Challenges for achieving safe and effective radical cure of Plasmodium vivax: a round table discussion of the APMEN Vivax Working Group

Operational feasibility of Plasmodium vivax radical cure with tafenoquine or primaquine following point-of-care, quantitative glucose-6-phosphate dehydrogenase testing in the Brazilian Amazon: a real-life retrospective analysis

BACKGROUND

To achieve malaria elimination, Brazil must implement Plasmodium vivax radical cure. We aimed to investigate the operational feasibility of point-of-care, quantitative, glucose-6-phosphate dehydrogenase (G6PD) testing followed by chloroquine plus tafenoquine or primaquine.

METHODS

This non-interventional, observational study was done at 43 health facilities in Manaus (Amazonas State) and Porto Velho (Rondônia State), Brazil, implementing a new P vivax treatment algorithm incorporating point-of-care quantitative G6PD testing to identify G6PD status and single-dose tafenoquine (G6PD normal, aged ≥16 years, and not pregnant or breastfeeding) or primaquine (intermediate or normal G6PD, aged ≥6 months, not pregnant, or breastfeeding >1 month). Following training of health-care providers, we collated routine patient records from the malaria epidemiological surveillance system (SIVEP-Malaria) retrospectively for all consenting patients aged at least 6 months with parasitologically confirmed P vivax malaria mono-infection or P vivax plus P falciparum mixed infection, presenting between Sept 9, 2021, and Aug 31, 2022. The primary endpoint was the proportion of patients aged at least 16 years with P vivax mono-infection treated or not treated appropriately with tafenoquine in accordance with their G6PD status. The trial is registered with ClinicalTrials.gov, NCT05096702, and is completed.

FINDINGS

Of 6075 patients enrolled, 6026 (99·2%) had P vivax mono-infection, 2685 (44·6%) of whom were administered tafenoquine. G6PD status was identified in 2685 (100%) of 2685 patients treated with tafenoquine. The proportion of patients aged at least 16 years with P vivax mono-infection who were treated or not treated appropriately with tafenoquine in accordance with their G6PD status was 99·7% (95% CI 99·4-99·8; 4664/4680).

INTERPRETATION

Quantitative G6PD testing before tafenoquine administration was operationally feasible, with high adherence to the treatment algorithm, supporting deployment throughout the Brazilian health system.

FUNDING

Brazilian Ministry of Health, Municipal and State Health Secretariats; Fiocruz; Medicines for Malaria Venture; Bill & Melinda Gates Foundation; Newcrest Mining; and the UK Government.

TRANSLATION

For the Portuguese translation of the abstract see Supplementary Materials section.

Primaquine dose and the risk of haemolysis in patients with uncomplicated Plasmodium vivax malaria: a systematic review and individual patient data meta-analysis

BACKGROUND

Primaquine radical cure is used to treat dormant liver-stage parasites and prevent relapsing Plasmodium vivax malaria but is limited by concerns of haemolysis. We undertook a systematic review and individual patient data meta-analysis to investigate the haematological safety of different primaquine regimens for P vivax radical cure.

METHODS

For this systematic review and individual patient data meta-analysis, we searched MEDLINE, Web of Science, Embase, and Cochrane Central for prospective clinical studies of uncomplicated P vivax from endemic countries published between Jan 1, 2000, and June 8, 2023. We included studies if they had active follow-up of at least 28 days, if they included a treatment group with daily primaquine given over multiple days where primaquine was commenced within 3 days of schizontocidal treatment and was given alone or coadministered with chloroquine or one of four artemisinin-based combination therapies (ie, artemether-lumefantrine, artesunate-mefloquine, artesunate-amodiaquine, or dihydroartemisinin-piperaquine), and if they recorded haemoglobin or haematocrit concentrations on day 0. We excluded studies if they were on prevention, prophylaxis, or patients with severe malaria, or if data were extracted retrospectively from medical records outside of a planned trial. For the meta-analysis, we contacted the investigators of eligible trials to request individual patient data and we then pooled data that were made available by Aug 23, 2021. The main outcome was haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL by day 14. Haemoglobin concentration changes between day 0 and days 2-3 and between day 0 and days 5-7 were assessed by mixed-effects linear regression for patients with glucose-6-phosphate dehydrogenase (G6PD) activity of (1) 30% or higher and (2) between 30% and less than 70%. The study was registered with PROSPERO, CRD42019154470 and CRD42022303680.

FINDINGS

Of 226 identified studies, 18 studies with patient-level data from 5462 patients from 15 countries were included in the analysis. A haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL occurred in one (0·1%) of 1208 patients treated without primaquine, none of 893 patients treated with a low daily dose of primaquine (<0·375 mg/kg per day), five (0·3%) of 1464 patients treated with an intermediate daily dose (0·375 mg/kg per day to <0·75 mg/kg per day), and six (0·5%) of 1269 patients treated with a high daily dose (≥0·75 mg/kg per day). The covariate-adjusted mean estimated haemoglobin changes at days 2-3 were -0·6 g/dL (95% CI -0·7 to -0·5), -0·7 g/dL (-0·8 to -0·5), -0·6 g/dL (-0·7 to -0·4), and -0·5 g/dL (-0·7 to -0·4), respectively. In 51 patients with G6PD activity between 30% and less than 70%, the adjusted mean haemoglobin concentration on days 2-3 decreased as G6PD activity decreased; two patients in this group who were treated with a high daily dose of primaquine had a reduction of more than 25% to a concentration of less than 7 g/dL. 17 of 18 included studies had a low or unclear risk of bias.

INTERPRETATION

Treatment of patients with G6PD activity of 30% or higher with 0·25-0·5 mg/kg per day primaquine regimens and patients with G6PD activity of 70% or higher with 0·25-1 mg/kg per day regimens were associated with similar risks of haemolysis to those in patients treated without primaquine, supporting the safe use of primaquine radical cure at these doses.

FUNDING

Australian National Health and Medical Research Council, Bill & Melinda Gates Foundation, and Medicines for Malaria Venture.

Safety and efficacy of primaquine in patients with Plasmodium vivax malaria from South Asia: a systematic review and individual patient data meta-analysis

BACKGROUND

The optimal dosing of primaquine to prevent relapsing Plasmodium vivax malaria in South Asia remains unclear. We investigated the efficacy and safety of different primaquine regimens to prevent P. vivax relapse.

METHODS

A systematic review identified P. vivax efficacy studies from South Asia published between 1 January 2000 and 23 August 2021. In a one-stage meta-analysis of available individual patient data, the cumulative risks of P. vivax recurrence at day 42 and 180 were assessed by primaquine total mg/kg dose and duration. The risk of recurrence by day 180 was also determined in a two-stage meta-analysis. Patients with a >25% drop in haemoglobin to <70 g/L, or an absolute drop of >50 g/L between days 1 and 14 were categorised by daily mg/kg primaquine dose.

RESULTS

In 791 patients from 7 studies in the one-stage meta-analysis, the day 180 cumulative risk of recurrence was 61.1% (95% CI 42.2% to 80.4%; 201 patients; 25 recurrences) after treatment without primaquine, 28.8% (95% CI 8.2% to 74.1%; 398 patients; 4 recurrences) following low total (2 to <5 mg/kg) and 0% (96 patients; 0 recurrences) following high total dose primaquine (≥5 mg/kg). In the subsequent two-stage meta-analysis of nine studies (3529 patients), the pooled proportions of P. vivax recurrences by day 180 were 12.1% (95% CI 7.7% to 17.2%), 2.3% (95% CI 0.3% to 5.4%) and 0.7% (95% CI 0% to 6.1%), respectively. No patients had a >25% drop in haemoglobin to <70 g/L.

CONCLUSIONS

Primaquine treatment led to a marked decrease in P. vivax recurrences following low (~3.5 mg/kg) and high (~7 mg/kg) total doses, with no reported severe haemolytic events.

PROSPERO REGISTRATION NUMBER

CRD42022313730.

Primaquine radical cure in patients with Plasmodium falciparum malaria in areas co-endemic for P falciparum and Plasmodium vivax (PRIMA): a multicentre, open-label, superiority randomised controlled trial

BACKGROUND

In areas co-endemic for Plasmodium vivax and Plasmodium falciparum there is an increased risk of P vivax parasitaemia following P falciparum malaria. Radical cure is currently only recommended for patients presenting with P vivax malaria. Expanding the indication for radical cure to patients presenting with P falciparum malaria could reduce their risk of subsequent P vivax parasitaemia.

METHODS

We did a multicentre, open-label, superiority randomised controlled trial in five health clinics in Bangladesh, Indonesia, and Ethiopia. In Bangladesh and Indonesia, patients were excluded if they were younger than 1 year, whereas in Ethiopia patients were excluded if they were younger than 18 years. Patients with uncomplicated P falciparum monoinfection who had fever or a history of fever in the 48 h preceding clinic visit were eligible for enrolment and were required to have a glucose-6-dehydrogenase (G6PD) activity of 70% or greater. Patients received blood schizontocidal treatment (artemether-lumefantrine in Ethiopia and Bangladesh and dihydroartemisinin-piperaquine in Indonesia) and were randomly assigned (1:1) to receive either high-dose short-course oral primaquine (intervention arm; total dose 7 mg/kg over 7 days) or standard care (standard care arm; single dose oral primaquine of 0·25 mg/kg). Random assignment was done by an independent statistician in blocks of eight by use of sealed envelopes. All randomly assigned and eligible patients were included in the primary and safety analyses. The per-protocol analysis excluded those who did not complete treatment or had substantial protocol violations. The primary endpoint was the incidence risk of P vivax parasitaemia on day 63. This trial is registered at ClinicalTrials.gov, NCT03916003.

FINDINGS

Between Aug 18, 2019, and March 14, 2022, a total of 500 patients were enrolled and randomly assigned, and 495 eligible patients were included in the intention-to-treat analysis (246 intervention and 249 control). The incidence risk of P vivax parasitaemia at day 63 was 11·0% (95% CI 7·5-15·9) in the standard care arm compared with 2·5% (1·0-5·9) in the intervention arm (hazard ratio 0·20, 95% CI 0·08-0·51; p=0·0009). The effect size differed with blood schizontocidal treatment and site. Routine symptom reporting on day 2 and day 7 were similar between groups. In the first 42 days, there were a total of four primaquine-related adverse events reported in the standard care arm and 26 in the intervention arm; 132 (92%) of all 143 adverse events were mild. There were two serious adverse events in the intervention arm, which were considered unrelated to the study drug. None of the patients developed severe anaemia (defined as haemoglobin <5 g/dL).

