Plasmodium Falciparum Clearance Research Articles

Genetic Evaluation of Interlukin-22 Single Nucleotide Polymorphism (rs1179251) with Plasmodium falciparum Clearance among Children Less Than 10 Years in the North Region of Cameroon

IL-22 is a pro and anti-inflammatory cytokine which induces the regeneration of hepatocytes cells during the immune response. Evidence has shown that genetic polymorphisms on IL-22 gene could affect the immune response and consequently the parasite clearance and the treatment outcome of malaria. This study aimed at determining the prevalence of the SNP rs1179251 of the Interleukin-22 gene and a possible association with P. falciparum clearance among children less than 10 years old in the North region of Cameroon. A case-control study was performed on 184 conveniently collected blood samples, spotted on Whartman No 3 filter paper from the SPAQ (Sulfadoxine-Pyrimethamine + Amodiaquine) clinical trial carried out in Garoua and Yagoua in 2015, from which DNA was extracted using Chelex-100 method. Genotyping of the IL-22 gene SNPs was performed using Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP). Parasite clearance was defined as the disappearance of pre-treatment parasites without subsequent recurrence, irrespective of whether recurrence is a reinfection or a recrudescing parasite. Treatment outcomes were classified according to the WHO guidelines; patients that experienced early treatment failure (ETF), and late parasitological failure (LPF) were classified as failures (56 cases), while patients that experienced adequate clinical parasitological response (ACPR) were classified as successes (128 controls). The chi square test was used to establish the association between the SNP rs1179251 and parasite clearance. A P-value less than 0.05 was considered as statistically significant. The findings revealed that the mutant allele C was the most predominant with a frequency of 74.46%, with the ancestral allele G having a frequency of 25.54%. These results showed that carriers of the mutant allele C could be 3.7 times more likely not to clear the parasites during treatment but this was not statistically significant (P=0.07, OR= 3.72). In conclusion, no association was found between the SNP rs1179251 of IL-22 gene and Plasmodium falciparum clearance. So, in spite of the importance of IL-22 gene in immune responses, the studied polymorphism does not serve a decisive role in Plasmodium falciparum clearance.

Adherence to Mass Drug Administration with Dihydroartemisinin-Piperaquine and Plasmodium falciparum Clearance in Southern Province, Zambia.

.Mass drug administration (MDA) with artemisinin combination therapy is a potentially useful tool for malaria elimination programs, but its success depends partly on drug effectiveness and treatment coverage in the targeted population. As part of a cluster-randomized controlled trial in Southern Province, Zambia evaluating the impact of MDA and household focal MDA (fMDA) with dihydroartemisinin–piperaquine (DHAp), sub-studies were conducted investigating population drug adherence rates and effectiveness of DHAp as administered in clearing Plasmodium falciparum infections following household mass administration. Adherence information was reported for 181,534 of 336,821 DHAp (53.9%) treatments administered during four rounds of MDA/fMDA, of which 153,197 (84.4%) reported completing the full course of DHAp. The proportion of participants fully adhering to the treatment regimen differed by MDA modality (MDA versus fMDA), RDT status, and whether the first dose was observed by those administering treatments. Among a subset of participants receiving DHAp and selected for longitudinal follow-up, 58 were positive for asexual-stage P. falciparum infection by microscopy at baseline. None of the 45 participants followed up at days 3 and/or 7 were slide positive for asexual-stage parasitemia. For those with longer term follow-up, one participant was positive 47 days after treatment, and two additional participants were positive after 69 days, although these two were determined to be new infections by genotyping. High completion of a 3-day course of DHAp and parasite clearance in the context of household MDA are promising as Zambia’s National Malaria Programme continues to weigh appropriate interventions for malaria elimination.

