ACP Broadsheet no 148. July 1996. Laboratory diagnosis of malaria

Portable optofluidic absorption flow analyzer for quantitative malaria diagnosis from whole blood

Fast and automated diagnostic devices are bound to play a significant role in the on-going efforts toward malaria eradication. In this article, we present the realization of a portable device for quantitative malaria diagnostic testing at the point-of-care. The device measures optical absorbance (at λ=405  nm) of single cells flowing through a custom-designed microfluidic channel. The device incorporates the required functionality to align the microfluidic channel with the optical interrogation region. Variation in optical absorbance is used to differentiate red blood cells (both healthy and infected) from other cellular components of whole blood. Using the instrument, we have measured single-cell optical absorbance levels of different types of cells present in blood. High-throughput single-cell-level measurements facilitated by the device enable detection of malaria, even from a few microliters of blood. Further, we demonstrate the detection of malaria from a suspension containing all cellular components of whole blood, which validates its usability in real-world diagnostic scenarios.

Prevalence and Risk Factors Associated with Hemoparasites in Cattle and Goats at the Edge of Kibale National Park, Western Uganda

Livestock production is a major sector of the Ugandan economy. Ugandan ruminant livestock (principally cattle and goats) are susceptible to hemoparasites that can cause serious clinical disease and production losses. Kibale National Park, in western Uganda, is a protected forest ecosystem surrounded by small-scale farms where cattle and goats are raised. We conducted a cross-sectional study of cattle and goats in this area and diagnosed hemoparasite infections by microscopy. We collected data on animal characteristics and management practices to assess risk factors associated with infection. We studied 186 cattle and 317 goats from 20 villages, including 16 villages directly adjacent to Kibale and 4 villages ≥3 km from the park boundary. Hemoparasites detected in cattle and goats were of the genera Theileria, Anaplasma, and Trypanosoma with a prevalence of 15.1%, 1.6%, and 4.3% respectively in cattle, and 10%, 6.0%, and 0.0%, respectively in goats. Trypanosomes infected approximately 8% of cattle in villages bordering Kibale but were never detected in cattle in "control" villages ≥3 km from the park. Trypanosomes were approximately 7 times more likely to infect animals in households that did not provide veterinary care to their animals than in households that provided routine veterinary care. Within cattle, Theileria infections were approximately 7 times more likely to occur in cross-bred cattle than in indigenous pure breeds. Anaplasma infections were approximately 3.5 times more likely to occur in cattle than in goats (no goats were diagnosed with Trypanosoma infection). These data suggest that proximity to the park, provision of veterinary care, and breed are significant risk factors for hemoparasites in this population of ruminants, and that, in general, cattle are more susceptible than goats.

Field evaluation of diagnostic performance of malaria rapid diagnostic tests in western Kenya

BACKGROUND

Malaria continues to be a major burden in the endemic regions of Kenya. Health outcomes associated with case management are dependent on the use of appropriate diagnostic methods. Rapid diagnostic tests (RDTs) have provided an important tool to help implement the WHO recommended parasite-based diagnosis in regions where expert microscopy is not available. One of the questions that must be answered when implementing RDTs is whether these tests are useful in a specific endemic region, as well as the most appropriate RDT to use. Data on the sensitivity and specificity of RDT test kits is important information to help guide test selection by national malaria control programmes.

METHODS

This study evaluated the diagnostic performance of RDTs including First Response (FR), CareStart (CS), SD Bioline (SD), and Binax Now (BN). The performance of these malaria kits was compared to microscopy, the gold standard, for the detection of malaria parasites. The malaria RDTs were also compared to PCR which is a more sensitive reference test. Five-hundred participants were included in the study through community screening (50 %) and testing suspected malaria cases referred from health facilities.

RESULTS

Of the 500 participants recruited, 33 % were malaria positive by microscopy while 51.2 % were positive by PCR. Compared to microscopy, the sensitivity of eight RDTs to detect malaria parasites was 90.3-94.8 %, the specificity was 73.3-79.3 %, the positive predictive value was 62.2-68.8 %, and the negative predictive value was 94.3-96.8 %. Compared to PCR, the sensitivity of the RDTs to detect malaria parasites was 71.1-75.4 %, the specificity was 80.3-84.4 %, the positive predictive value was 80.3-83.3 %, and the negative predictive value was 73.7-76.1 %. The RDTs had a moderate measure of agreement with both microscopy (>80.1 %) and PCR (>77.6 %) with a κ > 0.6.

CONCLUSION

The performance of the evaluated RDTs using field samples was moderate; hence they can significantly improve the quality of malaria case management in endemic regions in Kenya by ensuring appropriate treatment of malaria positive individuals and avoiding indiscriminate use of anti-malarial drugs for parasite negative patients.

Application of a cell microarray chip system for accurate, highly sensitive, and rapid diagnosis for malaria in Uganda

Accurate, sensitive, rapid, and easy operative diagnosis is necessary to prevent the spread of malaria. A cell microarray chip system including a push column for the recovery of erythrocytes and a fluorescence detector was employed for malaria diagnosis in Uganda. The chip with 20,944 microchambers (105 μm width and 50 μm depth) was made of polystyrene. For the analysis, 6 μl of whole blood was employed, and leukocytes were practically removed by filtration through SiO2-nano-fibers in a column. Regular formation of an erythrocyte monolayer in each microchamber was observed following dispersion of an erythrocyte suspension in a nuclear staining dye, SYTO 21, onto the chip surface and washing. About 500,000 erythrocytes were analyzed in a total of 4675 microchambers, and malaria parasite-infected erythrocytes could be detected in 5 min by using the fluorescence detector. The percentage of infected erythrocytes in each of 41 patients was determined. Accurate and quantitative detection of the parasites could be performed. A good correlation between examinations via optical microscopy and by our chip system was demonstrated over the parasitemia range of 0.0039-2.3438% by linear regression analysis (R(2) = 0.9945). Thus, we showed the potential of this chip system for the diagnosis of malaria.

Heparin micropatterning onto fouling-release perfluoropolyether-based polymers via photobiotin activation

A simple method for constructing versatile ordered biotin/avidin arrays on UV-curable perfluoropolyethers (PFPEs) is presented. The goal is the realization of a versatile platform where any biotinylated biological ligands can be further linked to the underlying biotin/avidin array. To this end, microcontact arrayer and microcontact printing technologies were developed for photobiotin direct printing on PFPEs. As attested by fluorescence images, we demonstrate that this photoactive form of biotin is capable of grafting onto PFPEs surfaces during irradiation. Bioaffinity conjugation of the biotin/avidin system was subsequently exploited for further self-assembly avidin family proteins onto photobiotin arrays. The excellent fouling release PFPEs surface properties enable performing avidin assembly step simply by arrays incubation without PFPEs surface passivation or chemical modification to avoid unspecific biomolecule adsorption. Finally, as a proof of principle biotinylated heparin was successfully grafted onto photobiotin/avidin arrays.

