Automated malaria diagnosis using pigment detection

Malaria diagnostic update: From conventional to advanced method

BACKGROUND

Update diagnostic methods play essential roles in dealing with the current global malaria situation and decreasing malaria incidence.

AIM

Global malaria control programs require the availability of adequate laboratory tests in the quick and convenient field.

RESULTS

There are several methods to find out the existence of parasites within the blood. The oldest one is by microscopy, which is still a gold standard, although rapid diagnostic tests (RDTs) have rapidly become a primary diagnostic test in many endemic areas. Because of microscopy and RDTs limitation, novel serological and molecular methods have been developed. Many kinds of polymerase chain reaction (PCR) provide rapid results and higher specificity and sensitivity. The loop-mediated isothermal amplification (LAMP) and biosensing-based molecular techniques as point of care tests (POCT) will become a cost-effective approach to advance diagnostic testing.

CONCLUSION

Despite conventional techniques are still being used in the field, the exploration and field implementation of advanced techniques for the diagnosis of malaria are still being developed rapidly.

Malaria Diagnosis in Non-Endemic Settings: The European Experience in the Last 22 Years

Accurate, prompt, and reliable tools for the diagnosis of malaria are crucial for tracking the successes or drawbacks of control and elimination efforts, and for future programs aimed at global malaria eradication. Although microscopy remains the gold standard method, the number of imported malaria cases and the risk of reappearance of autochthonous cases stimulated several laboratories located in European countries to evaluate methods and algorithms suited to non-endemic settings, where skilled microscopists are not always available. In this review, an overview of the field evaluation and a comparison of the methods used for the diagnosis of malaria by European laboratories is reported, showing that the development of numerous innovations is continuous. In particular, the combination of rapid diagnostic tests and molecular assays with microscopy represents a reliable system for the early diagnosis of malaria in non-endemic settings.

Portable bright-field, fluorescence, and cross-polarized microscope toward point-of-care imaging diagnostics

Emerging technologies are enabling the feasibility of new types of point-of-care diagnostic devices. A portable, multimodal microscopy platform intended for use in remote diagnostic applications is presented. Use of such a system could bring high-quality microscopy to field use for diseases such as malaria, allowing better diagnostic and surveillance information to be gathered. The microscope was designed using off-the-shelf components and a manual filter selection to generate bright-field, fluorescent, and cross-polarized images of samples mounted to microscopy slides. Design parameters for the system are discussed, and characterization is performed using standardized imaging targets, multimodal phantoms, and blood smears simulating those used in malaria diagnosis. The microscope is shown to be able to image below element 9-3 of a 1951 U.S. Air Force target, indicating that the system is capable of resolving features < 775  nm. Morphological indicators of Plasmodium falciparum can be visualized in images from each modality and combined into high-contrast composite images. To optimize parasitic feature contrast across all three imaging modes, several different staining techniques were compared, with results indicating that use of a single nucleic acid binding fluorophore is preferable.

Evaluation of automated malaria diagnosis using the Sysmex XN-30 analyser in a clinical setting

BACKGROUND

Early and accurate diagnosis of malaria is a critical aspect of efforts to control the disease, and several diagnostic tools are available. Microscopic assessment of a peripheral blood smear enables direct visualization of parasites in infected red blood cells and is the clinical diagnostic gold standard. However, it is subjective and requires a high level of skill. Numerous indirect detection methods are in use, but are not ideal since surrogate markers of infection are measured. This study describes the first clinical performance evaluation of the automated Sysmex XN-30 analyser, which utilizes fluorescence flow cytometry to directly detect and quantitate parasite-infected red blood cells.

RESULTS

Residual EDTA blood samples from suspected malaria cases referred for routine diagnosis were analysed on the XN-30. Parasitaemia was reported as a percentage, as well as absolute numbers of infected red blood cells, and scattergrams provided a visual image of the parasitized red blood cell clusters. The results reported by the XN-30 correlated with microscopy and the analyser demonstrated 100% sensitivity and specificity. Measurements were reproducible and storage of samples at room temperature did not affect the parameters. Several Plasmodium species were detected, including Plasmodium falciparum, Plasmodium vivax and Plasmodium ovale. The XN-30 also identified the transmissible gametocytes as a separate cluster on the scattergrams. Abnormal red blood cell indices (low haemoglobin and raised reticulocyte counts), haemoglobinopathies and thrombocytopenia did not interfere with the detection of parasites. The XN-30 also generated a concurrent full blood count for each sample.

CONCLUSIONS

The novel technology of the Sysmex XN-30 provides a robust, rapid, automated and accurate platform for diagnosing malaria in a clinical setting. The objective enumeration of red blood cells infected with Plasmodium species makes it suitable for global use and allows monitoring of the parasite load once therapy has been initiated, thereby providing an early marker of drug resistance. The automated generation of a full blood count for each sample provides an opportunity for detecting unsuspected cases. Asymptomatic carriers can also be identified, which will be useful in blood transfusion centres, and will enable treatment of these individuals to prevent the spread of the disease.

