Assessment of Markers of Antimalarial Drug Resistance in Plasmodium falciparum Isolates from Pregnant Women in Lagos, Nigeria

Xeno-monitoring of molecular drivers of artemisinin and partner drug resistance in P. falciparum populations in malaria vectors across Cameroon

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High Plasmodium infection rate in the major Anopheles vectors across Cameroon.

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Emerging signal of the R575I polymorphism in the k13 propeller domain backbone.

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Dominance of the N⁸⁶F¹⁸⁴mdr1 variants in natural P. falciparum populations.

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Low k13 and mdr1 genetic diversity in P. falciparum-infected mosquitoes.

Background

Monitoring of drug resistance in Plasmodium populations is crucial for malaria control. This has primarily been performed in humans and rarely in mosquitoes where parasites genetic recombination occurs. Here, we characterized the Plasmodium spp populations in wild Anopheles vectors by analyzing the genetic diversity of the P. falciparum kelch13 and mdr1 gene fragments implicated in artemisinin and partner drug resistance across Cameroon in three major malaria vectors.

Methods

Anopheles mosquitoes were collected across nine localities in Cameroon and dissected into the head/thorax (H/T) and abdomen (Abd) after species identification. A TaqMan assay was performed to detect Plasmodium infection. Fragments of the Kelch 13 and mdr1 genes were amplified in P. falciparum positive samples and directly sequenced to assess their drug resistance polymorphisms and genetic diversity profile.

Results

The study revealed a high Plasmodium infection rate in the major Anopheles vectors across Cameroon. Notably, An. funestus vector recorded the highest sporozoite (8.0%) and oocyst (14.4%) infection rates. A high P. falciparum sporozoite rate (80.08%) alongside epidemiological signatures of significant P. malariae (15.9%) circulation were recorded in these vectors. Low genetic diversity with six (A578S, R575I, G450R, L663L, G453D, N458D) and eight (H53H, V62L, V77E, N86Y, G102G, L132I, H143H, Y184F) point mutations were observed in the k13 and mdr1 backbones respectively. Remarkably, the R575I (4.4%) k13 and Y184F (64.2%) mdr1 mutations were the predominant variants in the P. falciparum populations.

Conclusion

The emerging signal of the R575I polymorphism in the Pfk13 propeller backbone entails the regular surveillance of molecular markers to inform evidence-based policy decisions. Moreover, the high frequency of the ⁸⁶N¹⁸⁴F allele highlights concerns on the plausible decline in efficacy of artemisinin-combination therapies (ACTs); further implying that parasite genotyping from mosquitoes can provide a more relevant scale for quantifying resistance epidemiology in the field.

Identification of polymorphisms in genes associated with drug resistance in Plasmodium falciparum isolates from school-age children in Kinshasa, Democratic Republic of Congo

BACKGROUND

The emergence and spread of Plasmodium falciparum parasites resistant to antimalarial drugs constitutes an obstacle to malaria control and elimination. This study aimed to identify the prevalence of polymorphisms in pfk13, pfmdr1, pfdhfr, pfdhps and pfcrt genes in isolates from asymptomatic and symptomatic school-age children in Kinshasa.

METHODS

Nested-PCR followed by sequencing was performed for the detection of pfk13, pfmdr1, pfdhfr, pfdhps and pfcrt polymorphisms.

RESULTS

Two mutations in pfk13, C532S and Q613E were identified in the Democratic Republic of Congo for the first time. The prevalence of the drug-resistance associated mutations pfcrt K76T, pfdhps K540E and pfmdr1 N86Y was low, being 27%, 20% and 9%, respectively.

CONCLUSION

We found a low prevalence of genetic markers associated with chloroquine and sulfadoxine-pyrimethamine resistance in Kinshasa. Furthermore, no mutations previously associated with resistance against artemisinin and is derivatives were observed in the pfK13 gene. These findings support the continued use of ACTs and IPTp-SP. Continuous molecular monitoring of antimalarial resistance markers is recommended.