INTERPRETATION

In patients with a G6PD activity of 70% or greater, high-dose short-course primaquine was safe and relatively well tolerated and reduced the risk of subsequent P vivax parasitaemia within 63 days by five fold. Universal radical cure therefore potentially offers substantial clinical, public health, and operational benefits, but these benefits will vary with endemic setting.

FUNDING

Australian Academy of Science Regional Collaborations Program, Bill & Melinda Gates Foundation, and National Health and Medical Research Council.

Severe Hemolysis during Primaquine Radical Cure of Plasmodium vivax Malaria: Two Systematic Reviews and Individual Patient Data Descriptive Analyses

Primaquine (PQ) kills Plasmodium vivax hypnozoites but can cause severe hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. We conducted two systematic reviews. The first used data from clinical trials to determine the variety of definitions and frequency of hematological serious adverse events (SAEs) related to PQ treatment of vivax malaria. The second used data from prospective studies and case reports to describe the clinical presentation, management, and outcome of severe PQ-associated hemolysis necessitating hospitalization. In the first review, SAEs were reported in 70 of 249 clinical trials. There were 34 hematological SAEs among 9,824 patients with P. vivax malaria treated with PQ, nine of which necessitated hospitalization or blood transfusion. Criteria used to define SAEs were diverse. In the second review, 21 of 8,487 articles screened reported 163 patients hospitalized after PQ radical cure; 79.9% of whom (123 of 154) were prescribed PQ at ≥ 0.5 mg/kg/day. Overall, 101 patients were categorized as having probable or possible severe PQ-associated hemolysis, 96.8% of whom were G6PD deficient (< 30% activity). The first symptoms of hemolysis were reported primarily on day 2 or 3 (45.5%), and all patients were hospitalized within 7 days of PQ commencement. A total of 57.9% of patients (77 of 133) had blood transfusion. Seven patients (6.9%) with probable or possible hemolysis died. Even when G6PD testing is available, enhanced monitoring for hemolysis is warranted after PQ treatment. Clinical review within the first 5 days of treatment may facilitate early detection and management of hemolysis. More robust definitions of severe PQ-associated hemolysis are required.

A model for malaria treatment evaluation in the presence of multiple species

Plasmodium falciparum and P. vivax are the two most common causes of malaria. While the majority of deaths and severe morbidity are due to P. falciparum, P. vivax poses a greater challenge to eliminating malaria outside of Africa due to its ability to form latent liver stage parasites (hypnozoites), which can cause relapsing episodes within an individual patient. In areas where P. falciparum and P. vivax are co-endemic, individuals can carry parasites of both species simultaneously. These mixed infections complicate dynamics in several ways: treatment of mixed infections will simultaneously affect both species, P. falciparum can mask the detection of P. vivax, and it has been hypothesised that clearing P. falciparum may trigger a relapse of dormant P. vivax. When mixed infections are treated for only blood-stage parasites, patients are at risk of relapse infections due to P. vivax hypnozoites. We present a stochastic mathematical model that captures interactions between P. falciparum and P. vivax, and incorporates both standard schizonticidal treatment (which targets blood-stage parasites) and radical cure treatment (which additionally targets liver-stage parasites). We apply this model via a hypothetical simulation study to assess the implications of different treatment coverages of radical cure for mixed and P. vivax infections and a "unified radical cure" treatment strategy where P. falciparum, P. vivax, and mixed infections all receive radical cure after screening glucose-6-phosphate dehydrogenase (G6PD) normal. In addition, we investigated the impact of mass drug administration (MDA) of blood-stage treatment. We find that a unified radical cure strategy leads to a substantially lower incidence of malaria cases and deaths overall. MDA with schizonticidal treatment was found to decrease P. falciparum with little effect on P. vivax. We perform a univariate sensitivity analysis to highlight important model parameters.

Weekly primaquine for radical cure of patients with Plasmodium vivax malaria and glucose-6-phosphate dehydrogenase deficiency

BACKGROUND

The World Health Organization recommends that primaquine should be given once weekly for 8-weeks to patients with Plasmodium vivax malaria and glucose-6-phosphate dehydrogenase (G6PD) deficiency, but data on its antirelapse efficacy and safety are limited.

METHODS

Within the context of a multicentre, randomised clinical trial of two primaquine regimens in P. vivax malaria, patients with G6PD deficiency were excluded and enrolled into a separate 12-month observational study. They were treated with a weekly dose of 0.75 mg/kg primaquine for 8 weeks (PQ8W) plus dihydroartemisinin piperaquine (Indonesia) or chloroquine (Afghanistan, Ethiopia, Vietnam). G6PD status was diagnosed using the fluorescent spot test and confirmed by genotyping for locally prevalent G6PD variants. The risk of P. vivax recurrence following PQ8W and the consequent haematological recovery were characterized in all patients and in patients with genotypically confirmed G6PD variants, and compared with the patients enrolled in the main randomised control trial.

RESULTS

Between July 2014 and November 2017, 42 male and 8 female patients were enrolled in Afghanistan (6), Ethiopia (5), Indonesia (19), and Vietnam (20). G6PD deficiency was confirmed by genotyping in 31 patients: Viangchan (14), Mediterranean (4), 357A-G (3), Canton (2), Kaiping (2), and one each for A-, Chatham, Gaohe, Ludhiana, Orissa, and Vanua Lava. Two patients had recurrent P. vivax parasitaemia (days 68 and 207). The overall 12-month cumulative risk of recurrent P. vivax malaria was 5.1% (95% CI: 1.3-18.9) and the incidence rate of recurrence was 46.8 per 1000 person-years (95% CI: 11.7-187.1). The risk of P. vivax recurrence was lower in G6PD deficient patients treated with PQ8W compared to G6PD normal patients in all treatment arms of the randomised controlled trial. Two of the 26 confirmed hemizygous males had a significant fall in haemoglobin (>5g/dl) after the first dose but were able to complete their 8 week regimen.

CONCLUSIONS

PQ8W was highly effective in preventing P. vivax recurrences. Whilst PQ8W was well tolerated in most patients across a range of different G6PD variants, significant falls in haemoglobin may occur after the first dose and require clinical monitoring.

TRIAL REGISTRATION

This trial is registered at ClinicalTrials.gov (NCT01814683).

Adherence to 14-day radical cure for Plasmodium vivax malaria in Papua, Indonesia: a mixed-methods study

BACKGROUND

Reducing the risk of recurrent Plasmodium vivax malaria is critical for malaria control and elimination. Primaquine (PQ) is the only widely available drug against P. vivax dormant liver stages, but is recommended as a 14-day regimen, which can undermine adherence to a complete course of treatment.

METHODS

This is a mixed-methods study to assess socio-cultural factors influencing adherence to a 14-day PQ regimen in a 3-arm, treatment effectiveness trial in Papua, Indonesia. The qualitative strand, consisting of interviews and participant observation was triangulated with a quantitative strand in which trial participants were surveyed using a questionnaire.

RESULTS

Trial participants differentiated between two types of malaria: tersiana and tropika, equivalent to P. vivax and Plasmodium falciparum infection, respectively. The perceived severity of both types was similar with 44.0% (267/607) perceiving tersiana vs. 45.1% (274/607) perceiving tropika as more severe. There was no perceived differentiation whether malaria episodes were due to a new infection or relapse; and 71.3% (433/607) acknowledged the possibility of recurrence. Participants were familiar with malaria symptoms and delaying health facility visit by 1-2 days was perceived to increase the likelihood of a positive test. Prior to health facility visits, symptoms were treated with leftover drugs kept at home (40.4%; 245/607) or bought over the counter (17.0%; 103/607). Malaria was considered to be cured with 'blue drugs' (referring to dihydroartemisinin-piperaquine). Conversely, 'brown drugs,' referring to PQ, were not considered malaria medication and instead were perceived as supplements. Adherence to malaria treatment was 71.2% (131/184), in the supervised arm, 56.9% (91/160) in the unsupervised arm and 62.4% (164/263) in the control arm; p = 0.019. Adherence was 47.5% (47/99) among highland Papuans, 51.7% (76/147) among lowland Papuans, and 72.9% (263/361) among non-Papuans; p < 0.001.

CONCLUSION

Adherence to malaria treatment was a socio-culturally embedded process during which patients (re-)evaluated the characteristics of the medicines in relation to the course of the illness, their past experiences with illness, and the perceived benefits of the treatment. Structural barriers that hinder the process of patient adherence are crucial to consider in the development and rollout of effective malaria treatment policies.

Lineage-informative microhaplotypes for spatio-temporal surveillance of Plasmodium vivax malaria parasites

Challenges in understanding the origin of recurrent Plasmodium vivax infections constrains the surveillance of antimalarial efficacy and transmission of this neglected parasite. Recurrent infections within an individual may arise from activation of dormant liver stages (relapse), blood-stage treatment failure (recrudescence) or new inoculations (reinfection). Molecular inference of familial relatedness (identity-by-descent or IBD) based on whole genome sequence data, together with analysis of the intervals between parasitaemic episodes ("time-to-event" analysis), can help resolve the probable origin of recurrences. Whole genome sequencing of predominantly low-density P. vivax infections is challenging, so an accurate and scalable genotyping method to determine the origins of recurrent parasitaemia would be of significant benefit. We have developed a P. vivax genome-wide informatics pipeline to select specific microhaplotype panels that can capture IBD within small, amplifiable segments of the genome. Using a global set of 615 P. vivax genomes, we derived a panel of 100 microhaplotypes, each comprising 3-10 high frequency SNPs within <200 bp sequence windows. This panel exhibits high diversity in regions of the Asia-Pacific, Latin America and the horn of Africa (median HE = 0.70-0.81) and it captured 89% (273/307) of the polyclonal infections detected with genome-wide datasets. Using data simulations, we demonstrate lower error in estimating pairwise IBD using microhaplotypes, relative to traditional biallelic SNP barcodes. Our panel exhibited high accuracy in predicting the country of origin (median Matthew's correlation coefficient >0.9 in 90% countries tested) and it also captured local infection outbreak and bottlenecking events. The informatics pipeline is available open-source and yields microhaplotypes that can be readily transferred to high-throughput amplicon sequencing assays for surveillance in malaria-endemic regions.

Single-Nucleotide Polymorphisms in Glucose-6-Phosphate Dehydrogenase and their Relevance for the Deployment of Primaquine as a Radical Cure for Malaria

Malaria remains an important public health problem despite efforts to control it. Besides active transmission, relapsing malaria caused by dormant liver stages of Plasmodium vivax and Plasmodium ovale hypnozoites is a major hurdle in malaria control and elimination programs. Primaquine (PQ) is the most widely used drug for radical cure of malaria. Due to its anti-hypnozoite and gametocidal activity, PQ plays a key role in malaria relapse and transmission. The human enzyme glucose-6-phosphate dehydrogenase (G6PD) is crucial in determining the safety of PQ because G6PD-deficient individuals are prone to hemolysis if treated with PQ. Therefore, there is a need to study the prevalence of G6PD-deficient genetic variants in endemic populations to assess the risk of PQ treatment and the necessity to develop alternative treatments. In this work, we discuss the common G6PD variants, their varying enzymatic activity, and their distribution on the three-dimensional structure of G6PD. Our work highlights the important G6PD variants and the need for large-scale G6PD gene polymorphism studies to predict populations at risk of PQ-induced toxicity.