Optofluidic single-cell absorption flow analyzer for point-of-care diagnosis of malaria

In this work, an optofluidic flow analyzer, which can be used to perform malaria diagnosis at the point-of-care is demonstrated. The presented technique is based on quantitative optical absorption measurements carried out on a single cell level for a given population of Human Red Blood Cells (RBCs). By measuring the optical absorption of each RBC, the decrease in the Hemoglobin (Hb) concentration in the cytoplasm of the cell due to the invasion of malarial parasite is detected. Cells are assessed on a single cell basis, as they pass through a microfluidic channel. The proposed technique has been implemented with inexpensive off-the-shelf components like laser diode, photo-detector and a micro-controller. The ability of the optofluidic flow analyzer to asses about 308,049 cells within 3 minutes has been demonstrated. The presented technique is capable of detecting very low parasitemia levels with high sensitivity.

MALARIA DIAGNOSIS BY LOOP-MEDIATED ISOTHERMAL AMPLIFICATION (LAMP) IN THAILAND

The loop-mediated isothermal amplification method (LAMP) is a recently developed molecular technique that amplifies nucleic acid under isothermal conditions. For malaria diagnosis, 150 blood samples from consecutive febrile malaria patients, and healthy subjects were screened in Thailand. Each sample was diagnosed by LAMP, microscopy and nested polymerase chain reaction (nPCR), using nPCR as the gold standard. Malaria LAMP was performed using Plasmodiumgenus and Plasmodium falciparum specific assays in parallel. For the genus Plasmodium, microscopy showed a sensitivity and specificity of 100%, while LAMP presented 99% of sensitivity and 93% of specificity. For P. falciparum, microscopy had a sensitivity of 95%, and LAMP of 90%, regarding the specificity; and microscopy presented 93% and LAMP 97% of specificity. The results of the genus-specific LAMP technique were highly consistent with those of nPCR and the sensitivity of P. falciparum detection was only marginally lower.

A highly sensitive self assembled monolayer modified copper doped zinc oxide nanofiber interface for detection of Plasmodium falciparum histidine-rich protein-2: Targeted towards rapid, early diagnosis of malaria

Rapid, ultrasensitive diagnostic/triaging kits for early detection of malarial parasites are critical for prevention of malarial epidemic, especially in developing and tropical countries. Unlike traditional microscopic diagnosis, these kits rely on the detection of antigens specific to malarial parasites. One such antigen which is routinely used in these diagnostic kits is Histidine-rich protein-2; a protein synthesized and released into the blood stream by the parasite Plasmodium falciparum. In this paper, we demonstrate an ultrasensitive nanobiosensor detection platform for Histidine-rich protein-2 having a limit of detection of attogram/ml. This nanobiosensor platform comprises of Mercaptopropylphosphonic acid functionalized copper doped zinc oxide nanofibers synthesized by electrospinning technique. Ultrasensitivity of attogram/ml can be attributed to the complimentary effects of Mercaptopropylphosphonic acid and copper doping in zinc oxide. Mercaptopropylphosphonic acid enhances the functional groups required for immobilizing antibody. Copper doping in zinc oxide not only increases the conductivity of the nanofibers but also pre-concentrates the target analyte onto the Mercaptopropylphosphonic acid treated nanofiber surface due to inherent electric field generated at the copper/zinc oxide heterojunction interface. The impedimetric detection response of copper-doped zinc oxide nanofiber modified electrode shows excellent sensitivity (28.5 kΩ/(gm/ml)/cm(2)) in the detection ranges of 10 ag/ml-10 µg/ml, and a detection limit of 6 attogram/ml. In addition, the proposed biosensor is highly selective to targeted HRP2 protein with a relative standard deviation of 1.9% in the presence of various interference of nonspecific molecules. To the best of our knowledge, this biosensor shows the lowest detection limit of malarial parasites reported in the literature spanning different nanomaterials and different detection mechanisms. Since the nanobiosensor platform is based on immunoassay technique, with a little modification, it can be extended for developing point-of-care diagnostic devices for several biomarkers of importance.

Loop-Mediated Isothermal Amplification Assay for Identification of Five Human Plasmodium Species in Malaysia

The lack of rapid, affordable, and accurate diagnostic tests represents the primary hurdle affecting malaria surveillance in resource- and expertise-limited areas. Loop-mediated isothermal amplification (LAMP) is a sensitive, rapid, and cheap diagnostic method. Five species-specific LAMP assays were developed based on 18S rRNA gene. Sensitivity and specificity of LAMP results were calculated as compared with microscopic examination and nested polymerase chain reaction. LAMP reactions were highly sensitive with the detection limit of one copy for Plasmodium vivax, Plasmodium falciparum, and Plasmodium malariae and 10 copies for Plasmodium knowlesi and Plasmodium ovale. LAMP positively detected all human malaria species in all positive samples (N = 134; sensitivity = 100%) within 35 minutes. All negative samples were not amplified by LAMP (N = 67; specificity = 100%). LAMP successfully detected two samples with very low parasitemia. LAMP may offer a rapid, simple, and reliable test for the diagnosis of malaria in areas where malaria is prevalent.

High Incidence of Malaria Along the Sino-Burmese Border Is Associated With Polymorphisms of CR1, IL-1A, IL-4R, IL-4, NOS, and TNF, But Not With G6PD Deficiency

Malaria is highly endemic in Yunnan Province, China, with the incidence of malaria being highest along the Sino-Burmese border. The aim of our study was to determine whether genetic polymorphisms are associated with the prevalence of malaria among Chinese residents of the Sino-Burmese border region. Fourteen otherwise healthy people with glucose-6-phosphate dehydrogenase (G6PD) deficiency, 50 malaria patients, and 67 healthy control subjects were included in our cross-sectional study. We analyzed the frequency of the G3093T and T520C single-nucleotide polymorphisms (SNPs) of CR1. Logistic regression was used to calculate the prevalence odds ratio (POR) and 95% confidence interval (CI) of malaria for the T520C SNP of CR1 and SNPs of G6PD, IL-4, IL-4R, IL-1A, NOS, CD40LG, TNF, and LUC7L. The frequency of the 3093T/3093T genotype of CR1 in the malaria group (0.16) was significantly higher than that in the control group (0.045, P < 0.05), and significantly lower than that in the G6PD deficiency group (0.43, P < 0.01). The frequency of the 520T/520T genotype of CR1 was significantly higher in the malaria patients (0.78) than that in the control group (0.67, P < 0.05) and G6PD-deficiency group (0.36, P < 0.05). The T allele of the T520C variant of CR1 was significantly associated with the prevalence of malaria (POR: 1.460; 95% CI: 0.703-3.034). Polymorphisms of G6PD did not significantly influence the prevalence malaria (P > 0.05). A GTGTGTC haplotype consisting of IL-1A (rs17561), IL-4 (rs2243250), TNF (rs1800750), IL-4R (rs1805015), NOS (rs8078340), CD40LG (rs1126535), and LUC7L (rs1211375) was significantly associated with the prevalence of malaria (POR: 1.822, 95% CI: 0.998-3.324). The 3093G/3093G and 520T/520T genotypes are the predominant genetic variants of CR1 among Chinese residents near the Sino-Burmese border, and the T allele of T520C is associated with the prevalence of malaria in this region. Although G6PD deficiency does not protect against malaria, it may diminish the association between malaria and the CR1 polymorphisms in this population. The GTGTGTC haplotype is also associated with the prevalence of malaria in this region.

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.