Evaluation of the LH780 hematology analyzer for detection and therapeutic monitoring of malaria: Cross-reactivity with nucleated RBCs

We evaluated the diagnostic usefulness of the LH780 Coulter blood cell counter for detection and therapeutic monitoring of malaria including cross-reactivity with nucleated RBC (NRBC) samples. A total of 405 patients (43 patients with Plasmodium vivax malaria and the control group of 120 healthy subjects, 111 patients with fever, and 131 patients with NRBCs) were analyzed with routine CBC using the LH780. We analyzed the CBC results according to three selected parameters: an abnormal peak in the WBC histogram before 35fL, the presence of red dots in the nonwhite cell zone of 2D WBC Diff Dataplot, and platelet-related flags suggesting platelet clumps or giant platelets. Of the 43 malaria samples collected at diagnosis, an abnormal peak (≥2.2mm) was present in 93.0% (95% confidential interval (CI), 80.9-98.5%). Of all samples, 97.7% (95% CI, 87.7-99.9%) exhibited red dots, and platelet-related flags were observed in 81.4% (95% CI, 66.6-91.6%). The specificity of these three selected parameters was 83.1% (95% CI, 78.9-86.9%), 77.3% (95% CI, 72.7-81.6%), and 90.1% (95% CI, 86.5-92.9%), respectively. The abnormal peak (≥2.2mm) showed moderate correlation with parasite level (r=0.79). The three selected LH780 parameters were useful for identifying malaria in healthy subjects and febrile patients, but unsatisfactory for discriminating malaria in NRBC samples. The parameters showed a substantial proportion of false positives in the NRBC group, ranging from 26.7% to 49.6%. Therefore, microscopic confirmation will be necessary for application of these parameters for malaria screening and treatment monitoring.

Automated Detection of P. falciparum Using Machine Learning Algorithms with Quantitative Phase Images of Unstained Cells

Malaria detection through microscopic examination of stained blood smears is a diagnostic challenge that heavily relies on the expertise of trained microscopists. This paper presents an automated analysis method for detection and staging of red blood cells infected by the malaria parasite Plasmodium falciparum at trophozoite or schizont stage. Unlike previous efforts in this area, this study uses quantitative phase images of unstained cells. Erythrocytes are automatically segmented using thresholds of optical phase and refocused to enable quantitative comparison of phase images. Refocused images are analyzed to extract 23 morphological descriptors based on the phase information. While all individual descriptors are highly statistically different between infected and uninfected cells, each descriptor does not enable separation of populations at a level satisfactory for clinical utility. To improve the diagnostic capacity, we applied various machine learning techniques, including linear discriminant classification (LDC), logistic regression (LR), and k-nearest neighbor classification (NNC), to formulate algorithms that combine all of the calculated physical parameters to distinguish cells more effectively. Results show that LDC provides the highest accuracy of up to 99.7% in detecting schizont stage infected cells compared to uninfected RBCs. NNC showed slightly better accuracy (99.5%) than either LDC (99.0%) or LR (99.1%) for discriminating late trophozoites from uninfected RBCs. However, for early trophozoites, LDC produced the best accuracy of 98%. Discrimination of infection stage was less accurate, producing high specificity (99.8%) but only 45.0%-66.8% sensitivity with early trophozoites most often mistaken for late trophozoite or schizont stage and late trophozoite and schizont stage most often confused for each other. Overall, this methodology points to a significant clinical potential of using quantitative phase imaging to detect and stage malaria infection without staining or expert analysis.

Hemoglobin consumption by P. falciparum in individual erythrocytes imaged via quantitative phase spectroscopy

Plasmodium falciparum infection causes structural and biochemical changes in red blood cells (RBCs). To quantify these changes, we apply a novel optical technique, quantitative phase spectroscopy (QPS) to characterize individual red blood cells (RBCs) during the intraerythrocytic life cycle of P. falciparum. QPS captures hyperspectral holograms of individual RBCs to measure spectroscopic changes across the visible wavelength range (475-700 nm), providing complex information, i.e. amplitude and phase, about the light field which has interacted with the cell. The complex field provides complimentary information on hemoglobin content and cell mass, which are both found to dramatically change upon infection by P. falciparum. Hb content progressively decreases with parasite life cycle, with an average 72.2% reduction observed for RBCs infected by schizont-stage P. falciparum compared to uninfected cells. Infection also resulted in a 33.1% reduction in RBC's optical volume, a measure of the cells' non-aqueous components. Notably, optical volume is only partially correlated with hemoglobin content, suggesting that changes in other dry mass components such as parasite mass may also be assessed using this technique. The unique ability of QPS to discriminate individual healthy and infected cells using spectroscopic changes indicates that the approach can be used to detect disease.

Malaria Diagnosis Using Automated Analysers: A Boon for Hematopathologists in Endemic Areas

BACKGROUND

Haematological abnormalities are common in acute febrile tropical illnesses. Malaria is a major health problem in tropics. In endemic areas especially in the post monsoon season, it is not practical to manually screen all peripheral blood films (PBF) for malarial parasite. Automated analysers offer rapid, sensitive and cost effective screening of all samples.

AIM

The study was done to evaluate the usefulness of automated cell counters analysing their histograms, scatter-grams and the flaggings generated in malaria positive and negative cases. The comparison of other haematological parameters were also studied which could help to identify malaria parasite in peripheral blood smear.

MATERIALS AND METHODS

The blood samples were analysed using Beckman coulter LH-750. The abnormal scatter grams and additional peaks in WBC histograms were observed diligently & compared with normal controls. Haematological abnormalities were also evaluated.