Polymorphism analysis of pfmdr1 gene in Plasmodium falciparum isolates 11 years post-adoption of artemisinin-based combination therapy in Saudi Arabia

A total of 227 Plasmodium falciparum isolates from Jazan region, southwestern Saudi Arabia were amplified for the P. falciparum multi-drug resistance 1 (pfmdr1) gene to detect point mutations 11 years after the introduction of artemisinin-based combination therapy (ACT) in Saudi Arabia. The pfmdr1 86Y mutation was found in 11.5% (26/227) of the isolates while the N86 wild allele was detected in 88.5%. Moreover, 184F point mutations dominated (86.3%) the instances of pfmdr1 polymorphism while no mutation was observed at codons 1034, 1042 and 1246. Three pfmdr1 haplotypes were identified, NFSND (74.9%), NYSND (13.7%) and YFSND (11.4%). Associations of the prevalence of 86Y mutation and YFSND haplotype with participants' nationality, residency and parasitaemia level were found to be significant (P < 0.05). The findings revealed significant decline in the prevalence of the pfmdr1 86Y mutation in P. falciparum isolates from Jazan region over a decade after the implementation of ACT treatment. Moreover, the high prevalence of the NFSND haplotype might be indicative of the potential emergence of CQ-sensitive but artemether-lumefantrine-resistant P. falciparum strains since the adoption of ACT. Therefore, continuous monitoring of the molecular markers of antimalarial drug resistance in Jazan region is highly recommended.

Mutations in Pfcrt and Pfmdr1 genes of Plasmodium falciparum isolates from two sites in Northcentral and Southwest Nigeria

The ability of malaria parasites to develop resistance to antimalarial drugs has made it necessary to continuously survey malaria parasite populations for resistance markers. Mutations in specific malaria parasite genes confer resistance to antimalarial drugs. The study compared mutations in Pfcrt and Pfmdr1 genes of P. falciparum from two ecologically different areas of Nigeria. Plasmodium falciparum dried blood spots collected from New Bussa (Northcentral Nigeria) and Ijede (Southwest Nigeria) were analysed by PCR-RFLP for Pfcrt, K76 T, Pfmdr1, N86Y and Y184F mutations. Pfmdr1 copy number was determined by quantitative-PCR. A total of 145 blood spots [Ijede = 55; New Bussa = 90 blood spots] were analysed, but Pfcrt gene was successfully amplified in 144 samples while Pfmdr1 was amplified in 132 samples. Overall, prevalence of mutant forms of Pfcrt 76 T,Pfmdr1 86Y and 184F were 74.3% (95% CI: 66.4-81.2%), 18.2% (95% CI: 12.0-25.8%) and 35.6% (95% CI: 27.5-44.4%). The frequency of Pfcrt 76 T was similar in both study sites [Ijede: 81.8% (95%CI: 69.1-90.9%); New Bussa: 69.7% (95%CI: 59.0-79.0), p = 0.105]. However, the frequencies of Pfmdr1 86Y and 184F were significantly higher in Ijede (28.3% and 62.3%) than in New Bussa (11.4% and 17.7%), respectively (P < 0.05). Eight parasite genotypes based on three codons of the two genes were identified. The most frequent genotype was TNY 53(40.5%) while the least was KYF 1 (0.8%). The most frequent genotype in Ijede and New Bussa were TNF 18(34.0%) and TNY 40 (51.3%) respectively. The frequency of wild strain KNF in Ijede and New Bussa were 3 (5.7%) and 18 (23.1%), respectively. The distribution of the genotypes differed significantly by location. The genotypes with more than two or more mutations were more in Ijede 32 (60.4%) than in New Bussa 16 (20.5%) (p < 0.001). Amplification of Pfmdr1 copy number was not observed in the two study sites. The prevalence of Pfcrt 76 T was similar in both locations while Pfmdr1 86Y and 184F differed in both locations. Single nucleotide polymorphisms in the three codons assessed were more in Ijede than in New Bussa.

Geographical and temporal variation in reduction of malaria infection among children under 5 years of age throughout Nigeria

INTRODUCTION

Global progress in reducing malaria has stalled since 2015. Analysis of the situation is particularly needed in Nigeria, the country with by far the largest share of the burden, where approximately a quarter of all cases in the world are estimated to occur.

METHODS

We analysed data from three nationwide surveys (Malaria Indicator Surveys in 2010 and 2015 and a National Demographic and Health Survey in 2018), with malaria parasite prevalence in children under 5 years of age determined by sampling from all 36 states of Nigeria, and blood slide microscopy performed in the same accredited laboratory for all samples. Changes over time were evaluated by calculating prevalence ratio (PR) values with 95% CIs for each state, together with Mantel-Haenszel-adjusted PRs (PR_adj) for each of the six major geopolitical zones of the country.