The Utility of Blood and Bone Marrow Films and Trephine Biopsy Sections in the Diagnosis of Parasitic Infections

The laboratory haematologist has a role in the diagnosis of parasitic infections. Peripheral blood examination is critical in the diagnosis of malaria, babesiosis, filariasis and trypanosomiasis. Bone marrow examination is important in the diagnosis of leishmaniasis and occasionally leads to the diagnosis of other parasitic infections. The detection of eosinophilia or iron deficiency anaemia can alert the laboratory haematologist or physician to the possibility of parasitic infection. In addition to morphological skills, an adequate clinical history is important for speedy and accurate diagnosis, particularly in non-endemic areas.

Simple Real-Time PCR and Amplicon Sequencing Method for Identification of Plasmodium Species in Human Whole Blood

Malaria is the leading identifiable cause of fever in returning travelers. Accurate Plasmodium species identification has therapy implications for P. vivax and P. ovale, which have dormant liver stages requiring primaquine. Compared to microscopy, nucleic acid tests have improved specificity for species identification and higher sensitivity for mixed infections. Here, we describe a SYBR green-based real-time PCR assay for Plasmodium species identification from whole blood, which uses a panel of reactions to detect species-specific non-18S rRNA gene targets. A pan-Plasmodium 18S rRNA target is also amplified to allow species identification or confirmation by sequencing if necessary. An evaluation of assay accuracy, performed on 76 clinical samples (56 positives using thin smear microscopy as the reference method and 20 negatives), demonstrated clinical sensitivities of 95.2% for P. falciparum (20/21 positives detected) and 100% for the Plasmodium genus (52/52), P. vivax (20/20), P. ovale (9/9), and P. malariae (6/6). The sensitivity of the P. knowlesi-specific PCR was evaluated using spiked whole blood samples (100% [10/10 detected]). The specificities of the real-time PCR primers were 94.2% for P. vivax (49/52) and 100% for P. falciparum (51/51), P. ovale (62/62), P. malariae (69/69), and P. knowlesi (52/52). Thirty-three specimens were used to test species identification by sequencing the pan-Plasmodium 18S rRNA PCR product, with correct identification in all cases. The real-time PCR assay also identified two samples with mixed P. falciparum and P. ovale infection, which was confirmed by sequencing. The assay described here can be integrated into a malaria testing algorithm in low-prevalence areas, allowing definitive Plasmodium species identification shortly after malaria diagnosis by microscopy.

New insight-guided approaches to detect, cure, prevent and eliminate malaria

New challenges posed by the development of resistance against artemisinin-based combination therapies (ACTs) as well as previous first-line therapies, and the continuing absence of vaccine, have given impetus to research in all areas of malaria control. This review portrays the ongoing progress in several directions of malaria research. The variants of RTS,S and apical membrane antigen 1 (AMA1) are being developed and test adapted as multicomponent and multistage malaria control vaccines, while many other vaccine candidates and methodologies to produce antigens are under experimentation. To track and prevent the spread of artemisinin resistance from Southeast Asia to other parts of the world, rolling circle-enhanced enzyme activity detection (REEAD), a time- and cost-effective malaria diagnosis in field conditions, and a DNA marker associated with artemisinin resistance have become available. Novel mosquito repellents and mosquito trapping and killing techniques much more effective than the prevalent ones are undergoing field testing. Mosquito lines stably infected with their symbiotic wild-type or genetically engineered bacteria that kill sympatric malaria parasites are being constructed and field tested for stopping malaria transmission. A complementary approach being pursued is the addition of ivermectin-like drug molecules to ACTs to cure malaria and kill mosquitoes. Experiments are in progress to eradicate malaria mosquito by making it genetically male sterile. High-throughput screening procedures are being developed and used to discover molecules that possess long in vivo half life and are active against liver and blood stages for the fast cure of malaria symptoms caused by simple or relapsing and drug-sensitive and drug-resistant types of varied malaria parasites, can stop gametocytogenesis and sporogony and could be given in one dose. Target-based antimalarial drug designing has begun. Some of the putative next-generation antimalarials that possess in their scaffold structure several of the desired properties of malaria cure and control are exemplified by OZ439, NITD609, ELQ300 and tafenoquine that are already undergoing clinical trials, and decoquinate, usnic acid, torin-2, ferroquine, WEHI-916, MMV396749 and benzothiophene-type N-myristoyltransferase (NMT) inhibitors, which are candidates for future clinical usage. Among these, NITD609, ELQ300, decoquinate, usnic acid, torin-2 and NMT inhibitors not only cure simple malaria and are prophylactic against simple malaria, but they also cure relapsing malaria.

Antimalarial properties of SAABMAL (®): an ethnomedicinal polyherbal formulation for the treatment of uncomplicated malaria infection in the tropics

Background & objectives:

Malaria is a serious problem in the countries of the developing world. As the malaria parasite has become resistant to most of the antimalaria drugs available currently, there is a need to search for newer drugs. This study reports the pharmaceutical quality and in vivo antimalarial activities of a polyherbal formulation (SAABMAL^®) used as malarial remedy in Nigeria.

Methods:

The antiplasmodial activity of SAABMAL^® was determined by using the 4-day suppressive test in Plasmodium berghei-infected mice. The formulation was tried on three different experimental animal models for in vivo antimalarial activities, which are prophylactic, suppressive and curative in mice. Chloroquine and pyrimethamine were used as standard drugs for comparison.

Results:

The suppressive study showed that, SAABMAL^® (200 and 400 mg/kg/bw) significantly (P<0.01) produced a suppression (29.39 - 100%) of parasitaemia in a dose-dependent manner, while the curative study showed that SAABMAL^® at 400 mg significantly (P<0.01) reduced (95.80%) parasitaemia compared with controls. The mean survival time of SAABMAL^®-treated groups (100 and 200 mg/kg) was higher than that of the chloroquine-treated group. Histopathologically, no changes were found in the spleen of both untreated and treated groups. SAABMAL^® capsules were of good mechanical properties with low weight variation and high degree of content mass uniformity.

Interpretation & conclusions:

The results obtained in this study showed the efficacy of SAABMAL^®, a herbal antimalarial formulation against chloroquine sensitive malaria and its potential use in the treatment of uncomplicated malaria infection. Further studies need to be done in humans to test its efficacy and safety for its potential use as an antimalarial drug.

Fitness cost of resistance for lumefantrine and piperaquine-resistant Plasmodium berghei in a mouse model

Background

The evolution of drug-resistant parasites is a major hindrance to malaria control, and thus understanding the behaviour of drug-resistant mutants is of clinical relevance. The study aimed to investigate how resistance against lumefantrine (LU) and piperaquine (PQ), anti-malarials used as partner drugs in artemisinin-based combination therapy (ACT), impacts parasite fitness. This is important since resistance to ACT, the first-line anti-malarial regimen is increasingly being reported.

Methods

The stability of Plasmodium berghei ANKA strain that was previously selected for LU and PQ resistance was evaluated using the 4-day assay and established infection test in mice. Fitness cost of resistance was determined by comparing parasites proliferation rates in absence of drug pressure for the drug-exposed parasites between day 4 and 7 post-infection (pi), relative to the wild-type. Statistical analysis of data to compare mean parasitaemia and growth rates of respective parasite lines was carried out using student’s t-test and one-way analysis of variance, with significance level set at p<0.05.

