Malaria Parasite Clearance Research Articles

Assessment of efficacy and safety of imatinib as an adjunct host-targeted therapy for parasite clearance in chloroquine-resistant malaria: a prospective case control study

OverviewChloroquine-resistant malaria poses a significant treatment challenge, especially in endemic areas. Host-targeted therapies, like tyrosine kinase inhibitors (TKIs) such as imatinib, have shown potential to improve malaria treatment outcomes by disrupting parasite egress from red blood cells. This study investigates the efficacy and safety of imatinib as an adjunct therapy to accelerate fever reduction and parasite clearance in male patients with chloroquine-resistant malaria.Patients and methodsThis open-label, prospective, randomized case–control study was conducted on 60 male patients aged 18–50, diagnosed with chloroquine-resistant malaria at Viswabharathi Medical College, India. Patients were randomized into two groups: a control group receiving standard anti-malarial therapy and a test group receiving standard therapy plus imatinib (400 mg daily for 3 days). Efficacy endpoints included the time to reduce parasite load by half and normalization of body temperature. Safety assessments monitored adverse reactions throughout the treatment period.ResultsThe imatinib group demonstrated a significantly faster reduction in fever, with normalization by day 2 compared to day 3 in the control group (p < 0.05). Parasite counts decreased more rapidly in the imatinib group, with mean levels falling to below 1000 parasites/mcl by day 3. Mild adverse effects, primarily headaches and gastrointestinal symptoms, were reported but resolved by day 3 with no severe events directly attributed to imatinib.ConclusionImatinib as an adjunct therapy may enhance the efficacy of standard anti-malarial treatments by accelerating parasite clearance and fever reduction in cases of chloroquine-resistant malaria. These findings support further investigation into TKIs as a complementary approach to existing malaria treatments, particularly in regions facing drug resistance challenges.

Diagnostic performance of PfHRP2/pLDH malaria rapid diagnostic tests in elimination setting, northwest Ethiopia.

Accurate diagnosis of malaria is vital for the effectiveness of parasite clearance interventions in elimination settings. Thus, evaluating the diagnostic performance of rapid diagnostic tests (RDTs) used in malaria parasite clearance interventions in elimination settings is essential. Therefore, this study aimed to evaluate the diagnostic performance of rapid diagnostic tests recently used in detecting malaria parasites in northwest Ethiopia. A facility-based cross-sectional study was conducted from November 2020 to February 2021 comparing PfHRP2/pLDH CareStart malaria RDTs with light microscopy and polymerase chain reaction (PCR). Blood samples were collected from 310 febrile patients who attended the outpatient department and examined using CareStart RDTs, light microscopy, and PCR. Statistical analyses were performed using STATA/SE version 17.0. The sensitivity of PfHRP2/pLDH CareStart malaria RDTs, regardless of species, was 81.0% [95% CI, 75.3, 86.7] and 75.8% [95% CI, 69.6, 82.0] compared to light microscopy and PCR, while the specificity was 96.8% [95% CI, 93.7, 99.9] and 93.2% [95% CI, 88.6, 97.8], respectively. The false-negative rate of CareStart malaria RDTs in comparison with light microscopy and PCR was 19.0% and 24.2%, respectively. The level of agreement beyond chance between tests was substantial, RDT versus microscopy was 75.0% and RDT versus PCR was 65.1%. The diagnostic performance of PfHRP2/pLDH CareStart RDTs in detecting malaria parasites among febrile patients in the study area was below the recommended WHO standard. The limited diagnostic performance of RDTs in the malaria elimination area undoubtedly affects the impact of malaria parasite clearance interventions. Therefore, parasite clearance intervention like targeted mass drug administration with antimalarial drugs is recommended to back up the limited diagnostic performance of the RDT or replace the existing malaria RDTs with more sensitive, field-deployable, and affordable diagnostic tests.

Biochemical characteristics of patients with imported malaria.