RESULTS

Between 2010 and 2018, there were significant reductions in parasite prevalence in 25 states, but not in the remaining 11 states. Prevalence decreased most in southern zones of the country (South West PR_adj=0.53; South East PR_adj=0.59; South South PR_adj=0.51) and the North Central zone (PR_adj=0.36). Changes in the north were less marked, but were significant and indicated overall reductions by more than 20% (North-West PR_adj=0.74; North East PR_adj=0.70). Changes in the south occurred mostly between 2010 and 2015, whereas those in the north were more gradual and most continued after 2015. Recent changes were not correlated with survey-reported variation in use of preventive measures.

CONCLUSION

Reductions in malaria infection in children under 5 have occurred in most individual states in Nigeria since 2010, but substantial geographical variation in the timing and extent indicate challenges to be overcome to enable global malaria reduction.

Antimalarial drug resistance markers in human immunodeficiency virus (HIV)-positive and HIV-negative adults with asymptomatic malaria infections in Port Harcourt, Nigeria

BACKGROUND

In Nigeria, indiscriminate use of antimalarial drugs may contribute to the threat of drug resistance, but this has not been evaluated among people living with human immunodeficiency virus (HIV).

METHODS

HIV-positive adults attending a university hospital HIV clinic and HIV-negative adult volunteers from the university hospital community with a positive blood film were treated with artemether-lumefantrine. Parasite DNA from before and after treatment was polymerase chain reaction amplified to identify molecular markers of drug susceptibility.

RESULTS

The pfcrt76T genotype was prevalent among both HIV-positive and HIV-negative participants (78.6% and 68.2%, respectively). Three new mutations in the pfmdr1 gene-F73S, S97L and G165R-and the uncommon pfdhps S436F variant were detected, whereas pfdhps K540E and pfdhfr I164L were absent. The A437G allele of pfdhps predominated (62/66 [94%]). The I431 V mutation was found in 19 of 66 pretreatment pfdhps sequences (28.8%). The pfmdr1 86N allele was significantly more common at day 3 post-treatment than at baseline (odds ratio 8.77 [95% confidence interval 1.21 to 380]).

CONCLUSIONS

We found evidence of continued chloroquine use among HIV-positive individuals. Selection for the pfmdr1 86N after artemether-lumefantrine treatment was observed, indicating a possible threat to antimalarial efficacy in the study area. The complexity of pfdhps haplotypes emphasises the need for careful monitoring of anti-folate susceptibility in Nigeria.

Geographical spread and structural basis of sulfadoxine-pyrimethamine drug-resistant malaria parasites

The global spread of sulfadoxine (Sdx, S) and pyrimethamine (Pyr, P) resistance is attributed to increasing number of mutations in DHPS and DHFR enzymes encoded by malaria parasites. The association between drug resistance mutations and SP efficacy is complex. Here we provide an overview of the geographical spread of SP resistance mutations in Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) encoded dhps and dhfr genes. In addition, we have collated the mutation data and mapped it on to the three-dimensional structures of DHPS and DHFR which have become available. Data from genomic databases and 286 studies were collated to provide a comprehensive landscape of mutational data from 2005 to 2019. Our analyses show that the Pyr-resistant double mutations are widespread in Pf/PvDHFR (P. falciparum ∼61% in Asia and the Middle East, and in the Indian sub-continent; in P. vivax ∼33% globally) with triple mutations prevailing in Africa (∼66%) and South America (∼33%). For PfDHPS, triple mutations dominate South America (∼44%), Asia and the Middle East (∼34%) and the Indian sub-continent (∼27%), while single mutations are widespread in Africa (∼45%). Contrary to the status for P. falciparum, Sdx-resistant single point mutations in PvDHPS dominate globally. Alarmingly, highly resistant quintuple and sextuple mutations are rising in Africa (PfDHFR-DHPS) and Asia (Pf/PvDHFR-DHPS). Structural analyses of DHFR and DHPS proteins in complexes with substrates/drugs have revealed that resistance mutations map proximal to Sdx and Pyr binding sites. Thus new studies can focus on discovery of novel inhibitors that target the non-substrate binding grooves in these two validated malaria parasite drug targets.

