Artemisinin-based Combination Therapy Resistance Research Articles

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

BackgroundDue 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.MethodsChildren 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.ResultsNo 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.ConclusionIn 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.

Evolution of Antimalarial Drug Resistance Markers in the Reservoir of Plasmodium falciparum Infections in the Upper East Region of Ghana.

The majority of Plasmodium falciparum infections, constituting the reservoir in all ages, are asymptomatic in high-transmission settings in Africa. The role of this reservoir in the evolution and spread of drug resistance was explored. Population genetic analyses of the key drug resistance-mediating polymorphisms were analyzed in a cross-sectional survey of asymptomatic P. falciparum infections across all ages in Bongo District, Ghana. Seven years after the policy change to artemisinin-based combination therapies in 2005, the pfcrt K76 and pfmdr1 N86 wild-type alleles have nearly reached fixation and have expanded via soft selective sweeps on multiple genetic backgrounds. By constructing the pfcrt-pfmdr1-pfdhfr-pfdhps multilocus haplotypes, we found that the alleles at these loci were in linkage equilibrium and that multidrug-resistant parasites have not expanded in this reservoir. For pfk13, 32 nonsynonymous mutations were identified; however, none were associated with artemisinin-based combination therapy resistance. The prevalence and selection of alleles/haplotypes by antimalarials were similar to that observed among clinical cases in Ghana, indicating that they do not represent 2 subpopulations with respect to these markers. Thus, the P. falciparum reservoir in all ages can contribute to the maintenance and spread of antimalarial resistance.

Molecular Surveillance for Polymorphisms Associated with Artemisinin-Based Combination Therapy Resistance in Plasmodium falciparum Isolates Collected in the State of Roraima, Brazil.

Given that the C580Y polymorphism in the Plasmodium falciparum propeller domain of the kelch 13 gene (pfk13) was documented in Guyana, monitoring for mutations associated with antimalarial resistance was undertaken in neighboring Roraima state in Brazil. Polymorphisms in the pfmdr1 and pfk13 genes were investigated in 275 P. falciparum samples. No pfk13 mutations were observed. Triple mutants 184F, 1042D, and 1246Y were observed in 100% of the samples successfully sequenced for the pfmdr1 gene, with 20.1% of these having an additional mutation at codon 1034C. Among them, 2.5% of samples harbored two copies of the pfmdr1 gene. We found no evidence of the spread of C580Y parasites to Roraima state, Brazil. As previously observed, the 184F, 1042D, and 1246Y mutations in the pfmdr1 gene appear to be fixed in this region. Continued molecular surveillance is essential to detect any potential migration or local emergence of artemisinin-resistant mutation.

Malaria Policy Advisory Committee to the WHO: conclusions and recommendations of eighth biannual meeting (September 2015).

The Malaria Policy Advisory Committee (MPAC) to the World Health Organization held its eighth meeting in Geneva, Switzerland from 16 to 18 September 2015. This article provides a summary of the discussions, conclusions and meeting recommendations. Meeting sessions included: recommendations from the Evidence Review Group (ERG) on mass drug administration; recommendations from the ERG on malaria in pregnancy; recommendations on when to scale back vector control; feedback on the Plasmodium vivax technical brief and the recommendation for G6PD testing before treatment; updates on artemisinin and artemisinin-based combination therapy resistance and the Greater Mekong Subregion elimination strategy; an update from the working group on malaria terminology; and updates on malaria elimination in the World Health Organization European region, the ERG on malaria elimination, and World Health Organization reform to support innovation, efficiency and quality in vector control tools. Policy statements, position statements, and guidelines that arise from the MPAC meeting conclusions and recommendations will be issued formally and disseminated to World Health Organization Member States by the World Health Organization Global Malaria Programme.

Artemisinin resistance or artemisinin-based combination therapy resistance?