This study aimed to investigate the clinical and biochemical profiles of patients with imported malaria infection between 1 January 2011 and 30 April 2022 and admitted to the Fourth People's Hospital of Nanning. This cohort study enrolled 170 patients with conformed imported malaria infection. The clinical and biochemical profiles of these participants were analyzed with malaria parasite clearance, and signs and symptoms related to malaria disappearance were defined as the primary outcome. A multivariable logistic regression model was used to evaluate the odds ratios (ORs) with 95% confidence intervals (CIs) for cerebral malaria. The Cox model was used to estimate the hazard ratios (HRs) with 95% CIs for parasite clearance. Adenosine deaminase and parasitemia were found to be independent risk factors for severe malaria in patients with imported malaria (OR = 1.0088, 95% CI: 1.0010-1.0167, p = 0.0272 and OR = 2.0700, 95% CI: 1.2584-3.4050, p = 0.0042, respectively). A 0.5-standard deviation (SD) increase of variation for urea (HR = 0.6714, 95% CI: 0.4911-0.9180), a 0.5-SD increase of variation for creatinine (HR = 0.4566, 95% CI: 0.2762-0.7548), a 0.25-SD increase of variation for albumin (HR = 0.4947, 95% CI: 0.3197-0.7653), a 0.25-SD increase of variation for hydroxybutyrate dehydrogenase (HR = 0.6129, 95% CI: 0.3995-0.9402), and a 1.0-SD increase of variation for ferritin (HR = 0.5887, 95% CI: 0.3799-0.9125) were associated with a higher risk for increased parasite clearance duration than a low-level change. Aspartate aminotransferase, urea, creatinine, albumin, hydroxybutyrate dehydrogenase, and ferritin are useful biochemical indicators in routine clinical practice to evaluate prognosis for imported malaria.

Effects of co-treatment of Plasmodium berghei-infected mice with aqueous extract of Ocimum gratissimum leaves and primaquine on glucose-6-phosphate dehydrogenase activity, hematological, and antioxidant parameters

BackgroundIt has been observed that most malaria patients especially G6PD-deficient patients usually experience oxidative stress and severe anemia when treated with primaquine. This calls for the need to search for a treatment option that will ameliorate these side effects. ObjectiveThe effect of co-treatment of malaria with aqueous extract of Ocimum gratissimum leaves (AEOGL) and primaquine on G6PD activity, antioxidant indices and hematological parameters in Plasmodium berghei-infected mice was investigated. Materials and methodsThirty mice divided into six groups of five mice each were recruited for this study. Whilst Group 1 (G1) served as the negative control (group not infected with plasmodium parasite), Groups 2 to 6 (G2-G6) were inoculated intraperitoneally with 0.2 ml of 1 × 105/ml Plasmodium berghei (NK 65 strain) infected erythrocytes. G2 (parasite control) received no treatment. Groups 3,4,5 and 6 were administered 0.25 mg/kg bw of primaquine only; 100 mg/kg b. w of AEOGL +0.25 mg/kg bw of primaquine; 200 mg/kg b. w of AEOGL +0.25 mg/kg bw of primaquine; 200 mg/kg b. w of AEOGL respectively, for 14 days. ResultsTreatment with only primaquine gave the highest mean malaria parasite clearance (82.10 ± 0.45 percent), followed by 100 mg/kg b. w of AEOGL + Primaquine (75.59 ± 0.47 percent), 200 mg/kg b. w of AEOGL + Primaquine (67.35 ± 0.67 percent), and AEOGL alone (55 ± 0.56 percent). In comparison with the untreated malaria groups, co-treatment with AEOGL + Primaquine produced a significant (p < 0.05) increase in G6PD activity, serum ascorbate, reduced glutathione, catalase activity, and a significant (p < 0.05) decrease in malondialdehyde level in a dose-dependent pattern and also a significant (p < 0.05) rise in packed cell volume, haemoglobin, and red blood cell count, unlike treatment with only primaquine which resulted in a non-significant (P > 0.05) difference in these parameters. ConclusionCo-treatment of Plasmodium berghei-infected mice with AEOGL and primaquine improved the G6PD activity, hematological parameters and antioxidant status relative to treatment with only primaquine.

