Prevalence of Plasmodium falciparum anti-malarial resistance-associated polymorphisms in pfcrt, pfmdr1 and pfnhe1 in Muheza, Tanzania, prior to introduction of artemisinin combination therapy

Cost-Utility Analysis of Community Case Management for Malaria Control in Burundi

BACKGROUND

The community case management (CCM) program for malaria control is a community-based strategy implemented to regulate malaria in children in Burundi. This study compared the cost and utility of implementing the CCM program combined with health facility management (HFM) versus HFM alone for malaria control in children under five in Burundi.

METHODS

This study constructed a five-year Markov model with one-week cycles to estimate cost-utility and budget impact analysis (BIA). The model defined 10 health states, simulating the progression of the disease and the risk of recurrent malaria in children under five years of age. Cost data were empirically collected and presented for 2019. Incremental cost per disability-adjusted life year (DALY) averted, and a five-year budget was estimated. One-way and probabilistic sensitivity analyses (PSAs) were then performed.

RESULTS

From provider and societal perspectives, combining the CCM program with HFM for malaria control in Burundi was more cost-effective than implementing HFM alone. The addition of CCM, using artesunate amodiaquine (ASAQ) as the first-line treatment, increased by US$1.70, and US$ 1.67 per DALY averted from the provider and societal perspectives, respectively. Using Artemether Lumefantrine (AL) as the first-line treatment, adding the CCM program to HFM increased by US$ 1.92, and US$ 1.87 per DALY averted from the provider and societal perspectives. At a willingness-to-pay of one GDP/capita, the CCM program remained a 100% chance of being cost-effective. In addition, implementing the program for five years requires a budget of US$ 15 800 486-19 765 117.

CONCLUSION

Implementing the CCM program and HFM is value for money for malaria control in Burundi. The findings can support decision-makers in Burundi in deciding on resource allocation, especially during the program's scale up.

Molecular surveillance for polymorphisms associated with artemisinin-based combination therapy resistance in Plasmodium falciparum isolates collected in Mozambique, 2018

Background

Due to the threat of emerging anti-malarial resistance, the World Health Organization recommends incorporating surveillance for molecular markers of anti-malarial resistance into routine therapeutic efficacy studies (TESs). In 2018, a TES of artemether-lumefantrine (AL) and artesunate-amodiaquine (ASAQ) was conducted in Mozambique, and the prevalence of polymorphisms in the pfk13, pfcrt, and pfmdr1 genes associated with drug resistance was investigated.

Methods

Children aged 6–59 months were enrolled in four study sites. Blood was collected and dried on filter paper from participants who developed fever within 28 days of initial malaria treatment. All samples were first screened for Plasmodium falciparum using a multiplex real-time PCR assay, and polymorphisms in the pfk13, pfcrt, and pfmdr1 genes were investigated by Sanger sequencing.

Results

No pfk13 mutations, associated with artemisinin partial resistance, were observed. The only pfcrt haplotype observed was the wild type CVMNK (codons 72–76), associated with chloroquine sensitivity. Polymorphisms in pfmdr1 were only observed at codon 184, with the mutant 184F in 43/109 (39.4%) of the samples, wild type Y184 in 42/109 (38.5%), and mixed 184F/Y in 24/109 (22.0%). All samples possessed N86 and D1246 at these two codons.

Conclusion

In 2018, no markers of artemisinin resistance were documented. Molecular surveillance should continue to monitor the prevalence of these markers to inform decisions on malaria treatment in Mozambique.

Molecular surveillance of Pfcrt and k13 propeller polymorphisms of imported Plasmodium falciparum cases to Zhejiang Province, China between 2016 and 2018

BACKGROUND

Resistance to anti-malarial drugs hinders malaria elimination. Monitoring the molecular markers of drug resistance helps improve malaria treatment policies. This study aimed to assess the distribution of molecular markers of imported Plasmodium falciparum infections.

METHODS

In total, 485 P. falciparum cases imported from Africa, Southeast Asia, and Oceania into Zhejiang province, China, from 2016 to 2018 were investigated. Most were imported from Africa, and only a few cases originated in Asia and Oceania. Blood samples were collected from each patient. Plasmodium falciparum chloroquine resistance transporter (Pfcrt) at residues 72-76 and Kelch13-propeller (k13) were determined by nested PCR and DNA sequence.

