Treatment Failure in a UK Malaria Patient Harboring Genetically Variant Plasmodium falciparum From Uganda With Reduced In Vitro Susceptibility to Artemisinin and Lumefantrine.

BACKGROUND: Recent cases of clinical failure in malaria patients in the United Kingdom (UK) treated with artemether-lumefantrine have implications for malaria chemotherapy worldwide. METHODS: Parasites were isolated from an index case of confirmed Plasmodium falciparum treatment failure after standard treatment, and from comparable travel-acquired UK malaria cases. Drug susceptibility in vitro and genotypes at 6 resistance-associated loci were determined for all parasite isolates and compared with clinical outcomes for each parasite donor. RESULTS: A traveler, who returned to the UK from Uganda in 2022 with Plasmodium falciparum malaria, twice failed treatment with full courses of artemether-lumefantrine. Parasites from the patient exhibited significantly reduced susceptibility to artemisinin (ring-stage survival, 17.3% [95% confidence interval {CI}, 13.6%-21.1%]; P < .0001) and lumefantrine (effective concentration preventing 50% of growth = 259.4 nM [95% CI, 130.6-388.2 nM]; P = .001). Parasite genotyping identified an allele of pfk13 encoding both the A675V variant in the Pfk13 propeller domain and a novel L145V nonpropeller variant. In vitro susceptibility testing of 6 other P. falciparum lines of Ugandan origin identified reduced susceptibility to artemisinin and lumefantrine in 1 additional line, also from a 2022 treatment failure case. These parasites did not harbor a pfk13 propeller domain variant but rather the novel nonpropeller variant T349I. Variant alleles of pfubp1, pfap2mu, and pfcoronin were also identified among the 7 parasite lines. CONCLUSIONS: We confirm, in a documented case of artemether-lumefantrine treatment failure imported from Uganda, the presence of pfk13 mutations encoding L145V and A675V. Parasites with reduced susceptibility to both artemisinin and lumefantrine may be emerging in Uganda.

Measuring protective efficacy and quantifying the impact of drug resistance: A novel malaria chemoprevention trial design and methodology.

BACKGROUND: Recently revised WHO guidelines on malaria chemoprevention have opened the door to more tailored implementation. Countries face choices on whether to replace old drugs, target additional age groups, and adapt delivery schedules according to local drug resistance levels and malaria transmission patterns. Regular routine assessment of protective efficacy of chemoprevention is key. Here, we apply a novel modelling approach to aid the design and analysis of chemoprevention trials and generate measures of protection that can be applied across a range of transmission settings. METHODS AND FINDINGS: We developed a model of genotype-specific drug protection, which accounts for underlying risk of infection and circulating genotypes. Using a Bayesian framework, we fitted the model to multiple simulated scenarios to explore variations in study design, setting, and participant characteristics. We find that a placebo or control group with no drug protection is valuable but not always feasible. An alternative approach is a single-arm trial with an extended follow-up (>42 days), which allows measurement of the underlying infection risk after drug protection wanes, as long as transmission is relatively constant. We show that the currently recommended 28-day follow-up in a single-arm trial results in low precision of estimated 30-day chemoprevention efficacy and low power in determining genotype differences of 12 days in the duration of protection (power = 1.4%). Extending follow-up to 42 days increased precision and power (71.5%) in settings with constant transmission over this time period. However, in settings of unstable transmission, protective efficacy in a single-arm trial was overestimated by 24.3% if recruitment occurred during increasing transmission and underestimated by 15.8% when recruitment occurred during declining transmission. Protective efficacy was estimated with greater precision in high transmission settings, and power to detect differences by resistance genotype was lower in scenarios where the resistant genotype was either rare or too common. CONCLUSIONS: These findings have important implications for the current guidelines on chemoprevention efficacy studies and will be valuable for informing where these studies should be optimally placed. The results underscore the need for a comparator group in seasonal settings and provide evidence that the extension of follow-up in single-arm trials improves the accuracy of measures of protective efficacy in settings with more stable transmission. Extension of follow-up may pose logistical challenges to trial feasibility and associated costs. However, these studies may not need to be repeated multiple times, as the estimates of drug protection against different genotypes can be applied to different settings by adjusting for transmission intensity and frequency of resistance.