Antimicrobial Activities and Malaria Parasite Clearance of Crude Extract of Carica papaya Seeds in Mice Infected with Plasmodium berghei

a peer-reviewed, open access online international journal which publishes original research papers. The journal welcomes submission from scholars and experts for possible publication from all over the world. The scope of the journal includes: Pharmaceutical research, chemistry and biochemistry of naturally occurring compounds, biological evaluation of crude extracts, ethnomedicine, traditional and complementary medicine, ethnopharmacology, biomedical research, Biotechnology, Evaluation of natural substances of land and sea and of plants, microbes and animals, pharmacognosy, bioavailability, clinical, pharmacological, toxicological studies and pharmacokinetics of phytochemicals, Isolation and characterization of compounds, structure elucidation, synthesis and experimental biosynthesis of natural Product as well as developments of methods in these areas are welcomed in the journal.

Natural Killer Cell Antibody-Dependent Cellular Cytotoxicity (ADCC) Activity Against Plasmodium falciparum-Infected Red Blood Cells.

Antibody-dependent cellular cytotoxicity (ADCC) is a mechanism of cell defense that bridges the innate and adaptive immune systems. ADCC has been found to be a major route of immune protection against both viral infections and cancer. Recently, natural killer (NK) cell-mediated ADCC has been shown as a mechanism of parasite clearance and protection against malaria (Hart et al. J Exp Med 216(6):1280-1290, 2019). NK cells bind to antibodies on the surface of Plasmodium falciparum infected red blood cells (iRBCs) via their Fc receptor, FcγRIIIa (CD16). This interaction induces the release of lytic granules (degranulation) by NK cells, which contain perforin, granzyme B, and granulysin, as well as the secretion of IFNγ. ADCC subsequently limits the growth of Plasmodium falciparum in vitro (Arora et al. Elife:7, e36806, 2018). Because NK cell-mediated ADCC has been shown to be important in malaria parasite clearance and protection, further studies understanding ADCC in malaria are warranted (Hart et al. J Exp Med 216(6):1280-1290, 2019). Therefore, this protocol describes methods to perform an in vitro ADCC functional assay with iRBCs. Specifically, it includes protocols on how to grow and culture iRBCs, how to culture peripheral blood mononuclear cells (PMBCs), and how to do in vitro PBMC assays to measure NK degranulation and IFNγ production as measures of NK ADCC function.

Combating multi-drug resistant malaria parasite by inhibiting falcipain-2 and heme-polymerization: Artemisinin-peptidyl vinyl phosphonate hybrid molecules as new antimalarials.

Artemisinin-based combination therapies (ACTs) have been able to reduce the clinical and pathological malaria cases in endemic areas around the globe. However, recent reports have shown a progressive decline in malaria parasite clearance in South-east Asia after ACT treatment, thus envisaging a need for new artemisinin (ART) derivatives and combinations. To address the emergence of drug resistance to current antimalarials, here we report the synthesis of artemisinin-peptidyl vinyl phosphonate hybrid molecules that show superior efficacy than artemisinin alone against chloroquine-resistant as well as multidrug-resistant Plasmodium falciparum strains with EC50 in pico-molar ranges. Further, the compounds effectively inhibited the survival of ring-stage parasite for laboratory-adapted artemisinin-resistant parasite lines as compared to artemisinin. These hybrid molecules showed complete parasite clearance invivo using P.berghei mouse malaria model in comparison to artemisinin alone. Studies on the mode of action of hybrid molecules suggested that these artemisinin-peptidyl vinyl phosphonate hybrid molecules possessed dual activities: inhibited falcipain-2 (FP-2) activity, a P.falciparum cysteine protease involved in hemoglobin degradation, and also blocked the hemozoin formation in the food-vacuole, a step earlier shown to be blocked by artemisinin. Since these hybrid molecules blocked multiple steps of a pathway and showed synergistic efficacies, we believe that these lead compounds can be developed as effective antimalarials to prevent the spread of resistance to current antimalarials.