Polymorphisms in Plasmodium falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) in Nigerian children 10 years post-adoption of artemisinin-based combination treatments

The emergence and spread of Plasmodium falciparum parasites resistant to artemisinin derivatives and their partners in southeastern Asia threatens malaria control and elimination efforts, and heightens the need for an alternative therapy. We have explored the distribution of P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) haplotypes 10 years following adoption of artemisinin-based combination therapies in a bid to investigate the possible re-emergence of Chloroquine-sensitive parasites in Nigeria, and investigated the effect of these P. falciparum haplotypes on treatment outcomes of patients treated with artemisinin-based combination therapies. A total of 271 children aged <5 years with uncomplicated falciparum malaria were included in this study. Polymorphisms on codons 72-76 of the Pfcrt gene and codon 86 and 184 of Pfmdr-1 were determined using the high resolution melting assay. Of 240 (88.6%) samples successfully genotyped with HRM for Pfcrt, wildtype C72M74N75K76 (42.9%) and mutant C72I74E75T76 (53.8%) were observed. Also, wildtype N86Y184 (62.9%) and mutant N86F184 (21.1%), Y86Y184 (6.4%), and Y86F184 (0.4%) haplotypes of Pfmdr-1 were observed. Measures of responsiveness to ACTs were similar in children infected with P. falciparum crt haplotypes (C72I74E75T76 and C72M74N75K76) and major mdr-1 haplotypes (N86Y184, N86F184 and Y86Y184). Despite a 10 year gap since the malaria treatment policy changed to ACTs, over 50% of the P. falciparum parasites investigated in this study harboured the Chloroquine-resistant C72I74E75T76 haplotype, however this did not compromise the efficacy of artemisinin-based combination therapies. Should complete artemisinin resistance emerge from or spread to Nigeria, chloroquine might not be a good alternative therapy.

Polymorphism Analysis of pfmdr1 and pfcrt from Plasmodium falciparum Isolates in Northwestern Nigeria Revealed the Major Markers Associated with Antimalarial Resistance

Suspicion of failure in the effectiveness of artemisinin-based combination therapies (currently the first-line treatment of malaria, worldwide) is leading to the unofficial use of alternative antimalarials, including chloroquine and sulfadoxine/pyrimethamine, across northern Nigeria. To facilitate evidence-based resistance management, antimalarial resistance mutations were investigated in Plasmodium falciparum multidrug resistance-1 (pfmdr1) and chloroquine resistance transporter (pfcrt), in isolates from Kano, northwestern Nigeria. Out of the 88 samples genotyped for pfmdr1N86Y mutation using PCR/restriction fragment length polymorphism, one sample contained the 86Y mutation (86Yfrequency = 1.14%). The analysis of 610 bp fragments of pfmdr1 from 16 isolates revealed two polymorphic sites and low haplotype diversity (Hd = 0.492), with only 86 Y mutations in one isolate, and 184 F replacements in five isolates (184Ffrequency = 31.25%). The analysis of 267 bp fragments of pfcrt isolates revealed high polymorphism (Hd = 0.719), with six haplotypes and seven non-synonymous polymorphic sites. Eleven isolates (61.11%) were chloroquine-resistant, CQR (C72V73I74E75T76 haplotype), two of which had an additional mutation, D57E. An additional sequence was CQR, but of the C72V73M74E75T76 haplotype, while the rest of the sequences (33.33%) were chloroquine susceptible (C72V73M74N75K76 haplotype). The findings of these well characterized resistance markers should be considered when designing resistance management strategies in the northwestern Nigeria.

Clinical Probe of Cyp2C8*2 Mutants in a Malaria Hyperendemic Zone: Evidence from North-Central, Nigeria

BACKGROUND

A tremendous level of success has been achieved since the introduction of chloroquine and the combination of amodiaquine and artemisinin for the treatment of both complicated and uncomplicated malaria infections in sub-Saharan Africa. However, the recent discovery of drug resistant strains of Plasmodium falciparum (P.f.) and the ability of the parasite to ingest CYP2C8 into its digestive vacuole is of great public health concern. This study probes the occurrence of CYP2C8*2 allelic mutant amongst malaria patients in North-Central Nigeria.

METHODS

Three hundred and eighty five (385) unrelated study participants were screened for current malaria episodes using routine microscopy and/or rapid diagnostic test strips (RDTs). Chelex extraction method was used for single nucleotide polymorphisms (SNPs) and identification of CYP2C8*2 (805A > T) variant respectively. Wild-type (A) and the defective allele (T) were differentiated with the use of Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). The results obtained were further validated with Sanger sequencing of a few samples and thereafter, the genotype data were statistically processed. All alleles obtained were in Hardy Weinberg equilibrium.

