Polymorphisms in the Haem Oxygenase-1 promoter are not associated with severity of Plasmodium falciparum malaria in Ghanaian children.

BACKGROUND: Haem oxygenase-1 (HO-1) catabolizes haem and has both cytotoxic and cytoprotective effects. Polymorphisms in the promoter of the Haem oxygenase-1 (HMOX1) gene encoding HO-1 have been associated with several diseases including severe malaria. The objective of this study was to determine the allele and genotype frequencies of two single nucleotide polymorphisms; A(-413)T and G(-1135)A, and a (GT)n repeat length polymorphism in the HMOX1 promoter in paediatric malaria patients and controls to determine possible associations with malaria disease severity. METHODS: Study participants were Ghanaian children (n=296) admitted to the emergency room at the Department of Child Health, Korle-Bu Teaching Hospital, Accra, Ghana during the malaria season from June to August in 1995, 1996 and 1997, classified as having uncomplicated malaria (n=101) or severe malaria (n=195; defined as severe anaemia (n=63) or cerebral malaria (n=132)). Furthermore, 287 individuals without a detectable Plasmodium infection or asymptomatic carriers of the parasite were enrolled as controls. Blood samples from participants were extracted for DNA and allele and genotype frequencies were determined with allele-specific PCR, restriction fragment length analysis and microsatellite analysis. RESULTS: The number of (GT)n repeats in the study participants varied between 21 and 46 with the majority of alleles having lengths of 26 (8.1%), 29/30 (13.2/17.9%) and 39/40 (8.0/13.8%) repeats, and was categorized into short, medium and long repeats. The (-413)T allele was very common (69.8%), while the (-1135)A allele was present in only 17.4% of the Ghanaian population. The G(-1135)A locus was excluded from further analysis after failing the Hardy-Weinberg equilibrium test. No significant differences in allele or genotype distribution of the A(-413)T and (GT)n repeat polymorphisms were found between the controls and the malaria patients, or between the disease groups, for any of the analysed polymorphisms and no associations with malaria severity were found. CONCLUSION: These results contribute to the understanding of the role of HMOX1/HO-1. This current study did not find any evidence of association between HMOX1 promoter polymorphisms and malaria susceptibility or severe malaria and hence contradicts previous findings. Further studies are needed to fully elucidate the relationship between HMOX1 polymorphisms and malarial disease.

Independent origin of plasmodium falciparum antifolate super-resistance, Uganda, Tanzania, and Ethiopia.

Super-resistant Plasmodium falciparum threatens the effectiveness of sulfadoxine-pyrimethamine in intermittent preventive treatment for malaria during pregnancy. It is characterized by the A581G Pfdhps mutation on a background of the double-mutant Pfdhps and the triple-mutant Pfdhfr. Using samples collected during 2004-2008, we investigated the evolutionary origin of the A581G mutation by characterizing microsatellite diversity flanking Pfdhps triple-mutant (437G+540E+581G) alleles from 3 locations in eastern Africa and comparing it with double-mutant (437G+540E) alleles from the same area. In Ethiopia, both alleles derived from 1 lineage that was distinct from those in Uganda and Tanzania. Uganda and Tanzania triple mutants derived from the previously characterized southeastern Africa double-mutant lineage. The A581G mutation has occurred multiple times on local Pfdhps double-mutant backgrounds; however, a novel microsatellite allele incorporated into the Tanzania lineage since 2004 illustrates the local expansion of emergent triple-mutant lineages.

Global and local genetic diversity at two microsatellite loci in Plasmodium vivax parasites from Asia, Africa and South America.

