Characteristics of molecular markers associated with chloroquine resistance in Plasmodium vivax strains from vivax malaria cases in Yunnan Province, China.

BACKGROUND: Chloroquine (CQ) has been the preferred clinical treatment for vivax malaria in Yunnan Province since 1958, with over 300,000 patients. This study aimed to help make trend predictions regarding variations the in anti-malarial drug susceptibility of Plasmodium vivax distributed in Yunnan Province and effectively implement monitoring measures on the efficacy of anti-malarial drugs for vivax malaria. METHODS: Blood samples collected from patients with mono-P. vivax infections were employed in this study based on the principle of cluster sampling. The whole gene of P. vivax multidrug resistance 1 protein gene (pvmdr1) was amplified by nested-PCR techniques and the PCR amplification produce were sequenced by Sanger bidirectional sequencing. The mutant loci and haplotypes of coding DNA sequence (CDS) were identified by comparison with the reference sequence (NC_009915.1) of the P. vivax Sal I isolate. Parameters such as Ka/Ks ratio were calculated using MEGA 5.04 software. RESULTS: A total of 753 blood samples from patients infected with mono-P. vivax were collected, of which 624 blood samples yielded the full gene sequence (4392 bp) of the pvmdr1 gene, with 283, 140, 119, and 82 sequences from 2014, 2020, 2021 and 2022, respectively. A total of 52 single nucleotide polymorphic (SNP) loci were detected for the 624 CDSs, of which 92.3% (48/52), 34.6% (18/52), 42.3% (22/52), and 36.5% (19/52) SNPs were detected in 2014, 2020, 2021 and 2022, respectively. All of 624 CDSs were defined for a total of 105 mutant haplotypes, with CDSs of 2014, 2020, 2021, and 2022 containing 88, 15, 21, and 13 haplotypes, respectively. Of the 105 haplotypes, the threefold mutant haplotype (Hap_87) was the starting point for stepwise evolution, and the most drastic tenfold mutations were Hap_14 and Hap_78, and the fivefold, sixfold, sevenfold, and eightfold mutations. CONCLUSIONS: In the majority of vivax malaria cases in Yunnan Province, most of them were infected with strains carrying demonstrating highly mutated in pvmdr1 genes. However, the dominant mutation strains types varied from year to year, which warrants further exploration in order to confirm the correlation between with phenotypic changes in P. vivax strains and their susceptibility to anti-malarial drugs such as chloroquine.

Genetic polymorphisms in genes associated with drug resistance in Plasmodium vivax parasites from northeastern Myanmar.

BACKGROUND: Anti-malarial drug resistance is still a major threat to malaria elimination in the Great Mekong Sub-region. Plasmodium vivax parasites resistant to anti-malarial drugs are now found in Myanmar. Molecular surveillance on drug resistance genes in P. vivax parasites from northeastern Myanmar was aimed at estimating the underlying drug resistance in this region. METHODS: Blood samples from patients with vivax malaria were collected from Laiza city in northeastern Myanmar in 2020. Drug resistance genes including Pvcrt-o, Pvmdr1, Pvdhfr and Pvdhps were amplified and sequenced. Genetic polymorphisms and haplotypes were analysed to evaluate the prevalence of mutant alleles associated with drug resistance. RESULTS: A total of 149 blood samples from P. vivax patients were collected. The prevalence of Pvmdr1 mutations at codons 958 and 1076 was 100.0% and 52.0%, respectively, whereas no single nucleotide polymorphism was present at codon 976. The proportions of single and double mutant types were 48.0% and 52.0%, respectively. A K10 "AAG" insertion in the Pvcrt-o gene was not detected. Mutations in Pvdhfr at codons 57, 58, 61, 99 and 117 were detected in 29.9%, 54.3%, 27.6%, 44.9% and 55.1% of the samples, respectively. Wild type was predominant (46.3%), followed by quadruple and double mutant haplotypes. Of three types of tandem repeat variations of Pvdhfr, Type B, with three copies of GGDN repeats, was the most common. Pvdhps mutations were only detected at codons 383 and 553 and the wild type Pvdhps was dominant (78.0%). Eleven haplotypes were identified when combining the mutations of Pvdhfr and Pvdhps, among which the predominant one was the wild type (33.9%), followed by double mutant alleles S58R/S117N /WT (24.6%). CONCLUSIONS: This study demonstrated resistant P. vivax phenotypes exists in northeastern Myanmar. Continued surveillance of drug resistance markers is needed to update treatment guidelines in this region.

Antimalarials for children with Plasmodium vivax infection: Current status, challenges, and research priorities.

