Genetic Diversity of Plasmodium falciparum Populations in Malaria Declining Areas of Sabah, East Malaysia

Abstract

Malaysia has a national goal to eliminate malaria by 2020. Understanding the genetic diversity of malaria parasites in residual transmission foci can provide invaluable information which may inform the intervention strategies used to reach elimination targets. This study was conducted to determine the genetic diversity level of P. falciparum isolates in malaria residual foci areas of Sabah. Malaria active case detection was conducted in Kalabakan and Kota Marudu. All individuals in the study sites were screened for malaria infection by rapid diagnostic test. Blood from P. falciparum-infected individuals were collected on filter paper prior to DNA extraction. Genotyping was performed using merozoite surface protein-1 (MSP-1), merozoite surface protein-2 (MSP-2), glutamate rich protein (GLURP) and 10 neutral microsatellite loci markers. The size of alleles, multiplicity of infection (MOI), mean number of alleles (Na), expected heterozygosity (He), linkage disequilibrium (LD) and genetic differentiation (FST) were determined. In Kalabakan, the MSP-1 and MSP-2 alleles were predominantly K1 and FC27 family types, respectively. The GLURP genotype VI (751–800 bp) was predominant. The MOI for MSP-1 and MSP-2 were 1.65 and 1.20, respectively. The Na per microsatellite locus was 1.70. The He values for MSP-1, MSP-2, GLURP and neutral microsatellites were 0.17, 0.37, 0.70 and 0.33, respectively. In Kota Marudu, the MSP-1 and MSP-2 alleles were predominantly MAD20 and 3D7 family types, respectively. The GLURP genotype IV (651–700 bp) was predominant. The MOI for both MSP-1 and MSP-2 was 1.05. The Na per microsatellite locus was 3.60. The He values for MSP-1, MSP-2, GLURP and neutral microsatellites were 0.24, 0.25, 0.69 and 0.30, respectively. A significant LD was observed in Kalabakan (0.495, p<0.01) and Kota Marudu P. falciparum populations (0.601, p<0.01). High genetic differentiation between Kalabakan and Kota Marudu P. falciparum populations was observed (FST = 0.532). The genetic data from the present study highlighted the limited diversity and contrasting genetic pattern of P. falciparum populations in the malaria declining areas of Sabah.

Genetic diversity and population structure of Plasmodium falciparum in Kenyan–Ugandan border areas

“…Explanations for the persisting high genetic diversity are the increasing number of asymptomatic malaria cases with higher gametocytaemias, vector resistance against pyrethroids which sustain transmission and the removal of antimalarial drug selection pressure following the replacement of the less effective sulphadoxine-pyrimethamine in 2006 by the highly efficacious ACT [8,12,15,16,39,40]. It is also worth noting that the P. falciparum genetic diversity reported here is similar to the genetic diversity of parasite populations from other countries in sub-Saharan Africa [22,41], and it is higher than the genetic diversity of populations from low malaria-endemic settings in the Pacific Region, Southeast Asia and South America [22,[42][43][44][45][46].…”

Prevalence of Plasmodium falciparum Molecular Markers of Antimalarial Drug Resistance in a Residual Malaria Focus Area in Sabah, Malaysia

“…In addition, the genetic differentiation analysis has assured the large variation of genetic pattern between the P . falciparum populations in the areas of Sabah [45, 46]. Another possible explanation to this is the different sampling period between present study and previous studies conducted in Kalabakan [6, 30] and Pahang [9] areas where samples were collected before the implementation of ACT in the country.…”

Population Genetics and Molecular Epidemiology of Eukaryotes

“…Even under ideal conditions, they tend to underestimate MOI compared to sequencing approaches (10). As control programs achieve lower prevalence, the loss of diversity can further decrease the ability to differentiate relapse from new infections locally (91), while genetic differentiation between foci of infection increases (79). The small number of markers also does not permit a higher order analysis of population dynamics such as effective population size or differentiation.…”

“…The distribution of P. falciparum in Malaysia stands in contrast to West Africa. Here endemicity has been declining for some time, and there are high levels of differentiation between sites and elevated LD suggesting elevated inbreeding (8, 79). While the fragmentation suggests an island-by-island approach may be successful for malaria control, the increased LD and even clonal expansion in some areas may make monitoring difficult, since it will become more difficult to distinguish recrudescence from reinfection where individuals are highly related.…”