Global perspectives on CYP2D6 associations with primaquine metabolism and Plasmodium vivax radical cure

Clinical trial and individual patient treatment outcomes have produced accumulating evidence that effective primaquine (PQ) treatment of Plasmodium vivax and P. ovale liver stage hypnozoites is associated with genetic variation in the human cytochrome P450 gene, CYP2D6. Successful PQ treatment of individual and population-wide infections by the Plasmodium species that generate these dormant liver stage forms is likely to be necessary to reach elimination of malaria caused by these parasites globally. Optimizing safe and effective PQ treatment will require coordination of efforts between the malaria and pharmacogenomics research communities.

Potential of nanoformulations in malaria treatment

Malaria is caused by the protozoan Plasmodium sp and affects millions of people worldwide. Its clinical form ranges from asymptomatic to potentially fatal and severe. Current treatments include single drugs such as chloroquine, lumefantrine, primaquine, or in combination with artemisinin or its derivatives. Resistance to antimalarial drugs has increased; therefore, there is an urgent need to diversify therapeutic approaches. The disease cycle is influenced by biological, social, and anthropological factors. This longevity and complexity contributes to the records of drug resistance, where further studies and proposals for new therapeutic formulations are needed for successful treatment of malaria. Nanotechnology is promising for drug development. Preclinical formulations with antimalarial agents have shown positive results, but only a few have progressed to clinical phase. Therefore, studies focusing on the development and evaluation of antimalarial formulations should be encouraged because of their enormous therapeutic potential.

Variation in Glucose-6-Phosphate Dehydrogenase activity following acute malaria

Primaquine and tafenoquine are the only licensed drugs with activity against Plasmodium vivax hypnozoites but cause haemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Malaria also causes haemolysis, leading to the replacement of older erythrocytes with low G6PD activity by reticulocytes and young erythrocytes with higher activity. Aim of this study was to assess the impact of acute malaria on G6PD activity. Selected patients with uncomplicated malaria were recruited in Bangladesh (n = 87), Indonesia (n = 75), and Ethiopia (n = 173); G6PD activity was measured at the initial presentation with malaria and a median of 176 days later (range 140 to 998) in the absence of malaria. Among selected participants (deficient participants preferentially enrolled in Bangladesh but not at other sites) G6PD activity fell between malaria and follow up by 79.1% (95%CI: 40.4 to 117.8) in 6 participants classified as deficient (<30% activity), 43.7% (95%CI: 34.2 to 53.1) in 39 individuals with intermediate activity (30% to <70%), and by 4.5% (95%CI: 1.4 to 7.6) in 290 G6PD normal (≥70%) participants. In Bangladesh and Indonesia G6PD activity was significantly higher during acute malaria than when the same individuals were retested during follow up (40.9% (95%CI: 33.4-48.1) and 7.4% (95%CI: 0.2 to 14.6) respectively), whereas in Ethiopia G6PD activity was 3.6% (95%CI: -1.0 to -6.1) lower during acute malaria. The change in G6PD activity was apparent in patients presenting with either P. vivax or P. falciparum infection. Overall, 66.7% (4/6) severely deficient participants and 87.2% (34/39) with intermediate deficiency had normal activities when presenting with malaria. These findings suggest that G6PD activity rises significantly and at clinically relevant levels during acute malaria. Prospective case-control studies are warranted to confirm the degree to which the predicted population attributable risks of drug induced haemolysis is lower than would be predicted from cross sectional surveys.

One Health approach to improve the malaria elimination programme in Henan Province

One Health is a collaborative, multi-sectoral, trans-disciplinary approach with the goal of achieving optimal health outcomes by recognizing the interconnection between people, animals, plants, and the environment and determining how this relates to the control of infectious diseases such as malaria, schistosomiasis and so on. Malarias caused by Plasmodium that commonly infects female Anopheles mosquitoes, which feed on human blood and act as a disease vector. It has been a worldwide important public health problem from ancient times. Also, malaria is one of the infectious diseases with the longest epidemic time and the most serious harm in the history of Henan Province, China. During the past decades, the multi-sectoral, cross-regional, and multi-disciplinary One Health approach contributed to a significant reduction in malaria incidence, resulting in initiation of the Henan Malaria Elimination Action Plan. Herein, we reviewed the history of the fight against malaria in Henan Province. A full picture of malaria epidemics, prevention, and control strategies were showed, with the objective that it will help stakeholders, and policy-makers to take informed decisions on public health issues and intervention designs on malaria control towards elimination in the similar areas.

Comparative pharmacokinetics and tissue distribution of primaquine enantiomers in mice

Background

Primaquine (PQ) has been used for the radical cure of relapsing Plasmodium vivax malaria for more than 60 years. PQ is also recommended for prophylaxis and prevention of transmission of Plasmodium falciparum. However, clinical utility of PQ has been limited due to toxicity in individuals with genetic deficiencies in glucose 6-phosphate dehydrogenase (G6PD). PQ is currently approved for clinical use as a racemic mixture. Recent studies in animals as well as humans have established differential pharmacological and toxicological properties of the two enantiomers of PQ. This has been attributed to differential metabolism and pharmacokinetics of individual PQ enantiomers. The aim of the current study is to evaluate the comparative pharmacokinetics (PK), tissue distribution and metabolic profiles of the individual enantiomers in mice.

Methods

Two groups of 21 male Albino ND4 Swiss mice were dosed orally with 45 mg/kg of S-(+)-PQ and R-(−)PQ respectively. Each of the enantiomers was comprised of a 50:50 mixture of 12C- and 13C- stable isotope labelled species (at 6 carbons on the benzene ring of the quinoline core). Three mice were euthanized from each group at different time points (at 0, 0.5, 1, 2, 4, 8, 24 h) and blood was collected by terminal cardiac bleed. Liver, spleen, lungs, kidneys and brain were removed, extracted and analysed using UPLC/MS. The metabolites were profiled by tandem mass (MS/MS) fragmentation profile and fragments with 12C–13C twin peaks. Non-compartmental analysis was performed using the Phoenix WinNonLin PK software module.

Results

The plasma AUC0-last (µg h/mL) (1.6 vs. 0.6), T1/2 (h) (1.9 vs. 0.45), and Tmax (h) (1 vs. 0.5) were greater for SPQ as compared to RPQ. Generally, the concentration of SPQ was higher in all tissues. At Tmax, (0.5–1 h in all tissues), the level of SPQ was 3 times that of RPQ in the liver. Measured Cmax of SPQ and RPQ in the liver were about 100 and 40 times the Cmax values in plasma, respectively. Similar observations were recorded in other tissues where the concentration of SPQ was higher compared to RPQ (2× in the spleen, 6× in the kidneys, and 49× in the lungs) than in the plasma. CPQ, the major metabolite, was preferentially generated from RPQ, with higher levels in all tissues (> 10× in the liver, and 3.5× in the plasma) than from SPQ. The PQ-o-quinone was preferentially formed from the SPQ (> 4× compared to RPQ), with higher concentrations in the liver.

Conclusion

These studies show that in mice, PQ enantiomers are differentially biodistributed and metabolized, which may contribute to differential pharmacologic and toxicity profiles of PQ enantiomers. The findings on higher levels of PQ-o-quinone in liver and RBCs compared to plasma and preferential generation of this metabolite from SPQ are consistent with the higher anti-malarial efficacy of SPQ observed in the mouse causal prophylaxis test, and higher haemolytic toxicity in the humanized mouse model of G6PD deficiency. Potential relevance of these findings to clinical use of racemic PQ and other 8-aminoquinolines vis-à-vis need for further clinical evaluation of individual enantiomers are discussed.

Genetic Variation of G6PD and CYP2D6: Clinical Implications on the Use of Primaquine for Elimination of Plasmodium vivax

Primaquine, an 8-aminoquinoline, is the only medication approved by the World Health Organization to treat the hypnozoite stage of Plasmodium vivax and P. ovale malaria. Relapse, triggered by activation of dormant hypnozoites in the liver, can occur weeks to years after primary infection, and provides the predominant source of transmission in endemic settings. Hence, primaquine is essential for individual treatment and P. vivax elimination efforts. However, primaquine use is limited by the risk of life-threatening acute hemolytic anemia in glucose-6-phosphate dehydrogenase (G6PD) deficient individuals. More recently, studies have demonstrated decreased efficacy of primaquine due to cytochrome P450 2D6 (CYP2D6) polymorphisms conferring an impaired metabolizer phenotype. Failure of standard primaquine therapy has occurred in individuals with decreased or absent CYP2D6 activity. Both G6PD and CYP2D6 are highly polymorphic genes, with considerable geographic and interethnic variability, adding complexity to primaquine use. Innovative strategies are required to overcome the dual challenge of G6PD deficiency and impaired primaquine metabolism. Further understanding of the pharmacogenetics of primaquine is key to utilizing its full potential. Accurate CYP2D6 genotype-phenotype translation may optimize primaquine dosing strategies for impaired metabolizers and expand its use in a safe, efficacious manner. At an individual level the current challenges with G6PD diagnostics and CYP2D6 testing limit clinical implementation of pharmacogenetics. However, further characterisation of the overlap and spectrum of G6PD and CYP2D6 activity may optimize primaquine use at a population level and facilitate region-specific dosing strategies for mass drug administration. This precision public health approach merits further investigation for P. vivax elimination.

Global economic costs due to vivax malaria and the potential impact of its radical cure: A modelling study

BACKGROUND

In 2017, an estimated 14 million cases of Plasmodium vivax malaria were reported from Asia, Central and South America, and the Horn of Africa. The clinical burden of vivax malaria is largely driven by its ability to form dormant liver stages (hypnozoites) that can reactivate to cause recurrent episodes of malaria. Elimination of both the blood and liver stages of the parasites ("radical cure") is required to achieve a sustained clinical response and prevent ongoing transmission of the parasite. Novel treatment options and point-of-care diagnostics are now available to ensure that radical cure can be administered safely and effectively. We quantified the global economic cost of vivax malaria and estimated the potential cost benefit of a policy of radical cure after testing patients for glucose-6-phosphate dehydrogenase (G6PD) deficiency.