The aim of this narrative review is to summarise efficacy and pharmacokinetic data for Plasmodium vivax in children. The burden of P. vivax malaria in children continues to remain a significant public health issue, and the need for improved treatment regimens for this vulnerable population is critical. Relapse after re-activation of dormant liver-stage hypnozoites poses additional challenges for treatment, elimination, and control strategies for P. vivax. Whilst it is recognised that paediatric pharmacology may be significantly influenced by anatomical and physiological changes of childhood, dosing regimens often continue to be extrapolated from adult data, highlighting the need for antimalarial dosing in children to be evaluated in early phase clinical trials. This will ensure that globally recommended treatment regimens do not result in suboptimal dosing in children. Furthermore, the development of affordable paediatric formulations to enhance treatment acceptability and widespread G6PD testing to facilitate use of anti-hypnozoite treatment such as primaquine and tafenoquine, should be further prioritised. As the world prepares for malaria elimination, a renewed focus on P. vivax malaria provides an ideal opportunity to harness momentum and ensure that all populations, including children have access to safe, efficacious, and correctly dosed antimalarial therapies.

Haematological response in experimental human Plasmodium falciparum and Plasmodium vivax malaria.

BACKGROUND: Malaria-associated anaemia, arising from symptomatic, asymptomatic and submicroscopic infections, is a significant cause of morbidity worldwide. Induced blood stage malaria volunteer infection studies (IBSM-VIS) provide a unique opportunity to evaluate the haematological response to early Plasmodium falciparum and Plasmodium vivax infection. METHODS: This study was an analysis of the haemoglobin, red cell counts, and parasitaemia data from 315 participants enrolled in IBSM-VIS between 2012 and 2019, including 269 participants inoculated with the 3D7 strain of P. falciparum (Pf3D7), 15 with an artemisinin-resistant P. falciparum strain (PfK13) and 46 with P. vivax. Factors associated with the fractional fall in haemoglobin (Hb-FF) were evaluated, and the malaria-attributable erythrocyte loss after accounting for phlebotomy-related losses was estimated. The relative contribution of parasitized erythrocytes to the malaria-attributable erythrocyte loss was also estimated. RESULTS: The median peak parasitaemia prior to treatment was 10,277 parasites/ml (IQR 3566-27,815), 71,427 parasites/ml [IQR 33,236-180,213], and 34,840 parasites/ml (IQR 13,302-77,064) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. The median Hb-FF was 10.3% (IQR 7.8-13.3), 14.8% (IQR 11.8-15.9) and 11.7% (IQR 8.9-14.5) in those inoculated with Pf3D7, PfK13 and P. vivax, respectively, with the haemoglobin nadir occurring a median 12 (IQR 5-21), 15 (IQR 7-22), and 8 (IQR 7-15) days following inoculation. In participants inoculated with P. falciparum, recrudescence was associated with a greater Hb-FF, while in those with P. vivax, the Hb-FF was associated with a higher pre-treatment parasitaemia and later day of anti-malarial treatment. After accounting for phlebotomy-related blood losses, the estimated Hb-FF was 4.1% (IQR 3.1-5.3), 7.2% (IQR 5.8-7.8), and 4.9% (IQR 3.7-6.1) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. Parasitized erythrocytes were estimated to account for 0.015% (IQR 0.006-0.06), 0.128% (IQR 0.068-0.616) and 0.022% (IQR 0.008-0.082) of the malaria-attributable erythrocyte loss in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. CONCLUSION: Early experimental P. falciparum and P. vivax infection resulted in a small but significant fall in haemoglobin despite parasitaemia only just at the level of microscopic detection. Loss of parasitized erythrocytes accounted for < 0.2% of the total malaria-attributable haemoglobin loss.

How radical is radical cure? Site-specific biases in clinical trials underestimate the effect of radical cure on Plasmodium vivax hypnozoites.

BACKGROUND: Plasmodium vivax blood-stage relapses originating from re-activating hypnozoites are a major barrier for control and elimination of this disease. Radical cure is a form of therapy capable of addressing this problem. Recent clinical trials of radical cure have yielded efficacy estimates ranging from 65 to 94%, with substantial variation across trial sites. METHODS: An analysis of simulated trial data using a transmission model was performed to demonstrate that variation in efficacy estimates across trial sites can arise from differences in the conditions under which trials are conducted. RESULTS: The analysis revealed that differences in transmission intensity, heterogeneous exposure and relapse rate can yield efficacy estimates ranging as widely as 12-78%, despite simulating trial data under the uniform assumption that treatment had a 75% chance of clearing hypnozoites. A longer duration of prophylaxis leads to a greater measured efficacy, particularly at higher transmission intensities, making the comparison between the protection of different radical cure treatment regimens against relapse more challenging. Simulations show that vector control and parasite genotyping offer two potential means to yield more standardized efficacy estimates that better reflect prevention of relapse. CONCLUSIONS: Site-specific biases are likely to contribute to variation in efficacy estimates both within and across clinical trials. Future clinical trials can reduce site-specific biases by conducting trials in low-transmission settings where re-infections from mosquito bite are less common, by preventing re-infections using vector control measures, or by identifying and excluding likely re-infections that occur during follow-up, by using parasite genotyping methods.

In vivo efficacy of anti-malarial drugs against clinical Plasmodium vivax malaria in Ethiopia: a systematic review and meta-analysis.