RESULTS

Out of the 385 participants (45.5% Male and 54.5% Female) genotyped for SNPs, 75 (19.5%) had the autosomal recessive mutant trait. Occurrence of mutant traits was gender and ethnic independent (p > 0.05). Yoruba ethnic group recorded a reduction in proportion of genotypic defective CYP2C8*2 allele (T) (1 in every 8 persons) with a carrier percentage of 13.3% compared with Hausa (26.62%); Igbo (25.37%) and other minority ethnic groups (17.6%).

CONCLUSIONS

A remarkable inter-ethnic differences in autosomal recessive CYP2C8*2 allele was observed. By implication, there is a gradual incursion of genetic drift for poor CQ and AQ-Artemisinin metabolizers among the inhabitants.

High multiple mutations of Plasmodium falciparum-resistant genotypes to sulphadoxine-pyrimethamine in Lagos, Nigeria

Background

Plasmodium falciparum-resistance to sulphadoxine-pyrimethamine (SP) has been largely reported among pregnant women. However, the profile of resistance markers to SP dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) in the general population are varied and not frequently monitored. Currently, SP is used as partner drug for artemisinin combination therapy (SP-artesunate) in some sub-Saharan African countries or as a prophylactic drug in intermittent preventive treatment of malaria during pregnancy and infants and in seasonal malaria chemoprevention (SMC). Profiling of P. falciparum-resistant genotypes to SP is dynamic and critical in providing data that would be useful for malaria control programmes. This study assessed the profile of dhfr and dhps genes genotypes among individuals with malaria in Lagos, Nigeria.

Methods

Molecular markers of SP resistance were identified by nested PCR and sequenced among malaria positive dried blood spots (DBS) that were collected from individuals attending health facilities from January 2013 to February 2014 and during community surveys from October 2010 to September 2011 across different Local Government Areas of Lagos State, Nigeria.

Results

A total of 242 and 167 samples were sequenced for dhfr and dhps, respectively. Sequence analysis of dhfr showed that 95.5% (231/242), 96.3% (233/242) and 96.7% (234/242) of the samples had N51I, C59R and S108N mutant alleles, respectively. The prevalence of dhps mutation at codons A437G, A613S, S436A, A581G, I431V and K540E were 95.8% (160/167), 41.9% (70/167), 41.3% (69/167), 31.1% (52/167), 25.1% (42/167), and 1.2% (2/167) respectively. The prevalence of triple mutations (CIRNI) in dhfr was 93.8% and 44.3% for the single dhps haplotype mutation (SGKAA). Partial SP-resistance due to quadruple dhfr-dhps haplotype mutations (CIRNI-SGKAA) and octuple haplotype mutations (CIRNI-VAGKGS) with rate of 42.6% and 22.0%, respectively has been reported.

Conclusions

There was increased prevalence in dhfr triple haplotype mutations when compared with previous reports in the same environment but aligned with high prevalence in other locations in Nigeria and other countries in Africa. Also, high prevalence of dhfr and dhps mutant alleles occurred in the study areas in Lagos, Nigeria five to eight years after the introduction of artemisinin combination therapy underscores the need for continuous monitoring.

Analysis of Plasmodium falciparum Pfcrt and Pfmdr1 genes in parasite isolates from asymptomatic individuals in Southeast Nigeria 11 years after withdrawal of chloroquine

BACKGROUND

A reversal of chloroquine (CQ) resistance following a period of withdrawal has raised the possibility of its re-introduction. This study evaluated the current prevalence of Pfcrt and Pfmdr1 alleles in Plasmodium falciparum isolates, 11 years after CQ withdrawal in Southeast Nigeria.

METHODS

Filter-paper blood samples were collected from 725 non-febrile individuals, comprising 250 children (≤ 12 years), 250 pregnant women and 225 other adults, between October 2014 and February 2015 in Nnewi town, Southeast Nigeria. Nested PCR followed by direct sequencing was employed for the genotyping of Pfcrt and Pfmdr1 genes.