METHODS AND FINDINGS

Estimates of the healthcare provider and household costs due to vivax malaria were collated and combined with national case estimates for 44 endemic countries in 2017. These provider and household costs were compared with those that would be incurred under 2 scenarios for radical cure following G6PD screening: (1) complete adherence following daily supervised primaquine therapy and (2) unsupervised treatment with an assumed 40% effectiveness. A probabilistic sensitivity analysis generated credible intervals (CrIs) for the estimates. Globally, the annual cost of vivax malaria was US$359 million (95% CrI: US$222 to 563 million), attributable to 14.2 million cases of vivax malaria in 2017. From a societal perspective, adopting a policy of G6PD deficiency screening and supervision of primaquine to all eligible patients would prevent 6.1 million cases and reduce the global cost of vivax malaria to US$266 million (95% CrI: US$161 to 415 million), although healthcare provider costs would increase by US$39 million. If perfect adherence could be achieved with a single visit, then the global cost would fall further to US$225 million, equivalent to $135 million in cost savings from the baseline global costs. A policy of unsupervised primaquine reduced the cost to US$342 million (95% CrI: US$209 to 532 million) while preventing 2.1 million cases. Limitations of the study include partial availability of country-level cost data and parameter uncertainty for the proportion of patients prescribed primaquine, patient adherence to a full course of primaquine, and effectiveness of primaquine when unsupervised.

CONCLUSIONS

Our modelling study highlights a substantial global economic burden of vivax malaria that could be reduced through investment in safe and effective radical cure achieved by routine screening for G6PD deficiency and supervision of treatment. Novel, low-cost interventions for improving adherence to primaquine to ensure effective radical cure and widespread access to screening for G6PD deficiency will be critical to achieving the timely global elimination of P. vivax.

Further evidence needed to change policy for the safe and effective radical cure of vivax malaria: Insights from the 2019 annual APMEN Vivax Working Group meeting

New diagnostics and treatment options for the radical cure of Plasmodium vivax malaria are now available. At the 2019 annual meeting of the Vivax Working Group of the Asia Pacific Malaria Elimination Network, participants took part in a roundtable discussion to identify further evidence required to introduce these new tools into policy and practice. Key gaps identified were accuracy and reliability of glucose-6-phosphate-dehydrogenase deficiency tests, health system capacity, and feasibility and cost effectiveness of novel treatment strategies in routine clinical practice. As expected, there were differences in the priorities between country partners and researcher partners. To achieve the 2030 target for the regional elimination of malaria, evidence to address these issues should be generated as a matter of priority. Review of global guidelines alongside locally generated data will help to ensure the timely revision and optimisation of national treatment guidelines that will be vital to meet regional elimination goals.

Rolling out the radical cure for vivax malaria in Asia: a qualitative study among policy makers and stakeholders

BACKGROUND

Wide-spread implementation of treatment regimens for the radical cure of vivax malaria is hindered by a range of factors. This has resulted in an increase in the relative proportion of vivax malaria and is an important obstacle in the achievement of global malaria elimination by 2030. The main objective of this study was to explore the current policies guiding the treatment plans on vivax malaria, and the factors affecting the implementation of radical cure in South/South East Asian and Asian Pacific countries.

METHODS

This was a qualitative study among respondents who represented national malaria control programmes (NMCPs) or had a role and influence in the national malaria policies. 33 respondents from 17 countries in South/South East Asia and Asia Pacific participated in interviews between October 15 and December 15, 2020. Semi-structured interviews were conducted virtually except for two face to face interviews and audio-recorded. Transcribed audio-records underwent thematic analysis using QSR NVivo.

RESULTS

Policies against vivax malaria were underprioritized, compared with the focus on falciparum malaria and, in particular, drug resistant Plasmodium falciparum strains. Despite the familiarity with primaquine (PQ) as the essential treatment to achieve the radical cure, the respondents contested the need for G6PD testing. Optional G6PD testing was reported to have poor adherence. The fear of adverse events led health workers to hesitate prescribing PQ. In countries where G6PD was mandatory, respondents experienced frequent stockouts of G6PD rapid diagnostic kits in peripheral health facilities, which was compounded by a short shelf life of these tests. These challenges were echoed across participating countries to various degrees. Most respondents agreed that a shorter treatment regimen, such as single dose tafenoquine could resolve these problems but mandatory G6PD testing will be needed. The recommendation of shorter regimens including tafenoquine or high dose PQ requires operational evidence demonstrating the robust performance of point of care G6PD tests (biosensors).

CONCLUSION

There was sparse implementation and low adherence to the radical cure in South/South East Asian and Asian pacific countries. Shorter treatment regimens with appropriate point of care quantitative G6PD tests may resolve the current challenges. Operational evidence on point of care quantitative G6PD tests that includes the feasibility of integrating such tests into the radical cure regimen are critical to ensure its implementation.

Optimizing Myanmar's community-delivered malaria volunteer model: a qualitative study of stakeholders' perspectives

BACKGROUND

In parallel with the change of malaria policy from control to elimination and declines in the malaria burden in Greater Mekong Sub-region, the motivation and social role of malaria volunteers has declined. To address this public health problem, in Myanmar, the role and responsibilities of malaria volunteers have been transformed into integrated community malaria volunteers (ICMV), that includes the integration of activities for five additional diseases (dengue, lymphatic filariasis, tuberculosis, HIV/AIDS and leprosy) into their current activities. However, this transformation was not evidence-based and did not consider inputs of different stakeholders. Therefore, qualitative stakeholder consultations were performed to optimize future malaria volunteer models in Myanmar.

METHODS

Semi-structured interviews were conducted with key health stakeholders from the Myanmar Ministry of Health and Sports (MoHS) and malaria implementing partners to obtain their perspectives on community-delivered malaria models. A qualitative descriptive approach was used to explore the experiences of the stakeholders in policymaking and programme implementation. Interview topic guides were used during the interviews and inductive thematic data analysis was performed.

RESULTS

While ICMVs successfully provided malaria services in the community, the stakeholders considered the ICMV model as not optimal and suggested that many aspects needed to be improved including better training, supervision, support, and basic health staff's recognition for ICMVs. Stakeholders believe that the upgraded ICMV model could contribute significantly to achieving malaria elimination and universal health care in Myanmar.

DISCUSSION AND CONCLUSION

In the context of high community demand for non-malaria treatment services from volunteers, the integrated volunteer service package must be developed carefully in order to make it effective in malaria elimination programme and to contribute in Myanmar's pathway to universal health coverage (UHC), but without harming the community. An evidenced-based, community-delivered and preferred model, that is also accepted by the MoHS, is yet to be developed to effectively contribute to achieving malaria elimination and UHC goals in Myanmar by 2030.

Transition of radical, preventive and presumptive treatment regimens for malaria in China: a systematic review

Background

Globally, malaria is still a major public health challenge. Drug-based treatment is the primary intervention in malaria control and elimination. However, optimal use of mass or targeted treatments remains unclear. A variety of radical, preventive and presumptive treatment regimens have been administrated in China and a systematic review was conducted to evaluate effectiveness, and discuss experiences, limitations, and lessons learnt in relation to the use of these regimens.

Methods

The search for information includes both paper documents, such as books, malaria control annals and guidelines for malaria prevention and treatment, as well as three computer-based databases in Chinese (CNKI, WanFangdata and Xueshu.baidu) and two databases in English (PubMed and Google Scholar), to identify original articles and reports associated with drug administration for malaria in China.

Results

Starting from hyperendemicity to elimination of malaria in China, a large number of radical, preventive and presumptive treatment regimens had been tried. Those effective regimens were scaled up for malaria control and elimination programmes in China. Between 1949 and 1959, presumptive treatment with available anti-malarial drugs was given to people with enlarged spleens and those who had symptoms suggestive of malaria within the last 6 months. Between 1960 and 1999, mass drug administration (MDA) was given for preventive and radical treatment. Between 2000 and 2009, the approach was more targeted, and drugs were administed only to prevent malaria infection in those at high risk of exposure and those who needed radical treatment for suspected malaria. Presumptive therapy was only given to febrile patients. From 2010, the malaria programme changed into elimination phase, radical treatment changed to target individuals with confirmed either Plasmodium vivax or Plasmodium ovale within the last year. Preventive treatment was given to those who will travel to other endemic countries. Presumptive treatment was normally not given during this elimination phase. All cases of suspected were confirmed by either microscopy or rapid diagnosis tests for malaria antigens before drugs were administered. The engagement of the broader community ensured high coverage of these drug-based interventions, and the directly-observed therapy improved patient safety during drug administration.

Conclusion

A large number of radical, preventive and presumptive treatment regimens for malaria had been tried in China with reported success, but the impact of drug-based interventions has been difficult to quantify because they are just a part of an integrated malaria control strategy. The historical experiences of China suggest that intervention trials should be done by the local health facilities with community involvement, and a local decision is made according to their own trial results.

Diagnostic Practices and Treatment for P. vivax in the InterEthnic Therapeutic Encounter of South-Central Vietnam: A Mixed-Methods Study

Malaria elimination in the Greater Mekong Sub-Region is challenged by a rising proportion of malaria attributable to P. vivax. Primaquine (PQ) is effective in eliminating the parasite's dormant liver stages and can prevent relapsing infections, but it induces severe haemolysis in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, highlighting the importance of testing enzyme activity prior to treatment. A mixed-method study was conducted in south-central Vietnam to explore the factors that affect acceptability of G6PD testing, treatment-seeking behaviors, and adherence to current regimens. The majority of respondents (75.7%) were unaware of the different parasite species and rather differentiated malaria by perceived severity. People sought a diagnosis if suspected of malaria fever but not if they perceived their fevers as mild. Most respondents agreed to take prescribed medication to treat asymptomatic infection (94.1%) and to continue medication even if they felt better (91.5%). Health professionals did not have G6PD diagnostic tools nor the means to prescribe PQ safely. Adherence to treatment was linked to trust in public providers, who were perceived to make therapeutic decisions in the interest of the patient. Greater focus on providing acceptable ways of assessing G6PD deficiency will be needed to ensure the timely elimination of malaria in Vietnam.

Hypnozoites in Plasmodium: Do Parasites Parallel Plants?

The phenomenon of relapsing malaria has been recognised for centuries. It is caused in humans by the parasite species Plasmodium vivax and Plasmodium ovale, which can arrest growth at an early, asymptomatic stage as hypnozoites inside liver cells. These dormant parasites can remain quiescent for months or years, then reactivate causing symptomatic malaria. The dynamics of hypnozoite dormancy and reactivation are well documented but the molecular basis remains a complete mystery. Here, I observe that the process has striking parallels with plant vernalisation, whereby plants remain dormant through the winter before flowering in spring. Vernalisation is thoroughly studied in several plant species and its mechanisms are known in exquisite detail. Vernalisation may thus provide a useful framework for interrogating hypnozoite biology.