BACKGROUND: Ethiopia is one of the few countries in Africa where Plasmodium vivax commonly co-exists with Plasmodium falciparum, and which accounts for ~ 40% of the total number of malaria infections in the country. Regardless of the growing evidence over many decades of decreasing sensitivity of this parasite to different anti-malarial drugs, there has been no comprehensive attempt made to systematically review and meta-analyse the efficacy of different anti-malarial drugs against P. vivax in the country. However, outlining the efficacy of available anti-malarial drugs against this parasite is essential to guide recommendations for the optimal therapeutic strategy to use in clinical practice. The aim of this study was to synthesize evidence on the efficacy of anti-malarial drugs against clinical P. vivax malaria in Ethiopia. METHODS: All potentially relevant, peer-reviewed articles accessible in PubMed, Scopus, Web of Science, and Clinical Trial.gov electronic databases were retrieved using a search strategy combining keywords and related database-specific subject terms. Randomized controlled trials (RCTs) and non-randomized trials aiming to investigate the efficacy of anti-malarial drugs against P. vivax were included in the review. Data were analysed using Review Manager Software. Cochrane Q (χ2) and the I2 tests were used to assess heterogeneity. The funnel plot and Egger's test were used to examine risk of publication bias. RESULTS: Out of 1294 identified citations, 14 articles that presented data on 29 treatment options were included in the analysis. These studies enrolled 2144 clinical vivax malaria patients. The pooled estimate of in vivo efficacy of anti-malarial drugs against vivax malaria in Ethiopia was 97.91% (95% CI: 97.29-98.52%), with significant heterogeneity (I2 = 86%, p < 0.0001) and publication bias (Egger's test = -12.86, p < 0.001). Different anti-malarial drugs showed varied efficacies against vivax malaria. The duration of follow-up significantly affected the calculated efficacy of any given anti-malarial drug, with longer duration of the follow-up (42 days) associated with significantly lower efficacy than efficacy reported on day 28. Also, pooled PCR-corrected efficacy and efficacy estimated from altitudinally lower transmission settings were significantly higher than PCR-uncorrected efficacy that estimated for moderate transmission settings, respectively. CONCLUSION: The overall efficacy of anti-malarial drugs evaluated for the treatment of vivax malaria in Ethiopia was generally high, although there was wide-ranging degree of efficacy, which was affected by the treatment options, duration of follow-up, transmission intensity, and the confirmation procedures for recurrent parasitaemia. Regardless of evidence of sporadic efficacy reduction reported in the country, chloroquine (CQ), the first-line regimen in Ethiopia, remained highly efficacious, supporting its continuous utilization for confirmed P. vivax mono-infections. The addition of primaquine (PQ) to CQ is recommended, as this is the only approved way to provide radical cure, and thus ensure sustained efficacy and longer protection against P. vivax. Continuous surveillance of the efficacy of anti-malarial drugs and clinical trials to allow robust conclusions remains necessary to proactively act against possible emergence and spread of drug-resistant P. vivax in Ethiopia.

Probing the distinct chemosensitivity of Plasmodium vivax liver stage parasites and demonstration of 8-aminoquinoline radical cure activity in vitro.

Improved control of Plasmodium vivax malaria can be achieved with the discovery of new antimalarials with radical cure efficacy, including prevention of relapse caused by hypnozoites residing in the liver of patients. We screened several compound libraries against P. vivax liver stages, including 1565 compounds against mature hypnozoites, resulting in one drug-like and several probe-like hits useful for investigating hypnozoite biology. Primaquine and tafenoquine, administered in combination with chloroquine, are currently the only FDA-approved antimalarials for radical cure, yet their activity against mature P. vivax hypnozoites has not yet been demonstrated in vitro. By developing an extended assay, we show both drugs are individually hypnozonticidal and made more potent when partnered with chloroquine, similar to clinically relevant combinations. Post-hoc analyses of screening data revealed excellent performance of ionophore controls and the high quality of single point assays, demonstrating a platform able to support screening of greater compound numbers. A comparison of P. vivax liver stage activity data with that of the P. cynomolgi blood, P. falciparum blood, and P. berghei liver stages reveals overlap in schizonticidal but not hypnozonticidal activity, indicating that the delivery of new radical curative agents killing P. vivax hypnozoites requires an independent and focused drug development test cascade.

The acceptability of targeted mass treatment with primaquine for local elimination of vivax malaria in a northern Myanmar township: a mixed-methods study.

BACKGROUND: Radical cure of the Plasmodium vivax latent liver stage is required to effectively manage vivax malaria. Targeted mass treatment with primaquine may be an effective mechanism for reducing reservoirs of the disease. Since community engagement and high coverage are essential for mass treatment programs, this study aimed to determine the acceptability of mass primaquine treatment in a targeted community in a northern Myanmar township. METHODS: A cross-sectional mixed-methods study was deployed among household leaders in July 2019. Face-to-face interviews using structured questionnaires and standardized qualitative guidelines were conducted to gather information. Descriptive and inferential statistics, including logistic regression models, were applied. RESULTS: Among 609 study respondents, > 90% agreed to participate in an upcoming targeted mass primaquine treatment (TPT) program. Factors contributing to higher odds of acceptability of the program were older age [adjusted odds ratios (aOR): 2.38, 95% confidence intervals (CI) 1.08-8.96], secondary education level (aOR: 3.99, 95% CI 1.12-20.01), having good knowledge of malaria (aOR: 2.12, 95% CI 1.04-4.76), experiencing malaria within the family (aOR: 1.92, 95% CI 1.14-5.13), and believing eliminating malaria from the village is possible (aOR: 2.83, 95% CI 1.07-4.07). Furthermore, 50 community respondents, 6 midwives, and 4 public health staff (grade II) participated in the qualitative component of the study. Many thought that TPT seemed feasible and stressed that high coverage of underserved groups and health education are needed before commencing the activity. CONCLUSIONS: Most respondents agreed to participate in the proposed mass treatment campaign. Older people with secondary education level and those who had experienced malaria within their families were most likely to report willingness to participate. These same individuals may be important in the community engagement process to increase community acceptance of the program.