Parasite clearance and protection from Plasmodium falciparum infection (PCPI): a three-arm, parallel, double-blinded, placebo-controlled, randomised trial of presumptive sulfadoxine-pyrimethamine versus sulfadoxine-pyrimethamine plus amodiaquine versus artesunate monotherapy among asymptomatic children 3-5 years of age in Cameroon.

BACKGROUND: The World Health Organization 2022 malaria chemoprevention guidelines recommend providing a full course of antimalarial treatment at pre-defined intervals, regardless of malaria status to prevent illness among children resident in moderate to high perennial malaria transmission settings as perennial malaria chemoprevention (PMC) with sulfadoxine-pyrimethamine (SP). The dhps I431V mutation circulating in West Africa has unknown effect on SP protective efficacy. METHODS: This protocol is for a three-arm, parallel, double-blinded, placebo-controlled, randomised trial in Cameroon among children randomly assigned to one of three directly-observed treatment groups: (i) Group 1 (n = 450) receives daily artesunate (AS) placebo on days - 7 to -1, then active SP plus placebo amodiaquine (AQ) on day 0, and placebo AQ on days 1 and 2; (ii) Group 2 (n = 250) receives placebo AS on days - 7 to -1, then active SP and AQ on day 0, and active AQ on days 1 and 2; and (iii) Group 3 (n = 200) receives active AS on days - 7 to -1, then placebo SP on day 0 and placebo AQ on days 0 to 2. On days 0, 2, 5, 7, and thereafter weekly until day 28, children provide blood for thick smear slides. Dried blood spots are collected on the same days and weekly from day 28 to day 63 for quantitative polymerase chain reaction (qPCR) and genotype analyses. DISCUSSION: Our aim is to quantify the chemopreventive efficacy of SP, and SP plus AQ, and measure the effect of the parasite genotypes associated with SP resistance on parasite clearance and protection from infection when exposed to SP chemoprevention. We will report unblinded results including: (i) time-to-parasite clearance among SP and SP plus AQ recipients who were positive on day 0 by qPCR and followed to day 63; (ii) mean duration of SP and SP plus AQ protection against infection, and (iii) mean duration of symptom-free status among SP and SP plus AQ recipients who were parasite free on day 0 by qPCR. Our study is designed to compare the 28-day follow-up of the new WHO malaria chemoprevention efficacy study protocol with extended follow-up to day 63. TRIAL REGISTRATION: ClinicalTrials.gov NCT06173206; 15/12/2023.

Baseline prevalence of molecular marker of sulfadoxine/pyrimethamine resistance in Ebonyi and Osun states, Nigeria: amplicon deep sequencing of dhps-540.

BACKGROUND: Chemoprevention plays an important role in malaria control strategy. Perennial malaria chemoprevention (PMC) using sulfadoxine/pyrimethamine (SP) is a WHO-approved strategy to combat malaria in young children and may lead to drug pressure. Introducing SP-PMC may therefore be compromised due to the emergence of Plasmodium falciparum resistant to SP, particularly mutation at K540E of the dihydropteroate synthase (dhps) gene. Molecular surveillance of resistance markers can support assessment of antimalarial efficacy and effectiveness. High prevalence of 540E is associated with reduced effectiveness of SP, and areas with more than 50% prevalence are considered unsuitable for intermittent preventative treatment in pregnancy (IPTp) implementation. Assessing 540E prevalence is an important undertaking before implementation of SP-PMC. METHODS: We conducted a rapid surveillance of dhps-540E to assess the suitability of SP as PMC in field studies from Ebonyi and Osun states in Nigeria. We used an in-house developed amplicon deep-sequencing method targeting part of the dhps gene. RESULTS: Our data reveal that 18.56% of individuals evaluated carried the 540E mutation mixed with the WT K540. Mutant variant 540E alone was not found, and 80% of isolates harboured only WT (K540). Clonal analysis of the sequencing data shows a very low proportion of 540E circulating in both states. CONCLUSIONS: Our data show that both states are suitable for SP-PMC implementation and, based on this finding, SP-PMC was implemented in Osun in 2022. Continuous monitoring of 540E will be required to ensure the chemoprevention effectiveness of SP in Nigeria.

