Towards harmonization of microscopy methods for malaria clinical research studies

Malaria Slide Bank to Strengthen and Improve the Quality of Malaria Diagnosis: A National Slide Repository in India

Malaria elimination is one of the top health care priorities in India, necessitating accessible and accurate diagnosis for effective treatment. A malaria slide bank in India is a collection of quality-controlled malaria-positive and -negative slides and is considered a vital asset for quality diagnosis. The collection of blood samples, preparation of blood smears, staining, quality control, molecular characterizations, and slide validation were carried out according to standard operating procedures in accordance with the WHO reference laboratory. The true count and parasite density per microliter were computed in accordance with WHO guidelines. Over 27 months, 48 batches (8,196 slides) were prepared. Overall, the majority of slide batches were Plasmodium vivax (45.9%; 22/48), followed by Plasmodium falciparum (25%; 12/48), malaria-negative infections (25%; 12/48), and mixed infections (4.1%; 2/48). All 48 batches passed internal validation by WHO-certified level-1 microscopists. For a batch, the true count was the median of the validators' counts (range, 111-280,795 parasites/µL). Except for mixed infections, the PCR results agreed with the verified microscopy results. Malaria slide bank slides would be a valuable tool for quality control, assurance, and microscopist training.

Current Status of Malaria Control and Elimination in Africa: Epidemiology, Diagnosis, Treatment, Progress and Challenges

The African continent carries the greatest malaria burden in the world. Falciparum malaria especially has long been the leading cause of death in Africa. Climate, economic factors, geographical location, human intervention and unstable security are factors influencing malaria transmission. Due to repeated infections and early interventions, the proportion of clinically atypical malaria or asymptomatic plasmodium carriers has increased significantly, which easily lead to misdiagnosis and missed diagnosis. African countries have made certain progress in malaria control and elimination, including rapid diagnosis of malaria, promotion of mosquito nets and insecticides, intermittent prophylactic treatment in high-risk groups, artemisinin based combination therapies, and the development of vaccines. Between 2000 and 2022, there has been a 40% decrease in malaria incidence and a 60% reduction in mortality rate in the WHO African Region. However, many challenges are emerging in the fight against malaria in Africa, such as climate change, poverty, substandard health services and coverage, increased outdoor transmission and the emergence of new vectors, and the growing threat of resistance to antimalarial drugs and insecticides. Joint prevention and treatment, identifying molecular determinants of resistance, new drug development, expanding seasonal malaria chemo-prevention intervention population, and promoting the vaccination of RTS, S/AS01 and R21/Matrix-M may help to solve the dilemma. China's experience in eliminating malaria is conducive to Africa's malaria prevention and control, and China-Africa cooperation needs to be constantly deepened and advanced. Our review aims to help the global public develop a comprehensive understanding of malaria in Africa, thereby contributing to malaria control and elimination.

Unravelling the quality of malaria microscopy across Kinshasa, DR Congo

Introduction

In the current study we assessed clinical laboratories' staff ability across the city of Kinshasa with particular focus on their practices and performance regarding malaria microscopy.

Materials and Methods

This was a non-random cross-sectional study included clinical laboratories in Kinshasa and focused on cross-checking of blood slides, a questionnaire and checklist according to standardised analytic malaria microscopy procedures. Regarding the cross-checking of slides, participant responses were considered 'corrects' in cases of complete congruence with the reference; 'acceptable' for malaria-positive slides but no identification of Plasmodium species, stage of development, parasite density and/or reported as P. falciparum instead of 'P. non falciparum'; and 'incorrect' if 'false positive' and 'false negative' cases.

Results

Eighty-eight among the 90 targeted clinical laboratories (participation 97.8%) took part in the investigation from February to July 2019. The ability assessment revealed that individuals qualified to perform thick blood films (TBF) according to the national malaria control program (NMCP) procedures ranged from 48.6% to 100.0%. Overall cross-checking performance of 167 eligible routine slides was relatively low: 37.7%; 25.8% and 36.5% of correct, acceptable and incorrect responses, respectively. The first routine slide was correctly and acceptably scored respectively by 35.3% and 28.2% of participating laboratories (n = 85); and the second, by 40.2% and 23.2% respectively (n = 82). The sensitivity and specificity were found to be 79.4% and 53.8%, respectively. However, the relative high scores reported in relation with the ability needed to perform TBF based on NMCP standards contrasted with the poor performance from cross-checking slides. Consecutively, only one-third of the 88 participating laboratories reached a score > 60% in agreement with NMCP procedures and had acceptable responses to cross-checked slides.