Identification of first-in-class plasmodium OTU inhibitors with potent anti-malarial activity.

OTU proteases antagonize the cellular defense in the host cells and involve in pathogenesis. Intriguingly, P. falciparum, P. vivax, and P. yoelii have an uncharacterized and highly conserved viral OTU-like proteins. However, their structure, function or inhibitors have not been previously reported. To this end, we have performed structural modeling, small molecule screening, deconjugation assays to characterize and develop first-in-class inhibitors of P. falciparum, P. vivax, and P. yoelii OTU-like proteins. These Plasmodium OTU-like proteins have highly conserved residues in the catalytic and inhibition pockets similar to viral OTU proteins. Plasmodium OTU proteins demonstrated Ubiquitin and ISG15 deconjugation activities as evident by intracellular ubiquitinated protein content analyzed by western blot and flow cytometry. We screened a library of small molecules to determine plasmodium OTU inhibitors with potent anti-malarial activity. Enrichment and correlation studies identified structurally similar molecules. We have identified two small molecules that inhibit P. falciparum, P. vivax, and P. yoelii OTU proteins (IC50 values as low as 30 nM) with potent anti-malarial activity (IC50 of 4.1-6.5 µM). We also established enzyme kinetics, druglikeness, ADME, and QSAR model. MD simulations allowed us to resolve how inhibitors interacted with plasmodium OTU proteins. These findings suggest that targeting malarial OTU-like proteases is a plausible strategy to develop new anti-malarial therapies.

Development of weight and age-based dosing of daily primaquine for radical cure of vivax malaria.

BACKGROUND: In many endemic areas, Plasmodium vivax malaria is predominantly a disease of young adults and children. International recommendations for radical cure recommend fixed target doses of 0.25 or 0.5 mg/kg/day of primaquine for 14 days in glucose-6-phosphate dehydrogenase normal patients of all ages. However, for many anti-malarial drugs, including primaquine, there is evidence that children have lower exposures than adults for the same weight-adjusted dose. The aim of the study was to develop 14-day weight-based and age-based primaquine regimens against high-frequency relapsing tropical P. vivax. METHODS: The recommended adult target dose of 0.5 mg/kg/day (30 mg in a 60 kg patient) is highly efficacious against tropical P. vivax and was assumed to produce optimal drug exposure. Primaquine doses were calculated using allometric scaling to derive a weight-based primaquine regimen over a weight range from 5 to 100 kg. Growth curves were constructed from an anthropometric database of 53,467 individuals from the Greater Mekong Subregion (GMS) to define weight-for-age relationships. The median age associated with each weight was used to derive an age-based dosing regimen from the weight-based regimen. RESULTS: The proposed weight-based regimen has 5 dosing bands: (i) 5-7 kg, 5 mg, resulting in 0.71-1.0 mg/kg/day; (ii) 8-16 kg, 7.5 mg, 0.47-0.94 mg/kg/day; (iii) 17-40 kg, 15 mg, 0.38-0.88 mg/kg/day; (iv) 41-80 kg, 30 mg, 0.37-0.73 mg/kg/day; and (v) 81-100 kg, 45 mg, 0.45-0.56 mg/kg/day. The corresponding age-based regimen had 4 dosing bands: 6-11 months, 5 mg, 0.43-1.0 mg/kg/day; (ii) 1-5 years, 7.5 mg, 0.35-1.25 mg/kg/day; (iii) 6-14 years, 15 mg, 0.30-1.36 mg/kg/day; and (iv) ≥ 15 years, 30 mg, 0.35-1.07 mg/kg/day. CONCLUSION: The proposed weight-based regimen showed less variability around the primaquine dose within each dosing band compared to the age-based regimen and is preferred. Increased dose accuracy could be achieved by additional dosing bands for both regimens. The age-based regimen might not be applicable to regions outside the GMS, which must be based on local anthropometric data. Pharmacokinetic data in small children are needed urgently to inform the proposed regimens.

Increased primaquine total dose prevents Plasmodium vivax relapses in patients with impaired CYP2D6 activity: report of three cases.