STATISTICAL ANALYSIS

Statistical analysis was done by using software Epi-Info version 7.1.4 freely available from CDC website. Fisher exact test was applied to calculate the p-value and value < 0.05 was considered as significant. Final identification of malarial parasite species was done independently by peripheral blood smear examination by two pathologists.

RESULTS

Of all the 200 cases evaluated abnormal scatter grams were observed in all the cases of malaria while abnormal WBC histogram peaks were noted in 96% cases demonstrating a peak at the threshold of the histogram. The difference between number of slides positive for abnormal WBC scatter gram and abnormal WBC histogram peaks were statistically highly significant (p=0.007). So abnormal WBC scatter gram can better give idea of malarial parasite presence. Of the haematological parameters thrombocytopenia (92% cases) emerged as the strongest predictor of malaria.

CONCLUSION

It is recommended for haematopathologists to review the haematological data and the scatter plots on the analyser along with peripheral blood smear examination.

Light depolarization measurements in malaria: A new job for an old friend

The use of flow cytometry in malaria research has increased over the last decade. Most approaches use nucleic acid stains to detect parasite DNA and RNA and require complex multi-color, multi-parameter analysis to reliably detect infected red blood cells (iRBCs). We recently described a novel and simpler approach to parasite detection based on flow cytometric measurement of scattered light depolarization caused by hemozoin (Hz), a pigment formed by parasite digestion of hemoglobin in iRBCs. Depolarization measurement by flow cytometry was described in 1987; however, patent issues restricted its use to a single manufacturer's hematology analyzers until 2009. Although we recently demonstrated that depolarization measurement of Hz, easily implemented on a bench top flow cytometer (Cyflow), provided useful information for malaria work, doubts regarding its application and utility remain in both the flow cytometry and malaria communities, at least in part because instrument manufacturers do not offer the option of measuring depolarized scatter. Under such circumstances, providing other researchers with guidance as to how to do this seemed to offer the most expeditious way to resolve the issue. We accordingly examined how several commercially available flow cytometers (CyFlow SL, MoFLo, Attune and Accuri C6) could be modified to detect depolarization due to the presence of free Hz on solution, or of Hz in leukocytes or erythrocytes from rodent or human blood. All were readily adapted, with substantially equivalent results obtained with lasers emitting over a wide wavelength range. Other instruments now available may also be modifiable for Hz measurement. Cytometric detection of Hz using depolarization is useful to study different aspects of malaria. Adding additional parameters, such as DNA content and base composition and RNA content, can demonstrably provide improved accuracy and sensitivity of parasite detection and characterization, allowing malaria researchers and eventually clinicians to benefit from cytometric technology.

Advances in malaria diagnosis

Malaria is a leading cause of mortality worldwide and accurate diagnostic testing for malaria can potentially save an estimated 100,000 lives annually. New technologies have the potential to circumvent limitations of the traditional diagnostic method, light microscopy, which is labor intensive and requires considerable technician expertise. Immunochromatographic tests, which are easy to use in field conditions and relatively inexpensive, offer a potential solution to the problem of malaria overtreatment in resource-poor endemic countries. Assays based on the PCR are highly sensitive, can be used for unambiguous species identification and, thus, may increasingly complement or even replace light microscopy in developed countries. Experimental diagnostics using flow cytometry and mass spectrometry are currently under investigation for high-throughput screening.

A novel flow cytometric hemozoin detection assay for real-time sensitivity testing of Plasmodium falciparum

Resistance of Plasmodium falciparum to almost all antimalarial drugs, including the first-line treatment with artemisinins, has been described, representing an obvious threat to malaria control. In vitro antimalarial sensitivity testing is crucial to detect and monitor drug resistance. Current assays have been successfully used to detect drug effects on parasites. However, they have some limitations, such as the use of radioactive or expensive reagents or long incubation times. Here we describe a novel assay to detect antimalarial drug effects, based on flow cytometric detection of hemozoin (Hz), which is rapid and does not require any additional reagents. Hz is an optimal parasite maturation indicator since its amount increases as the parasite matures. Due to its physical property of birefringence, Hz depolarizes light, hence it can be detected using optical methods such as flow cytometry. A common flow cytometer was adapted to detect light depolarization caused by Hz. Synchronized in vitro cultures of P. falciparum were incubated for 48 hours with several antimalarial drugs. Analysis of depolarizing events, corresponding to parasitized red blood cells containing Hz, allowed the detection of parasite maturation. Moreover, chloroquine resistance and the inhibitory effect of all antimalarial drugs tested, except for pyrimethamine, could be determined as early as 18 to 24 hours of incubation. At 24 hours incubation, 50% inhibitory concentrations (IC50) were comparable to previously reported values. These results indicate that the reagent-free, real-time Hz detection assay could become a novel assay for the detection of drug effects on Plasmodium falciparum.

Quality and reliability of current malaria diagnostic methods

Malaria is a life threatening disease with a major impact on global health. The WHO declared an early diagnosis as one of the most important steps to fight the disease. The quality and the reliability of test results depend on the diagnostic tools used. Not every test meets the needs in every situation. PCR tests have the best sensitivity and specifity but are not as rapid as other tests and also due to the costs not available everywhere. The 'gold standard' method is to check stained blood slides, thick films require experienced persons to obtain correct results. So-called rapid tests are only additional tools no matter whether they are based on the detection of antigens, enzymes or plasmodial DNA by fluorescent staining. Some other blood bound markers may also provide a hint but are no sufficient tool for malaria diagnosis.