Results

During serial passaging in the absence of the drug, the PQ-resistant parasite maintained low growth rates at day 7 pi (mean parasitaemia, 5.6% ± 2.3) relative to the wild-type (28.4% ± 6.6), translating into a fitness cost of resistance of 80.3%. Whilst resistance phenotype for PQ was stable, that of LU was transient since after several serial passages in the absence of drug, the LU-exposed line assumed the growth patterns of the wild-type.

Conclusions

The contrasting behaviour of PQ- and LU-resistance phenotypes support similar findings which indicate that even for drugs within the same chemical class, resistance-conferred traits may vary on how they influence parasite fitness and virulence. Resistance-mediating polymorphisms have been associated with less fit malaria parasites. In the absence of drug pressure in the field, it is therefore likely that the wild-type parasite will out-compete the mutant form. This implies the possibility of reintroducing a drug previously lost to resistance, after a period of suspended use. Considering the recent reports of high failure rates associated with ACT, high fitness cost of resistance to PQ is therefore of clinical relevance as the drug is a partner in ACT.

Evaluation of the accuracy of the EasyTest™ malaria Pf/Pan Ag, a rapid diagnostic test, in Uganda

In recent years, rapid diagnostic tests (RDTs) have been widely used for malaria detection, primarily because of their simple operation, fast results, and straightforward interpretation. The Asan EasyTest™ Malaria Pf/Pan Ag is one of the most commonly used malaria RDTs in several countries, including Korea and India. In this study, we tested the diagnostic performance of this RDT in Uganda to evaluate its usefulness for field diagnosis of malaria in this country. Microscopic and PCR analyses, and the Asan EasyTest™ Malaria Pf/Pan Ag rapid diagnostic test, were performed on blood samples from 185 individuals with suspected malaria in several villages in Uganda. Compared to the microscopic analysis, the sensitivity of the RDT to detect malaria infection was 95.8% and 83.3% for Plasmodium falciparum and non-P. falciparum, respectively. Although the diagnostic sensitivity of the RDT decreased when parasitemia was ≤500 parasites/µl, it showed 96.8% sensitivity (98.4% for P. falciparum and 93.8% for non-P. falciparum) in blood samples with parasitemia ≥100 parasites/µl. The specificity of the RDT was 97.3% for P. falciparum and 97.3% for non-P. falciparum. These results collectively suggest that the accuracy of the Asan EasyTest™ Malaria Pf/Pan Ag makes it an effective point-of-care diagnostic tool for malaria in Uganda.

Micromagnetic resonance relaxometry for rapid label-free malaria diagnosis

We report a new technique for sensitive, quantitative and rapid detection of Plasmodium spp.-infected red blood cells (RBCs) by means of magnetic resonance relaxometry (MRR). During the intraerythrocytic cycle, malaria parasites metabolize large amounts of cellular hemoglobin and convert it into hemozoin crystallites. We exploit the relatively large paramagnetic susceptibility of these hemozoin particles, which induce substantial changes in the transverse relaxation rate of proton nuclear magnetic resonance of RBCs, to infer the 'parasite load' in blood. Using an inexpensive benchtop 0.5-Tesla MRR system, we show that with minimal sample preparatory steps and without any chemical or immunolabeling, a parasitemia level of fewer than ten parasites per microliter in a volume below 10 μl of whole blood is detected in a few minutes. We demonstrate this method both for cultured Plasmodium falciparum parasites and in vivo with Plasmodium berghei-infected mice.

Tumour necrosis factor, interleukin-6 and interleukin-10 are possibly involved in Plasmodium vivax-associated thrombocytopaenia in southern Pakistani population

Background

In Pakistan, Plasmodium vivax is endemic causing approximately 70% of the malaria cases. A number of haematological changes, especially thrombocytopaenia have been reported for P. vivax. Several host factors including cell-mediated immune cells, such as IL-1, IL-6 and IL-10 have been documented for P. vivax-induced thrombocytopaenia. However, study on correlation of cytokines and thrombocytopaenia in P. vivax, particularly in patients with severe signs and symptoms has not been reported from Pakistan.

Methods

A case control study to correlate TNF, IL-6 and IL-10 in healthy controls and thrombocytopaenic P. vivax-infected patients (both uncomplicated and complicated cases) from southern Pakistan was carried out during January 2009 to December 2011. One Hundred and eighty two patients presenting with microscopy-confirmed asexual P. vivax mono-infection and 100 healthy controls were enrolled in the study at Aga Khan University Hospital, Karachi. Enzyme-linked immunosorbent assay (ELISA) was performed for determination of TNF, IL-6 and IL-10 levels.

Results

Out of 182 cases, mild thrombocytopaenia (platelet count 100,000-150,000 mm³) was observed in ten (5.5%), moderate (50,000-100,000 mm³) in 93 (51.1%), and profound thrombocytopaenia (<50,000 mm³) was detected in 79 (43.4%) patients. IL-6 and IL-10 levels were found approximately three-fold higher in the mild cases compared to healthy controls. Two-fold increase in TNF and IL-10 (p < 0.0001) was observed in profound thrombocytopaenic when compared with moderate cases, while IL-6 was not found to be significantly elevated.

Conclusion

Cytokines may have a possible role in P. vivax-induced thrombocytopaenia in Pakistani population. Findings from this study give first insight from Pakistan on the role of cytokines in P.vivax-associated thrombocytopaenia. However, further studies are required to understand the relevance of cytokines in manifestations of thrombocytopaenia in P. vivax malaria.

Application of loop-mediated isothermal amplification assay combined with lateral flow dipstick for detection of Plasmodium falciparum and Plasmodium vivax

Malaria is largely a preventable and curable disease. However, a delay or an inappropriate treatment can result in serious adverse outcomes for patient. Rapid, simple and cost-effective diagnostic tests that can be easily adapted and rapidly scaled-up at the field or community levels are needed. In this study, accelerated detection methods for the Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) dihydrofolate reductase-thymidylate synthase were developed based on the loop-mediated isothermal amplification (LAMP) method. The developed methods included the use of species-specific biotinylated primers to amplify LAMP amplicons, which were then hybridized to specific FITC-labeled DNA probes and visualized on a chromatographic lateral flow dipstick (LFD). The total LAMP-LFD assay time was approximately 1.5h. The LAMP-LFD assays showed similar detection limit to conventional PCR assay when performed on plasmid DNA carrying the malaria dhfr-ts genes. The LAMP-LFD showed 10 folds higher detection limit than PCR when performed on genomic DNA samples from Pf and Pv parasites. The dhfr-ts LAMP-LFD assays also have the advantages of reduced assay time and easy format for interpretation of results.

A paper microfluidic cartridge for automated staining of malaria parasites with an optically transparent microscopy window

A paper microfluidic cartridge for the automated staining of malaria parasites (Plasmodium) with acridine orange prior to microscopy is presented. The cartridge enables simultaneous, sub-minute generation of both thin and thick smears of acridine orange stained parasites. Parasites are stained in a cellulose matrix, after which the parasites are ejected via capillary forces into an optically transparent chamber. The unique slanted design of the chamber ensures that a high percentage of the stained blood will be of the required thickness for a thin smear, without resorting to spacers or other methods that can increase production cost or require tight quality controls. A hydrophobic snorkel facilitates the removal of air bubbles during filling. The cartridge contains both a thin smear region, where a single layer of cells is presented unobstructed, for ease of species identification, and a thick smear region, containing multiple cell layers, for enhanced limit of detection.