BACKGROUND: The relapsing nature of Plasmodium vivax infection is a major barrier to its control and elimination. Factors such as adequate dosing, adherence, drug quality, and pharmacogenetics can impact the effectiveness of radical cure of P. vivax and need to be adequately evaluated. CYP2D6 pathway mediates the activation of primaquine (primaquine) into an active metabolite(s) in hepatocytes, and impaired activity has been linked to a higher risk of relapse. CASES PRESENTATION: Three patients diagnosed with P. vivax malaria presented repeated relapses after being initially treated with chloroquine (25 mg/kg) and primaquine (3.5 mg/kg in 14 days) at a non-endemic travel clinic. Recurring episodes were subsequently treated with a higher dose of primaquine (7 mg/kg in 14 days), which prevented further relapses in two patients. However, one patient still presented two episodes after a higher primaquine dose and was prescribed 300 mg of chloroquine weekly to prevent further episodes. Impaired CYP2D6 function was observed in all of them. CONCLUSION: Lack of response to primaquine was associated with impaired CYP2D6 activity in three patients presenting multiple relapses followed in a non-endemic setting. Higher primaquine dosage was safe and effectively prevented relapses in two patients and should be further investigated as an option in Latin America. It is crucial to investigate the factors associated with unsuccessful radical cures and alternative therapeutic options.

Impact of CYP2D6 Genetic Variation on Radical Cure of Plasmodium vivax Malaria.

Plasmodium vivax (P. vivax) is the most widespread human malaria parasite, with 2.5 billion people at risk of infection worldwide. P. vivax forms liver hypnozoites, which trigger further symptomatic episodes (relapses) weeks or months after the initial episode. Radical cure of vivax malaria requires hypnozoitocide therapy to prevent relapses. The two US Food and Drug Administration (FDA)-approved hypnozoiticides for human use, primaquine, and tafenoquine, are pro-drugs, that require in vivo conversion into metabolites with redox activity. This mini-review focuses on the association between CYP2D6-mediated hydroxylation and hypnozoitocide efficacy of primaquine and tafenoquine. Studies in murine models show that the antimalarial activity of primaquine and tafenoquine is abolished by CYP2D knock-out and partially restored by knock-in of humanized CYP2D6. Human studies explored the impact of CYP2D6 genetic variation and genotype-inferred CYP2D6 phenotype on anti-relapse efficacy. Most, but not all, studies with primaquine report higher rates of relapse in patients with decreased CYP2D6 activity (activity scores (AS) ≤ 1) compared to normal activity (AS ≥ 1.5). Potential factors for discordance among studies include risk of reinfection in endemic areas, adherence to primaquine-treatment, assignment of CYP2D6 phenotypes based on CYP2D6 polymorphism and choice of AS values for dichotomizing the study cohorts. Tafenoquine anti-relapse efficacy did not differ between patients with AS < 1 vs. AS ≥ 1.5 in 2 studies. Absence/small number of poor CYP2D6 metabolizers in AS ≤ 1 groups, combined with lesser dependence of tafenoquine on CYP2D6-mediated conversion into active redox metabolites may account for this result. Additional tafenoquine studies with larger representation of poor CYP2D6 metabolizers are warranted.

Distinctive genetic structure and selection patterns in Plasmodium vivax from South Asia and East Africa.

Despite the high burden of Plasmodium vivax malaria in South Asian countries, the genetic diversity of circulating parasite populations is not well described. Determinants of antimalarial drug susceptibility for P. vivax in the region have not been characterised. Our genomic analysis of global P. vivax (n = 558) establishes South Asian isolates (n = 92) as a distinct subpopulation, which shares ancestry with some East African and South East Asian parasites. Signals of positive selection are linked to drug resistance-associated loci including pvkelch10, pvmrp1, pvdhfr and pvdhps, and two loci linked to P. vivax invasion of reticulocytes, pvrbp1a and pvrbp1b. Significant identity-by-descent was found in extended chromosome regions common to P. vivax from India and Ethiopia, including the pvdbp gene associated with Duffy blood group binding. Our investigation provides new understanding of global P. vivax population structure and genomic diversity, and genetic evidence of recent directional selection in this important human pathogen.

The high risk of malarial recurrence in patients with Plasmodium-mixed infection after treatment with antimalarial drugs: a systematic review and meta-analysis.