RESULTS

A total of 103 parasites-positive samples were recovered, comprising of 48 (19.20%) among children, 20 (20.00%) among pregnant women and 35 (15.50%) among other adults cohort. The frequency of the mutant genotype of Pfcrt 76T, 75E and 74I was 94.50% each. Parasite isolates from children had a frequency of 100% for mutant alleles in all Pfcrt codons while isolates from pregnant women and other adults had a frequency of 91% each in all codons. Haplotype distribution of pfcrt gene were 5.45, 0.00 and 76.37% for CVMNK, SVMNT and CVIET, respectively. For Pfmdr1 gene, the frequency of 86Y, 184F and 1246Y mutant alleles were 8.54, 29.27 and 3.66%, respectively. Amongst the Pfmdr1 haplotypes analysed, NFD had the highest frequency of 24.4%, followed by YFD at 6.10%. NYF and NYY occurred the least (1.20%).

CONCLUSION

The high level of Pfcrt mutations is suggestive of a sustained CQ pressure on P. falciparum isolates in the study area, despite the change of first line treatment from CQ to artemisinin combination therapy for 11 years. A new strategy to ensure the complete withdrawal of CQ from the country is recommended.

Molecular epidemiology and evolution of drug-resistant genes in the malaria parasite Plasmodium falciparum in southwestern Nigeria

Malaria is an age-old disease of human kind living in the tropical and sub-tropical regions of the globe, with Africa contributing the highest incidence of morbidity and mortality. Among many hurdles, evolution and spread of drug-resistant Plasmodium falciparum parasites constitute major challenges to malaria control and elimination. Information on molecular epidemiology and pattern of evolution of genes conferring resistance to different antimalarials are needed to track the route of the spread of resistant parasites and also to inform if the drug-resistant genes are adapted in the population following the Darwinian model of evolution. In the present study, we have followed molecular methods to detect both the known and emerging mutations in three genes (Pfcrt, Pfdhfr and Pfdhps) of P. falciparum conferring resistance to chloroquine and sulfadoxine-pyrimethamine from two different states (Edo: meso-endemic and Lagos: hypo-endemic) in southwestern Nigeria. High diversities in haplotypes and nucleotides in genes responsible for chloroquine (Pfcrt) and sulfadoxine (Pfdhps) resistance are recorded. About 96% of Pfdhfr and Pfdhps gene in both the meso- and hypo- endemic areas were mutant type, followed by 61% in Pfcrt gene. Many unique haplotypes of Pfdhps and Pfcrt were found to be segregated in these two populations. One particular mutant haplotype of Pfdhfr (AIRNI) was found to be in very high frequency in both Lagos and Edo. While the net haplotype diversity was highest in Pfdhps (0.81 in Lagos, 0.87 in Edo), followed by Pfcrt (0.69 in Lagos, 0.65 in Edo); highest number of haplotype was found in Pfdhps with 13 distinct haplotypes, followed by seven in Pfcrt and four in Pfdhfr gene. Moreover, detection of strong linkage among mutations of Pfcrt and Pfdhfr and feeble evidence for balancing selection in Pfdhps are indicative of evolutionary potential of mutation in genes responsible for drug resistance in Nigerian populations of P. falciparum.

Pharmacotherapy for the prevention of malaria in pregnant women: currently available drugs and challenges

INTRODUCTION

Malaria in pregnancy continues to be a significant public health burden globally, with over 100 million women at risk each year. Sulfadoxine-pyrimethamine (SP) is the only antimalarial recommended for intermittent preventive therapy in pregnancy (IPTp) but increasing parasite resistance threatens its viability. There are few other available antimalarial therapies that currently have sufficient evidence of tolerability, safety, and efficacy to replace SP.

AREAS COVERED

Novel antimalarial combinations are under investigation for potential use as chemoprophylaxis and in IPTp regimens. The present review summarizes currently available therapies, emerging candidate combination therapies, and the potential challenges to integrating these into mainstream policy.

EXPERT OPINION

Alternative drugs or combination therapies to SP for IPTp are desperately required. Dihydroartemisinin-piperaquine and azithromycin-based combinations are showing great promise as potential candidates for IPTp but pharmacokinetic data suggest that dose modification may be required to ensure adequate prophylactic efficacy. If a suitable candidate regimen is not identified in the near future, the success of chemopreventive strategies such as IPTp may be in jeopardy.