In his recent Comment in The Lancet Infectious Diseases, Joel Breman discussed parasite resistance to artemisinin-based combination therapy (ACT) and the heritability of this resistance.1Breman JG Resistance to artemisinin-based combination therapy.Lancet Infect Dis. 2012; 12: 820-822Summary Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 2Amaratunga C Sreng S Suon S et al.Artemisinin-resistant Plasmodium falciparum malaria in Pursat province, western Cambodia: a parasite-clearance-rate study.Lancet Infect Dis. 2012; 12: 851-858Summary Full Text Full Text PDF PubMed Scopus (253) Google Scholar The differences between artemisinin resistance and resistance to ACT (also termed ACT resistance) merit further clarification. Researchers have used many methods to try to prove the existence of artemisinin resistance. Lengthening of the parasite clearance time suggests artemisinin resistance. Amaratunga and colleagues2Amaratunga C Sreng S Suon S et al.Artemisinin-resistant Plasmodium falciparum malaria in Pursat province, western Cambodia: a parasite-clearance-rate study.Lancet Infect Dis. 2012; 12: 851-858Summary Full Text Full Text PDF PubMed Scopus (253) Google Scholar delayed mefloquine administration to exclude the contribution of mefloquine in parasite clearance during the first 72 h—the period most relevant to artemisinin action. This approach deviates from the standard treatment schedule for the purpose of their study—ie, to investigate the genetic basis of artemisinin resistance. This study design does not have a primary aim to show ACT resistance, which leads to ACT failures. The term “ACT resistance” is used loosely and often interchangeably with “artemisinin resistance”, although it should not be. Artemisinin resistance could contribute to ACT failure, but the combination of artemisinin with an efficacious partner drug can improve cure rates to an adequate level.3World Health Organization Global Malaria ProgrammeUpdate on artemisinin resistance.http://www.who.int/malaria/publications/atoz/arupdate042012.pdfDate: April 2012Google Scholar Evidence of artemisinin resistance has been scarce so far, and only a working definition of such resistance exists. The longer parasite clearance times reported in the Mekong subregion could be due to a non-progressive weakening of artemisinin activity. ACTs are still highly efficacious in most of this subregion, especially in Laos, Burma, and Vietnam.4World Health Organization Global Malaria ProgrammeThe status of drug-resistant malaria along the ThailandûMyanmar border. Revised 9 May 2012.http://www.who.int/malaria/publications/atoz/drug_resistance_myanmar_thailand_border_may_2012.pdfGoogle Scholar One exception is the decreasing efficacy of artesunate–mefloquine at the Cambodian–Thai border. Two locations in western Cambodia are good examples of ACT resistance, where, despite the policy switch from failing artesunate–mefloquine to dihydroartemisinin–piperaquine treatment, the 42 day treatment efficacies are only 73–89%, and more than 40% of patients have positive parasitaemia on day 3.3World Health Organization Global Malaria ProgrammeUpdate on artemisinin resistance.http://www.who.int/malaria/publications/atoz/arupdate042012.pdfDate: April 2012Google Scholar Existing mefloquine resistance and the unregulated availability of dihydroartemisinin–piperaquine in the private sector for the past 10 years could explain its failure. Scientists are trying to elucidate the basis of artemisinin resistance, whereas malaria control programmes focus on ACT resistance, especially the morbidity and mortality associated with inefficacy of the combined drugs. WHO, senior health authorities, and donor agencies have correctly emphasised artemisinin resistance as a public health warning, support for which is essential for maintenance of parasite susceptibility to artemisinins at the highest possible level or for elimination of those parasites. In view of the scarce choices of appropriate partner drugs, if artemisinin resistance becomes established, it will negatively affect global achievements in malaria control. I agree with Breman's concern about Africa, where great care should be taken in deployment of ACTs.5Wongsrichanalai C Thimasarn K Sirichaisinthop J Antimalarial drug combination policy: a caveat.Lancet. 2000; 355: 2245-2247Summary Full Text Full Text PDF PubMed Scopus (26) Google Scholar The availability of ACTs in Africa from drug vendors without parasitological diagnosis is a dangerous problem. For the online parasite clearance estimator see http://www.wwarn.org/toolkit/data-management/parasite-clearance-estimator For the online parasite clearance estimator see http://www.wwarn.org/toolkit/data-management/parasite-clearance-estimator I declare that I have no conflicts of interest. Artemisinin-resistant Plasmodium falciparum in Pursat province, western Cambodia: a parasite clearance rate studyHeritable artemisinin resistance is established in a second Cambodian province. To accurately identify parasites that are intrinsically susceptible or resistant to artemisinins, future studies should explore the effect of erythrocyte polymorphisms and specific immune responses on half-life variation. Full-Text PDF