BACKGROUND: Malaria mixed infections are often unrecognized by microscopists in the hospitals, and a delay or failure to treat Plasmodium-mixed infection may lead to aggravated morbidity and increased mortality. The present study aimed to quantify the pooled proportion and risk of malarial recurrences after the treatment of Plasmodium-mixed infection. The results of the study may provide benefits in the management of Plasmodium-mixed infection in co-endemic regions. METHODS: This systematic review and meta-analysis searched the international Prospective Register of Systematic Reviews (PROSPERO; ID = CRD42020199709), MEDLINE, Web of Science, and Scopus for potentially relevant studies in any language published between January 1, 1936, and July 20, 2020, assessing drug efficacy in patients with Plasmodium-mixed infection. The primary outcome was the pooled prevalence of Plasmodium parasitemia after initiating antimalarial treatment for Plasmodium-mixed infection. The secondary outcome was the pooled risk ratio (RR) of malarial recurrence in Plasmodium-mixed infection compared with those in Plasmodium falciparum and Plasmodium vivax mono-infection. The pooled analyses were calculated by random-effects meta-analysis. After the initial treatment in different days of recurrences (≤ 28 days or > 28 days), the risk of Plasmodium parasitemia was compared in subgroup analysis. RESULTS: Out of 5217 screened studies, 11 were included in the meta-analysis, including 4390 patients from six countries. The pooled prevalence of all recurrences of Plasmodium-mixed parasitemia was 30% (95% confidence interval (CI) 16-43; I2: 99.2%; 11 studies). The RR of malarial recurrence within 28 days after the initial treatment (clinical treatment failure) of Plasmodium-mixed parasitemia compared with the treatment of P. falciparum was 1.22 (p: 0.029; 95% CI 1.02-1.47; Cochran Q: 0.93; I2: 0%; six studies), while there was no significant difference in the risk of recurrence 28 days after initial treatment compared with the treatment of P. falciparum (p: 0.696, RR: 1.14; 95% CI 0.59-2.18; Cochran Q < 0.05; I2: 98.2%; four studies). The subgroup analysis of antimalarial drugs showed that significant malarial recurrence within 28 days was observed in patients treated with artemisinin-based combination therapies (ACTs) with no significant heterogeneity (p: 0.028, RR: 1.31; 95% CI 1.03-1.66; Cochran Q: 0.834; I2: 0%). CONCLUSIONS: The present findings showed a high prevalence of malarial recurrence after the initial treatment of Plasmodium-mixed infection. Moreover, significant malaria recurrence of mixed infection occurred within 28 days after treatment with ACTs.

Evaluation of pharmacokinetics of single-dose primaquine in undernourished versus normally nourished children diagnosed with Plasmodium vivax malaria in Mumbai.

BACKGROUND: The pharmacokinetics of primaquine [PQ] have been the subject of studies in both adults and healthy participants. However, there is no study on its pharmacokinetics in a setting of undernourishment. In India, there is evidence to show considerable malnourishment in children that in turn can affect drug pharmacokinetics. Given that the country is moving towards malaria elimination, the present study was planned with the objective of comparing pharmacokinetics of the drug in undernourished children relative to normally nourished children. MATERIALS AND METHODS: After Institutional Ethics Committee approval, children of either gender between the ages of 5 and 12 years and smear-positive for Plasmodium vivax malaria were included. Nourishment status was determined using the Indian Academy of Pediatrics classification of protein energy malnutrition based on Khadilkar's growth charts. Twelve children each were enrolled in the two groups. PQ was given in the dose of 0.3 mg/kg/d and blood collections were made at 0, 1, 2, 3, 4, 6, 8 and 24 hours post-dosing. Levels were estimated by high-performance liquid chromatography. Chloroquine in the dose of 25 mg/kg was given over three days along with supportive care. RESULTS: Of the 24 children, there were 17 boys and 7 girls. There was a statistically significant difference in the body weight between the undernourished and the normally nourished children [21.5 ± 5.52 vs. 28.8 ± 8.84, P < 0.05]. PQ levels showed wide inter-individual variation in both groups. No significant difference was seen in any pharmacokinetic parameter between the two groups. DISCUSSION: This study adds to the limited body of evidence on the pharmacokinetics of PQ in children with malaria and indicates that the dosing of primaquine could potentially be independent of the nourishment status.

Estimated impact of tafenoquine for Plasmodium vivax control and elimination in Brazil: A modelling study.

BACKGROUND: Despite recent intensification of control measures, Plasmodium vivax poses a major challenge for malaria elimination efforts. Liver-stage hypnozoite parasites that cause relapsing infections can be cleared with primaquine; however, poor treatment adherence undermines drug effectiveness. Tafenoquine, a new single-dose treatment, offers an alternative option for preventing relapses and reducing transmission. In 2018, over 237,000 cases of malaria were reported to the Brazilian health system, of which 91.5% were due to P. vivax. METHODS AND FINDINGS: We evaluated the impact of introducing tafenoquine into case management practices on population-level transmission dynamics using a mathematical model of P. vivax transmission. The model was calibrated to reflect the transmission dynamics of P. vivax endemic settings in Brazil in 2018, informed by nationwide malaria case reporting data. Parameters for treatment pathways with chloroquine, primaquine, and tafenoquine with glucose-6-phosphate dehydrogenase deficiency (G6PDd) testing were informed by clinical trial data and the literature. We assumed 71.3% efficacy for primaquine and tafenoquine, a 66.7% adherence rate to the 7-day primaquine regimen, a mean 5.5% G6PDd prevalence, and 8.1% low metaboliser prevalence. The introduction of tafenoquine is predicted to improve effective hypnozoite clearance among P. vivax cases and reduce population-level transmission over time, with heterogeneous levels of impact across different transmission settings. According to the model, while achieving elimination in only few settings in Brazil, tafenoquine rollout in 2021 is estimated to improve the mean effective radical cure rate from 42% (95% uncertainty interval [UI] 41%-44%) to 62% (95% UI 54%-68%) among clinical cases, leading to a predicted 38% (95% UI 7%-99%) reduction in transmission and over 214,000 cumulative averted cases between 2021 and 2025. Higher impact is predicted in settings with low transmission, low pre-existing primaquine adherence, and a high proportion of cases in working-aged males. High-transmission settings with a high proportion of cases in children would benefit from a safe high-efficacy tafenoquine dose for children. Our methodological limitations include not accounting for the role of imported cases from outside the transmission setting, relying on reported clinical cases as a measurement of community-level transmission, and implementing treatment efficacy as a binary condition. CONCLUSIONS: In our modelling study, we predicted that, provided there is concurrent rollout of G6PDd diagnostics, tafenoquine has the potential to reduce P. vivax transmission by improving effective radical cure through increased adherence and increased protection from new infections. While tafenoquine alone may not be sufficient for P. vivax elimination, its introduction will improve case management, prevent a substantial number of cases, and bring countries closer to achieving malaria elimination goals.