Screening strategies and laboratory assays to support Plasmodium falciparum histidine-rich protein deletion surveillance: where we are and what is needed.

Rapid diagnostic tests (RDTs) detecting Plasmodium falciparum histidine-rich protein 2 (HRP2) have been an important tool for malaria diagnosis, especially in resource-limited settings lacking quality microscopy. Plasmodium falciparum parasites with deletion of the pfhrp2 gene encoding this antigen have now been identified in dozens of countries across Asia, Africa, and South America, with new reports revealing a high prevalence of deletions in some selected regions. To determine whether HRP2-based RDTs are appropriate for continued use in a locality, focused surveys and/or surveillance activities of the endemic P. falciparum population are needed. Various survey and laboratory methods have been used to determine parasite HRP2 phenotype and pfhrp2 genotype, and the data collected by these different methods need to be interpreted in the appropriate context of survey and assay utilized. Expression of the HRP2 antigen can be evaluated using point-of-care RDTs or laboratory-based immunoassays, but confirmation of a deletion (or mutation) of pfhrp2 requires more intensive laboratory molecular assays, and new tools and strategies for rigorous but practical data collection are particularly needed for large surveys. Because malaria diagnostic strategies are typically developed at the national level, nationally representative surveys and/or surveillance that encompass broad geographical areas and large populations may be required. Here is discussed contemporary assays for the phenotypic and genotypic evaluation of P. falciparum HRP2 status, consider their strengths and weaknesses, and highlight key concepts relevant to timely and resource-conscious workflows required for efficient diagnostic policy decision making.

Persistent Submicroscopic Plasmodium falciparum Parasitemia 72 Hours after Treatment with Artemether-Lumefantrine Predicts 42-Day Treatment Failure in Mali and Burkina Faso.

A recent randomized controlled trial, the WANECAM (West African Network for Clinical Trials of Antimalarial Drugs) trial, conducted at seven centers in West Africa, found that artemether-lumefantrine, artesunate-amodiaquine, pyronaridine-artesunate, and dihydroartemisinin-piperaquine all displayed good efficacy. However, artemether-lumefantrine was associated with a shorter interval between clinical episodes than the other regimens. In a further comparison of these therapies, we identified cases of persisting submicroscopic parasitemia by quantitative PCR (qPCR) at 72 h posttreatment among WANECAM participants from 5 sites in Mali and Burkina Faso, and we compared treatment outcomes for this group to those with complete parasite clearance by 72 h. Among 552 evaluable patients, 17.7% had qPCR-detectable parasitemia at 72 h during their first treatment episode. This proportion varied among sites, reflecting differences in malaria transmission intensity, but did not differ among pooled drug treatment groups. However, patients who received artemether-lumefantrine and were qPCR positive at 72 h were significantly more likely to have microscopically detectable recurrent Plasmodium falciparum parasitemia by day 42 than those receiving other regimens and experienced, on average, a shorter interval before the next clinical episode. Haplotypes of pfcrt and pfmdr1 were also evaluated in persisting parasites. These data identify a possible threat to the parasitological efficacy of artemether-lumefantrine in West Africa, over a decade since it was first introduced on a large scale.

Plasmodium-associated changes in human odor attract mosquitoes.

Malaria parasites (Plasmodium) can change the attractiveness of their vertebrate hosts to Anopheles vectors, leading to a greater number of vector-host contacts and increased transmission. Indeed, naturally Plasmodium-infected children have been shown to attract more mosquitoes than parasite-free children. Here, we demonstrate Plasmodium-induced increases in the attractiveness of skin odor in Kenyan children and reveal quantitative differences in the production of specific odor components in infected vs. parasite-free individuals. We found the aldehydes heptanal, octanal, and nonanal to be produced in greater amounts by infected individuals and detected by mosquito antennae. In behavioral experiments, we demonstrated that these, and other, Plasmodium-induced aldehydes enhanced the attractiveness of a synthetic odor blend mimicking "healthy" human odor. Heptanal alone increased the attractiveness of "parasite-free" natural human odor. Should the increased production of these aldehydes by Plasmodium-infected humans lead to increased mosquito biting in a natural setting, this would likely affect the transmission of malaria.