Study towards improving artemisinin-based combination therapies.

Covering: Up to 2020 Artemisinin has made a significant contribution towards global malaria control since its initial discovery. Countless lives have been saved by this unique and miraculous molecule. In 2006, artemisinin-based combination therapies (ACTs) were recommended by the World Health Organization (WHO) as the first-line treatment for uncomplicated malaria infection and have since remained as the mainstays of the antimalarial treatment. Even so, substantial efforts to pursue better curative effects for the treatment of malaria have never ceased, particularly with regards to the circumstances surrounding the appearance of delayed clearance of malaria parasites by 3 day ACT treatments in South-East Asian countries. Strategies to further optimize artemisinin-based therapies, including synthesizing better artemisinin derivatives, developing advanced drug delivery systems, and diversifying artemisinin partner drugs, have been proposed over the past few years. Here, we provide an updated account of the continuous efforts in improving ACTs for better efficacy in curing malarial infection.

Comparing drug regimens for clearance of malaria parasites in asymptomatic adults using PCR in Kilifi County, Kenya: an open-label randomised controlled clinical trial (MalPaC)

Background: To restrict trial endpoints to infections acquired after vaccination in Phase IIb trials of candidate malaria vaccines, participants are treated with anti-malarial drugs to clear existing infections. Anti-malarial drugs with a long half-life may inhibit the acquisition of new infections. This study evaluated the effects of three anti-malarial drug regimens on the clearance of existing infections and acquisition of new infections. Methods: An open-label randomised controlled trial (MalPaC) was conducted between November 2013 and February 2014. Ninety adults were randomised 1:1:1 to receive one of three treatments: atovaquone/proguanil and artesunate (AP+AS); artesunate (AS); or sulphadoxine-pyrimethamine, artesunate, and primaquine (SP+AS+PQ). Parasite monitoring was determined over 84-day follow-up by assessing Plasmodium falciparum positivity by 18s qPCR, live and sexual stage parasites by RT-PCR, and recrudescence of infections by msp2 genotyping. Results: At enrolment, parasite prevalence by qPCR was 44% (40/90, day 0), which fell to 10% (9/90, day 16), then rose to almost the initial rates by day 84 (39%, 35/90). Individuals treated with AS and SP+AS+PQ were more likely to have higher qPCR positive rates compared to participants treated with AP+AS in the immediate post-treatment phase (days 16-28) (OR=7.7 [95%CI 4.6-12.8] p&lt;0.0005 and OR=4.2 [95%CI 2.6-6.8] p&lt;0.0005, respectively). In the immediate post-treatment phase, qPCR positivity was less likely associated with evidence of live parasites and gametocytaemia. Prevalence of “old”, “new” or “undetectable” infections did not differ significantly over time or drug regimen. However, participants on the AP+AS drug regimen were less likely to have parasite infection recrudescence compared to participants treated with AS and SP+AS+PQ. Conclusion: Falciparum DNA remained detectable by PCR post-treatment with incomplete parasite clearance regardless of drug regimen. Though AP+AS drug regimen may also have partially suppressed the acquisition of new infections during post-treatment follow-up. Trial registration: Pan African Clinical Trials Registry, 22nd of August 2013, PACTR201309000625311.

