Plasmodium falciparum populations from northeastern Myanmar display high levels of genetic diversity at multiple antigenic loci

Abstract

Levels of genetic diversity of the malaria parasites and multiclonal infections are correlated with transmission intensity. In order to monitor the effect of strengthened malaria control efforts in recent years at the China-Myanmar border area, we followed the temporal dynamics of genetic diversity of three polymorphic antigenic markers msp1, msp2, and glurp in the Plasmodium falciparum populations. Despite reduced malaria prevalence in the region, parasite populations exhibited high levels of genetic diversity. Genotyping 258 clinical samples collected in four years detected a total of 22 PCR size alleles. Multiclonal infections were detected in 45.7% of the patient samples, giving a minimum multiplicity of infection of 1.41. The majority of alleles experienced significant temporal fluctuations through the years. Haplotype diversity based on the three-locus genotypes ranged from the lowest in 2009 at 0.33 to the highest in 2010 at 0.80. Sequencing of msp1 fragments from 36 random samples of five allele size groups detected 13 different sequences, revealing an additional layer of genetic complexity. This study suggests that despite reduced prevalence of malaria infections in this region, the parasite population size and transmission intensity remained high enough to allow effective genetic recombination of the parasites and continued maintenance of genetic diversity.

In Vitro Sensitivities of Plasmodium falciparum Isolates from the China-Myanmar Border to Piperaquine and Association with Polymorphisms in Candidate Genes

“…Briefly, frozen parasite stocks were thawed, washed twice with RPMI 1640 medium at 37°C, and mixed with fresh type O ϩ human red blood cells (RBCs) suspended at a 5% hematocrit in a complete medium containing HEPES (5.94 g/liter), hypoxanthine (50 mg/liter), Albumax II (5 g/liter), RPMI 1640 (10.4 g/liter), gentamicin (5 mg/liter), NaHCO 3 (2.1 g/liter), and 9% AB ϩ human serum. In order to select monoclonal infections, parasites were genotyped at three polymorphic genes-merozoite surface protein 1 (msp1), msp2, and glutamaterich protein (glurp)-as previously described (33,34). On average, parasites were continuously cultured for 3 to 4 weeks before the drug sensitivities were measured.…”

Competition between Plasmodium falciparum strains in clinical infections during in vitro culture adaptation

“…Based on earlier genotyping results of clinical samples (Yuan et al, 2013), we selected 15 mixed infections to follow the dynamics of the parasite clones during in vitro culture adaptation. To reduce the complexity of the analysis, we only selected isolates with mixed alleles at the msp1 locus, while msp2 and glurp were both monomorphic (Table 1).…”

“…Thus, it would be interesting to compare the in vitro competition of the strains in the presence of antibodies from the endemic host populations. As antibodies against Plasmodium antigens such as MSP1 can be long-lived in exposed host populations even in hypoendemic areas (Wipasa et al, 2010), they could be responsible for the observed temporal dynamics of the different msp1 allele morphs through the years (Yuan et al, 2013). …”

“…Even in areas of low endemicity and seasonality of malaria such as the Greater Mekong Subregion of Southeast Asia, mixed-species and mixed-strain infections are also common (Cui et al, 2003; Mayxay et al, 2001; Yuan et al, 2013). Mixed infections arise from inoculations of genetically diverse parasites by a single or multiple mosquitoes, which serve to generate genetic diversity of the parasite population.…”

“…For immune-mediated apparent competition, immunity elicited by one parasite strain contributes to the suppression of population densities of the co-infecting strains (Raberg et al, 2006). Due to the highly polymorphic nature of parasite antigens, immunity against malaria parasites can be strain transcending, which may partially account for the temporal dynamics of parasite genotypes (Yuan et al, 2013). …”