The risk of adverse clinical outcomes following treatment of Plasmodium vivax malaria with and without primaquine in Papua, Indonesia

The widespread use of primaquine (PQ) radical cure for P. vivax, is constrained by concerns over its safety. We used routinely collected patient data to compare the overall morbidity and mortality in patients treated with and without PQ without prior testing of Glucose-6-Phosphate-Dehydrogenase (G6PD) deficiency in Papua, Indonesia, where there is a low prevalence of G6PD deficiency. Records were collated from patients older than 1 year, with P. vivax infection, who were treated with an artemisinin combination therapy (ACT). The risks of re-presentation, hospitalization, major fall in haemoglobin and death within 30 days were quantified and compared between patients treated with and without PQ using a Cox regression model. In total 26,216 patients with P. vivax malaria presented to the hospital with malaria during the study period. Overall 27.56% (95% Confidence Interval (95%CI): 26.96-28.16) of 21,344 patients treated with PQ re-presented with any illness within 30 days and 1.69% (1.51-1.88) required admission to hospital. The corresponding risks were higher in the 4,872 patients not treated with PQ; Adjusted Hazard Ratio (AHR) = 0.84 (0.79-0.91; p<0.001) and 0.54 (0.41-0.70; p<0.001) respectively. By day 30, 14.15% (12.45-16.05) of patients who had received PQ had a fall in haemoglobin (Hb) below 7g/dl compared to 20.43% (16.67-24.89) of patients treated without PQ; AHR = 0.66 (0.45-0.97; p = 0.033). A total of 75 (0.3%) patients died within 30 days of treatment with a mortality risk of 0.27% (0.21-0.35) in patients treated with PQ, compared to 0.38% (0.24-0.60) without PQ; AHR = 0.79 (0.43-1.45; p = 0.448). In Papua, Indonesia routine administration of PQ radical cure without prior G6PD testing, was associated with lower risk of all cause hospitalization and other serious adverse clinical outcomes. In areas where G6PD testing is not available or cannot be delivered reliably, the risks of drug induced haemolysis should be balanced against the potential benefits of reducing recurrent P. vivax malaria and its associated morbidity and mortality.

Precarity at the Margins of Malaria Control in the Chittagong Hill Tracts in Bangladesh: A Mixed-Methods Study

Bangladesh has achieved significant progress towards malaria elimination, although health service delivery for malaria remains challenging in remote forested areas such as the Chittagong Hill Tracts (CHT). The aim of this study was to investigate perceptions of malaria and its treatment among the local population to inform contextualized strategies for rolling out radical cure for P. vivax in Bangladesh. The study comprised two sequential strands whereby the preliminary results of a qualitative strand informed the development of a structured survey questionnaire used in the quantitative strand. Results show that ethnic minority populations in the CHT live in precarious socio-economic conditions which increase their exposure to infectious diseases, and that febrile patients often self-treat, including home remedies and pharmaceuticals, before attending a healthcare facility. Perceived low quality of care and lack of communication between Bengali health providers and ethnic minority patients also affects access to public healthcare. Malaria is viewed as a condition that affects vulnerable people weakened by agricultural work and taking away blood is perceived to increase such vulnerability. Healthcare providers that initiate and sustain a dialogue about these issues with ethnic minority patients may foster the trust that is needed for local malaria elimination efforts.

G6PD deficiency in malaria endemic areas of Nepal

Background

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is currently a threat to malaria elimination due to risk of primaquine-induced haemolysis in G6PD deficient individuals. The World Health Organization (WHO) recommends G6PD screening before providing primaquine as a radical treatment against vivax malaria. However, evidence regarding the prevalence and causing mutations of G6PD deficiency in Nepal is scarce.

Methods

A cross-sectional, population-based, prevalence study was carried out from May to October 2016 in 12 malaria-endemic districts of Nepal. The screening survey included 4067 participants whose G6PD status was determined by G6PD Care Start™ rapid diagnostic test and genotyping.

Results

The prevalence of G6PD deficiency at the national level was 3.5% (4.1% among males and 2.1% among females). When analysed according to ethnic groups, G6PD deficiency was highest among the Janajati (6.2% overall, 17.6% in Mahatto, 7.7% in Chaudhary and 7.5% in Tharu) and low among Brahman and Chhetri (1.3%). District-wise, prevalence was highest in Banke (7.6%) and Chitwan (6.6%). Coimbra mutation (592 C>T) was found among 75.5% of the G6PD-deficient samples analysed and Mahidol (487 G>A) and Mediterranean (563 C>T) mutations were found in equal proportions in the remaining 24.5%. There was no specific geographic or ethnic distribution for the three mutations.

Conclusions

This study has identified populations with moderate to high prevalence of G6PD deficiency which provides strong evidence supporting the WHO recommendations to screen G6PD deficiency at health facility level before the use of primaquine-based radical curative regimen for Plasmodium vivax.

Implementing parasite genotyping into national surveillance frameworks: feedback from control programmes and researchers in the Asia-Pacific region

The Asia-Pacific region faces formidable challenges in achieving malaria elimination by the proposed target in 2030. Molecular surveillance of Plasmodium parasites can provide important information on malaria transmission and adaptation, which can inform national malaria control programmes (NMCPs) in decision-making processes. In November 2019 a parasite genotyping workshop was held in Jakarta, Indonesia, to review molecular approaches for parasite surveillance and explore ways in which these tools can be integrated into public health systems and inform policy. The meeting was attended by 70 participants from 8 malaria-endemic countries and partners of the Asia Pacific Malaria Elimination Network. The participants acknowledged the utility of multiple use cases for parasite genotyping including: quantifying the prevalence of drug resistant parasites, predicting risks of treatment failure, identifying major routes and reservoirs of infection, monitoring imported malaria and its contribution to local transmission, characterizing the origins and dynamics of malaria outbreaks, and estimating the frequency of Plasmodium vivax relapses. However, the priority of each use case varies with different endemic settings. Although a one-size-fits-all approach to molecular surveillance is unlikely to be applicable across the Asia-Pacific region, consensus on the spectrum of added-value activities will help support data sharing across national boundaries. Knowledge exchange is needed to establish local expertise in different laboratory-based methodologies and bioinformatics processes. Collaborative research involving local and international teams will help maximize the impact of analytical outputs on the operational needs of NMCPs. Research is also needed to explore the cost-effectiveness of genetic epidemiology for different use cases to help to leverage funding for wide-scale implementation. Engagement between NMCPs and local researchers will be critical throughout this process.

Plasmodium vivax in the Era of the Shrinking P. falciparum Map

Plasmodium vivax is an important cause of malaria, associated with a significant public health burden. Whilst enhanced malaria-control activities have successfully reduced the incidence of Plasmodium falciparum malaria in many areas, there has been a consistent increase in the proportion of malaria due to P. vivax in regions where both parasites coexist. This article reviews the epidemiology and biology of P. vivax, how the parasite differs from P. falciparum, and the key features that render it more difficult to control and eliminate. Since transmission of the parasite is driven largely by relapses from dormant liver stages, its timely elimination will require widespread access to safe and effective radical cure.

Single dose tafenoquine for preventing relapse in people with plasmodium vivax malaria-an updated meta-analysis

BACKGROUND

Plasmodium vivax is a frequent cause of recurring malaria in endemic areas as in its latent stage it resides in liver, and is responsible for relapse. Treatment with 8 aminoquinoline Primaquine is given for 14 days, however studies have shown dismal results with adherence to therapy. A new long acting 8 aminoquinoline, Tafenoquine was introduced that showed efficacy and safety almost similar to Primaquine in a single dose regimen, hence giving hopes for improved compliance and help in eradicating malaria.

METHODS

We searched for randomized controlled trials (RCTs) that compared the efficacy of Tafenoquine with Primaquine or placebo. Our primary outcome was the recurrence of Plasmodium vivax parasitemia at 6 months and our safety outcomes included total number of adverse events as well as serious adverse events. We performed pooled data analysis by the random effects model and I2 was used to assess heterogeneity.

RESULTS

4 RCTs were included. Our pooled analysis showed that the number of episodes of recurrence at 6 months between Tafenoquine and Primaquine (RR = 1.08, 95% CI = 0.74-1.59), and between Tafenoquine and placebo (RR = 0.17, 95%CI = 0.03-1.11) was statistically insignificant. Comparison of serious adverse events did not show any significant risk associated with the use of Tafenoquine as compared to Primaquine when analyzed till day 29, which was the time period considered to show most probable drug associated events.

CONCLUSION

Tafenoquine as a single dose is an effective alternative to Primaquine for prevention of recurrence of P vivax malaria, with a reasonable safety profile.

Malaria-related hospitalization during childhood in Papua, Indonesia: A retrospective cohort study

BACKGROUND

In endemic regions, the age distribution of malaria varies according to the infecting Plasmodium species. We aimed to delineate the pattern of malaria-related hospitalization from birth in Timika, Papua-an area co-endemic for P. falciparum and P. vivax.

METHODS

Between April 2004 and December 2013, infants born at Mitra Masyarakat Hospital, or presenting within the first 7 days of life, were enrolled retrospectively into a cohort study and followed passively using routinely-collected hospital surveillance data. Outcomes were stratified by the presence or absence of Plasmodium parasitemia and included re-presentation to hospital, requirement for hospital admission and death.

RESULTS

Overall, 11,408 infants were enrolled into the cohort. Median follow-up was 4.3 (maximum 9.7) years. In total, 7,847 (68.9%) infants made 90,766 re-presentations to hospital, 18,105 (19.9%) of which were associated with Plasmodium parasitemia. The incidence of re-presentations with malaria during the first year of life was 213 per 1,000 person-years (py) for P. vivax and 79 per 1,000py for P. falciparum (Incidence Rate Ratio (IRR) = 2.69, 95% Confidence Interval (95%CI): 2.48-2.92). After the age of 5 years, the incidence of P. vivax had fallen to 77/1,000py and the incidence of P. falciparum had risen to 95/1,000py (IRR = 0.80, 95%CI: 0.73-0.88). Overall, 79.7% (14,431/18,105) of malaria re-presentations were recurrences rather than initial infections. Malaria accounted for 31.7% (2,126/3,120) of all hospital admissions. The infant mortality rate in this study was 52 deaths per 1,000 live births. Beyond the early neonatal period, 13.4% of deaths were associated with Plasmodium parasitemia.

CONCLUSIONS

In Papua, Indonesia, malaria is a major cause of hospital presentation and admission in early life. The initial predominance of P. vivax over P. falciparum inverts after five years of age. Malaria is directly associated with nearly one in seven deaths after the early neonatal period.