Different Plasmodium falciparum clearance times in two Malian villages following artesunate monotherapy

BackgroundArtemisinin resistance described as increased parasite clearance time (PCT) is rare in Africa. More sensitive methods such as qPCR might better characterize the clearance phenotype in sub-Saharan Africa. MethodsPCT is explored in Mali using light microscopy and qPCR after artesunate for uncomplicated malaria. In two villages, patients were followed for 28 days. Blood smears and spots were collected respectively for microscopy and qPCR. Parasitemia slope half-life was calculated after microscopy. Patient residual parasitemia were measured by qPCR. ResultsUncorrected adequate clinical and parasitological responses (ACPR) observed in Faladje and Bougoula-Hameau were 78% and 92%, respectively (p=0.01). This reached 100% for both after molecular correction.Proportions of 24H microscopy positive patients in Faladje and Bougoula-Hameau were 97.2% and 72%, respectively (p<0.0001).Slope half-life was 2.8h in Faladje vs 2H in Bougoula-Hameau (p<0.001) andProportions of 72H patients with residual parasitemia were 68.5% and 40% in Faladje and Bougoula-Hameau, respectively (p=0.003). The mean residual parasitemia was 2.9 in Faladje vs. 0.008 in Bougoula-Hameau (p=0.002).Although artesunate is efficacious in Mali, the longer parasite clearance time with submicroscopic parasitemia observed may represent early signs of developing P. falciparum resistance to artemisinins.

Plasmodium Falciparum Clearance in Malaria Treated Children at Lake Alau Settlements, North Eastern Nigeria: Effects of Body Weight

The influence of body weights on Plasmodium falcifarum clearance in malaria positive children was conducted using AT+SP and AQ+SP combination therapies, at the malaria holo - endemic and risk settlements of lake - alau, North Eastern Nigeria. A total of 313 children (6 - 59 months) were admitted into the study, to assess the efficacies of the combination therapies in children (6 - 59 months) using the effects of Body weights (kg) on parasite densities. Each child's weight was determined on days 0, 1, 2, 3, 4, 7, 14 and 28 during the follow up periods. The drugs were administered between 0-3 days. Finger prick and venipuncture (syringe) techniques were employed and blood was sampled by pricking using sterilized needle on days 0, 1, 2, 3, 4, 7, 14 and 28 for the assessment of parasite densities count (per µl) while blood smear was prepared using Giemsa stained slides making thick and thin blood smears. The result shows body weight exerted negative effects on Plasmodium falciparum between the range of 71.63 to 96.0% for AT+SP and 87.79 to 96.38% for AQ+SP in the first three days of treatment. Furthermore, results showed for each kg gain in body weight there was a synchronous parasite clearance by 325.79 versus 1199.91∕µ, 16.621 versus 157.06∕µ, 17.445 versus 153.5∕µ for AT+SP versus AQ+SP on days 1, 2, and 3, respectively. The terminal resultsindicated a higher residual parasitaemia at the onset of late phase in children treated with AQ+SP (195.17 to 113.92∕µ) tcompared to AT+SP (182.48 to 25.531∕µ). The respective parasite densities clearance per kg body weight for days 7, 14 and 28 for AT+SP versus AQ+SP was 33.82 versus 35.887∕µ, 10.076 versus 29.578∕µ and 2.3548 versus 26.368∕µ respectively. Thus, on each of the late follow-up days, the rate of parasite depletion was higher in AQ+SP than AT+SP.*Corresponding Author: muskokoss@gmail.com

In Vivo Efficacy and Parasite Clearance of Artesunate + Sulfadoxine-Pyrimethamine Versus Artemether-Lumefantrine in Mali.

Although artemisinin resistance has yet to be reported in Africa, surveillance of the efficacy of artemisinin-based combination therapies (ACTs) is warranted. Here, the efficacy of artesunate + sulfadoxine-pyrimethamine (AS + SP) and artemether-lumefantrine (AL) was evaluated in Mali. Randomized open-label comparative in vivo assay of AS + SP versus AL were carried out using the 28-day follow-up World Health Organization protocol. Patients with uncomplicated falciparum malaria and at least 6 months of age were recruited between October 2010 and January 2014. A subset of these patients was selected to measure Plasmodium falciparum clearance time. Polymerase chain reaction-corrected adequate clinical and parasitological responses were 100% for AS + SP and 98.2% for AL with no significant difference (P = 0.06). The reinfection rates were comparable (P = 0.63) with 8.0% for AS + SP and 12.6% for AL. Individuals under 8 years were more susceptible to treatment failure (relative risk = 1.9; 95% confidence interval = 1.2, 3.3). Median parasite clearance half-life was 1.7 hours (interquartile range [IQR] = 1.3-2.2) for AS + SP and 1.9 hours (IQR = 1.5-2.5) for AL with no statistically significant difference (P = 0.24). Efficacy of AS + SP and AL was high. This study provides baseline information on parasite clearance half-lives after ACT treatment, particularly AS + SP, in Mali.