Malaria parasite clearance rate regression: an R software package for a Bayesian hierarchical regression model

BackgroundEmerging resistance to anti-malarial drugs has led malaria researchers to investigate what covariates (parasite and host factors) are associated with resistance. In this regard, investigation of how covariates impact malaria parasites clearance is often performed using a two-stage approach in which the WWARN Parasite Clearance Estimator or PCE is used to estimate parasite clearance rates and then the estimated parasite clearance is regressed on the covariates. However, the recently developed Bayesian Clearance Estimator instead leads to more accurate results for hierarchial regression modelling which motivated the authors to implement the method as an R package, called “bhrcr”.MethodsGiven malaria parasite clearance profiles of a set of patients, the “bhrcr” package performs Bayesian hierarchical regression to estimate malaria parasite clearance rates along with the effect of covariates on them in the presence of “lag” and “tail” phases. In particular, the model performs a linear regression of the log clearance rates on covariates to estimate the effects within a Bayesian hierarchical framework. All posterior inferences are obtained by a “Markov Chain Monte Carlo” based sampling scheme which forms the core of the package.ResultsThe “bhrcr” package can be utilized to study malaria parasite clearance data, and specifically, how covariates affect parasite clearance rates. In addition to estimating the clearance rates and the impact of covariates on them, the “bhrcr” package provides tools to calculate the WWARN PCE estimates of the parasite clearance rates as well. The fitted Bayesian model to the clearance profile of each individual, as well as the WWARN PCE estimates, can also be plotted by this package.ConclusionsThis paper explains the Bayesian Clearance Estimator for malaria researchers including describing the freely available software, thus making these methods accessible and practical for modelling covariates’ effects on parasite clearance rates.

English

This study aims to determine the malaria parasite clearance rate of crude methanol extract of Cryptolepis sanguinolenta in mice infected with chloroquine sensitive strain of Plasmodium berghei. P. berghei was injected in mice and left for 3 days for establishment. Blood sample collected and diluted with phosphate buffer saline was used for infection. Five (5) groups of animals (mice) were used in this study each containing 5 animals each. The body weights of the entire animal were recorded before and after treatment. Group 1 (normal control), Group 2 (positive control, untreated malaria-passaged mice), Group 3 (standard control, malaria -passaged mice treated with 25 mg/kg body weight of chloroquine), Group 4 (malaria-passaged mice treated with 200 mg/kg body weight of extract), and Group 5 (malaria-passaged mice treated with 400 mg/kg body weight of extract). Hematological assessments were carried out before the experiment, 5 days after infection and after treatment. The percentage of parasite load in malaria passaged mice was found to be significantly (p &lt; 0.05) lower in animals treated with mid and high doses of the extract when compared to control groups. Before treatment, no significant (p &gt; 0.05) elevation was observed in the body weight of mice. On day 5 after infection, dose-dependent significant (p &lt; 0.05) decrease was observed in the test groups. After treatment period, the body weights of the animals exhibited dose-dependent increase. The study thus revealed that Cryptolepis sanguinolenta root extracts possesses antimalarial activity in the in vivo mice model and has the ability of re-establishing the blood cells by boosting and stabilizing the blood parameters. Key words: Cryptolepis sanguinolenta, chloroquine, Plasmodium berghei, malaria and clearance rate. &nbsp

Malaria parasite clearance from patients following artemisinin-based combination therapy in Côte d'Ivoire.

IntroductionParasite clearance is useful to detect artemisinin resistance. The aim of this study was to investigate parasite clearance in patients treated with artesunate + amodiaquine (AS + AQ) and artemether + lumefantrine (AL): the two artemisinin-based combination therapies (ACTs) recommended in the first-line treatment of uncomplicated malaria in Côte d’Ivoire.MethodsThis study was conducted in Bouaké, Côte d’Ivoire, from April to June 2016. Patients aged at least 6 months with uncomplicated malaria and treated with AS + AQ or AL were hospitalized for 3 days, and follow-up assessments were performed on days 3, 7, 14, 21, 28, 35, and 42. Blood smears were collected at the time of screening, pre-dose, and 6-hour intervals following the first dose of administration until two consecutive negative smears were recorded, thereafter at day 3 and follow-up visits. Parasite clearance was determined using the Worldwide Antimalarial Resistance Network’s parasite clearance estimator. The primary end points were parasite clearance rate and time.ResultsA total of 120 patients (57 in the AS + AQ group and 63 in the AL group) were randomized among 298 patients screened. The median parasite clearance time was 30 hours (IQR, 24–36 hours), for each ACT. The median parasite clearance rate had a slope half-life of 2.36 hours (IQR, 1.85–2.88 hours) and 2.23 hours (IQR, 1.74–2.63 hours) for AS + AQ and AL, respectively. The polymerase chain reaction-corrected adequate clinical and parasitological response was 100% and 98.07% at day 42 for AS + AQ and AL, respectively.ConclusionPatients treated with AS + AQ and AL had cleared parasites rapidly. ACTs are still efficacious in Bouaké, Côte d’Ivoire, but continued efficacy monitoring of ACTs is needed.