Provider and household costs of Plasmodium vivax malaria episodes: a multicountry comparative analysis of primary trial data

OBJECTIVE

To determine household and health-care provider costs associated with Plasmodium vivax infection across a range of endemic settings.

METHODS

We collected cost data alongside three multicentre clinical trials of P. vivax treatment in Afghanistan, Brazil, Colombia, Ethiopia, Indonesia, Philippines, Peru, Thailand and Viet Nam conducted between April 2014 to December 2017. We derived household costs from trial participant surveys administered at enrolment and again 2 weeks later to determine the costs of treatment and transportation, and the number of days that patients and their household caregivers were unable to undertake their usual activities. We determined costs of routine care by health-care providers by micro-costing the resources used to diagnose and treat P. vivax at the study sites.

FINDINGS

The mean total household costs ranged from 8.7 United States dollars (US$; standard deviation, SD: 4.3) in Afghanistan to US$ 254.7 (SD: 148.4) in Colombia. Across all countries, productivity losses were the largest household cost component, resulting in mean indirect costs ranging from US$ 5.3 (SD: 3.0) to US$ 220.8 (SD: 158.40). The range of health-care provider costs for routine care was US$ 3.6-6.6. The cost of administering a glucose-6-phosphate-dehydrogenase rapid diagnostic test, ranged from US$ 0.9 to 13.5, consistently lower than the costs of the widely-used fluorescent spot test (US$ 6.3 to 17.4).

CONCLUSION

An episode of P. vivax malaria results in high costs to households. The costs of diagnosing and treating P. vivax are important inputs for future cost-effectiveness analyses to ensure optimal allocation of resources for malaria elimination.

Short-course primaquine for the radical cure of Plasmodium vivax malaria: a multicentre, randomised, placebo-controlled non-inferiority trial

BACKGROUND

Primaquine is the only widely used drug that prevents Plasmodium vivax malaria relapses, but adherence to the standard 14-day regimen is poor. We aimed to assess the efficacy of a shorter course (7 days) of primaquine for radical cure of vivax malaria.

METHODS

We did a randomised, double-blind, placebo-controlled, non-inferiority trial in eight health-care clinics (two each in Afghanistan, Ethiopia, Indonesia, and Vietnam). Patients (aged ≥6 months) with normal glucose-6-phosphate dehydrogenase (G6PD) and presenting with uncomplicated vivax malaria were enrolled. Patients were given standard blood schizontocidal treatment and randomly assigned (2:2:1) to receive 7 days of supervised primaquine (1·0 mg/kg per day), 14 days of supervised primaquine (0·5 mg/kg per day), or placebo. The primary endpoint was the incidence rate of symptomatic P vivax parasitaemia during the 12-month follow-up period, assessed in the intention-to-treat population. A margin of 0·07 recurrences per person-year was used to establish non-inferiority of the 7-day regimen compared with the 14-day regimen. This trial is registered at ClinicalTrials.gov (NCT01814683).

FINDINGS

Between July 20, 2014, and Nov 25, 2017, 2336 patients were enrolled. The incidence rate of symptomatic recurrent P vivax malaria was 0·18 (95% CI 0·15 to 0·21) recurrences per person-year for 935 patients in the 7-day primaquine group and 0·16 (0·13 to 0·18) for 937 patients in the 14-day primaquine group, a difference of 0·02 (-0·02 to 0·05, p=0·3405). The incidence rate for 464 patients in the placebo group was 0·96 (95% CI 0·83 to 1·08) recurrences per person-year. Potentially drug-related serious adverse events within 42 days of starting treatment were reported in nine (1·0%) of 935 patients in the 7-day group, one (0·1%) of 937 in the 14-day group and none of 464 in the control arm. Four of the serious adverse events were significant haemolysis (three in the 7-day group and one in the 14-day group).

INTERPRETATION

In patients with normal G6PD, 7-day primaquine was well tolerated and non-inferior to 14-day primaquine. The short-course regimen might improve adherence and therefore the effectiveness of primaquine for radical cure of P vivax malaria.

FUNDING

UK Department for International Development, UK Medical Research Council, UK National Institute for Health Research, and the Wellcome Trust through the Joint Global Health Trials Scheme (MR/K007424/1) and the Bill & Melinda Gates Foundation (OPP1054404).

The haematological consequences of Plasmodium vivax malaria after chloroquine treatment with and without primaquine: a WorldWide Antimalarial Resistance Network systematic review and individual patient data meta-analysis

BACKGROUND

Malaria causes a reduction in haemoglobin that is compounded by primaquine, particularly in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. The aim of this study was to determine the relative contributions to red cell loss of malaria and primaquine in patients with uncomplicated Plasmodium vivax.

METHODS

A systematic review identified P. vivax efficacy studies of chloroquine with or without primaquine published between January 2000 and March 2017. Individual patient data were pooled using standardised methodology, and the haematological response versus time was quantified using a multivariable linear mixed effects model with non-linear terms for time. Mean differences in haemoglobin between treatment groups at day of nadir and day 42 were estimated from this model.

RESULTS

In total, 3421 patients from 29 studies were included: 1692 (49.5%) with normal G6PD status, 1701 (49.7%) with unknown status and 28 (0.8%) deficient or borderline individuals. Of 1975 patients treated with chloroquine alone, the mean haemoglobin fell from 12.22 g/dL [95% CI 11.93, 12.50] on day 0 to a nadir of 11.64 g/dL [11.36, 11.93] on day 2, before rising to 12.88 g/dL [12.60, 13.17] on day 42. In comparison to chloroquine alone, the mean haemoglobin in 1446 patients treated with chloroquine plus primaquine was - 0.13 g/dL [- 0.27, 0.01] lower at day of nadir (p = 0.072), but 0.49 g/dL [0.28, 0.69] higher by day 42 (p < 0.001). On day 42, patients with recurrent parasitaemia had a mean haemoglobin concentration - 0.72 g/dL [- 0.90, - 0.54] lower than patients without recurrence (p < 0.001). Seven days after starting primaquine, G6PD normal patients had a 0.3% (1/389) risk of clinically significant haemolysis (fall in haemoglobin > 25% to < 7 g/dL) and a 1% (4/389) risk of a fall in haemoglobin > 5 g/dL.

CONCLUSIONS

Primaquine has the potential to reduce malaria-related anaemia at day 42 and beyond by preventing recurrent parasitaemia. Its widespread implementation will require accurate diagnosis of G6PD deficiency to reduce the risk of drug-induced haemolysis in vulnerable individuals.

TRIAL REGISTRATION

This trial was registered with PROSPERO: CRD42016053312. The date of the first registration was 23 December 2016.

Plasmodium Genomics and Genetics: New Insights into Malaria Pathogenesis, Drug Resistance, Epidemiology, and Evolution

Protozoan Plasmodium parasites are the causative agents of malaria, a deadly disease that continues to afflict hundreds of millions of people every year. Infections with malaria parasites can be asymptomatic, with mild or severe symptoms, or fatal, depending on many factors such as parasite virulence and host immune status. Malaria can be treated with various drugs, with artemisinin-based combination therapies (ACTs) being the first-line choice. Recent advances in genetics and genomics of malaria parasites have contributed greatly to our understanding of parasite population dynamics, transmission, drug responses, and pathogenesis. However, knowledge gaps in parasite biology and host-parasite interactions still remain. Parasites resistant to multiple antimalarial drugs have emerged, while advanced clinical trials have shown partial efficacy for one available vaccine. Here we discuss genetic and genomic studies of Plasmodium biology, host-parasite interactions, population structures, mosquito infectivity, antigenic variation, and targets for treatment and immunization. Knowledge from these studies will advance our understanding of malaria pathogenesis, epidemiology, and evolution and will support work to discover and develop new medicines and vaccines.

Malaria morbidity and mortality following introduction of a universal policy of artemisinin-based treatment for malaria in Papua, Indonesia: A longitudinal surveillance study

BACKGROUND

Malaria control activities can have a disproportionately greater impact on Plasmodium falciparum than on P. vivax in areas where both species are coendemic. We investigated temporal trends in malaria-related morbidity and mortality in Papua, Indonesia, before and after introduction of a universal, artemisinin-based antimalarial treatment strategy for all Plasmodium species.

METHODS AND FINDINGS

A prospective, district-wide malariometric surveillance system was established in April 2004 to record all cases of malaria at community clinics and the regional hospital and maintained until December 2013. In March 2006, antimalarial treatment policy was changed to artemisinin combination therapy for uncomplicated malaria and intravenous artesunate for severe malaria due to any Plasmodium species. Over the study period, a total of 418,238 patients presented to the surveillance facilities with malaria. The proportion of patients with malaria requiring admission to hospital fell from 26.9% (7,745/28,789) in the pre-policy change period (April 2004 to March 2006) to 14.0% (4,786/34,117) in the late transition period (April 2008 to December 2009), a difference of -12.9% (95% confidence interval [CI] -13.5% to -12.2%). There was a significant fall in the mortality of patients presenting to the hospital with P. falciparum malaria (0.53% [100/18,965] versus 0.32% [57/17,691]; difference = -0.21% [95% CI -0.34 to -0.07]) but not in patients with P. vivax malaria (0.28% [21/7,545] versus 0.23% [28/12,397]; difference = -0.05% [95% CI -0.20 to 0.09]). Between the same periods, the overall proportion of malaria due to P. vivax rose from 44.1% (30,444/69,098) to 53.3% (29,934/56,125) in the community clinics and from 32.4% (9,325/28,789) to 44.1% (15,035/34,117) at the hospital. After controlling for population growth and changes in treatment-seeking behaviour, the incidence of P. falciparum malaria fell from 511 to 249 per 1,000 person-years (py) (incidence rate ratio [IRR] = 0.49 [95% CI 0.48-0.49]), whereas the incidence of P. vivax malaria fell from 331 to 239 per 1,000 py (IRR = 0.72 [95% CI 0.71-0.73]). The main limitations of our study were possible confounding from changes in healthcare provision, a growing population, and significant shifts in treatment-seeking behaviour following implementation of a new antimalarial policy.

CONCLUSIONS

In this area with high levels of antimalarial drug resistance, adoption of a universal policy of efficacious artemisinin-based therapy for malaria infections due to any Plasmodium species was associated with a significant reduction in total malaria-attributable morbidity and mortality. The burden of P. falciparum malaria was reduced to a greater extent than that of P. vivax malaria. In coendemic regions, the timely elimination of malaria will require that safe and effective radical cure of both the blood and liver stages of the parasite is widely available for all patients at risk of malaria.