Surveillance of Genetic Variations Associated with Antimalarial Resistance of Plasmodium falciparum Isolates from Returned Migrant Workers in Wuhan, Central China

Antimalarial drug resistance developed in Plasmodium falciparum has become a problem for malaria control. Evaluation of drug resistance is the first step for effective malaria control. In this study, we investigated the gene mutations of P. falciparum using blood samples from returned Chinese migrant workers in order to identify drug resistance-associated molecular markers. These workers returned from Africa and Southeast Asia (SEA) during 2011 to 2016. Polymorphisms in pfcrt, pfmdr1, and k13-propeller genes and the haplotype patterns of Pfcrt and Pfmdr1 were analyzed. The results showed the presence of four haplotypes of Pfcrt codons 72 to 76, including CVMNK (wild type), SVMNT and CVIET (mutation types), and CV M/I N/E K/T (mixed type), with 50.57%, 1.14%, 25.00%, and 23.30% prevalence, respectively. For Pfmdr1, N86Y (22.28%) and Y184F (60.01%) were the main prevalent mutations (mutations are underlined). The prevalence of mutation at position 550, 561, 575, and 589 of K13-propeller were 1.09%, 0.54%, 0.54%, and 0.54%, respectively. These data suggested that Pfcrt, Pfmdr1, and K13-propeller polymorphisms are potential markers to assess drug resistance of P. falciparum in China, Africa, and SEA.

Human Genetic Markers and Structural Prediction of Plasmodium falciparum Multidrug Resistance Gene (pfmdr1) for Ligand Binding in Pregnant Women Attending General Hospital Minna

The study aims to determine the association of malaria infection with ABO blood groups and genotype and also to detect point mutations at positions 86, 184, 1034, and 1042 of the Plasmodium falciparum multidrug resistance gene (pfmdr1) in blood samples collected from pregnant women attending General Hospital Minna. Out of 250 pregnant women screened, 39 (15.60%) had malaria infection. Prevalence was higher in women, during the third trimester (46.15%), genotype AA (64.10%), and O blood group (53.84%) individuals when compared with others. There was significant (p < 0.05) decrease in Packed Cell Volume (PCV), hemoglobin (HGB), Red Blood Cells (RBC), and platelet (PLC) count in infected group when compared with noninfected group. Although, two of the isolates showed disrupted protein sequence at codon 1034–1042, no mutation was found in any of the P. falciparum isolates. Structural prediction of chemical ligand led to the identification of Neu5Acα2-3Galβ1-3/β1-4Glc/GlcNAc. This compound can theoretically bind and change the functional integrity of the pfmdr1 protein, thus providing a new window for malaria drug target.

High prevalence of dihydrofolate reductase gene mutations in Plasmodium falciparum parasites among pregnant women in Nigeria after reported use of sulfadoxine-pyrimethamine

This study assesses the prevalence of asymptomatic Plasmodium falciparum parasitemia positivity and P. falciparum dihydrofolate reductase (pfdhfr) mutations in parasite isolates among pregnant women in Southwest Nigeria. Plasmodium falciparum parasitemia was confirmed by microscopy and nested PCR in 200 pregnant women attending antenatal care. The prevalence of pfdhfr polymorphisms was determined by direct sequencing of the gene fragments containing the C50R, N51I, C59R, S108N, and I164L mutations. Information on the use of antimalarial drugs and methods applied to prevent malaria were obtained by a questionnaire. The prevalence of asymptomatic P. falciparum infection was 30% (60/200). The frequency of the pfdhfr triple-mutant alleles (N51I, C59R, and S108N) was 63% (38/60); none of the isolates carried the I164L mutation. Among the investigated pregnant women, 40% used un-prescribed antimalarials such as dihydroartemisinin (18%), chloroquine (14%) or pyrimethamine (9%), while only 20.5% used sulfadoxine-pyrimethamine for prevention and 39.5% did not use any drug. The prevalence of P. falciparum parasitemia (37%) was higher among pregnant women who had not taken any antimalarial drugs. A significant difference in the prevalence of the pfdhfr triple-mutant alleles was observed among women who took SP (90%) compared to those who did not take any drug (82%) and women who took dihydroartemisinin (67%) p = 0.007). Poor adherence to the World Health Organisation (WHO) strategies for malaria prevention among pregnant women was observed in addition to high prevalence of pfdhfr mutations. These findings underline the need to improve control of malaria among pregnant women in the study area.

Does mosquito mass-rearing produce an inferior mosquito?

BACKGROUND

The success of the sterile insect technique depends, among other things, on continuous releases of sexually competitive sterile males within the target area. Several factors (including high rearing density and physical manipulation, such as larvae and pupae separation) can influence the quality of males produced in mass-rearing facilities. The different steps in mass production in the laboratory may modify the behaviour of mosquitoes, directly or through loss of natural characters as a result of adaptation to lab rearing, and lead to the competitiveness of sterile male being reduced. In the present study, the objective was to evaluate the effect of mass-rearing conditions on sterile male sexual competitiveness in semi-field cages compared to routine small scale laboratory rearing methods.