Clearance Failure Rates of Plasmodium falciparum after Treatment among Children (6-11 years) in Kisumu East Sub County

Plasmodium falciparum is said to be yet sensitive to artemether-lumefantrine (AL) among all age groups in Kisumu County, despites report of its isolated strain with reduced sensitivity in Kilifi and reported reduced sensitivity to artemisinins in South East Asia. This trial intended to compare Plasmodium falciparum clearance failure rates among children (6-11 years) with uncomplicated falciparum malaria randomly allocated to artesunate-mefloquine or generic artemether-lumefantrine. We conducted a two arms open label randomized controlled trial with a fourteen day follow up and a sample size of 130 children with uncomplicated falciparum malaria in government primary schools of Kisumu East Sub County. This study showed Plasmodium falciparum clearance failure rates significantly higher (P = 0.02) with generic artemether-lumefantrine than with artesunate-mefloquine on day one of treatment. However, no significant difference (P = 0.999) was observed between the two arms on day seven and day fourteen of treatment. Thus, Plasmodium falciparum was less likely to fail to clear as it responded to artesunate-mefloquine than to generic artemether-lumefantrine on day one of treatment. Nevertheless, it was unlikely to fail to clear as it responded to both artesunate-mefloquine and generic artemether-lumefantrine on day seven and day fourteen of treatment.

Bayesian hierarchical regression on clearance rates in the presence of "lag" and "tail" phases with an application to malaria parasites.

We present a principled technique for estimating the effect of covariates on malaria parasite clearance rates in the presence of "lag" and "tail" phases through the use of a Bayesian hierarchical linear model. The hierarchical approach enables us to appropriately incorporate the uncertainty in both estimating clearance rates in patients and assessing the potential impact of covariates on these rates into the posterior intervals generated for the parameters associated with each covariate. Furthermore, it permits us to incorporate information about individuals for whom there exists only one observation time before censoring, which alleviates a systematic bias affecting inference when these individuals are excluded. We use a changepoint model to account for both lag and tail phases, and hence base our estimation of the parasite clearance rate only on observations within the decay phase. The Bayesian approach allows us to treat the delineation between lag, decay, and tail phases within an individual's clearance profile as themselves being random variables, thus taking into account the additional uncertainty of boundaries between phases. We compare our method to existing methodology used in the antimalarial research community through a simulation study and show that it possesses desirable frequentist properties for conducting inference. We use our methodology to measure the impact of several covariates on Plasmodium falciparum clearance rate data collected in 2009 and 2010. Though our method was developed with this application in mind, it can be easily applied to any biological system exhibiting these hindrances to estimation.

Plasmodium falciparum clearance is rapid and pitting independent in immune Malian children treated with artesunate for malaria.

In Plasmodium falciparum-infected patients treated with artemisinins, parasitemia declines through so-called pitting, an innate splenic process that transforms infected red blood cells (iRBCs) into once-infected RBCs (O-iRBCs). We measured pitting in 83 French travelers and 42 Malian children treated for malaria with artesunate. In travelers, O-iRBCs peaked at 107.7% initial parasitemia. In Malian children aged 1.5-4 years, O-iRBCs peaked at higher concentrations than in children aged 9-13 years (91.60% vs 31.95%; P = .0097). The parasite clearance time in older children was shorter than in younger children (P = .0001), and the decline in parasitemia in children aged 1.5-4 years often started 6 hours after treatment initiation, a lag phase generally absent in infants and older children. A 6-hour lag phase in artificial pitting of artesunate-exposed iRBCs was also observed in vitro. The proportion of iRBCs recognized by autologous immunoglobulin G (IgG) correlated with the parasite clearance time (r = -0.501; P = .0006) and peak O-iRBC concentration (r = -0.420; P = .0033). Antimalarial immunity correlates with fast artemisinin-induced parasite clearance and low pitting rates. In nonimmune populations, artemisinin-induced P. falciparum clearance is related to pitting and starts after a 6-hour lag phase. In immune populations, passively and naturally acquired immune mechanisms operating faster than pitting may exist. This mechanism may mitigate the emergence of artemisinin-resistant P. falciparum in Africa.