BACKGROUND: Even though Plasmodium vivax has the widest worldwide distribution of the human malaria species and imposes a serious impact on global public health, the investigation of genetic diversity in this species has been limited in comparison to Plasmodium falciparum. Markers of genetic diversity are vital to the evaluation of drug and vaccine efficacy, tracking of P. vivax outbreaks, and assessing geographical differentiation between parasite populations. METHODS: The genetic diversity of eight P. vivax populations (n=543) was investigated by using two microsatellites (MS), m1501 and m3502, chosen because of their seven and eight base-pair (bp) repeat lengths, respectively. These were compared with published data of the same loci from six other P. vivax populations. RESULTS: In total, 1,440 P. vivax samples from 14 countries on three continents were compared. There was highest heterozygosity within Asian populations, where expected heterozygosity (He) was 0.92-0.98, and alleles with a high repeat number were more common. Pairwise FST revealed significant differentiation between most P. vivax populations, with the highest divergence found between Asian and South American populations, yet the majority of the diversity (~89%) was found to exist within rather than between populations. CONCLUSIONS: The MS markers used were informative in both global and local P. vivax population comparisons and their seven and eight bp repeat length facilitated population comparison using data from independent studies. A complex spatial pattern of MS polymorphisms among global P. vivax populations was observed which has potential utility in future epidemiological studies of the P. vivax parasite.

Genotyping Plasmodium vivax isolates from the 2011 outbreak in Greece.

BACKGROUND: Plasmodium vivax malaria was common in Greece until the 1950s with epidemics involving thousands of cases every year. Greece was declared free of malaria by the World Health Organization in 1974. From 1974 to 2010, an average of 39 cases per year were reported, which were mainly imported. However, in 2009 and 2010 six and one autochthonous cases were reported culminating with a total of 40 autochthonous cases reported in 2011, of which 34 originated from a single region: Laconia of Southern Peloponnese. In this study the genotypic complexity of the P. vivax infections from the outbreak in Greece during 2011 is described, to elucidate the possible origin and spread of the disease. METHODS: Three polymorphic markers of P. vivax were used; Pvmsp-3α and the microsatellites m1501 and m3502 on P. vivax isolates sampled from individuals diagnosed in Greece. Thirty-nine isolates were available for this study (20 autochthonous and 19 imported), mostly from Evrotas municipality in Laconia region, in southern Greece, (n = 29), with the remaining representing sporadic cases originating from other areas of Greece. RESULTS: Genotyping the Evrotas samples revealed seven different haplotypes where the majority of the P. vivax infections expressed two particular Pvmsp-3α-m1501-m3502 haplotypes, A10-128-151 (n = 14) and A10-121-142 (n = 7). These haplotypes appeared throughout the period in autochthonous and imported cases, indicating continuous transmission. In contrast, the P. vivax autochthonous cases from other parts of Greece were largely comprised of unique haplotypes, indicating limited transmission in these other areas. CONCLUSIONS: The results indicate that several P. vivax strains were imported into various areas of Greece in 2011, thereby increasing the risk of re-introduction of malaria. In the region of Evrotas ongoing transmission occurred exemplifying that further control measures are urgently needed in this region of southern Europe. In circumstances where medical or travel history is scarce, methods of molecular epidemiology may prove highly useful for the correct classification of the cases.

Prevalence of molecular markers of anti-malarial drug resistance in Plasmodium vivax and Plasmodium falciparum in two districts of Nepal.

BACKGROUND: Sulphadoxine-pyrimethamine (SP) and chloroquine (CQ) have been used in treatment of falciparum and vivax malaria in Nepal. Recently, resistance to both drugs have necessitated a change towards artemisinin combination therapy (ACT) against Plasmodium falciparum in highly endemic areas. However, SP is still used against P. falciparum infections in low endemic areas while CQ is used in suspected cases in areas with lack of diagnostic facilities. This study examines the prevalence of molecular markers of CQ and SP resistance in P. falciparum and Plasmodium vivax to determine if high levels of in vivo resistance are reflected at molecular level as well. METHODS: Finger prick blood samples (n=189) were collected from malaria positive patients from two high endemic districts and analysed for single nucleotide polymorphisms (SNPs) in the resistance related genes of P. falciparum and P. vivax for CQ (Pfcrt, Pfmdr1, Pvmdr1) and SP (Pfdhfr, Pfdhps, Pvdhfr), using various PCR-based methods. RESULTS AND DISCUSSION: Positive P. vivax and P. falciparum infections were identified by PCR in 92 and 41 samples respectively. However, some of these were negative in subsequent PCRs. Based on a few P. falciparum samples, the molecular level of CQ resistance in P. falciparum was high since nearly all parasites had the Pfcrt mutant haplotypes CVIET (55%) or SVMNT (42%), though frequency of the Pfmdr1 wild type haplotype was relatively low (35%). Molecular level of SP resistance in P. falciparum was found to be high. The most prevalent Pfdhfr haplotype was double mutant CNRNI (91%), while frequency of Pfdhps double mutant SGEAA and AGEAA were 38% and 33% respectively. Combined, the frequency of quadruple mutations (CNRNI-SGEAA/AGEAA) was 63%. Based on P. vivax samples, low CQ and SP resistance were most likely due to low prevalence of Pvmdr1 Y976F mutation (5%) and absence of triple/quadruple mutations in Pvdhfr. CONCLUSIONS: Based on the limited number of samples, prevalence of CQ and SP resistance at molecular levels in the population in the study area were determined as high in P. falciparum and low in P. vivax. Therefore, CQ could still be used in the treatment of P. vivax infections, but this remains to be tested in vivo while the change to ACT for P. falciparum seems justified.