Defining the malaria burden in Nchelenge District, northern Zambia using the World Health Organization malaria indicators survey

BACKGROUND

Malaria is considered as one of the major public health problems and among the diseases of poverty. In areas of stable and relatively high transmission, pregnant women and their newborn babies are among the higher risk groups. A multicentre trial on the safety and efficacy of several formulations of artemisinin-based combination therapy (ACT) during pregnancy is currently on-going in four African countries, including Zambia, whose study site is in Nchelenge district. As the study outcomes may be influenced by the local malaria endemicity, this needs to be characterized. A cross-sectional survey to determine the prevalence and intensity of infection among <10 years old was carried out in March-April 2012 in Nchelenge district.

METHODS

The sampling unit was the household where all children < 10 years of age were included in the survey using simple random household selection on a GPS coded list. A blood sample for determining haemoglobin concentration and identifying malaria infection was collected from each recruited child.

RESULTS

Six hundred thirty households were selected and 782 children tested for malaria and anaemia. Prevalence of malaria infection was 30.2% (236/782), the large majority (97.9%, 231/236) being Plasmodium falciparum and the remaining ones (2.1%, 5/236) Plasmodium malariae. Anaemia, defined as haemoglobin concentration <11 g/dl, was detected in 51.2% (398/782) children.

CONCLUSION

In Zambia, despite the reported decline in malaria burden, pockets of high malaria endemicity, such as Nchelenge district, still remain. This is a border area and significant progress can be achieved only by concerted efforts aimed at increasing coverage of current control interventions across the border.

Cytokine profiles amongst Sudanese patients with visceral leishmaniasis and malaria co-infections

BACKGROUND

The immune system plays a critical role in the development of co-infections, promoting or preventing establishment of multiple infections and shaping the outcome of pathogen-host interactions. Its ability to mediate the interplay between visceral leishmaniasis (VL) and malaria has been suggested, but poorly documented. The present study investigated whether concomitant infection with Leishmania donovani complex and Plasmodium falciparum in naturally co-infected patients altered the immunological response elicited by the two pathogens individually.

RESULTS

Circulating levels of interferon (IFN)-γ, interleukin (IL)-2, IL-4, IL-6, IL-10, IL-12p70, IL-13, IL-17A and tumor necrosis factor (TNF) were assessed in sera of patients infected with active VL and/or malaria and healthy individuals from Gedarif State, Sudan. Comparative analysis of cytokine profiles from co- and mono-infected patients highlighted significant differences in the immune response mounted upon co-infection, confirming the ability of L. donovani and P. falciparum to mutually interact at the immunological level. Progressive polarization towards type-1 and pro-inflammatory cytokine patterns characterized the co-infected patients, whose response partly reflected the effect elicited by VL (IFN-γ, TNF) and malaria (IL-2, IL-13), and partly resulted from a synergistic interaction of the two diseases upon each other (IL-17A). Significantly reduced levels of P. falciparum parasitaemia (P <0.01) were detected in the co-infected group as opposed to the malaria-only patients, suggesting either a protective or a non-detrimental effect of the co-infection against P. falciparum infection.

CONCLUSIONS

These findings suggest that a new immunological scenario may occur when L. donovani and P. falciparum co-infect the same patient, with potential implications on the course and resolution of these diseases.

Rapid detection of malaria parasite by toluidine blue method: a new staining method

Background:

Malaria is a commonest mosquito-borne infectious disease worldwide. Early identification and management of malaria prevents complications and mortality. Identification of the malaria mainly relies on detection of the parasite on blood smears. The present study was conducted to compare Toluidine blue method with Leishman method for detection of malaria parasite and also to study the efficacy and advantages of using Toluidine blue method.

Materials and Methods:

In 540 consecutive patients with clinical suspicion of malaria, peripheral smears were prepared. Smears were processed for both conventional Leishman method and Toluidine blue method simultaneously. The significance of Toluidine blue method over Leishman method was analyzed using Chi-square (χ²) test.

Results:

Out of 540 smears, 28.3% (153/540) were positive for malaria parasite on conventional Leishman method, while the smear positivity was more by Toluidine blue method to 33.3% (180/540) [P value < 0.01]. The remaining 66.67% (360/540) were negative by both Toluidine blue method and conventional Leishman method.

Conclusion:

The Toluidine blue method is simple, rapid, inexpensive, and easily available. The implementation of Toluidine blue method clearly improves microscopic detection of malaria parasite and can be a useful contribution to routine hematology even at rural health sectors.

Comparison of microscopy, nested-PCR, and Real-Time-PCR assays using high-throughput screening of pooled samples for diagnosis of malaria in asymptomatic carriers from areas of endemicity in Myanmar

Asymptomatic infection is an important obstacle for controlling disease in countries where malaria is endemic. Because asymptomatic carriers do not seek treatment for their infections, they can have high levels of gametocytes and constitute a reservoir available for new infection. We employed a sample pooling/PCR-based molecular detection strategy for screening malaria infection in residents from areas of Myanmar where malaria is endemic. Blood samples (n = 1,552) were collected from residents in three areas of malaria endemicity (Kayin State, Bago, and Tanintharyi regions) of Myanmar. Two nested PCR and real-time PCR assays showed that asymptomatic infection was detected in about 1.0% to 9.4% of residents from the surveyed areas. The sensitivities of the two nested PCR and real-time PCR techniques were higher than that of microscopy examination (sensitivity, 100% versus 26.4%; kappa values, 0.2 to 0.5). Among the three regions, parasite-positive samples were highly detected in subjects from the Bago and Tanintharyi regions. Active surveillance of residents from regions of intense malaria transmission would reduce the risk of morbidity and mitigate transmission to the population in these areas of endemicity. Our data demonstrate that PCR-based molecular techniques are more efficient than microscopy for nationwide surveillance of malaria in countries where malaria is endemic.

Development and evaluation of a 28S rRNA gene-based nested PCR assay for P. falciparum and P. vivax

The 28S rRNA gene was amplified and sequenced from P. falciparum and P. vivax isolates collected from northwest India. Based upon the sequence diversity of the Plasmodium 28SrRNA gene in comparison with its human counterpart, various nested polymerase chain reaction (PCR) primers were designed from the 3R region of the 28SrRNA gene and evaluated on field isolates. This is the first report demonstrating the utility of this gene for species-specific diagnosis of malaria for these two species, prevalent in India. The initial evaluation on 363 clinical isolates indicated that, in comparison with microscopy, which showed sensitivity and specificity of 85·39% and 100% respectively, the sensitivity and specificity of the nested PCR assay was found to be 99·08% and 100% respectively. This assay was also successful in detecting mixed infections that are undetected by microscopy. Our results demonstrate the utility of the 28S rRNA gene as a diagnostic target for the detection of the major plasmodial species infecting humans.

Tumor necrosis factor -α, interleukin-10, intercellular and vascular adhesion molecules are possible biomarkers of disease severity in complicated Plasmodium vivax isolates from Pakistan

BACKGROUND

Cytokine-mediated endothelial activation pathway is a known mechanism of pathogenesis employed by Plasmodium falciparum to induce severe disease symptoms in human host. Though considered benign, complicated cases of Plasmodium vivax are being reported worldwide and from Pakistan. It has been hypothesized that P.vivax utilizes similar mechanism of pathogenesis, as that of P.falciparum for manifestations of severe malaria. Therefore, the main objective of this study was to characterize the role of cytokines and endothelial activation markers in complicated Plasmodium vivax isolates from Pakistan.