The Relationship between the Plasmodium Falciparum Clearance and the Clinical Effect of the Case with Cerebral Malaria Treated with Artemisinin

The Relationship between the Plasmodium Falciparum Clearance and the Clinical Effect of the Case with Cerebral Malaria Treated with Artemisinin

Plasmodium falciparum clearance in clinical studies of artesunate-amodiaquine and comparator treatments in sub-Saharan Africa, 1999–2009

BackgroundArtemisinin-based combination therapy (ACT) is the recommended first-line therapy for uncomplicated Plasmodium falciparum malaria worldwide but decreased artemisinin susceptibility, phenotypically characterized as slow parasite clearance time (PCT), has now been reported in Southeast Asia. This makes it all too important to measure the dynamics of parasite clearance in African patients treated with ACT over time, to understand trends and detect changes early enough to interveneMethodsIndividual patient data from 27 clinical trials of artesunate-amodiaquine (ASAQ) vs comparators conducted between 1999 and 2009 were analysed for parasite clearance on modified intent-to-treat (ITT) basis.ResultsOverall 15,017 patients treated for uncomplicated P. falciparum malaria at 44 sites in 20 sub-Saharan African countries were included in the analysis; 51% (n=7,660) vs 49% (n=7,357) were treated with ASAQ and comparator treatments, respectively. Seventy-seven per cent (77%) were children under six years of age. The proportion of the patients treated with ASAQ with persistent parasitaemia on Day 2 was 8.6%, and 1.5% on Day 3. Risk factor for not clearing parasites on Day 2 and Day 3 calculated by multivariate logistic regression with random effect on site and controlling for treatment were: high parasitaemia before treatment was (adjusted risk ratios (AOR) 2.12, 95% CI 1.91-2.35, AOR 2.43, 95% CI 1.98-3.00, respectively); non-ACT treatment (p=0.001, for all comparisons). Anaemia (p=0.001) was an additional factor for Day 2 and young age (p=0.005) for Day 3.In patients treated with ASAQ in studies who had complete parasitaemia data every 24 hours up to Day 3 and additionally Day 7, the parasite reduction ratio was 93.9% by Day 1 and 99.9% by Day 2. Using the median parasitaemia before treatment (p0=27,125 μL) and a fitted model, the predicted PCT (pPCT = 3.614*ln (p0) – 6.135, r² = 0.94) in ASAQ recipients was 31 hours.ConclusionWithin the period covered by these studies, rapid Plasmodium falciparum clearance continues to be achieved in Sub-Saharan African patients treated with ACT, and in particular with ASAQ. The prediction formula for parasite clearance time could be a pragmatic tool for studies with binary outcomes and once-daily sampling, both for research and monitoring purposes.

Optimal sampling designs for estimation of Plasmodium falciparum clearance rates in patients treated with artemisinin derivatives