Plasmodium falciparum Isolates Carrying pfk13 Polymorphisms Harbor the SVMNT Allele of pfcrt in Northwestern Indonesia.

Artemisinin-based combination therapy (ACT) is the first-line antimalarial regimen in Indonesia. Susceptibility of Plasmodium falciparum to artemisinin is falling in the Greater Mekong subregion, but it is not known whether the efficacy of current combinations is also threatened in nearby Sumatera. We evaluated the genetic loci pfcrt, pfmdr1, and pfk13, considered to be under selection by artemisinin combination therapy, among 404 P. falciparum infections identified by PCR detection in a cross-sectional survey of 3,731 residents of three regencies. The pfcrt haplotype SVMNT (codons 72 to 76) was the most prevalent and displayed significant linkage disequilibrium with the pfmdr1 haplotype YY (codons 86 and 184) (odds ratio [OR] 26.7; 95% confidence interval [CI], 5.96 to 239.4; P < 0.001). This contrasts with Mekong countries, where the CVIET haplotype of pfcrt predominates. Among 231 evaluable isolates, only 9 (3.9%) showed any evidence of nonsynonymous gene variants in the propeller domain of pfk13 The Thr474Ala variant was seen in six individuals, and Cys580Tyr was identified with low confidence in only a single isolate from an asymptomatic individual. Among a subset of 117 symptomatic P. falciparum-infected individuals randomized to receive either dihydroartemisinin-piperaquine or artemether-lumefantrine, the treatment outcome was not associated with pretreatment genotype. However, submicroscopic persistent parasites at day 28 or day 42 of follow-up were significantly more likely to harbor the pfmdr1 haplotype NF (codons 86 and 184) than were pretreatment isolates (P < 0.001 for both treatment groups). Current ACT regimens appear to be effective in Sumatera, but evidence of persistent submicroscopic infection in some patients suggests further detailed studies of drug susceptibility should be undertaken.

pfhrp2 and pfhrp3 Gene Deletions That Affect Malaria Rapid Diagnostic Tests for Plasmodium falciparum: Analysis of Archived Blood Samples From 3 African Countries.

BACKGROUND: Malaria rapid diagnostic tests (mRDTs) that target histidine-rich protein 2 (HRP2) are important tools for Plasmodium falciparum diagnosis. Parasites with pfhrp2/3 gene deletions threaten the use of these mRDTs and have been reported in Africa, Asia, and South America. We studied blood samples from 3 African countries to determine if these gene deletions were present. METHODS: We analyzed 911 dried blood spots from Ghana (n = 165), Tanzania (n = 176), and Uganda (n = 570). Plasmodium falciparum infection was confirmed by 18S rDNA polymerase chain reaction (PCR), and pfhrp2/3 genes were genotyped. True pfhrp2/3 gene deletions were confirmed if samples were (1) microscopy positive; (2) 18S rDNA PCR positive; (3) positive for merozoite surface protein genes by PCR or positive by loop-mediated isothermal amplification; or (4) quantitative PCR positive with >5 parasites/µL. RESULTS: No pfhrp2/3 deletions were detected in samples from Ghana, but deletions were identified in Tanzania (3 pfhrp2; 2 pfhrp3) and Uganda (7 pfhrp2; 2 pfhrp3). Of the 10 samples with pfhrp2 deletions, 9 tested negative by HRP2-based mRDT. CONCLUSIONS: The presence of pfhrp2/3 deletions in Tanzania and Uganda, along with reports of pfhrp2/3-deleted parasites in neighboring countries, reinforces the need for systematic surveillance to monitor the reliability of mRDTs in malaria-endemic countries.

Seasonal malaria chemoprevention combined with community case management of malaria in children under 10 years of age, over 5 months, in south-east Senegal: A cluster-randomised trial.