METHODS

Anopheles arabiensis immature stages were reared both on a large scale using a rack and tray system developed by the FAO/IAEA (MRS), and on a small scale using standard laboratory rearing trays (SRS). Mosquito life history traits such as pupation rate, emergence rate, adult size as well as the effect of irradiation on adult longevity were evaluated. Moreover, 5-6 day old mosquitoes were released into field cages and left for two nights to mate and the mating competitiveness between sterile mass-reared males and fertile males reared on a small scale when competing for small scale reared virgin females was investigated. Resulting fertility in a treatment ratio of 1:1:1 (100 irradiated males: 100 non-irradiated males: 100 virgin females) was compared to control cages with 0:100:100 (non-irradiated control) and 100:0:100 (irradiated control).

RESULTS

No significant differences in life history parameters were observed between rearing methods. The competitiveness index of mass reared males (0.58) was similar to males reared on a small scale (0.59). A residual fertility rate of 20% was observed in the irradiated control (100:0:100), measured as the percentage of eggs collected from the cages which developed to adulthood. No significant difference was observed (t = 0.2896, df = 4, P = 0.7865) between the rearing treatments (MRS and SRS) in the fertility rate, a measure of mating competitiveness.

CONCLUSIONS

The results showed that the FAO/IAEA mass-rearing process did not affect mosquito life history parameters or the mating competitiveness of males.

Increase in the prevalence of mutations associated with sulfadoxine-pyrimethamine resistance in Plasmodium falciparum isolates collected from early to late pregnancy in Nanoro, Burkina Faso

BACKGROUND

Pregnant women are a high-risk group for Plasmodium falciparum infections, which may result in maternal anaemia and low birth weight newborns, among other adverse birth outcomes. Intermittent preventive treatment with sulfadoxine-pyrimethamine during pregnancy (IPTp-SP) is widely implemented to prevent these negative effects of malaria. However, resistance against SP by P. falciparum may decrease efficacy of IPTp-SP. Combinations of point mutations in the dhps (codons A437, K540) and dhfr genes (codons N51, C59, S108) of P. falciparum are associated with SP resistance. In this study the prevalence of SP resistance mutations was determined among P. falciparum found in pregnant women and the general population (GP) from Nanoro, Burkina Faso and the association of IPTp-SP dosing and other variables with mutations was studied.

METHODS

Blood spots on filter papers were collected from pregnant women at their first antenatal care visit (ANC booking) and at delivery, from an ongoing trial and from the GP in a cross-sectional survey. The dhps and dhfr genes were amplified by nested PCR and products were sequenced to identify mutations conferring resistance (ANC booking, n = 400; delivery, n = 223; GP, n = 400). Prevalence was estimated with generalized estimating equations and for multivariate analyses mixed effects logistic regression was used.

RESULTS

The prevalence of the triple dhfr mutation was high, and significantly higher in the GP and at delivery than at ANC booking, but it did not affect birth weight. Furthermore, quintuple mutations (triple dhfr and double dhps mutations) were found for the first time in Burkina Faso. IPTp-SP did not significantly affect the occurrence of any of the mutations, but high transmission season was associated with increased mutation prevalence in delivery samples. It is unclear why the prevalence of mutations was higher in the GP than in pregnant women at ANC booking.

CONCLUSION

The high number of mutants and the presence of quintuple mutants in Burkina Faso confirm concerns about the efficacy of IPTp-SP in the near future. Other drug combinations to tackle malaria in pregnancy should, therefore, be explored. An increase in mutation prevalence due to IPTp-SP dosing could not be confirmed.

Novel nucleoside-based antimalarial compounds

The malaria-causing parasite Plasmodium falciparum employs a salvage pathway for the biosynthesis of nucleotides, in contrast to de novo biosynthesis that is utilized by the human host. A series of twenty-two 2-, 6- and 5'-modified adenosine ribonucleosides was synthesized, with the expectation that these compounds would generate toxic metabolites instead of active nucleotides by the pathogen, while remaining inert in host cells. Bioassays with P. falciparum (K1 strain) indicated IC50 values as low as 110nM and a selectivity index with respect to cytotoxicity toward an L6 rat myoblast cell line of >1000 for the most potent analogue.