RESULTS

Wild-type Pfcrt at residues 72-76 was predominant (72.61%), but mutant and mixed alleles were also detected, of which CVIET (22.72%) was the most common. Mutant Pfcrt haplotypes were more frequent in patients from West Africa (26.92%), North Africa (25%), and Central Africa (21.93%). The number of cases of P. falciparum infections was small in Southeast Asia and Oceania, and these cases involved Pfcrt mutant type. For the k13 propeller gene, 26 samples presented 19 different point mutations, including eight nonsynonymous mutations (P441S, D464E, K503E, R561H, A578S, R622I, V650F, N694K). In addition, R561H, one of the validated SNPs in k13, was detected in one patient from Myanmar and one patient from Rwanda. A578S, although common in Africa, was found in only one patient from Cameroon. R622I was detected in one sample from Mozambique and one sample from Somalia. The genetic diversity of k13 was low in most regions of Africa and purifying selection was suggested by Tajima's D test.

CONCLUSIONS

The frequency and spatial distributions of Pfcrt and k13 mutations associated with drug resistance were determined. Wild-type Pfcrt was dominant in Africa. Among k13 mutations correlated with delayed parasite clearance, only the R561H mutation was found in one case from Rwanda in Africa. Both Pfcrt and k13 mutations were detected in patients from Southeast Asia and Oceania. These findings provide insights into the molecular epidemiological profile of drug resistance markers in the study region.

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.

Analysis of Plasmodium falciparum Na+/H+ exchanger (pfnhe1) polymorphisms among imported African malaria parasites isolated in Wuhan, Central China

Background

Quinine (QN) remains an effective drug for malaria treatment. However, quinine resistance (QNR) in Plasmodium falciparum has been reported in many malaria-endemic regions particularly in African countries. Genetic polymorphism of the P. falciparum Na⁺/H⁺ exchanger (pfnhe1) is considered to influence QN susceptibility. Here, ms4760 alleles of pfnhe1 were analysed from imported African P. falciparum parasites isolated from returning travellers in Wuhan, Central China.

Methods

A total of 204 dried-blood spots were collected during 2011–2016. The polymorphisms of the pfnhe1 gene were determined using nested PCR with DNA sequencing.

Results

Sequences were generated for 99.51% (203/204) of the PCR products and 68.63% (140/204) of the isolates were analysed successfully for the pfnhe1 ms4760 haplotypes. In total, 28 distinct ms4760 alleles containing 0 to 5 DNNND and 1 to 3 NHNDNHNNDDD repeats were identified. For the alleles, ms4760–1 (22.86%, 32/140), ms4760–3 (17.86%, 25/140), and ms4760–7 (10.71%, 15/140) were the most prevalent profiles. Furthermore, 5 undescribed ms4760 alleles were reported.

Conclusions

The study offers an initial comprehensive analysis of pfnhe1 ms4760 polymorphisms from imported P. falciparum isolates in Wuhan. Pfnhe1 may constitute a good genetic marker to evaluate the prevalence of QNR in malaria-endemic and non-endemic regions.

Persistence of chloroquine resistance alleles in malaria endemic countries: a systematic review of burden and risk factors

Background

Chloroquine, a previous highly efficacious, easy to use and affordable anti-malarial agent was withdrawn from malaria endemic regions due to high levels of resistance. This review collated evidence from published-reviewed articles to establish prevalence of Pfcrt 76T and Pfmdr-1 86Y alleles in malaria affected countries following official discontinuation of chloroquine use.

Methods

A review protocol was developed, registered in PROSPERO (#CRD42018083957) and published in a peer-reviewed journal. Article search was done in PubMed, Scopus, Lilacs/Vhl and Embase databases by two experienced librarians (AK, RS) for the period 1990-to-Febuary 2018. Mesh terms and Boolean operators (AND, OR) were used. Data extraction form was designed in Excel spread sheet 2007. Data extraction was done by three reviewers (NL, BB and MO), discrepancies were resolved by discussion. Random effects analysis was done in Open Meta Analyst software. Heterogeneity was established using I²-statistic.