Factors associated with children's health facility visits for primaquine treatment in rural Papua New Guinea

Background

To control and eventually eliminate vivax malaria, radical treatment with primaquine (PQ) is essential after completion of blood-stage treatment. Although in many malaria-endemic countries, village health volunteers (VHVs) are engaged in diagnostic treatment of malaria in remote communities, they principally provide blood-stage treatment. In such a situation, access to PQ following blood-stage treatment can be a barrier to complete treatment. However, studies on access to PQ treatment have been scarce and limited in health facility-based settings. This study aimed to identify factors associated with access to PQ treatment in rural Papua New Guinea (PNG) from the community case management perspective.

Methods

A community-based, cross-sectional survey was conducted to collect sociodemographic information on children under 15 years of age, their households, and their caretakers in East Sepik Province, PNG. Data collection lasted from February to March, 2015. Information on the diagnoses of potential non-falciparum malaria and prescription of PQ in preceding year (January to December 2014) were obtained from child health-record books. Then, multilevel logistic regression model was used to determine the factors associated with formal health facility visits for PQ treatment among children with potential non-falciparum malaria.

Results

Of 420 episodes diagnosed as potential non-falciparum malaria, 46 (11%) were immediately given PQ. The rest were instructed to visit formal health facilities (HFs) for PQ, and the patients obtained PQ during the second visit to HFs was 44%. Consequently, the overall proportion of PQ prescription was 50%. Logistic regression analysis suggested that among the patients who were instructed to visit HFs for PQ treatment, the initial visit to VHV and higher transportation costs to HF were inversely associated with PQ prescription during the second visit to an HF.

Conclusions

Few children received PQ treatment during the second visit to HFs following diagnosis of potential non-falciparum malaria. These findings suggest a need to establish a policy to reduce structural and economic barriers and improve rural inhabitant access to PQ treatment.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2675-4) contains supplementary material, which is available to authorized users.

Tafenoquine versus Primaquine to Prevent Relapse of Plasmodium vivax Malaria

BACKGROUND

Tafenoquine, a single-dose therapy for Plasmodium vivax malaria, has been associated with relapse prevention through the clearance of P. vivax parasitemia and hypnozoites, termed "radical cure."

METHODS

We performed a phase 3, prospective, double-blind, double-dummy, randomized, controlled trial to compare tafenoquine with primaquine in terms of safety and efficacy. The trial was conducted at seven hospitals or clinics in Peru, Brazil, Colombia, Vietnam, and Thailand and involved patients with normal glucose-6-phosphate dehydrogenase (G6PD) enzyme activity and female patients with moderate G6PD enzyme deficiency; all patients had confirmed P. vivax parasitemia. The patients were randomly assigned, in a 2:1 ratio, to receive a single 300-mg dose of tafenoquine or 15 mg of primaquine once daily for 14 days (administered under supervision); all patients received a 3-day course of chloroquine and were followed for 180 days. The primary safety outcome was a protocol-defined decrease in the hemoglobin level (>3.0 g per deciliter or ≥30% from baseline or to a level of <6.0 g per deciliter). Freedom from recurrence of P. vivax parasitemia at 6 months was the primary efficacy outcome in a planned patient-level meta-analysis of the current trial and another phase 3 trial of tafenoquine and primaquine (per-protocol populations), and an odds ratio for recurrence of 1.45 (tafenoquine vs. primaquine) was used as a noninferiority margin.

RESULTS

A protocol-defined decrease in the hemoglobin level occurred in 4 of 166 patients (2.4%; 95% confidence interval [CI], 0.9 to 6.0) in the tafenoquine group and in 1 of 85 patients (1.2%; 95% CI, 0.2 to 6.4) in the primaquine group, for a between-group difference of 1.2 percentage points (95% CI, -4.2 to 5.0). In the patient-level meta-analysis, the percentage of patients who were free from recurrence at 6 months was 67.0% (95% CI, 61.0 to 72.3) among the 426 patients in the tafenoquine group and 72.8% (95% CI, 65.6 to 78.8) among the 214 patients in the primaquine group. The efficacy of tafenoquine was not shown to be noninferior to that of primaquine (odds ratio for recurrence, 1.81; 95% CI, 0.82 to 3.96).

CONCLUSIONS

Among patients with normal G6PD enzyme activity, the decline in hemoglobin level with tafenoquine did not differ significantly from that with primaquine. Tafenoquine showed efficacy for the radical cure of P. vivax malaria, although tafenoquine was not shown to be noninferior to primaquine. (Funded by GlaxoSmithKline and Medicines for Malaria Venture; GATHER ClinicalTrials.gov number, NCT02216123 .).

Single-Dose Tafenoquine to Prevent Relapse of Plasmodium vivax Malaria

BACKGROUND

Treatment of Plasmodium vivax malaria requires the clearing of asexual parasites, but relapse can be prevented only if dormant hypnozoites are cleared from the liver (a treatment termed "radical cure"). Tafenoquine is a single-dose 8-aminoquinoline that has recently been registered for the radical cure of P. vivax.

METHODS

This multicenter, double-blind, double-dummy, parallel group, randomized, placebo-controlled trial was conducted in Ethiopia, Peru, Brazil, Cambodia, Thailand, and the Philippines. We enrolled 522 patients with microscopically confirmed P. vivax infection (>100 to <100,000 parasites per microliter) and normal glucose-6-phosphate dehydrogenase (G6PD) activity (with normal activity defined as ≥70% of the median value determined at each trial site among 36 healthy male volunteers who were otherwise not involved in the trial). All patients received a 3-day course of chloroquine (total dose of 1500 mg). In addition, patients were assigned to receive a single 300-mg dose of tafenoquine on day 1 or 2 (260 patients), placebo (133 patients), or a 15-mg dose of primaquine once daily for 14 days (129 patients). The primary outcome was the Kaplan-Meier estimated percentage of patients who were free from recurrence at 6 months, defined as P. vivax clearance without recurrent parasitemia.

RESULTS

In the intention-to-treat population, the percentage of patients who were free from recurrence at 6 months was 62.4% in the tafenoquine group (95% confidence interval [CI], 54.9 to 69.0), 27.7% in the placebo group (95% CI, 19.6 to 36.6), and 69.6% in the primaquine group (95% CI, 60.2 to 77.1). The hazard ratio for the risk of recurrence was 0.30 (95% CI, 0.22 to 0.40) with tafenoquine as compared with placebo (P<0.001) and 0.26 (95% CI, 0.18 to 0.39) with primaquine as compared with placebo (P<0.001). Tafenoquine was associated with asymptomatic declines in hemoglobin levels, which resolved without intervention.

CONCLUSIONS

Single-dose tafenoquine resulted in a significantly lower risk of P. vivax recurrence than placebo in patients with phenotypically normal G6PD activity. (Funded by GlaxoSmithKline and Medicines for Malaria Venture; DETECTIVE ClinicalTrials.gov number, NCT01376167 .).

The effect of chloroquine dose and primaquine on Plasmodium vivax recurrence: a WorldWide Antimalarial Resistance Network systematic review and individual patient pooled meta-analysis

BACKGROUND

Chloroquine remains the mainstay of treatment for Plasmodium vivax malaria despite increasing reports of treatment failure. We did a systematic review and meta-analysis to investigate the effect of chloroquine dose and the addition of primaquine on the risk of recurrent vivax malaria across different settings.

METHODS

A systematic review done in MEDLINE, Web of Science, Embase, and Cochrane Database of Systematic Reviews identified P vivax clinical trials published between Jan 1, 2000, and March 22, 2017. Principal investigators were invited to share individual patient data, which were pooled using standardised methods. Cox regression analyses with random effects for study site were used to investigate the roles of chloroquine dose and primaquine use on rate of recurrence between day 7 and day 42 (primary outcome). The review protocol is registered in PROSPERO, number CRD42016053310.

FINDINGS

Of 134 identified chloroquine studies, 37 studies (from 17 countries) and 5240 patients were included. 2990 patients were treated with chloroquine alone, of whom 1041 (34·8%) received a dose below the target 25 mg/kg. The risk of recurrence was 32·4% (95% CI 29·8-35·1) by day 42. After controlling for confounders, a 5 mg/kg higher chloroquine dose reduced the rate of recurrence overall (adjusted hazard ratio [AHR] 0·82, 95% CI 0·69-0·97; p=0·021) and in children younger than 5 years (0·59, 0·41-0·86; p=0·0058). Adding primaquine reduced the risk of recurrence to 4·9% (95% CI 3·1-7·7) by day 42, which is lower than with chloroquine alone (AHR 0·10, 0·05-0·17; p<0·0001).

INTERPRETATION

Chloroquine is commonly under-dosed in the treatment of vivax malaria. Increasing the recommended dose to 30 mg/kg in children younger than 5 years could reduce substantially the risk of early recurrence when primaquine is not given. Radical cure with primaquine was highly effective in preventing early recurrence and may also improve blood schizontocidal efficacy against chloroquine-resistant P vivax.

FUNDING

Wellcome Trust, Australian National Health and Medical Research Council, and Bill & Melinda Gates Foundation.

Metabolism of primaquine in normal human volunteers: investigation of phase I and phase II metabolites from plasma and urine using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry

BACKGROUND

Primaquine (PQ), an 8-aminoquinoline, is the only drug approved by the United States Food and Drug Administration for radical cure and prevention of relapse in Plasmodium vivax infections. Knowledge of the metabolism of PQ is critical for understanding the therapeutic efficacy and hemolytic toxicity of this drug. Recent in vitro studies with primary human hepatocytes have been useful for developing the ultra high-performance liquid chromatography coupled with high-resolution mass spectrometric (UHPLC-QToF-MS) methods for simultaneous determination of PQ and its metabolites generated through phase I and phase II pathways for drug metabolism.

METHODS

These methods were further optimized and applied for phenotyping PQ metabolites from plasma and urine from healthy human volunteers treated with single 45 mg dose of PQ. Identity of the metabolites was predicted by MetaboLynx using LC-MS/MS fragmentation patterns. Selected metabolites were confirmed with appropriate standards.

RESULTS

Besides PQ and carboxy PQ (cPQ), the major plasma metabolite, thirty-four additional metabolites were identified in human plasma and urine. Based on these metabolites, PQ is viewed as metabolized in humans via three pathways. Pathway 1 involves direct glucuronide/glucose/carbamate/acetate conjugation of PQ. Pathway 2 involves hydroxylation (likely cytochrome P450-mediated) at different positions on the quinoline ring, with mono-, di-, or even tri-hydroxylations possible, and subsequent glucuronide conjugation of the hydroxylated metabolites. Pathway 3 involves the monoamine oxidase catalyzed oxidative deamination of PQ resulting in formation of PQ-aldehyde, PQ alcohol and cPQ, which are further metabolized through additional phase I hydroxylations and/or phase II glucuronide conjugations.