Sensitive detection and accurate monitoring of Plasmodium vivax parasites on routine complete blood count using automatic blood cell analyzer (DxH800(TM))

INTRODUCTION

Plasmodium vivax malaria is one of the most important infectious diseases plaguing humanity and causes significant mortality and morbidity worldwide. The gold standard of P. vivax malaria diagnosis is the microscopy of blood smears. Although microscopy is a rapid, cost-effective, and readily applicable method, it has many disadvantages, including low sensitivity, specificity, and precision. Therefore, there is a clear need for an effective screening test for P. vivax malaria detection both in high-prevalence areas and developed countries.

METHODS

A total of 1761 complete blood count (CBC) samples generated by the automated hematology analyzer (DxH 800™; Beckman Coulter Inc., Miami, FL, USA) were retrospectively analyzed. The sample pool contained 123 samples from 52 P. vivax malaria patients and 1504 nonmalarial samples including 509 patients with leukopenia (white blood cell <2000/μL) and 134 normal subjects.

RESULTS

The P. vivax malaria samples exhibited easily recognizable typical malaria signals on the nucleated red blood cell (nRBC) plots (sensitivity 100%) in DxH 800™. All 1504 samples without P. vivax infection were negative for malaria signal (specificity 100%). The size of P. vivax malaria signals correlated roughly with the parasite burden.

CONCLUSION

DxH800™ provides very sensitive and specific, easily recognizable P. vivax malaria signals on routine CBC without need for the additional reagents or special procedures.

Methodology and application of flow cytometry for investigation of human malaria parasites

Historically, examinations of the inhibition of malaria parasite growth/invasion, whether using drugs or antibodies, have relied on the use of microscopy or radioactive hypoxanthine uptake. These are considered gold standards for measuring the effectiveness of antimalarial treatments, however, these methods have well known shortcomings. With the advent of flow cytometry coupled with the use of fluorescent DNA stains allowed for increased speed, reproducibility, and qualitative estimates of the effectiveness of antibodies and drugs to limit malaria parasite growth which addresses the challenges of traditional techniques. Because materials and machines available to research facilities are so varied, different methods have been developed to investigate malaria parasites by flow cytometry. This review is intended to serve as a reference guide for advanced users and importantly, as a primer for new users, to support expanded use and improvements to malaria flow cytometry, particularly in endemic countries.

Automated haematology analysis to diagnose malaria

For more than a decade, flow cytometry-based automated haematology analysers have been studied for malaria diagnosis. Although current haematology analysers are not specifically designed to detect malaria-related abnormalities, most studies have found sensitivities that comply with WHO malaria-diagnostic guidelines, i.e. ≥ 95% in samples with > 100 parasites/μl. Establishing a correct and early malaria diagnosis is a prerequisite for an adequate treatment and to minimizing adverse outcomes. Expert light microscopy remains the 'gold standard' for malaria diagnosis in most clinical settings. However, it requires an explicit request from clinicians and has variable accuracy. Malaria diagnosis with flow cytometry-based haematology analysers could become an important adjuvant diagnostic tool in the routine laboratory work-up of febrile patients in or returning from malaria-endemic regions. Haematology analysers so far studied for malaria diagnosis are the Cell-Dyn^®, Coulter^® GEN·S and LH 750, and the Sysmex XE-2100^® analysers. For Cell-Dyn analysers, abnormal depolarization events mainly in the lobularity/granularity and other scatter-plots, and various reticulocyte abnormalities have shown overall sensitivities and specificities of 49% to 97% and 61% to 100%, respectively. For the Coulter analysers, a 'malaria factor' using the monocyte and lymphocyte size standard deviations obtained by impedance detection has shown overall sensitivities and specificities of 82% to 98% and 72% to 94%, respectively. For the XE-2100, abnormal patterns in the DIFF, WBC/BASO, and RET-EXT scatter-plots, and pseudoeosinophilia and other abnormal haematological variables have been described, and multivariate diagnostic models have been designed with overall sensitivities and specificities of 86% to 97% and 81% to 98%, respectively. The accuracy for malaria diagnosis may vary according to species, parasite load, immunity and clinical context where the method is applied. Future developments in new haematology analysers such as considerably simplified, robust and inexpensive devices for malaria detection fitted with an automatically generated alert could improve the detection capacity of these instruments and potentially expand their clinical utility in malaria diagnosis.

Laboratory diagnosis of malaria in nonhuman primates

Nonhuman primates (NHPs) are commonly used for biomedical research because of the high level of gene homology that underlies physiologic similarity to human beings. Malaria parasites of the genus Plasmodium cause one of the most frequent parasitic diseases of NHPs originating from tropical and subtropical areas and as such represent a significant research confounder. Malaria in NHPs presents a diagnostic challenge especially to those laboratories that see no more than a few malaria cases per year in NHPs. The accurate and timely diagnosis of malaria infection in NHPs facilitates the appropriate treatment of individuals infected with the malaria parasites. Conventional microscopy based on the examination of Giemsa-stained thick and thin blood films remains the mainstay of laboratory diagnosis of malaria infection because of the high diagnostic sensitivity and specificity and also the capability for Plasmodium species identification and parasite counts. This procedure is recognized as technically difficult and time-consuming, requiring considerable training to obtain the necessary skills. In the past few years, efforts to replace the traditional but tedious reading of blood films have led to different techniques for the detection of malaria parasites, including fluorescence microscopy, detection of intraleukocytic hemozoin or malaria pigment using automated blood cell analyzers, immunochromatographic rapid diagnostic tests based on malaria antigen detection, and PCR assays. These techniques offer new approaches for diagnosing malaria in NHPs. This review focuses on the available laboratory diagnostic tools for malaria in NHPs.

