend towards a higher mean genotype number per isolate in the children aged >5 years compared to those below 5 years of age. These data suggest differences in prevalence rates of mixed infections in different geographical/epidemiological settings in Malawi. Further studies are needed to confirm, with larger sample sizes, the observation of a non-significant trend towards higher multiclonality of infection in older children in malaria endemic areas of Malawi Key words: Population structure, genetic diversity, merozoite surface protein-2, DNA extraction, epidemiology, Malaria, allele-specific, polymerase chain reaction (PCR), Plasmodium