METHODS AND PRINCIPLE FINDINGS

A case control study using plasma samples from well-characterized groups suffering from P.vivax infection including uncomplicated cases (n=100), complicated cases (n=82) and healthy controls (n=100) were investigated. Base line levels of Tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6), Interleukin-10 (IL-10), Intercellular adhesion molecule-1 (ICAM-1), Vascular adhesion molecule-1(VCAM-1) and E-selectin were measured by ELISA. Correlation of cytokines and endothelial activation markers was done using Spearman's correlation analysis. Furthermore, significance of these biomarkers as indicators of disease severity was also analyzed. The results showed that TNF-α, IL-10, ICAM-1and VCAM-1 were 3-fold, 3.7 fold and 2 fold increased between uncomplicated and complicated cases. Comparison of healthy controls with uncomplicated cases showed no significant difference in TNF-α concentrations while IL-6, IL-10, ICAM-1, VCAM-1 and E-selectin were found to be elevated respectively. In addition, significant positive correlation was observed between TNF-α and IL-10/ ICAM-1, IL-6 and IL-10, ICAM-1 and VCAM-1.A Receiver operating curve (ROC) was generated which showed that TNF-α, IL-10, ICAM-1 and VCAM-1 were the best individual predictors of complicated P.vivax malaria.

CONCLUSION

The results suggest that though endothelial adhesion molecules are inducible by pro-inflammatory cytokine TNF-α, however, cytokine-mediated endothelial activation pathway is not clearly demonstrated as a mechanism of pathogenesis in complicated P.vivax malaria cases from Pakistan.

Guideline: the laboratory diagnosis of malaria. General Haematology Task Force of the British Committee for Standards in Haematology

UK National External Quality Assessment Service surveys indicate continuing problems in malaria diagnosis: inaccurate calculation of parasitaemia or failure to estimate it altogether, difficulty distinguishing Plasmodium vivax from P. ovale, reporting malaria parasites when none were present and misidentification of P. falciparum as another species still occur. Therefore, the British Committee for Standards in Haematology Guidelines for the Laboratory Diagnosis of Malaria have been revised. They are intended for use in the UK but may also prove useful in other non-endemic areas. Routine use of thick and thin films is advised for malaria diagnosis. Thick films should be stained using Giemsa or Field stain. Thin films should be stained with Giemsa stain or Leishman stain. Thick films should be examined by two observers, each viewing a minimum of 200 high power fields. If thick films are positive, the species should be determined by examination of a thin film. In the case of P. falciparum or P. knowlesi infection, the percentage of parasitized cells or the number of parasites per microlitre (/μl) should be estimated and reported. Rapid diagnostic tests (RDTs) for malarial antigen cannot replace microscopy but are indicated as a supplementary test when malaria diagnosis is performed by relatively inexperienced staff. Malaria RDTs are negative in babesiosis.

Estimating the parasitaemia of Plasmodium falciparum: experience from a national EQA scheme

Background

To examine performance of the identification and estimation of percentage parasitaemia of Plasmodium falciparum in stained blood films distributed in the UK National External Quality Assessment Scheme (UKNEQAS) Blood Parasitology Scheme.

Methods

Analysis of performance for the diagnosis and estimation of the percentage parasitaemia of P. falciparum in Giemsa-stained thin blood films was made over a 15-year period to look for trends in performance.

Results

An average of 25% of participants failed to estimate the percentage parasitaemia, 17% overestimated and 8% underestimated, whilst 5% misidentified the malaria species present.

Conclusions

Although the results achieved by participants for other blood parasites have shown an overall improvement, the level of performance for estimation of the parasitaemia of P. falciparum remains unchanged over 15 years. Possible reasons include incorrect calculation, not examining the correct part of the film and not examining an adequate number of microscope fields.

The underlying aetiologies of coma in febrile Sudanese children

BACKGROUND

Cerebral malaria, acute bacterial meningitis and viral encephalitis are the main causes of fever and altered consciousness in the tropics. In areas where reliable laboratory testing is unavailable, over diagnosis and misdiagnosis of these conditions is likely. In malaria endemic countries non-malarial contributors to coma may be overlooked, overburdening available resources. The aim of this study is to evaluate the underlying causes of altered mental state in children presenting with fever and coma to tertiary medical facilities in Sudan.

METHODS

Children over one month of age admitted to the emergency departments of three main hospitals in Khartoum with fever and coma were investigated for cerebral malaria, acute bacterial meningitis and Herpes simplex encephalitis during April to November 2011.

RESULTS

One hundred and four children presenting with fever and coma were evaluated. Cerebral malaria was clinically suspected in 38 patients and 5 were confirmed. Acute bacterial meningitis was suspected in 63 patients and confirmed in 15. Herpes encephalitis was confirmed in only one case. There were five cases of mixed infection and the remainder were unknown.

CONCLUSION

The clinical diagnoses of cerebral malaria, acute bacterial meningitis and viral encephalitis are unreliable. Further studies to evaluate the underlying causes of coma in febrile Sudanese children are warranted.

Sequence Diversity of pfmdr1 and Sequence Conserve of pldh in Plasmodium falciparum from Indonesia: Its implications on Designing a Novel Antimalarial Drug with Less Prone to Resistance

BACKGROUND

pfmdr1 and its variants are molecular marker which are responsible for antibiotics resistance in Plasmodium falciparum, a parasitic carrier for malaria disease. A novel strategy to treat malaria disease is by disrupting parasite lactate dehydrogenase (pLDH), a crucial enzyme for Plasmodium survival during their erythrocytic stages. This research was aimed to investigate and characterize the pfmdr1 and pldh genes of P. falciparum isolated from Nusa Tenggara Indonesia.

METHODS

Genomic DNA of P.falciparum was isolated from malaria patients in Nusa Tenggara Indonesia. pfmdr1 was amplified using nested PCR and genotyped using Restriction Fragment Length Polymorphism (RFLP). pldh was amplified, sequenced, and analyzed using NCBI public domain databases and alignment using Clustal W ver. 1.83.

RESULTS

Genotyping of the pfmdr1 revealed that sequence diversity was extremely high among isolates. However, a sequence analysis of pldh indicated that open reading frame of 316 amino acids of the gene showing 100% homology to the P. falciparum 3D7 reference pldh (GeneBank: XM_001349953.1).

CONCLUSION

This is the first report which confirms the heterologous of pfmdr1 and the homologous sequences of P.falciparum pldh isolated from Nusa Tenggara Islands of Indonesia, indicating that the chloroquine could not be used effectively as antimalarial target in the region and the pLDH-targeted antimalarial compound would have higher chance to be successful than using chloroquine for curbing malaria worldwide.

Inter-observer agreement according to malaria parasite density

Background

Recent developments in diagnostic techniques for malaria, particularly DNA probes and sero-immunology, have raised questions as to how these techniques might be used to facilitate malaria diagnosis at the most peripheral levels of the primary health care system. At present, malaria diagnosis is based on the standard microscopic examination of blood films in most field epidemiologic studies and is likely to remain so in the immediate future in Africa. The objective of this study was to assess inter-observer agreement for the examination of Giemsa-stained slides for Plasmodium falciparum parasites.