Island-wide diversity in single nucleotide polymorphisms of the Plasmodium vivax dihydrofolate reductase and dihydropteroate synthetase genes in Sri Lanka.

BACKGROUND: Single nucleotide polymorphisms (SNPs) in the Plasmodium vivax dihydrofolate reductase (Pfdhfr) and dihydropteroate synthetase (Pvdhps) genes cause parasite resistance to the antifolate drug combination, sulphadoxine/pyrimethamine (SP). Monitoring these SNPs provide insights into the level of drug pressure caused by SP use and presumably other antifolate drugs. In Sri Lanka, chloroquine (CQ) with primaquine (PQ) and SP with PQ is used as first and second line treatment, respectively, against uncomplicated Plasmodium falciparum and/or P. vivax infections. CQ/PQ is still efficacious against P. vivax infections, thus SP is rarely used and it is assumed that the prevalence of SNPs related to P. vivax SP resistance is low. However, this has not been assessed in Sri Lanka as in most other parts of Asia. This study describes the prevalence and distribution of SNPs related to P. vivax SP resistance across Sri Lanka. SUBJECTS AND METHODS: P. vivax-positive samples were collected from subjects presenting at government health facilities across nine of the major malaria endemic districts on the island. The samples were analysed for SNPs/haplotypes at codon 57, 58, 61 and 117 of the Pvdhfr gene and 383, 553 and 585 of the Pvdhps gene by applying PCR followed by a hybridization step using sequence specific oligonucleotide probes (SSOPs) in an ELISA format. RESULTS: In the study period, the government of Sri Lanka recorded 2,149 P. vivax cases from the nine districts out of which, 454 (21.1%) blood samples were obtained. Pvdhfr haplotypes could be constructed for 373 of these. The FSTS wild-haplotype was represented in 257 samples (68.9%), the double mutant LRTS haplotype was the most frequently observed mutant (24.4%) while the triple mutation (LRTN) was only identified once. Except for two samples of the single mutated Pvdhps GAV haplotype, the remaining samples were wildtype. Geographical differences were apparent, notably a significantly higher frequency of mutant Pvdhfr haplotypes was observed in the Northern districts. CONCLUSION: Since SP is rarely used in Sri Lanka, the high frequency and diversity of Pvdhfr mutations was unexpected indicating the emergence of drug resistant parasites despite a low level of SP drug pressure.

Multiple Origins of Mutations in the mdr1 Gene--A Putative Marker of Chloroquine Resistance in P. vivax.