The prevention and treatment of Plasmodium vivax malaria.

Cindy S Chu and co-authors review options for diagnosis, safe and radical cure, and relapse prevention of Plasmodium Vivax.

Anti-malarial drug effects on parasite dynamics in vivax malaria.

Relapses of Plasmodium vivax malaria are prevented by 8-aminoquinolines. If hypnozoites survive, then the subsequent blood stage infections in early relapses (< 2 months) are suppressed by the slowly eliminated anti-malarial drugs used to treat the blood stage infection (chloroquine, artemisinin combination treatments), but they are not usually eliminated. The 8-aminoquinolines have significant blood stage activity which contributes to therapeutic responses. The latent interval from primary infection to early relapse depends on the number of activatable hypnozoites, the dose of anti-malarial, its pharmacokinetic properties, the level of resistance (minimum inhibitory concentration) and immunity. The dose-response relationship for radical curative efficacy of primaquine and tafenoquine is steep over the total dose range from 1.5 to 5 mg base/kg which may explain the poor efficacy of tafenoquine at the currently recommended dose.

Tafenoquina para tratamento de pacientes com malária por Plasmodium vivax / Tafenoquine for the treatment of patients with Plasmodium vivax malaria

CONITEC CONTEXTO: A malária é uma doença infecciosa parasitária aguda causada por protozoários do gênero Plasmodium, transmitidos ao homem pela picada da fêmea do mosquito Anopheles darlingi. O período de incubação da condição varia de 7 a 14 dias e a crise aguda é caracterizada por episódios de calafrios, febre e sudorese, geralmente acompanhados de cefaleia, mialgia, náuseas e vômitos. De acordo com o Relatório Mundial da Malária, 228 milhões de casos foram reportados, no ano de 2019, representando um grave problema de saúde pública para o mundo. No Brasil, a área endêmica compreende a região amazônica brasileira. Em 2019, foram notificadas no território nacional 157.454 casos de malária, uma redução de 19,1% em relação a 2018, quando foram registrados 194.572 casos da doença. Já a deficiência de glicose-6-fosfato desidrogenase (G6PD) é uma anomalia hereditária ligada ao cromossomo X, que acomete majoritariamente homens (hemizigóticos). Estima-se que afeta aproximadamente 400 milhões de pessoas em todo o mundo e a prevalência varia de 5% a 25% em áreas endêmicas, como África, Oriente Médio e Ásia. Essa enzima desempenha papel importante na sobrevivência dos eritrócitos: está envolvida na via da pentose fosfato (PPP) e fornece NADPH (nicotina adenina dinucleótido fosfato reduzido) e GSH (glutationa reduzida). GSH pode reagir com peróxido de hidrogênio (H2O2) e reduzir para H2O. Isso ajuda a proteger os eritrócitos de espécies reativas de oxigênio, que resultam em estresse oxidativo e consequentemente, hemólise. A principal preocupação de segurança com relação à tafenoquina é o alto risco de anemia hemolítica aguda (AHA) em pacientes com deficiência de G6PD (atividade da enzima < 30% do normal), que pode resultar em óbitos em indivíduos com menos de 10% da atividade enzimática normal. TECNOLOGIA: Tafenoquina (Kozenis®). PERGUNTAS DE PESQUISA: A tafenoquina 300 mg em dose única é eficaz e segura para cura radical (prevenção de recidiva) da malária por Plasmodium vivax? O teste quantitativo da atividade da enzima glicose-6-fosfato desidrogenase (G6PD) é sensível e específico na detecção da atividade da G6PD em pacientes com diagnóstico confirmado de malária por Plasmodium vivax? EVIDÊNCIAS CIENTÍFICAS: Foram incluídos dois estudos no corpo da evidência, duas revisões sistemáticas com meta-análise, de qualidade da evidência moderada a grave. No que tange às evidências que respondem à primeira pergunta de pesquisa, referente ao medicamento, para os desfechos avaliados nos grupos tafenoquina versus nenhum tratamento antihipinozoíto: tafenoquina reduziu a recidiva em comparação com não tratamento (RR 0,32, IC 95% 0,12 a 0,88); não houve mortes durante acompanhamento; não foram encontradas diferenças significativas entre tafenoquina e nenhum tratamento anti-hipnozoíto (RR 1,34, IC 95% 0,63 a 2,84) e não foram observadas diferença entre os grupos avaliados em relação ao número ou tipo de eventos adversos relatados com exceção de dor de cabeça. O grupo tratado com tafenoquina mais cloroquina demonstrou pouca ou nenhuma diferença na ocorrência geral de eventos adversos em comparação com cloroquina isolada (RR 0,96, IC 95% 0,81 a 1,13). Para o desfechos avaliados que compararam tafenoquina versus