CONCLUSION

This approach and these findings augment our understanding and provide comprehensive view of pathways for PQ metabolism in humans. These will advance the clinical studies of PQ metabolism in different populations for different therapeutic regimens and an understanding of the role these play in PQ efficacy and safety outcomes, and their possible relation to metabolizing enzyme polymorphisms.

Low and heterogeneous prevalence of glucose-6-phosphate dehydrogenase deficiency in different settings in Ethiopia using phenotyping and genotyping approaches

BACKGROUND

8-Aminoquinolines such as primaquine clear mature Plasmodium falciparum gametocytes that are responsible for transmission from human to mosquitoes and bring radical cure in Plasmodium vivax by clearing dormant liver stages. Deployment of primaquine is thus of relevance for malaria elimination efforts but challenged by the widespread prevalence of glucose-6-phosphate dehydrogenase deficiency (G6PDd) in endemic countries since primaquine in G6PDd individuals may lead to acute haemolysis. In this study, the prevalence of G6PDd was investigated in different settings in Ethiopia using phenotyping and genotyping approaches.

METHODS

Community and school based cross-sectional surveys were conducted from October to December 2016 in four administrative regions (Gambela, Benishangul Gumuz, Oromia, and Amhara) in Ethiopia. Finger prick blood samples were collected for G6PD enzyme activity using the CareStart™ G6PD screening test and genotyping of 36 selected single nucleotide polymorphisms (SNPs) located in the G6PD gene and its flanking regions.

RESULTS

Overall, the prevalence of phenotypic G6PDd was 1.4% (22/1609). For the first time in the Ethiopian population, the African variant (A-) was detected in 3.5% (7/199) of the limited set of genotyped samples, which were all phenotypically normal. Interestingly, all of these individuals had a variation at the rs2515904 locus. Strong geographical variation was observed for both phenotypic and genotypic G6PDd; three-quarters of the phenotypically G6PDd individuals were detected in Gambela.

CONCLUSION

A very low prevalence of G6PDd was detected in the present study populations. The presence of the A- variant alongside other G6PD mutants and the patchy distribution of G6PDd indicate that larger studies specifically designed to unravel the distribution of G6PDd at small geographical scale may be needed to tailor malaria elimination efforts in Ethiopia to the local context.

Primaquine ineligibility in anti-relapse therapy of Plasmodium vivax malaria: the problem of G6PD deficiency and cytochrome P-450 2D6 polymorphisms

The hypnozoite reservoir of Plasmodium vivax represents both the greatest obstacle and opportunity for ultimately eradicating this species. It is silent and cannot be diagnosed until it awakens and provokes a clinical attack with attendant morbidity, risk of mortality, and opportunities for onward transmission. The only licensed drug that kills hypnozoites is primaquine, which attacks the hypnozoite reservoir but imposes serious obstacles in doing so—at hypnozoitocidal doses, it invariably causes a threatening acute haemolytic anaemia in patients having an inborn deficiency in glucose-6-phosphate dehydrogenase (G6PD), affecting about 8% of people living in malaria endemic nations. That problem excludes a large number of people from safe and effective treatment of the latent stage of vivax malaria: the G6PD deficient, pregnant or lactating women, and young infants. These groups were estimated to comprise 14.3% of populations resident in the 95 countries with endemic vivax malaria. Another important obstacle regarding primaquine in the business of killing hypnozoites is its apparent metabolism to an active metabolite exclusively via cytochrome P-450 isozyme 2D6 (CYP2D6). Natural polymorphisms of this allele create genotypes expressing impaired enzymes that occur in over 20% of people living in Southeast Asia, where more than half of P. vivax infections occur globally. Taken together, the estimated frequencies of these primaquine ineligibles due to G6PD toxicity or impaired CYP2D6 activity composed over 35% of the populations at risk of vivax malaria. Much more detailed work is needed to refine these estimates, derive probabilities of error for them, and improve their ethnographic granularity in order to inform control and elimination strategy and tactics.

malERA: An updated research agenda for malaria elimination and eradication

Achieving a malaria-free world presents exciting scientific challenges as well as overwhelming health, equity, and economic benefits. WHO and countries are setting ambitious goals for reducing the burden and eliminating malaria through the "Global Technical Strategy" and 21 countries are aiming to eliminate malaria by 2020. The commitment to achieve these targets should be celebrated. However, the need for innovation to achieve these goals, sustain elimination, and free the world of malaria is greater than ever. Over 180 experts across multiple disciplines are engaged in the Malaria Eradication Research Agenda (malERA) Refresh process to address problems that need to be solved. The result is a research and development agenda to accelerate malaria elimination and, in the longer term, transform the malaria community's ability to eradicate it globally.

Synthesis, characterization, and cellular localization of a fluorescent probe of the antimalarial 8-aminoquinoline primaquine

Primaquine (PQ) is the only commercially available drug that clears dormant liver stages of malaria and blocks transmission to mosquito vectors. Although an old drug, much remains to be known about the mechanism(s) of action. Herein we develop a fluorescent tagged PQ to discover cellular localization in the human malaria parasite, Plasmodium falciparum. Successful synthesis and characterization of a primaquine-coumarin fluorescent probe (PQCP) demonstrated potency equivalent to the parent drug and the probe was not cytotoxic to HepG2 carcinoma cells. Cellular localization was found primarily in the cytosol of the asexual erythrocytic and gametocyte stages of parasite development.

Methods for the field evaluation of quantitative G6PD diagnostics: a review

Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk of severe haemolysis following the administration of 8-aminoquinoline compounds. Primaquine is the only widely available 8-aminoquinoline for the radical cure of Plasmodium vivax. Tafenoquine is under development with the potential to simplify treatment regimens, but point-of-care (PoC) tests will be needed to provide quantitative measurement of G6PD activity prior to its administration. There is currently a lack of appropriate G6PD PoC tests, but a number of new tests are in development and are likely to enter the market in the coming years. As these are implemented, they will need to be validated in field studies. This article outlines the technical details for the field evaluation of novel quantitative G6PD diagnostics such as sample handling, reference testing and statistical analysis. Field evaluation is based on the comparison of paired samples, including one sample tested by the new assay at point of care and one sample tested by the gold-standard reference method, UV spectrophotometry in an established laboratory. Samples can be collected as capillary or venous blood; the existing literature suggests that potential differences in capillary or venous blood are unlikely to affect results substantially. The collection and storage of samples is critical to ensure preservation of enzyme activity, it is recommended that samples are stored at 4 °C and testing occurs within 4 days of collection. Test results can be visually presented as scatter plot, Bland-Altman plot, and a histogram of the G6PD activity distribution of the study population. Calculating the adjusted male median allows categorizing results according to G6PD activity to calculate standard performance indicators and to perform receiver operating characteristic (ROC) analysis.

Barriers to routine G6PD testing prior to treatment with primaquine

BACKGROUND

Primaquine is essential for the radical cure of vivax malaria, however its broad application is hindered by the risk of drug-induced haemolysis in individuals with glucose-6-phosphate-dehydrogenase (G6PD) deficiency. Rapid diagnostic tests capable of diagnosing G6PD deficiency are now available, but these are not used widely.

METHODS

A series of qualitative interviews were conducted with policy makers and healthcare providers in four vivax-endemic countries. Routine G6PD testing is not part of current policy in Bangladesh, Cambodia or China, but it is in Malaysia. The interviews were analysed with regard to respondents perceptions of vivax malaria, -primaquine based treatment for malaria and the complexities of G6PD deficiency.

RESULTS

Three barriers to the roll-out of routine G6PD testing were identified in all sites: (a) a perceived low risk of drug-induced haemolysis; (b) the perception that vivax malaria was benign and accordingly treatment with primaquine was not regarded as a priority; and, (c) the additional costs of introducing routine testing. In Malaysia, respondents considered the current test and treat algorithm suitable and the need for an alternative approach was only considered relevant in highly mobile and hard to reach populations.

CONCLUSIONS

Greater efforts are needed to increase awareness of the benefits of the radical cure of Plasmodium vivax and this should be supported by economic analyses exploring the cost effectiveness of routine G6PD testing.

Unsupervised primaquine for the treatment of Plasmodium vivax malaria relapses in southern Papua: A hospital-based cohort study

BACKGROUND

Primaquine is the only licensed drug for eradicating Plasmodium vivax hypnozoites and, therefore, preventing relapses of vivax malaria. It is a vital component of global malaria elimination efforts. Primaquine is efficacious when supervised in clinical trials, but its effectiveness in real-world settings is unknown. We aimed to determine whether unsupervised primaquine was effective for preventing re-presentation to hospital with vivax malaria in southern Papua, Indonesia.

METHODS AND FINDINGS

Routinely-collected hospital surveillance data were used to undertake a pragmatic comparison of the risk of re-presentation to hospital with vivax malaria in patients prescribed dihydroartemisinin-piperaquine (DHP) combined with primaquine versus those patients prescribed DHP alone. The omission of primaquine was predominantly due to 3 stock outages. Individual clinical, pharmacy, and laboratory data were merged using individual hospital identification numbers and the date of presentation to hospital. Between April 2004 and December 2013, there were 86,797 documented episodes of vivax malaria, of which 62,492 (72.0%) were included in the analysis. The risk of re-presentation with vivax malaria within 1 year was 33.8% (95% confidence Interval [CI] 33.1%-34.5%) after initial monoinfection with P. vivax and 29.2% (95% CI 28.1%-30.4%) after mixed-species infection. The risk of re-presentation with P. vivax malaria was higher in children 1 to <5 years of age (49.6% [95% CI 48.4%-50.9%]) compared to patients 15 years of age or older (24.2% [95% CI 23.4-24.9%]); Adjusted Hazard Ratio (AHR) = 2.23 (95% CI 2.15-2.31), p < 0.001. Overall, the risk of re-presentation was 37.2% (95% CI 35.6%-38.8%) in patients who were prescribed no primaquine compared to 31.6% (95% CI 30.9%-32.3%) in those prescribed either a low (≥1.5 mg/kg and <5 mg/kg) or high (≥5 mg/kg) dose of primaquine (AHR = 0.90 [95% CI 0.86-0.95, p < 0.001]). Limiting the comparison to high dose versus no primaquine in the period during and 12 months before and after a large stock outage resulted in minimal change in the estimated clinical effectiveness of primaquine (AHR 0.91, 95% CI 0.85-0.97, p = 0.003). Our pragmatic study avoided the clinical influences associated with prospective study involvement but was subject to attrition bias caused by passive follow-up.

CONCLUSIONS

Unsupervised primaquine for vivax malaria, prescribed according to the current World Health Organization guidelines, was associated with a minimal reduction in the risk of clinical recurrence within 1 year in Papua, Indonesia. New strategies for the effective radical cure of vivax malaria are needed in resource-poor settings.