Split dosing of artemisinins does not improve antimalarial therapeutic efficacy

It has been suggested recently, based on pharmacokinetic-pharmacodynamic modelling exercises, that twice daily dosing of artemisinins increases malaria parasite killing and so could “dramatically enhance and restore drug effectiveness” in artemisinin resistant P. falciparum malaria infections. It was recommended that split dosing should be incorporated into all artemisinin combination regimen designs. To explain why parasite clearance rates were not faster with split dose regimens it was concluded that splenic malaria parasite clearance capacity was readily exceeded, resulting in the accumulation of dead parasites in the circulation, that parasite clearance was therefore an unreliable measure of drug efficacy, and instead that human immunity is the primary determinant of clearance rates. To test these various hypotheses we performed a logistic meta-regression analysis of cure rates from all falciparum malaria treatment trials (n = 40) with monotherapy arms containing artemisinin or a derivative (76 arms). There was no evidence that split dosing enhanced cure rates.

Adaptive immunity is essential in preventing recrudescence of Plasmodium yoelii malaria parasites after artesunate treatment.

Artemisinin-based antimalarials, such as artesunate (ART), alone or in combination, are the mainstay of the therapy against malaria caused by Plasmodium falciparum. However, the emergence and spread of artemisinin resistance threatens the future success of its global malaria eradication. Although much of the reported artemisinin resistance can be attributed to mutations intrinsic to the parasite, a significant proportion of treatment failures are thought to be due to other factors such as the host's immune system. Exactly how the immune system participates in the clearance and elimination of malaria parasites during ART treatment is unknown. Here, we show that a developing primary immune response, involving both B and CD4+ T cells, is necessary for the complete elimination but not initial clearance, of Plasmodium yoelii YM parasites in mice treated with ART. Our study uncovers a dynamic interplay between ART and host adaptive immunity in Plasmodium sp. elimination.

Do anti-malarials in Africa meet quality standards? The market penetration of non quality-assured artemisinin combination therapy in eight African countries

BackgroundQuality of artemisinin-based combination therapy (ACT) is important for ensuring malaria parasite clearance and protecting the efficacy of artemisinin-based therapies. The extent to which non quality-assured ACT (non-QAACT), or those not granted global regulatory approval, are available and used to treat malaria in endemic countries is poorly documented. This paper uses national and sub-national medicine outlet surveys conducted in eight study countries (Benin, Kinshasa and Kantanga [Democratic Republic of the Congo, DRC], Kenya, Madagascar, Nigeria, Tanzania, Uganda and Zambia) between 2009 and 2015 to describe the non-QAACT market and to document trends in availability and distribution of non-QAACT in the public and private sector.ResultsIn 2014/15, non-QAACT were most commonly available in Kinshasa (83%), followed by Katanga (53%), Nigeria (48%), Kenya (42%), and Uganda (33%). Non-QAACT accounted for 20% of the market share in the private sector in Kenya, followed by Benin and Uganda (19%), Nigeria (12%) and Zambia (8%); this figure was 27% in Katanga and 40% in Kinshasa. Public sector non-QAACT availability and distribution was much lower, with the exception of Zambia (availability, 85%; market share, 32%). Diverse generics and formulations were available, but non-QAACT were most commonly artemether–lumefantrine (AL) or dihydroartemisinin-piperaquine (DHA PPQ), in tablet formulation, imported, and distributed in urban areas at either pharmacies or drug stores. The number of unique manufacturers supplying non-QAACT to each country ranged from 9 in Uganda to 92 in Nigeria.ConclusionsAddressing the availability and distribution of non-QAACT will require effective private sector engagement and evidence-based strategies to address provider and consumer demand for these products. Given the variation in non-QAACT markets observed across the eight study countries, active efforts to limit registration, importation and distribution of non-QAACT must be tailored to the country context, and will involve addressing complex and challenging aspects of medicine registration, private sector pharmaceutical regulation, local manufacturing and drug importation. These efforts may be critical not only to patient health and safety, but also to effective malaria control and protection of artemisinin drug efficacy in the face of spreading resistance.