BACKGROUND: Chloroquine combined with primaquine has been the recommended antimalarial treatment of Plasmodium vivax malaria infections for six decades but the efficacy of this treatment regimen is threatened by chloroquine resistance (CQR). Single nucleotide polymorphisms (SNPs) in the multidrug resistance gene, Pvmdr1 are putative determinants of CQR but the extent of their emergence at population level remains to be explored. OBJECTIVE: In this study we describe the prevalence of SNPs in the Pvmdr1 among samples collected in seven P. vivax endemic countries and we looked for molecular evidence of drug selection by characterising polymorphism at microsatellite (MS) loci flanking the Pvmdr1 gene. METHODS: We examined the prevalence of SNPs in the Pvmdr1 gene among 267 samples collected from Pakistan, Afghanistan, Sri Lanka, Nepal, Sudan, São Tomé and Ecuador. We measured and diversity in four microsatellite (MS) markers flanking the Pvmdr1 gene to look evidence of selection on mutant alleles. RESULTS: SNP polymorphism in the Pvmdr1 gene was largely confined to codons T958M, Y976F and F1076L. Only 2.4% of samples were wildtype at all three codons (TYF, n = 5), 13.3% (n = 28) of the samples were single mutant MYF, 63.0% of samples (n = 133) were double mutant MYL, and 21.3% (n = 45) were triple mutant MFL. Clear geographic differences in the prevalence of these Pvmdr mutation combinations were observed. Significant linkage disequilibrium (LD) between Pvmdr1 and MS alleles was found in populations sampled in Ecuador, Nepal and Sri Lanka, while significant LD between Pvmdr1 and the combined 4 MS locus haplotype was only seen in Ecuador and Sri Lanka. When combining the 5 loci, high level diversity, measured as expected heterozygosity (He), was seen in the complete sample set (He = 0.99), while He estimates for individual loci ranged from 0.00-0.93. Although Pvmdr1 haplotypes were not consistently associated with specific flanking MS alleles, there was significant differentiation between geographic sites which could indicate directional selection through local drug pressure. CONCLUSIONS: Our observations suggest that Pvmdr1 mutations emerged independently on multiple occasions even within the same population. In Sri Lanka population analysis at multiple sites showed evidence of local selection and geographical dispersal of Pvmdr1 mutations between sites.

Analysis of polymorphisms in the merozoite surface protein-3α gene and two microsatellite loci in Sri Lankan Plasmodium vivax: evidence of population substructure in Sri Lanka.

The geographical distribution of genetic variation in Plasmodium vivax samples (N = 386) from nine districts across Sri Lanka is described using three markers; the P. vivax merozoite surface protein-3α (Pvmsp-3α) gene, and the two microsatellites m1501 and m3502. At Pvmsp-3α, 11 alleles were found with an expected heterozygosity (H(e)) of 0.81, whereas at m1501 and m3502, 24 alleles (H(e) = 0.85) and 8 alleles (H(e) = 0.74) were detected, respectively. Overall, 95 unique three locus genotypes were detected among the 279 samples positive at all three loci (H(e) = 0.95). Calculating the pairwise fixation index (F(ST)) revealed statistically significant population structure. The presence of identical 2-loci microsatellite genotypes in a significant proportion of samples revealed local clusters of closely related isolates contributing to strong linkage disequilibrium between marker alleles. The results show evidence of high genetic diversity and possible population substructure of P. vivax populations in Sri Lanka.

Geographic structure of Plasmodium vivax: microsatellite analysis of parasite populations from Sri Lanka, Myanmar, and Ethiopia.

Genetic diversity and population structure of Plasmodium vivax parasites can predict the origin and spread of novel variants within a population enabling population specific malaria control measures. We analyzed the genetic diversity and population structure of 425 P. vivax isolates from Sri Lanka, Myanmar, and Ethiopia using 12 trinucleotide and tetranucleotide microsatellite markers. All three parasite populations were highly polymorphic with 3-44 alleles per locus. Approximately 65% were multiple-clone infections. Mean genetic diversity (H(E)) was 0.7517 in Ethiopia, 0.8450 in Myanmar, and 0.8610 in Sri Lanka. Significant linkage disequilibrium was maintained. Population structure showed two clusters (Asian and African) according to geography and ancestry. Strong clustering of outbreak isolates from Sri Lanka and Ethiopia was observed. Predictive power of ancestry using two-thirds of the isolates as a model identified 78.2% of isolates accurately as being African or Asian. Microsatellite analysis is a useful tool for mapping short-term outbreaks of malaria and for predicting ancestry.