BACKGROUND: Seasonal malaria chemoprevention (SMC) is recommended in the Sahel region of Africa for children under 5 years of age, for up to 4 months of the year. It may be appropriate to include older children, and to provide protection for more than 4 months. We evaluated the effectiveness of SMC using sulfadoxine-pyrimethamine plus amodiaquine given over 5 months to children under 10 years of age in Saraya district in south-east Senegal in 2011. METHODS AND FINDINGS: Twenty-four villages, including 2,301 children aged 3-59 months and 2,245 aged 5-9 years, were randomised to receive SMC with community case management (CCM) (SMC villages) or CCM alone (control villages). In all villages, community health workers (CHWs) were trained to treat malaria cases with artemisinin combination therapy after testing with a rapid diagnostic test (RDT). In SMC villages, CHWs administered SMC to children aged 3 months to 9 years once a month for 5 months. The study was conducted from 27 July to 31 December 2011. The primary outcome was malaria (fever or history of fever with a positive RDT). The prevalence of anaemia and parasitaemia was measured in a survey at the end of the transmission season. Molecular markers associated with resistance to SMC drugs were analysed in samples from incident malaria cases and from children with parasitaemia in the survey. SMC was well tolerated with no serious adverse reactions. There were 1,472 RDT-confirmed malaria cases in the control villages and 270 in the SMC villages. Among children under 5 years of age, the rate difference was 110.8/1,000/month (95% CI 64.7, 156.8; p < 0.001) and among children 5-9 years of age, 101.3/1,000/month (95% CI 66.7, 136.0; p < 0.001). The mean haemoglobin concentration at the end of the transmission season was higher in SMC than control villages, by 6.5 g/l (95% CI 2.0, 11; p = 0.007) among children under 5 years of age, and by 5.2 g/l (95% CI 0.4, 9.9; p = 0.035) among children 5-9 years of age. The prevalence of parasitaemia was 18% in children under 5 years of age and 25% in children 5-9 years of age in the control villages, and 5.7% and 5.8%, respectively, in these 2 age groups in the SMC villages, with prevalence differences of 12.5% (95% CI 6.8%, 18.2%; p < 0.001) in children under 5 years of age and 19.3% (95% CI 8.3%, 30.2%; p < 0.001) in children 5-9 years of age. The pfdhps-540E mutation associated with clinical resistance to sulfadoxine-pyrimethamine was found in 0.8% of samples from malaria cases but not in the final survey. Twelve children died in the control group and 14 in the SMC group, a rate difference of 0.096/1,000 child-months (95% CI 0.99, 1.18; p = 0.895). Limitations of this study include that we were not able to obtain blood smears for microscopy for all suspected malaria cases, such that we had to rely on RDTs for confirmation, which may have included false positives. CONCLUSIONS: In this study SMC for children under 10 years of age given over 5 months was feasible, well tolerated, and effective in preventing malaria episodes, and reduced the prevalence of parasitaemia and anaemia. SMC with CCM achieved high coverage and ensured children with malaria were promptly treated with artemether-lumefantrine. TRIAL REGISTRATION: www.clinicaltrials.gov NCT01449045.

Contribution of Plasmodium knowlesi to Multispecies Human Malaria Infections in North Sumatera, Indonesia.

Background: As Indonesia works toward the goal of malaria elimination, information is lacking on malaria epidemiology from some western provinces. As a basis for studies of antimalarial efficacy, we set out to survey parasite carriage in 3 communities in North Sumatera Province. Methods: A combination of active and passive detection of infection was carried out among communities in Batubara, Langkat, and South Nias regencies. Finger-prick blood samples from consenting individuals of all ages provided blood films for microscopic examination and blood spots on filter paper. Plasmodium species were identified using nested polymerase chain reaction (PCR) of ribosomal RNA genes and a novel assay that amplifies a conserved sequence specific for the sicavar gene family of Plasmodium knowlesi. Results: Of 3731 participants, 614 (16.5%) were positive for malaria parasites by microscopy. PCR detected parasite DNA in samples from 1169 individuals (31.3%). In total, 377 participants (11.8%) harbored P. knowlesi. Also present were Plasmodium vivax (14.3%), Plasmodium falciparum (10.5%) and Plasmodium malariae (3.4%). Conclusions: Amplification of sicavar is a specific and sensitive test for the presence of P. knowlesi DNA in humans. Subpatent and asymptomatic multispecies parasitemia is relatively common in North Sumatera, so PCR-based surveillance is required to support control and elimination activities.