Laboratory evaluation on the sensitivity and specificity of a novel and rapid detection method for malaria diagnosis based on magneto-optical technology (MOT)

Background

This study describes the laboratory evaluation of a novel diagnostic platform for malaria. The Magneto Optical Test (MOT) is based on the bio-physical detection of haemozoin in clinical samples. Having an assay time of around one minute, it offers the potential of high throughput screening.

Methods

Blood samples of confirmed malaria patients from different regions of Africa, patients with other diseases and healthy non-endemic controls were used in the present study. The samples were analysed with two reference tests, i.e. an histidine rich protein-2 based rapid diagnostic test (RDT) and a conventional Pan-Plasmodium PCR, and the MOT as index test. Data were entered in 2 × 2 tables and analysed for sensitivity and specificity. The agreement between microscopy, RDT and PCR and the MOT assay was determined by calculating Kappa values with a 95% confidence interval.

Results

The observed sensitivity/specificity of the MOT test in comparison with clinical description, RDT or PCR ranged from 77.2 - 78.8% (sensitivity) and from 72.5 - 74.6% (specificity). In general, the agreement between MOT and the other assays is around 0.5 indicating a moderate agreement between the reference and the index test. However, when RDT and PCR are compared to each other, an almost perfect agreement can be observed (k = 0.97) with a sensitivity and specificity of >95%.

Conclusions

Although MOT sensitivity and specificity are currently not yet at a competing level compared to other diagnostic test, such as PCR and RDTs, it has a potential to rapidly screen patients for malaria in endemic as well as non-endemic countries.

Design of malaria diagnostic criteria for the Sysmex XE-2100 hematology analyzer

Thick film, the standard diagnostic procedure for malaria, is not always ordered promptly. A failsafe diagnostic strategy using an XE-2100 analyzer is proposed, and for this strategy, malaria diagnostic models for the XE-2100 were developed and tested for accuracy. Two hundred eighty-one samples were distributed into Plasmodium vivax, P. falciparum, and acute febrile syndrome groups for model construction. Model validation was performed using 60% of malaria cases and a composite control group of samples from AFS and healthy participants from endemic and non-endemic regions. For P. vivax, two observer-dependent models (accuracy = 95.3-96.9%), one non-observer-dependent model using built-in variables (accuracy = 94.7%), and one non-observer-dependent model using new and built-in variables (accuracy = 96.8%) were developed. For P. falciparum, two non-observer-dependent models (accuracies = 85% and 89%) were developed. These models could be used by health personnel or be integrated as a malaria alarm for the XE-2100 to prompt early malaria microscopic diagnosis.

Automated detection of malaria-associated pseudoeosinophilia and abnormal WBC scattergram by the Sysmex XE-2100 hematology analyzer: a clinical study with 1,801 patients and real-time quantitative PCR analysis in vivax malaria-endemic area

Recently, the XE-2100 hematology analyzer was investigated in a rather small patient group; pseudoeosinophilia or abnormal white blood cell (WBC) scattergrams reported by this instrument were considered as significantly valuable diagnostic parameters in detecting vivax malaria. This study was conducted not only to assess the usefulness of pseudoeosinophilia or abnormal WBC scattergram in vivax malaria-endemic areas with large patient groups (N = 1,801) but also to investigate the correlation of parasitemia and platelet count with pseudoeosinophilia and abnormal WBC scattergrams. Of the 1,801 analyzed patients, 413 (22.9%) were found to have malaria by Wright-Giemsa stained blood smears. Overall, either pseudoeosinophilia or abnormal WBC scattergram was detected in 191 of 413 malaria patients and 4 of 1,388 patients without malaria (sensitivity = 46.2%, specificity = 99.7%). We suggest that clinical hematology laboratories using the XE-2100 analyzer should be aware of such specific parameters, even with the absence of a clinical request.

Automated detection of haemozoin-containing monocytes for the diagnosis of malaria in microscopically negative cases during pregnancy

Plasmodium falciparum sequesters in the placenta. Cell-Dyn automated flow cytometric haematology analysers have the capacity to detect haemozoin-containing circulating leukocytes during routine FBC analysis. In Lambaréné, Gabon, 685 FBCs of pregnant women were analysed, yielding 86.8% sensitivity and 78.5% specificity compared to microscopy. In a subset of 37 Cell-Dyn positive but microscopy negative samples, PCR detected five positive cases. This methodology may serve as an adjunct rapid diagnostic tool for malaria during pregnancy, even in microscopically negative cases.

Full blood count and haemozoin-containing leukocytes in children with malaria: diagnostic value and association with disease severity

BACKGROUND

Diligent and correct laboratory diagnosis and up-front identification of risk factors for progression to severe disease are the basis for optimal management of malaria.