Methods

Children aged 0 to 10 years were enrolled yearly in Bancoumana village (West Africa), mainly during the transmission season (June to October). The blood smears obtained from the persistently negative children in June 1996, August 1996, October 1996 and March 1997 were systematically re-examined. A stratified random sample (10%) proportional to the following parasite density classes 1–100, 101–5000, and 5001 and over was taken from the slides collected. The kappa statistics and the intra-class correlation were used as measures of agreement the first and the second slide examinations.

Results

The weighted kappa statistic, widely used as a chance-corrected measure for nominal agreement, showed excellent inter-observer agreement (κ_w=0.7926; 95% CI [0.7588, 0.8263]; p=0.01). The intra-class correlation co-efficient had the same value of 0.7926 confirming the appropriateness of the weighted kappa statistic. Inter-observer agreement for slides read as negative by one observer, or as containing more than 100 parasites per μl, was excellent: 97% (493/506) and 92% (145/158), respectively. In contrast, the inter-observer agreement for slides read by one observer as containing 1–100 parasites/μl was poor, 36% (96/268).

Conclusions

In field conditions in Mali, there was a high reproducibility for slides reported as negative or as having more than 100 parasites per μl. However, smears with readings of 1–100 parasites per μl were less reproducible and should be re-examined carefully.

Prevalence of drug resistance associated mutations in Plasmodium vivax against sulphadoxine-pyrimethamine in southern Pakistan

Background

In Pakistan, Plasmodium vivax and Plasmodium falciparum co-exist and usage of sulphadoxine-pyrimethamine (SP) against P. falciparum exposes P. vivax to the drug leading to generation of resistant alleles. The main aim of this study was to investigate frequency distribution of drug resistance associated mutations in pvdhfr, pvdhps genes and provide baseline molecular epidemiological data on SP-associated resistance in P. vivax from southern Pakistan.

Methods

From January 2008 to May 2009, a total of 150 samples were collected from patients tested slide-positive for P. vivax, at the Aga Khan University Hospital, Karachi, or its collection units located in Baluchistan and Sindh Province. Nested PCR using pvdhfr and pvdhps specific primers was performed for all samples.91.3% (137/150) of the samples were tested PCR positive of which 87.3% (131/137) were successfully sequenced. Sample sequencing data was analysed and compared against wild type reference sequences.

Results

In dhfr, mutations were observed at codons F57L, S58R and S117N/T. Novel non-synonymous mutations were observed at codon positions N50I, G114R and E119K while a synonymous mutation was observed at codon position 69Y. In dhps, mutations were observed at codon position A383G and A553G while novel non-synonymous mutations were observed at codon positions S373T, E380K, P384L, N389T, V392D, T393P, D459A, M601I, A651D and A661V.

Conclusion

This is the first report from southern Pakistan on SP resistance in clinical isolates of P. vivax. Results from this study confirm that diverse drug resistant alleles are circulating within this region.

A method for reducing the sloughing of thick blood films for malaria diagnosis

BACKGROUND

The gold standard for malaria diagnosis is the examination of thick and thin blood films. Thick films contain 10 to 20 times more blood than thin films, correspondingly providing increased sensitivity for malaria screening. A potential complication of thick film preparations is sloughing of the blood droplet from the slide during staining or rinsing, resulting in the loss of sample. In this work, two methods for improving thick film slide adherence ('scratch' (SCM) and 'acetone dip' (ADM) methods) were compared to the 'standard method' (SM) of thick film preparation.

METHODS

Standardized blood droplets from 26 previously examined EDTA whole blood specimens (22 positive and four negative) were concurrently spread on glass slides using the SM, ADM, and SCM. For the SM and ADM prepared slides, the droplet was gently spread to an approximate 22 millimeters in diameter spot on the slide using the edge of a second glass slide. For the SCM, the droplet was spread by carefully grinding (or scratching) it into the slide with the point of a second glass slide. Slides were dried for one hour in a laminar flow hood. For the ADM, slides were dipped once in an acetone filled Coplin jar and allowed to air dry. All slides were then Giemsa-stained and examined in a blinded manner. Adherence was assessed by blinded reviewers.

RESULTS

No significant or severe defects were observed for slides prepared with the SCM. In contrast, 8 slides prepared by the ADM and 3 prepared using the SM displayed significant or severe defects. Thick films prepared by the three methods were microscopically indistinguishable and concordant results (positive or negative) were obtained for the three methods. Estimated parasitaemia of the blood samples ranged from 25 to 429,169 parasites/μL of blood.

CONCLUSIONS

The SCM is an inexpensive, rapid, and simple method that improves the adherence of thick blood films to standard glass slides without altering general slide preparation, microscopic appearance or interpretability. Using the SCM, thick films can be reliably examined less than two hours after sample receipt. This represents a significant diagnostic improvement over protocols requiring extended drying periods.

Simple, rapid, inexpensive platform for the diagnosis of malaria by loop mediated isothermal amplification (LAMP)

We attempted to improve the loop-mediated isothermal amplification (LAMP) method for malaria diagnosis by using a simple DNA extraction procedure, and a portable device performing both the amplification and detection of LAMP in one platform. Additionally, the device served as a heating block for the DNA preparation. We refer this method as LAMP-Tube scanner, and evaluated using 209 microscopically positive malaria samples and compared them to RDTs and LAMP-Thermocycler. Two most common human infecting Plasmodium species were detected. The LAMP-Tube scanner method is found to be simple and allowed real-time detection of DNA amplification. The time to amplification varied but was closely less than 60 min. Sensitivity and specificity of LAMP-Tube scanner in detecting Plasmodium falciparum were 95% and 93.3%, compared to microscopy and 98.3% and 100% respectively, compared to standard LAMP-Thermocycler. In addition, it showed a detection limit of 10 and 40 copies of the parasitemia for Plasmodium vivax and P. falciparum. Accordingly, in comparison to the results obtained by microscopy, the LAMP-Tube scanner had a less divergence in sensitivity and specificity, and yielded results similar to those of LAMP-Thermocycler. This method has the great potential as a field usable molecular tool for the diagnosis of malaria and is an alternative to conventional PCR-based diagnostic methods for field use.

Co-infection and cross-species transmission of divergent Hepatocystis lineages in a wild African primate community

Hemoparasites of the apicomplexan family Plasmodiidae include the etiological agents of malaria, as well as a suite of non-human primate parasites from which the human malaria agents evolved. Despite the significance of these parasites for global health, little information is available about their ecology in multi-host communities. Primates were investigated in Kibale National Park, Uganda, where ecological relationships among host species are well characterized. Blood samples were examined for parasites of the genera Plasmodium and Hepatocystis using microscopy and PCR targeting the parasite mitochondrial cytochrome b gene, followed by Sanger sequencing. To assess co-infection, "deep sequencing" of a variable region within cytochrome b was performed. Out of nine black-and-white colobus (Colobus guereza), one blue guenon (Cercopithecus mitis), five grey-cheeked mangabeys (Lophocebus albigena), 23 olive baboons (Papio anubis), 52 red colobus (Procolobus rufomitratus) and 12 red-tailed guenons (Cercopithecus ascanius), 79 infections (77.5%) were found, all of which were Hepatocystis spp. Sanger sequencing revealed 25 different parasite haplotypes that sorted phylogenetically into six species-specific but morphologically similar lineages. "Deep sequencing" revealed mixed-lineage co-infections in baboons and red colobus (41.7% and 64.7% of individuals, respectively) but not in other host species. One lineage infecting red colobus also infected baboons, but always as the minor variant, suggesting directional cross-species transmission. Hepatocystis parasites in this primate community are a diverse assemblage of cryptic lineages, some of which co-infect hosts and at least one of which can cross primate species barriers.