EFFICACY AND SAFETY OF ARTEMISININ-BASED COMBINATION THERAPIES IN PEOPLE WITH PLASMODIUM FALCIPARUM MALARIA RECEIVING ANTIRETROVIRAL THERAPY IN ZAMBIA

BackgroundThe coverage of Artemisinin-based Combination Therapies (ACTs) for treatment of malaria and antiretroviral therapy (ART) is increasing rapidly in Sub-Saharan Africa. Because of the geographical overlap in areas of high...

Evidencing the Role of Erythrocytic Apoptosis in Malarial Anemia.

In the last decade it has become clear that, similarly to nucleated cells, enucleated red blood cells (RBCs) are susceptible to programmed apoptotic cell death. Erythrocytic apoptosis seems to play a role in physiological clearance of aged RBCs, but it may also be implicated in anemia of different etiological sources including drug therapy and infectious diseases. In malaria, severe anemia is a common complication leading to death of children and pregnant women living in malaria-endemic regions of Africa. The pathogenesis of malarial anemia is multifactorial and involves both ineffective production of RBCs by the bone marrow and premature elimination of non-parasitized RBCs, phenomena potentially associated with apoptosis. In the present overview, we discuss evidences associating erythrocytic apoptosis with the pathogenesis of severe malarial anemia, as well as with regulation of parasite clearance in malaria. Efforts to understand the role of erythrocytic apoptosis in malarial anemia can help to identify potential targets for therapeutic intervention based on apoptotic pathways and consequently, mitigate the harmful impact of malaria in global public health.

Evidence for spleen dysfunction in malaria-HIV co-infection in a subset of pediatric patients

The spleen has an important role in the clearance of malaria parasites, and the role of HIV co-infection on this process is yet to be described. Using a combination of histological and molecular methods, we systematically evaluated parasite load across multiple organs from HIV-positive and HIV-negative cases of an autopsy study of pediatric comatose children with malaria infection (n=103) in Blantyre, Malawi. Quantification of parasite load across organs was done using histology. A subset of cases was further characterized for parasite localization and stage of development using immunohistochemistry-based labeling of parasite and host cells (5 HIV-positive, 10 HIV-negative), and quantitative RT-PCR (qRT-PCR) of asexual and sexual-specific genes (4 HIV-positive, 5 HIV-negative). The results were compared with clinical information including HIV status. The HIV-positive rate was 21% for the group studied (20 of 95) and HIV-positive patients had a significantly shorter duration of time between onset of illness and death, and were significantly older than HIV-negative patients. We found that spleens of HIV-positive cases had significantly higher parasite loads compared with those of HIV-negative cases in each of the three methods we used: (i) standard histology, (ii) immunohistochemistry-based labeling of Plasmodium lactate dehydrogenase (pLDH), and (iii) molecular detection of asexual parasite transcript apical membrane antigen 1 (AMA1). Immunohistochemistry-based labeling of macrophage marker CD163 in a subset of spleens revealed fewer activated macrophages containing engulfed parasites and a greater number of free unphagocytosed parasites in the HIV-positive cases. The mechanism by which HIV infection is associated with more rapid progression to severe cerebral malaria disease is possibly impairment of parasite destruction by splenic macrophages, supported by published in vitro studies showing inefficient phagocytosis of malaria parasites by HIV-infected macrophages.