METHODS

Febrile children presenting to the Medical Research Unit at the Albert Schweitzer Hospital (HAS) in Lambaréné, Gabon, were assessed for malaria. Giemsa-stained thick films for qualitative and quantitative diagnosis and enumeration of malaria pigment, or haemozoin (Hz)-containing leukocytes (PCL) were performed, and full blood counts (FBC) were generated with a Cell Dyn 3000 instrument.

RESULTS

Compared to standard light microscopy of Giemsa-stained thick films, diagnosis by platelet count only, by malaria pigment-containing monocytes (PCM) only, or by pigment-containing granulocytes (PCN) only yielded sensitivities/specificities of 92%/93%; 96%/96%; and 85%/96%, respectively. The platelet count was significantly lower in children with malaria compared to those without (p < 0.001), and values showed little overlap between groups. Compared to microscopy, scatter flow cytometry as applied in the Cell-Dyn 3000(R) instrument detected significantly more patients with PCL (p < 0.01). Both PCM and PCN numbers were higher in severe versus non-severe malaria yet reached statistical significance only for PCN (p < 0.0001; PCM: p = 0.14). Of note was the presence of another, so far ill-defined pigment-containing group of phagocytic cells, identified by laser-flow cytometry as lymphocyte-like gated events, and predominantly found in children with malaria-associated anaemia.

CONCLUSION

In the age group examined in the Lambaréné area, platelets are an excellent adjuvant tool to diagnose malaria. Pigment-containing leukocytes (PCL) are more readily detected by automated scatter flow cytometry than by microscopy. Automated Hz detection by an instrument as used here is a reliable diagnostic tool and correlates with disease severity. However, clinical usefulness as a prognostic tool is limited due to an overlap of PCL numbers recorded in severe versus non-severe malaria. However, this is possibly because of the instrument detection algorithm was not geared towards this task, and data lost during processing; and thus adjusting the instrument's algorithm may allow to establish a meaningful cut-off value.

Molecular diagnostic and surveillance tools for global malaria control

Malaria is the most devastating parasitic infection in the world, annually causing over 1 million deaths and extensive morbidity. The global burden of malaria has increased over the last several decades, as have rates of imported malaria into non-endemic regions. Rapid and accurate diagnostics are a crucial component of malaria control strategies, and epidemiological surveillance is required to monitor trends in malaria prevalence and antimalarial drug resistance. Conventional malaria diagnostic and surveillance tools can be cumbersome and slow with limitations in both sensitivity and specificity. New molecular techniques have been developed in an attempt to overcome these restrictions. These molecular techniques are discussed with regard to their technical advantages and disadvantages, with an emphasis on the practicality of implementation in malaria-endemic and non-endemic regions.

Haemozoin: from melatonin pigment to drug target, diagnostic tool, and immune modulator

Plasmodium spp produce a pigment (haemozoin) to detoxify the free haem that is generated by haemoglobin degradation. Haemozoin was originally thought to be an inert waste byproduct of the parasite. However, recent research has led to the recognition that haemozoin is possibly of great importance in various aspects of malaria. Haemozoin is the target of many antimalarial drugs, and the unravelling of the exact modes of action may allow the design of novel antimalarial compounds. The detection of haemozoin in erythrocytes or leucocytes facilitates the diagnosis of malaria. The number of haemozoin-containing monocytes and granulocytes has been shown to correlate well with disease severity and may hold the potential for becoming a novel, automated laboratory marker in the assessment of patients. Finally, haemozoin has a substantial effect on the immune system. Further research is needed to clarify these aspects, many of which are important in clinical practice.

Automated detection of malaria pigment: feasibility for malaria diagnosing in an area with seasonal malaria in northern Namibia

OBJECTIVE

To evaluate the feasibility of automated malaria detection with the Cell-Dyn 3700 (Abbott Diagnostics, Santa Clara, CA, USA) haematology analyser for diagnosing malaria in northern Namibia.

METHODS

From April to June 2003, all patients with a positive blood smear result and a subset of patients with no suspicion of malaria were included. Blood smear and a venous blood sample (to determine haemoglobin, platelet and malaria pigment levels) were collected from each patient. Malaria pigment test characteristics, correlations with blood parameters and pigment clearance time were calculated. Finally, a subset of blood samples was run twice to evaluate the consistency of test outcome.

RESULTS

Two hundred and eight patients were included. Ninety had a positive blood smear result of which 84 tested positive for malaria pigment and 118 patients had a negative blood smear result of which four tested positive for malaria pigment. Test characteristics as compared with microscopy were as follows: sensitivity 0.93, specificity 0.97, positive predictive value 0.95, negative predictive value 0.95. Rerun of the blood samples resulted in a change of diagnosis in 14%. After 4 weeks, 33% of patients with an initially positive pigment result still tested positive. Malaria pigment was found to be negatively correlated with haemoglobin.

CONCLUSIONS

Automated detection of malaria pigment is a useful diagnostic tool in this semi-rural area. In low-risk malaria season, the test can be used for diagnosing malaria because of the high sensitivity. In high-risk malaria season, the test can be used for excluding malaria in case of a negative pigment result because of the high specificity.