Statistical properties of parasite density estimators in malaria

Malaria is a global health problem responsible for nearly one million deaths every year around 85% of which concern children younger than five years old in Sub-Saharan Africa. In addition, around 300 million clinical cases are declared every year. The level of infection, expressed as parasite density, is classically defined as the number of asexual parasites relative to a microliter of blood. Microscopy of Giemsa-stained thick blood films is the gold standard for parasite enumeration. Parasite density estimation methods usually involve threshold values; either the number of white blood cells counted or the number of high power fields read. However, the statistical properties of parasite density estimators generated by these methods have largely been overlooked. Here, we studied the statistical properties (mean error, coefficient of variation, false negative rates) of parasite density estimators of commonly used threshold-based counting techniques depending on variable threshold values. We also assessed the influence of the thresholds on the cost-effectiveness of parasite density estimation methods. In addition, we gave more insights on the behavior of measurement errors according to varying threshold values, and on what should be the optimal threshold values that minimize this variability.

Genetic diversity of Plasmodium vivax clinical isolates from southern Pakistan using pvcsp and pvmsp1 genetic markers

Background

Plasmodium vivax is the prevalent malarial species accounting for 70% of malaria burden in Pakistan; however, there is no baseline data on the circulating genotypes. Studies have shown that polymorphic loci of gene encoding antigens pvcsp and pvmsp1 can be used reliably for conducting molecular epidemiological studies. Therefore, this study aimed to bridge the existing knowledge gap on population structure on P. vivax from Pakistan using these two polymorphic genes.

Methods

During the period January 2008 to May 2009, a total of 250 blood samples were collected from patients tested slide positive for P. vivax, at the Aga Khan University Hospital, Karachi, or its collection units located in Baluchistan and Sindh Province. Nested PCR/RFLP was performed, using pvcsp and pvmsp1 markers to detect the extent of genetic diversity in clinical isolates of P. vivax from southern Pakistan.

Results

A total of 227/250 (91%) isolates were included in the analysis while the remainder were excluded due to negative PCR outcome for P.vivax. Pvcsp analysis showed that both VK 210 (85.5%, 194/227) and VK 247 type (14.5%, 33/227) were found to be circulating in P. vivax isolates from southern Pakistan. A total of sixteen and eighty-seven genotypes of pvcsp and pvmsp-1 were detected respectively.

Conclusion

This is the first report from southern Pakistan on characterization of P. vivax isolates confirming that extensively diverse pvcsp and pvmsp1 variants are present within this region. Results from this study provide valuable data on genetic diversity of P. vivax that will be helpful for further epidemiological studies.

Emerging nucleic acid-based tests for point-of-care detection of malaria

Malaria remains a serious disease in the developing world. There is a growing consensus that new diagnostics are needed in low-resource settings. The ideal malaria diagnostic should be able to speciate; measure parasitemia; low-cost, quick, and simple to use; and capable of detecting low-level infections. A promising development are nucleic acid tests (NATs) for the diagnosis of malaria, which are well suited for point-of-care use because of their ability to detect low-level infections and speciate, and because they have high sensitivity and specificity. The greatest barrier to NAT use in the past has been its relatively high cost, and the amount of infrastructure required in the form of equipment, stable power, and reagent storage. This review describes recent developments to decrease the cost and run time, and increase the ease of use of NAT while maintaining their high sensitivity and specificity and low limit of detection at the point-of-care.

Prevalence of PCR detectable malaria infection among febrile patients with a negative Plasmodium falciparum specific rapid diagnostic test in Zanzibar

We screened for malaria in 594 blood samples from febrile patients who tested negative by a Plasmodium falciparum-specific histidine-rich protein-2-based rapid diagnostic test at 12 health facilities in Zanzibar districts North A and Micheweni, from May to August 2010. Screening was with microscopy, polymerase chain reaction (PCR) targeting the cytochrome b gene (cytbPCR) of the four major human malaria species, and quantitative PCR (qPCR). The prevalence of cytbPCR-detectable malaria infection was 2% (12 of 594), including 8 P. falciparum, 3 Plasmodium malariae, and 1 Plasmodium vivax infections. Microscopy identified 4 of 8 P. falciparum infections. Parasite density as estimated by microscopy or qPCR was > 4,000 parasites/μL in 5 of 8 cytbPCR-detectable P. falciparum infections. The infections that were missed by the rapid diagnostic test represent a particular challenge in malaria elimination settings and highlight the need for more sensitive point-of-care diagnostic tools to improve case detection of all human malaria species in febrile patients.

Application of loop-mediated isothermal amplification for malaria diagnosis during a follow-up study in São Tomé

BACKGROUND

A reliable and simple test for the detection of malaria parasite is crucial in providing effective treatment and therapeutic follow-up, especially in malaria elimination programmes. A comparison of four methods, including nested polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) were used for the malaria diagnosis and treatment follow-up in São Tomé and Príncipe, during a successful pre-elimination campaign.

METHOD

During the period September to November 2009, blood samples from 128 children (five to 14 years old) with temperature ≥38°C (tympanic) in the District of Agua Grande were examined using four different methods, i.e., histidine-rich protein 2 (HRP-2) based rapid diagnostic tests (HRP-2-RDTs), optical microscopy, nested PCR, and LAMP. First-line treatment with artesunate-amodiaquine was given for uncomplicated malaria and intravenous quinine was given for complicated malaria. Children with persistent positivity for malaria by microscopy, or either by nested PCR, or by LAMP on day 7 were given second-line treatment with artemether-lumefantrine. Treatment follow-up was made weekly, for up to four weeks.

RESULTS

On day 0, positive results for HRP-2-RDTs, microscopy, nested PCR, and LAMP, were 68(53%), 47(37%), 64(50%), and 65(51%), respectively. When nested PCR was used as a reference standard, only LAMP was comparable; both HRP-2-RDTs and microscopy had moderate sensitivity; HRP-2-RDTs had poor positive predictive value (PPV) and a moderate negative predictive value (NPV) for the treatment follow-up. Seventy-one children with uncomplicated malaria and eight children with complicated falciparum malaria were diagnosed based on at least one positive result from the four tests as well as clinical criteria. Twelve of the 79 children receiving first-line treatment had positive results by nested PCR on day 7 (nested PCR-corrected day 7 cure rate was 85%). After the second-line treatment, nested PCR/LAMP-corrected day 28 cure rate was 83% for these 12 children.

CONCLUSIONS

HRP-2-RDTs have similar sensitivity as microscopy but less specificity. However, as compared to nested PCR, the poor sensitivity of HRP-2-RDTs indicates that low parasitaemia may not be detected after treatment, as well as the low specificity of HRP-2-RDTs indicates it cannot be applied for treatment follow-up. LAMP has similar sensitivity and specificity to nested PCR. With high PPV and NPV, LAMP is simpler and faster as compared to nested PCR with the advantage of detecting low parasitaemia becoming a potential point-of-care test for treatment follow-up.