primaquina: não foi identificada diferença estatisticamente significativa na prevenção de recaídas entre os pacientes dos tratamentos (RR 1,04, IC 95% 0,8 a 1,34), assim, tafenoquina é possivelmente tão eficaz quanto primaquina; também não foi identificada diferença estatisticamente significativa entre os tratamentos em pacientes sem deficiência de G6PD; entre os EA mais comuns estão a queda no nível de hemoglobina e prolongamento QT assintomático (RR 1,41, IC 95% 0,70 a 2,83); para avaliação de qualquer evento adverso tafenoquina não apresentou diferença em todos os tipos de EA em comparação com primaquina, incluindo anemia e queda do nível de hemoglobina (RR 1,01, IC 95% 0,89 a 1,14). Para avaliação da acurácia do teste quantitativo de G6PD, a sensibilidade combinada do teste foi de 0,96 (IC 95% 0,90 a 0,99) e a especificidade combinada foi de 0,95 (IC 95% 0,92 a 0,96), sendo que o desempenho combinado não variou significativamente, independentemente do tipo de amostra sanguínea. CONSIDERAÇÕES: Com nível de certeza moderado, a dose única de tafenoquina 300 mg não teve diferença significativa quando comparado com o tratamento de primaquina 15 mg/dia por 14 dias. Também não foi identificada diferença significativa em relação aos eventos adversos graves e gerais entre os outros grupos comparadores, com uma certeza de evidência moderada a alta. O perfil de segurança dos dois tratamentos foi semelhante e ambos causaram declínios no nível de hemoglobina, no entanto de fácil manejo, entre os pacientes com atividade normal da enzima G6PD. Também com nível de certeza da evidência moderado, o teste quantitativo de atividade da enzima G6PD performou valores de sensibilidade e especificidade maiores que 95%. As razões de verossimilhança positiva e negativa sugerem que o teste é adequado para confirmação da atividade da enzima, bem como auxilia na exclusão de casos em que há deficiência de G6PD em um limiar de 30% de atividade enzimática. RECOMENDAÇÃO PRELIMINAR DA CONITEC: Diante do exposto, a Conitec, em sua 94ª reunião ordinária, realizada no dia 04 de fevereiro de 2021, deliberou que a matéria fosse disponibilizada em consulta pública com recomendação preliminar favorável à incorporação, no SUS, da tafenoquina para o tratamento, ou cura radical, de malária causada pelo Plasmodium vivax em pacientes com 16 anos de idade ou mais e atividade enzimática maior que 70% de glicose-6-fosfato desidrogenase (G6PD), confirmada por meio de teste rápido validado. Os membros do plenário concordaram que, embora a evidência de eficácia disponível em literatura tenha sido avaliada de boa qualidade, esta apresenta dados modestos, se considerado o principal desfecho que avalia o desempenho da tafenoquina versus primaquina. Para tanto, faz-se necessária a obtenção de dados de efetividade que serão coletados após condução do estudo observacional TRuST, focalizado nas cidades de Manaus e Porto Velho. A matéria foi disponibilizada em consulta pública. CONSULTA PÚBLICA: A Consulta Pública nº 04/2021 foi realizada entre os dias 08/02/2021 a 1º/03/2021. Foram recebidas 87 contribuições, sendo 32 pelo formulário para contribuições técnico-científicas e 55 pelo formulário para contribuições sobre experiência ou opinião de pacientes, familiares, amigos ou cuidadores de pacientes, profissionais de saúde ou pessoas interessadas no tema. As contribuições recebidas foram majoritariamente a favor da recomendação preliminar da Conitec, de incorporação de uso das tecnologias no SUS. RECOMENDAÇÃO FINAL: Os membros do plenário presentes na 95ª reunião ordinária da Conitec, no dia 03 de março de 2021, deliberaram, por unanimidade, recomendar a incorporação da tafenoquina para o tratamento, ou cura radical, de malária causada pelo Plasmodium vivax em pacientes com 16 anos de idade ou mais e atividade enzimática de glicose-6- fosfato desidrogenase (G6PD) maior que 70%, confirmada por meio de teste rápido quantitativo de G6PD. A recomendação para incorporação do medicamento está condicionada à apresentação de dados de mundo real ao final do estudo de 12 meses. Cabe informar que não foram adicionadas na consulta pública referências que alterassem a análise da evidência apresentada no relatório preliminar. Foi assinado o Registro de Deliberação nº 591/2021. DECISÃO: Incorporar a tafenoquina para tratamento de pacientes com malária por Plasmodium vivax condicionada à apresentação de dados de mundo real ao final do estudo, do Sistema Único de Saúde - SUS, conforme Portaria nº 07, publicada no Diário Oficial da União nº 48, seção 1, página 170, em 12 de março de 2021.