Lack of K13 mutations in Plasmodium falciparum persisting after artemisinin combination therapy treatment of Kenyan children.

BACKGROUND: Studies in Southeast Asia reported a strong relationship between polymorphisms at the propeller domain of the Kelch 13 (K13) protein encoded by the Plasmodium falciparum k13 (pfk13) gene and delayed parasite clearance after artemisinin treatment. In Africa, P. falciparum remains susceptible and combination therapy regimens which include an artemisinin component display good efficacy. Using quantitative real-time PCR (qPCR), sub-microscopic persistence of P. falciparum has previously been reported in one-third of children treated with artemisinin combination therapy (ACT) in western Kenya. In this study, further investigation was made to evaluate whether these sub-microscopic residual parasites also harbour mutations at the propeller region of pfk13 and whether the mutations, if any, affect treatment outcome. METHODS: The pfk13 propeller domain was genotyped in DNA samples obtained in 2009 from Kenyan children treated with artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP). Paired samples at pre-treatment (day 0) and day of treatment failure (day 28 or 42) for 32 patients with documented recurrent parasitaemia were available for genotyping. Additional day 3 DNA samples were available for 10 patients. RESULTS: No mutation associated with artemisinin resistance in Southeast Asia was observed. Only one DP-treated patient harboured a non-synonymous mutation at codon 578 (A578S) of pfk13-propeller gene in the day 0 sample, but this allele was replaced by the wild-type (A578) form on day 3 and on the day of recurrent parasitaemia. The mutation at amino acid codon 578 showed no association with any phenotype. Polymorphisms in pfk13 were not responsible for parasite persistence and gametocyte carriage in the children treated with ACT. CONCLUSION: This study contributes to the ongoing surveillance of suspected artemisinin resistance parasites in Africa by providing baseline prevalence of k13-propeller mutations in western Kenya with samples collected from a longitudinal study. Clinical Trials Registration NCT00868465.

Alternatively spliced transcripts and novel pseudogenes of the Plasmodium falciparum resistance-associated locus pfcrt detected in East African malaria patients.

OBJECTIVES: Polymorphisms in the lysosomal transporter encoded by the pfcrt gene directly impact on Plasmodium falciparum susceptibility to aminoquinolines. The Lys76Thr mutation is the critical change conferring chloroquine resistance in vitro and in vivo, but always occurs with additional non-synonymous changes in the pfcrt coding sequence. We sought to better describe pfcrt polymorphisms distal to codon 76. METHODS: Small-volume samples (≤ 500 µL) of parasite-infected blood collected directly from malaria patients presenting for treatment in Sudan and Tanzania were immediately preserved for RNA extraction. The pfcrt locus was amplified from cDNA preparations by nested PCR and sequenced directly to derive full-length mRNA sequences. RESULTS: In one of two sites in Sudan, two patients were found with an unorthodox spliced form of pfcrt mRNA in which two exons were skipped, but it was not possible to test for the presence of the putative protein products of these aberrant transcripts. Genomic DNA sequencing from dried blood spots collected in parallel confirmed the presence of spliced pfcrt pseudogenes in a minority of parasite isolates. Full-length cDNA from conventionally spliced mRNA molecules in all study sites demonstrated the existence of a variety of pfcrt haplotypes in East Africa, and thus provides evidence of intragenic recombination. CONCLUSIONS: The presence of pseudogenes, although unlikely to have any direct public health impact, may confound results obtained from simple genotyping methods that consider only codon 76 and the adjacent residues of pfcrt.

Directional selection at the pfmdr1, pfcrt, pfubp1, and pfap2mu loci of Plasmodium falciparum in Kenyan children treated with ACT.