Malaria and HIV among pediatric inpatients in two Tanzanian referral hospitals: A prospective study

Malaria remains common in sub-Saharan Africa, but it is frequently over-diagnosed and over-treated in hospitalized children. HIV is prevalent in many malaria endemic areas and may delay parasite clearance and increase mortality among children with malaria. This prospective cohort study enrolled children with suspected malaria between 3 months and 12 years of age hospitalized at two referral hospitals in Tanzania. Both a thick blood smear (BS) and a malaria rapid diagnostic test (mRDT) were performed. If discordant results were obtained, PCR was performed for Plasmodium falciparum. Malaria was confirmed if two out of three tests were positive. Malaria parasite densities were determined for two consecutive days after diagnosis and treatment of malaria. All participants were tested for HIV. Among 1492 hospitalized children, 400 (26.8%) were enrolled with suspected malaria infection. There were 196/400 (49.0%) males, and the median age was 18 [9–36] months. BS was positive in 95/400 (23.8%), and mRDT was positive in 70/400 (17.5%), with moderate agreement (Kappa=0.598). Concordant results excluded malaria in 291/400 (72.8%) and confirmed malaria in 56/400 (14.0%). PCR performed on 53 discordant results confirmed malaria in 1/39 of the BS-positive/mRDT-negative cases, and 6/14 of the BS-negative/mRDT-positive cases. The prevalence of confirmed malaria was 63/400 (15.8%). In multivariable logistic regression, malaria was associated with HIV (OR 3.45 [1.65–7.20], p=0.001). Current breastfeeding (OR 0.25 [0.11–0.56], p=0.001) and higher hemoglobin (OR 0.70 [0.60–0.81], p<0.001 per 1g/dL) were associated with decreased odds of malaria. Malaria parasite clearance was delayed in HIV-infected participants (p<0.001). Malaria is over-diagnosed even at referral centers in high transmission areas. Hospitalized HIV-infected children are more likely to have malaria and exhibit delayed clearance of parasites. Hospitals should consider using mRDTs as a first step for malaria testing among hospitalized children in sub-Saharan Africa.

How Robust Are Malaria Parasite Clearance Rates as Indicators of Drug Effectiveness and Resistance?

Artemisinin-based combination therapies (ACTs) are currently the first-line drugs for treating uncomplicated falciparum malaria, the most deadly of the human malarias. Malaria parasite clearance rates estimated from patients' blood following ACT treatment have been widely adopted as a measure of drug effectiveness and as surveillance tools for detecting the presence of potential artemisinin resistance. This metric has not been investigated in detail, nor have its properties or potential shortcomings been identified. Herein, the pharmacology of drug treatment, parasite biology, and human immunity are combined to investigate the dynamics of parasite clearance following ACT. This approach parsimoniously recovers the principal clinical features and dynamics of clearance. Human immunity is the primary determinant of clearance rates, unless or until artemisinin killing has fallen to near-ineffective levels. Clearance rates are therefore highly insensitive metrics for surveillance that may lead to overconfidence, as even quite substantial reductions in drug sensitivity may not be detected as lower clearance rates. Equally serious is the use of clearance rates to quantify the impact of ACT regimen changes, as this strategy will plausibly miss even very substantial increases in drug effectiveness. In particular, the malaria community may be missing the opportunity to dramatically increase ACT effectiveness through regimen changes, particularly through a switch to twice-daily regimens and/or increases in artemisinin dosing levels. The malaria community therefore appears overreliant on a single metric of drug effectiveness, the parasite clearance rate, that has significant and serious shortcomings.