BackgroundThe emergence of Plasmodium falciparum resistance to artemisinins in Southeast Asia threatens the control of malaria worldwide. The pharmacodynamic hallmark of artemisinin derivatives is rapid parasite clearance (a short parasite half-life), therefore, the in vivo phenotype of slow clearance defines the reduced susceptibility to the drug. Measurement of parasite counts every six hours during the first three days after treatment have been recommended to measure the parasite clearance half-life, but it remains unclear whether simpler sampling intervals and frequencies might also be sufficient to reliably estimate this parameter.MethodsA total of 2,746 parasite density-time profiles were selected from 13 clinical trials in Thailand, Cambodia, Mali, Vietnam, and Kenya. In these studies, parasite densities were measured every six hours until negative after treatment with an artemisinin derivative (alone or in combination with a partner drug). The WWARN Parasite Clearance Estimator (PCE) tool was used to estimate “reference” half-lives from these six-hourly measurements. The effect of four alternative sampling schedules on half-life estimation was investigated, and compared to the reference half-life (time zero, 6, 12, 24 (A1); zero, 6, 18, 24 (A2); zero, 12, 18, 24 (A3) or zero, 12, 24 (A4) hours and then every 12 hours). Statistical bootstrap methods were used to estimate the sampling distribution of half-lives for parasite populations with different geometric mean half-lives. A simulation study was performed to investigate a suite of 16 potential alternative schedules and half-life estimates generated by each of the schedules were compared to the “true” half-life. The candidate schedules in the simulation study included (among others) six-hourly sampling, schedule A1, schedule A4, and a convenience sampling schedule at six, seven, 24, 25, 48 and 49 hours.ResultsThe median (range) parasite half-life for all clinical studies combined was 3.1 (0.7-12.9) hours. Schedule A1 consistently performed the best, and schedule A4 the worst, both for the individual patient estimates and for the populations generated with the bootstrapping algorithm. In both cases, the differences between the reference and alternative schedules decreased as half-life increased. In the simulation study, 24-hourly sampling performed the worst, and six-hourly sampling the best. The simulation study confirmed that more dense parasite sampling schedules are required to accurately estimate half-life for profiles with short half-life (≤three hours) and/or low initial parasite density (≤10,000 per μL). Among schedules in the simulation study with six or fewer measurements in the first 48 hours, a schedule with measurements at times (time windows) of 0 (0–2), 6 (4–8), 12 (10–14), 24 (22–26), 36 (34–36) and 48 (46–50) hours, or at times 6, 7 (two samples in time window 5–8), 24, 25 (two samples during time 23–26), and 48, 49 (two samples during time 47–50) hours, until negative most accurately estimated the “true” half-life. For a given schedule, continuing sampling after two days had little effect on the estimation of half-life, provided that adequate sampling was performed in the first two days and the half-life was less than three hours. If the measured parasitaemia at two days exceeded 1,000 per μL, continued sampling for at least once a day was needed for accurate half-life estimates.ConclusionsThis study has revealed important insights on sampling schedules for accurate and reliable estimation of Plasmodium falciparum half-life following treatment with an artemisinin derivative (alone or in combination with a partner drug). Accurate measurement of short half-lives (rapid clearance) requires more dense sampling schedules (with more than twice daily sampling). A more intensive sampling schedule is, therefore, recommended in locations where P. falciparum susceptibility to artemisinins is not known and the necessary resources are available. Counting parasite density at six hours is important, and less frequent sampling is satisfactory for estimating long parasite half-lives in areas where artemisinin resistance is present.

Plasmodium falciparum Clearance Rates in Response to Artesunate in Malian Children With Malaria: Effect of Acquired Immunity

Background. Artemisinin resistance, a long parasite clearance half-life in response to artemisinin, has been described in patients with Plasmodium falciparum malaria in southeast Asia. Few baseline half-lives have been reported from Africa, where artemisinins were recently introduced.Methods. We treated P. falciparum malaria in 215 Malian children aged 0.5–15 years with artesunate (0, 24, 48 hours) and amodiaquine (72, 96, 120 hours). We estimated half-life by measuring parasite density every 6 hours until undetectable and evaluated the effects of age, sex, ethnicity, and red blood cell (RBC) polymorphisms on half-life. We quantified the proportion of parasitized RBCs recognized by autologous immunoglobulin G (IgG).Results. The geometric mean half-life was 1.9 hours (95% confidence interval, 1.8–2.0) and did not correlate with parasite ex vivo susceptibility to artemisinins. In a linear model accounting for host factors, half-life decreased by 4.1 minutes for every 1-year increase in age. The proportion of parasitized RBCs recognized by IgG correlated inversely with half-life (r = −0.475; P = .0006).Conclusions. Parasite clearance in response to artesunate is faster in Mali than in southeast Asia. IgG responses to parasitized RBCs shorten half-life and may influence this parameter in areas where age is not an adequate surrogate of immunity and correlates of parasite-clearing immunity have not been identified.Clinical Trials Registration. NCT00669084.