Hemozoin formation in Echinostoma trivolvis rediae

Rediae of the trematode Echinostoma trivolvis, from naturally infected Helisoma trivolvis snails, form a black pigment while inside the snail host. Here we examine the black pigment to show that the insolubility characteristics in detergent and weak base solution are identical to Plasmodium falciparum hemozoin. Laser desorption mass spectrometry of the purified pigment demonstrates the presence of heme. Examination of purified pigment under polarized light microscopy illuminates ordered birefringent crystals. Field emission in lens scanning electron microscopy reveals irregular ovoid crystals of 200-300 nm in diameter. The purified pigment crystals seeded extension of monomeric heme onto the crystal which by Fourier Transform Infrared analysis is beta-hematin. Rediae of a second echinostome parasite, Echinostoma caproni, from experimentally infected Biomphalaria glabrata, do not produce measurable or recoverable heme crystals. These observations are consistent with heme crystal formation by a hematophagous parasite within a non-vertebrate intermediate host.

Performance evaluation of automated depolarization analysis for detecting clinically unsuspected malaria in endemic countries

This prospective study evaluated the efficiency of automated depolarization analysis for recognition of unsuspected malaria by haemozoin detection during routine full blood count (FBC) screening of 676 randomly selected out-patients in a malaria hypoendemic area of Senegal. An additional 123 patients with clinically suspected malaria were studied for comparison. Of the 799 samples, 648 (81.1%) were categorized as malaria-negative, 83 (10.4%) as malaria-positive, and 68 as treated (early convalescence) or subclinical malaria (indirect evidence of infection). At a discrimination level of one or more atypical pigment-containing monocytes (PCM), negative and positive agreement was found to be 95.6% and 91.6% respectively for all malaria-negative and parasite-positive samples combined. Increasing the discriminator to two or more PCM events improved the overall agreement to 97.5%. Multivariate analysis showed that the only significant risk factor for the presence of PCM (odds ratio>200) was malaria infection. In the randomly selected group of 676 patients, 41 unsuspected cases of malaria infection were detected using the panel of reference diagnostic tests, and 37 (90.2%) of these had atypical PCM. The detection of clinically unrecognized malaria infection as part of a routine FBC procedure is a potentially useful extended application for laboratories in countries with endemic malaria.

Malaria

Malaria is a parasitic infection of global importance. Although relatively uncommon in developed countries, where the disease occurs mainly in travellers who have returned from endemic regions, it remains one of the most prevalent infections of humans worldwide. In endemic regions, malaria is a significant cause of morbidity and mortality and creates enormous social and economic burdens. Current efforts to control malaria focus on reducing attributable morbidity and mortality. Targeted chemoprophylaxis and use of insecticide-treated bed nets have been successful in some endemic areas. For travellers to malaria-endemic regions, personal protective measures and appropriate chemoprophylaxis can significantly reduce the risk of infection. Prompt evaluation of the febrile traveller, a high degree of suspicion of malaria, rapid and accurate diagnosis, and appropriate antimalarial therapy are essential in order to optimize clinical outcomes of infected patients. Additional approaches to malaria control, including genetic manipulation of mosquitoes and malaria vaccines, are areas of ongoing research.

Evaluation of the Abbott Cell-Dyn 4000 hematology analyzer for detection and therapeutic monitoring of Plasmodium vivax in the Republic of Korea

The Cell-Dyn 4000 automated hematology analyzer (CD4000) has the ability to detect malaria patients, but it remained unclear whether it could detect persistent malaria post-treatment. To investigate this, we used the CD4000 to evaluate 68 Korean patients with Plasmodium vivax malaria, and control groups of 50 patients with fever and 50 asymptomatic patients. The results from the instrument-generated scatter plot (derived by laser light depolarization) were compared with microscopy results. During the initial diagnosis, the sensitivity of the CD4000 in detecting malaria was 91.2%. On day 3 of follow-up, the CD4000 results matched those from microscopy by 96.7%. Malaria was not detected by either method beyond 14 days post-presentation. Interestingly, the atypical depolarizing events, which typify the presence of malaria in the analyzer, were highly correlated with the levels of parasitaemia in serially diluted samples of the leucocyte-depleted blood, and the CD4000 detected parasites down to the level of 288 +/- 17.7/microl. Our findings suggest that the phenomenon of atypical light depolarization could be influenced by parasitaemia levels, and be used as a screening method for P. vivax malaria patients, as well as for the therapeutic monitoring.

Sensitivity of hemozoin detection by automated flow cytometry in non- and semi-immune malaria patients

BACKGROUND

Cell-Dyn automated blood cell analyzers use laser flow cytometry technology, allowing detection of malaria pigment (hemozoin) in monocytes. We evaluated the value of such an instrument to diagnose malaria in febrile travelers returning to Berlin, Germany, the relation between the instrument's performance and the patients' immune status, and the capacity to increase its sensitivity.

METHODS

Malaria diagnosis was routinely established by thick-film microscopy. The patients' immune status was determined by an indirect fluorescent antibody test. Hemozoin detection was performed with a Cell-Dyn 3000. To assess the capacity for sensitivity increase, the relative frequencies of pigment-containing monocytes were determined for a subgroup of patients with the Cell-Dyn 3000 in comparison with a flow cytometer specifically adapted to rare-event analysis.

RESULTS

Of 403 patients screened microscopically, 107 had malaria. Overall sensitivity with the Cell-Dyn 3000 reached 48.6% (73.7% in semi-immune and 28.6% in nonimmune individuals; P < 0.0001). Specificity was 96.2%. The detection limit was at a relative concentration of 2 x 10(-4) pigment-containing monocytes (PCMs). By employing rare-event flow cytometry, the detection limit decreased to 3.25 x 10(-5), thus yielding a considerably increased sensitivity for the subgroup studied.