BACKGROUND: The efficacy of artemisinin-based combination therapy (ACT) for Plasmodium falciparum malaria may be threatened by parasites with reduced responsiveness to artemisinins. Among 298 ACT-treated children from Mbita, Kenya, submicroscopic persistence of P. falciparum on day 3 posttreatment was associated with subsequent microscopically detected parasitemia at days 28 or 42. METHODS: DNA sequences of resistance-associated parasite loci pfcrt, pfmdr1, pfubp1, and pfap2mu were determined in the Mbita cohort before treatment, on days 2 and 3 after initiation of treatment, and on the day of treatment failure. RESULTS: Parasites surviving ACT on day 2 or day 3 posttreatment were significantly more likely than the baseline population to carry the wild-type haplotypes of pfcrt (CVMNK at codons 72-76; P < .001) and pfmdr1 (NFD at codons 86, 184, 1246; P < .001). In contrast, variant alleles of the novel candidate resistance genes pfap2mu (S160N/T; P = .006) and pfubp-1 (E1528D; P < .001) were significantly more prevalent posttreatment. No genetic similarities were found to artemisinin-tolerant parasites recently described in Cambodia. CONCLUSIONS: Among treated children in western Kenya, certain P. falciparum genotypes defined at pfcrt, pfmdr1, pfap2mu, and pfubp1 more often survive ACT at the submicroscopic level, and contribute to onward transmission and subsequent patent recrudescence.

Malaria transmission after artemether-lumefantrine and dihydroartemisinin-piperaquine: a randomized trial.

BACKGROUND: Artemisinin-based combination therapy (ACT) reduces the potential for malaria transmission, compared with non-ACTs. It is unclear whether this effect differs between ACTs. METHODS: A total of 298 children (age, 6 months to 10 years) with uncomplicated falciparum malaria were randomized to artemether-lumefantrine (AL; n = 153) or dihydroartemisinin-piperaquine (DP; n = 145) in Mbita, a community in western Kenya. Gametocyte carriage was determined by molecular methods on days 0, 1, 2, 3, 7, 14, 28, and 42 after treatment initiation. The gametocyte infectiousness to mosquitoes was determined by mosquito-feeding assays on day 7 after beginning therapy. RESULTS: The cumulative risk of recurrent parasitemia on day 42 after initiation of treatment, unadjusted by polymerase chain reaction findings, was 20.7% (95% confidence interval [CI], 14.4-28.2) for AL, compared with 3.7% (95% CI, 1.2-8.5) for DP (P < .001). The mean duration of gametocyte carriage was 5.5 days (95% CI, 3.6-8.5) for AL and 15.3 days (95% CI, 9.7-24.2) for DP (P = .001). The proportion of mosquitoes that became infected after feeding on blood from AL-treated children was 1.88% (43 of 2293), compared with 3.50% (83 of 2371) for those that fed on blood from DP-treated children (P = .06); the oocyst burden among mosquitoes was lower among those that fed on blood from AL-treated children (P = .005) CONCLUSIONS: While DP was associated with a longer prophylactic time after treatment, gametocyte carriage and malaria transmission to mosquitoes was lower after AL treatment. CLINICAL TRIALS REGISTRATION: NCT00868465.

Residual Plasmodium falciparum parasitemia in Kenyan children after artemisinin-combination therapy is associated with increased transmission to mosquitoes and parasite recurrence.

BACKGROUND: Parasite clearance time after artemisinin-based combination therapy (ACT) may be increasing in Asian and African settings. The association between parasite clearance following ACT and transmissibility is currently unknown. METHODS: We determined parasite clearance dynamics by duplex quantitative polymerase chain reaction (qPCR) in samples collected in the first 3 days after treatment of uncomplicated malaria with ACT. Gametocyte carriage was determined by Pfs25 quantitative nucleic acid sequence-based amplification assays; infectiousness to mosquitoes by membrane-feeding assays on day 7 after treatment. RESULTS: Residual parasitemia was detected by qPCR in 31.8% (95% confidence interval [CI], 24.6-39.8) of the children on day 3 after initiation of treatment. Residual parasitemia was associated with a 2-fold longer duration of gametocyte carriage (P = .0007), a higher likelihood of infecting mosquitoes (relative risk, 1.95; 95% CI, 1.17-3.24; P = .015), and a higher parasite burden in mosquitoes (incidence rate ratio, 2.92; 95% CI, 1.61-5.31; P < .001). Children with residual parasitemia were also significantly more likely to experience microscopically detectable parasitemia during follow-up (relative risk, 11.25; 95% CI, 4.08-31.01; P < .001). CONCLUSIONS: Residual submicroscopic parasitemia is common after ACT and is associated with a higher transmission potential. Residual parasitemia may also have consequences for individual patients because of its higher risk of recurrent parasitemia.