Delayed Plasmodium falciparum clearance following artesunate-mefloquine combination therapy in Thailand, 1997–2007

BackgroundThere is concern that artesunate resistance is developing in Southeast Asia. The purpose of this study is to investigate the prevalence of parasitaemia in the few days following treatment with artesunate-mefloquine (AM), which is an indirect measure of decreased artesunate susceptibility.MethodsThis is a retrospective analysis of 31 therapeutic efficacy studies involving 1,327 patients treated with AM conducted by the Thai National Malaria Control Programme from 1997–2007.ResultsThe prevalence of patients with parasitaemia on day 2 was higher in the east compared to the west (east: 20%, west: 9%, OR 2.47, 95% CI: 1.77, 3.45). In addition, the prevalence of day-2 parasitaemia increased over time (OR for each year = 1.10, 95% CI: 1.03, 1.19). After controlling for initial parasitaemia and age, year and region remained important determinants of day-2 parasitaemia (OR for region = 3.98, 95%CI 2.63, 6.00; OR for year = 1.28, 95%CI: 1.17, 1.39). The presence of parasitaemia on day 2 and day 3 were specific, but not sensitive predictors of treatment failure.DiscussionDelayed resolution of parasitaemia after AM treatment increased in eastern Thailand between 1997 and 2007, which may be an early manifestation of decreased artesunate susceptibility. However, clinical and parasitological treatment failure after 28 days (which is related to both mefloquine and artesunate decreased susceptibility) is not changing over time. The presence of parasitaemia on day 2 is a poor indicator of AM 28-day treatment failure.

Plasmodium falciparum clearance with artemisinin-based combination therapy (ACT) in patients with glucose-6-phosphate dehydrogenase deficiency in Mali

BackgroundArtemisinin-based combination therapy (ACT) is currently the most effective medicine for the treatment of uncomplicated malaria. Artemisinin has previously been shown to increase the clearance of Plasmodium falciparum in malaria patients with haemoglobin E trait, but it did not increase parasite inhibition in an in vitro study using haemoglobin AS erythrocytes. The current study describes the efficacy of artemisinin derivatives on P. falciparum clearance in patients with glucose-6-phosphate dehydrogenase deficiency (G6PD), a haemoglobin enzyme deficiency, not yet studied in the same context, but nonetheless is a common in malaria endemic areas, associated with host protection against uncomplicated and severe malaria. The impact of G6PD deficiency on parasite clearance with ACT treatment was compared between G6PD-deficient patients and G6PD-normal group.MethodsBlood samples from children and adults participants (1 to 70 years old) with uncomplicated P. falciparum malaria residing in Kambila, Mali were analysed. Study participants were randomly assigned to receive either artemether-lumefantrine (Coartem®) or artesunate plus mefloquine (Artequin™). A restriction-fragment length polymorphism analysis of PCR-amplified DNA samples was used to identify the (A-) allele of the gene mutation responsible for G6PD deficiency (G6PD*A-). 470 blood samples were thus analysed and of these, DNA was extracted from 315 samples using the QIAamp kit for PCR to identify the G6PD*A- gene.ResultsThe DNA amplified from 315 samples using PCR showed that G6PD*A- deficiency was present in 56 participants (17.8%). The distribution of the specific deficiency was 1%, 7% and, 9.8% respectively for homozygous, hemizygous, and heterozygous genotypes. Before treatment, the median parasitaemia and other baseline characteristics (mean haemoglobin, sex and age groups) between G6PD deficiency (hemizygous, heterozygous, and homozygous) and G6PD-normal participants were comparable (p > 0.05). After treatment, parasite clearance did not change significantly whether the participants were G6PD deficient or G6PD normal on day 1 (OR = 1.3; CI = 0.70-2.47; p > 0.05) and on day 2 (OR = 0.859; CI = 0.097-7.61; p > 0.05).ConclusionsThe presence of G6PD deficiency does not appear to significantly influence the clearance of P. falciparum in the treatment of uncomplicated malaria using ACT.