CONCLUSIONS

The correlation between immune status and relative concentration of PCMs explains the failure of the routine instrument for nonimmune patients and its significantly higher sensitivity for semi-immune individuals. The technique can be significantly improved by rare-event flow cytometry.

Current strategies to avoid misdiagnosis of malaria

Malaria remains the most important parasitic disease, and tens of thousands of cases are imported into non-endemic countries annually. However, any single institution may see only a very few cases-this is probably the reason why laboratory and clinical misdiagnosis may not be uncommon. In the laboratory, unfamiliarity with microscopic diagnosis may be the main reason, considering the large number of laboratory staff who provide on-call services, often without expert help at hand, as well as the difficulty in detecting cases with low-level parasitemia. Staff should therefore be provided with continuing microscopic training to maintain proficiency. The complementary use of immunochromatographic rapid detection tests (RDTs) may be useful, especially during on-call hours, although, in order to ensure correct interpretation, their inherent limitations have to be well known. Diagnosis based on the polymerase chain reaction is still unsuitable for routine use, due to its long turnaround time, its cost, and its unavailability outside regular hours, although it may be helpful in selected cases. Once the alert clinician has considered the possibility of malaria, and suspicion continues to be high, malaria can be excluded by repeat smears or RDTs. However, the absence of clinical suspicion may not be infrequent, and may have more serious consequences. Depending on the local number of malaria cases seen, laboratory staff should have a low threshold for the decision to perform unsolicited malaria diagnostic tests on suspicious samples, especially if other laboratory tests are abnormal (e.g. thrombocytopenia, presence of atypical lymphocytes, or raised lactate dehydrogenase). The detection of intraleukocytic hemozoin during automated full blood counts is a promising new way to avoid misdiagnosis of clinically unsuspected malaria.

Automated detection of malaria-associated intraleucocytic haemozoin by Cell-Dyn CD4000 depolarization analysis

Laboratory tests for malaria are only performed if there is clinical suspicion of the disease, and a missed diagnosis contributes substantially to morbidity and mortality. Malaria parasites produce haemozoin, which is able to depolarize light and this allows the automated detection of malaria during routine complete blood count analysis (CBC) with some Abbott Cell-Dyn instruments. In this study, we evaluated the Cell-Dyn CD4000 with 831 blood samples submitted for malaria investigations. Samples were categorized as malaria negative (n = 417), convalescent malaria (n = 64) or malaria positive (n = 350) by reference to thin/thick film microscopy, 'rapid test' procedures, polymerase chain reaction analysis and clinical history. With regard to CD4000 depolarization analysis, a malaria positive CD4000 pattern was ascribed to samples that showed one or more abnormal depolarizing purple events, which corresponded to monocytes containing ingested malaria pigment (haemozoin). Positive CD4000 patterns were observed in 11 of 417, 50 of 64 and 281 of 350 of malaria negative, convalescent malaria and malaria positive samples respectively. The specificity and positive predictive values for malaria (active and convalescent) were very high (97.4 and 96.8%, respectively), while sensitivity and negative predictive values were 80.0 and 83.0% respectively. Depolarization analysis was particularly effective for Plasmodium falciparum malaria but there was lower detection sensitivity for White compared with Black African patients. CD4000 90 degrees depolarization vs 0 degrees analysis revealed a proportion of samples with small nonleucocyte-associated depolarizing particles. Appearance of such events in the form of a discrete cluster was associated with P. vivax rather than P. falciparum infection.

Relative frequency of malaria pigment-carrying monocytes of nonimmune and semi-immune patients from flow cytometric depolarized side scatter

BACKGROUND

Recently, it was observed that malaria can be detected by performing automated complete blood count analysis including depolarization measurement of scattered laser light. To explain large discrepancies in sensitivity and specificity observed in semi-immune and nonimmune malaria patients, we determined the relative frequencies of malaria pigment-carrying monocytes (PCM) by flow cytometric measurements combined with rare event analysis.

METHODS

An experimental cell-sorting unit utilizing argon, krypton, and helium-neon lasers measured the relative frequencies of leukocytes of malaria patients. Single white blood cells showing high intensity in their depolarized side scatter were sorted for subsequent microscopic analysis.

RESULTS

From microscopic inspection of sorted cells, we identified malaria PCM as a distinct cluster in scatter diagrams that is well separated from normal leukocytes. For nonimmune patients, the average relative frequency of PCM is 1.5 x 10(-4) (median), for semi-immune patients 8.8 x 10(-4), and for malaria-negative persons 4.4 x 10(-6). Results derived from depolarized side scatter at 488, 633, or 647 nm agree well. Furthermore, malaria pigment-carrying neutrophilic granulocytes were identified microscopically after sorting. We discuss briefly how pigment-carrying neutrophils might be differentiated from normal leukocytes and PCM by using flow cytometry and measuring depolarized side scatter at two wavelengths.

CONCLUSION

Our results confirm the feasibility of malaria detection by flow cytometry for semi-immune patients and extend malaria detection to nonimmune patients with low frequencies of PCM. High sensitivity and specificity for malaria detection were obtained.