Results

A total of 4721 citations were retrieved from article search (Pubmed = 361, Lilac/vhl = 28, Science Direct = 944, Scopus = 3388). Additional targeted search resulted in three (03) eligible articles. After removal of duplicates (n = 523) and screening, 38 articles were included in the final review. Average genotyping success rate was 63.6% (18,343/28,820) for Pfcrt K76T and 93.5% (16,232/17,365) for Pfmdr-1 86Y mutations. Prevalence of Pfcrt 76T was as follows; East Africa 48.9% (2528/5242), Southern Africa 18.6% (373/2163), West Africa 58.3% (3321/6608), Asia 80.2% (1951/2436). Prevalence of Pfmdr-1 86Y was; East Africa 32.4% (1447/5722), Southern Africa 36.1% (544/1640), West Africa 52.2% (1986/4200), Asia 46.4% (1276/2217). Over half, 52.6% (20/38) of included studies reported continued unofficial chloroquine use following policy change. Studies done in Madagascar and Kenya reported re-emergence of chloroquine sensitive parasites (IC₅₀ < 30.9 nM). The average time (years) since discontinuation of chloroquine use to data collection was 8.7 ± 7.4. There was high heterogeneity (I² > 95%).

Conclusion

The prevalence of chloroquine resistance alleles among Plasmodium falciparum parasites have steadily declined since discontinuation of chloroquine use. However, Pfcrt K76T and Pfmdr-1 N86Y mutations still persist at moderate frequencies in most malaria affected countries.

Mechanisms of resistance to the partner drugs of artemisinin in the malaria parasite

The deployment of artemisinin-based combination therapies (ACTs) has been, and continues to be, integral to reducing the number of malaria cases and deaths. However, their efficacy is being increasingly jeopardized by the emergence and spread of parasites that are resistant (or partially resistant) to the artemisinin derivatives and to their partner drugs, with the efficacy of the latter being especially crucial for treatment success. A detailed understanding of the genetic determinants of resistance to the ACT partner drugs, and the mechanisms by which they mediate resistance, is required for the surveillance of molecular markers and to optimize the efficacy and lifespan of the partner drugs through resistance management strategies. We summarize new insights into the molecular basis of parasite resistance to the ACTs, such as recently-uncovered determinants of parasite susceptibility to the artemisinin derivatives, piperaquine, lumefantrine, and mefloquine, and outline the mechanisms through which polymorphisms in these determinants may be conferring resistance.

The Malaria TaqMan Array Card Includes 87 Assays for Plasmodium falciparum Drug Resistance, Identification of Species, and Genotyping in a Single Reaction

Antimalarial drug resistance exacerbates the global disease burden and complicates eradication efforts. To facilitate the surveillance of resistance markers in countries of malaria endemicity, we developed a suite of TaqMan assays for known resistance markers and compartmentalized them into a single array card (TaqMan array card, TAC). We included 87 assays for species identification, for the detection of Plasmodium falciparum mutations associated with chloroquine, atovaquone, pyrimethamine, sulfadoxine, and artemisinin resistance, and for neutral single nucleotide polymorphism (SNP) genotyping. Assay performance was first optimized using DNA from common laboratory parasite lines and plasmid controls. The limit of detection was 0.1 to 10 pg of DNA and yielded 100% accuracy compared to sequencing. The tool was then evaluated on 87 clinical blood samples from around the world, and the malaria TAC once again achieved 100% accuracy compared to sequencing and in addition detected the presence of mixed infections in clinical samples. With its streamlined protocol and high accuracy, this malaria TAC should be a useful tool for large-scale antimalarial resistance surveillance.

Disease burden and the role of pharmacogenomics in African populations

Background

The burden of communicable and non-communicable diseases in Sub-Saharan Africa poses a challenge in achieving quality healthcare. Although therapeutic drugs have generally improved health, their efficacy differs from individual to individual. Variability in treatment response is mainly because of genetic variants that affect the pharmacokinetics and pharmacodynamics of drugs.

Method

The intersection of disease burden and therapeutic intervention is reviewed, and the status of pharmacogenomics knowledge in African populations is explored.

Results

The most commonly studied variants with pharmacogenomics relevance are discussed, especially in genes coding for enzymes that affect the response to drugs used for HIV, malaria, sickle cell disease and cardiovascular diseases.

Conclusions

The genetically diverse African population is likely to benefit from a pharmacogenomics-based healthcare approach, especially with respect to reduction of drug side effects, and separation of responders and non-responders leading to optimized drug choices and doses for each patient.