Comparison of prevalence estimates of pfhrp2 and pfhrp3 deletions in Plasmodium falciparum determined by conventional PCR and multiplex qPCR and implications for surveillance and monitoring.

OBJECTIVES: The accuracy of malaria rapid diagnostic tests is threatened by Plasmodium falciparum with pfhrp2/3 deletions. This study compares gene deletion prevalence determined by multiplex real time polymerase chain reaction (qPCR) and conventional polymerase chain reaction (cPCR) using existing samples with clonality previously determined by microsatellite genotyping. METHODS: Multiplex qPCR was used to estimate prevalence of pfhrp2/3 deletions in three sets of previously collected patient samples from Eritrea and Peru. The qPCR was validated by multiplex digital polymerase chain reaction. Sample classification was compared with cPCR, and receiver operating characteristic curve analysis was used to determine the optimal ΔCq threshold that aligned the results of the two assays. RESULTS: qPCR classified 75% (637 of 849) of samples as single, and 212 as mixed-pfhrp2/3 genotypes, with a positive association between clonality and proportion of mixed-pfhrp2/3 genotype samples. The sample classification agreement between cPCR and qPCR was 75.1% (95% confidence interval [CI] 68.6-80.7%) and 47.8% (95% CI 38.9-56.9%) for monoclonal and polyclonal infections. The qPCR prevalence estimates of pfhrp2/3 deletions showed almost perfect (κ = 0.804, 95% CI 0.714-0.895) and substantial agreement (κ = 0.717, 95% CI 0.562-0.872) with cPCR for Peru and 2016 Eritrean samples, respectively. For 2019 Eritrean samples, the prevalence of double pfhrp2/3 deletions was approximately two-fold higher using qPCR. The optimal threshold for matching the assay results was ΔCq = 3. CONCLUSIONS: Multiplex qPCR and cPCR produce comparable estimates of gene deletion prevalence when monoclonal infections dominate; however, qPCR provides higher estimates where multi-clonal infections are common.

HIV-positive nigerian adults harbor significantly higher serum lumefantrine levels than HIV-negative individuals seven days after treatment for Plasmodium falciparum infection.

Management of coinfection with malaria and HIV is a major challenge to public health in developing countries, and yet potential drug-drug interactions between antimalarial and antiviral regimens have not been adequately investigated in people with both infections. Each of the constituent components of artemether-lumefantrine, the first-line regimen for malaria treatment in Nigeria, and nevirapine, a major component of highly active antiretroviral therapy, are drugs metabolized by the cytochrome P450 3A4 isoenzyme system, which is also known to be induced by nevirapine. We examined potential interactions between lumefantrine and nevirapine in 68 HIV-positive adults, all of whom were diagnosed with asymptomatic Plasmodium falciparum infections by microscopy. Post hoc PCR analysis confirmed the presence of P. falciparum in only a minority of participants. Day 7 capillary blood levels of lumefantrine were significantly higher in HIV-positive participants than in 99 HIV-negative controls (P = 0.0011). Associations between day 7 levels of lumefantrine and risk of persistent parasitemia could not be evaluated due to inadequate power. Further investigations of the impact of nevirapine on in vivo malaria treatment outcomes in HIV-infected patients are thus needed.

The polymorphic linker domain of pfmdr1 is associated with resistance-conferring mutations in Plasmodium falciparum populations from East and West Africa.

Sequence variation in the asparagine/aspartate-rich domain of pfmdr1 in 215 isolates of Plasmodium falciparum from three African countries was compared with published data. The role of this domain in modulating antimalarial sensitivity has not been established. The pfmdr1 86Y allele was significantly associated with different configurations of the Asn/Asp-rich domain in West and East Africa. In Kenya, a specific form of the Asn/Asp-rich domain was significantly linked to the 86Y, 184Y, and 1246Y haplotype of pfmdr1.