Conclusions

The study was conducted as part of the activities relating to "Ensuring early diagnosis and prompt malaria treatment" component of the national malaria control strategy with NMCP support. More laboratories must implement clear and standardised malaria microscopy procedures, and need to include more rigorous quality control.

Variability in white blood cell count during uncomplicated malaria and implications for parasite density estimation: a WorldWide Antimalarial Resistance Network individual patient data meta-analysis

BACKGROUND

The World Health Organization (WHO) recommends that when peripheral malarial parasitaemia is quantified by thick film microscopy, an actual white blood cell (WBC) count from a concurrently collected blood sample is used in calculations. However, in resource-limited settings an assumed WBC count is often used instead. The aim of this study was to describe the variability in WBC count during acute uncomplicated malaria, and estimate the impact of using an assumed value of WBC on estimates of parasite density and clearance.

METHODS

Uncomplicated malaria drug efficacy studies that measured WBC count were selected from the WorldWide Antimalarial Resistance Network data repository for an individual patient data meta-analysis of WBC counts. Regression models with random intercepts for study-site were used to assess WBC count variability at presentation and during follow-up. Inflation factors for parasitaemia density, and clearance estimates were calculated for methods using assumed WBC counts (8000 cells/µL and age-stratified values) using estimates derived from the measured WBC value as reference.

RESULTS

Eighty-four studies enrolling 27,656 patients with clinically uncomplicated malaria were included. Geometric mean WBC counts (× 1000 cells/µL) in age groups < 1, 1-4, 5-14 and ≥ 15 years were 10.5, 8.3, 7.1, 5.7 and 7.5, 7.0, 6.5, 6.0 for individuals with falciparum (n = 24,978) and vivax (n = 2678) malaria, respectively. At presentation, higher WBC counts were seen among patients with higher parasitaemia, severe anaemia and, for individuals with vivax malaria, in regions with shorter regional relapse periodicity. Among falciparum malaria patients, using an assumed WBC count of 8000 cells/µL resulted in parasite density underestimation by a median (IQR) of 26% (4-41%) in infants < 1 year old but an overestimation by 50% (16-91%) in adults aged ≥ 15 years. Use of age-stratified assumed WBC values removed systematic bias but did not improve precision of parasitaemia estimation. Imprecision of parasite clearance estimates was only affected by the within-patient WBC variability over time, and remained < 10% for 79% of patients.

CONCLUSIONS

Using an assumed WBC value for parasite density estimation from a thick smear may lead to underdiagnosis of hyperparasitaemia and could adversely affect clinical management; but does not result in clinically consequential inaccuracies in the estimation of the prevalence of prolonged parasite clearance and artemisinin resistance.

High prevalence of persistent residual parasitemia on days 3 and 14 after artemether-lumefantrine or pyronaridine-artesunate treatment of uncomplicated Plasmodium falciparum malaria in Nigeria

BACKGROUND

Microscopic evaluation of parasite clearance is the gold standard in antimalarial drug efficacy trials. However, the presence of sub-microscopic residual parasitemia after artemisinin-based combination therapy (ACT) needs to be investigated.

METHODS

One hundred and twenty (AL: n = 60, PA: n = 60) days 3 and 14 dried blood spots, negative by microscopy were analysed for residual parasitemia using nested PCR. Isolates with residual parasitemia on days 3 and 14 were further genotyped with their corresponding day-0 isolates using merozoite surface proteins msp-1, msp-2, and glurp genes for allelic similarity.

RESULTS

Persistent PCR-determined sub-microscopic residual parasitemia at day 3 post ACT treatment was 83.3 (AL) and 88.3% (PA), respectively (ρ = 0.600), while 63.6 and 36.4% (ρ = 0.066) isolates were parasitemic at day 14 for AL and PA, respectively. Microscopy-confirmed gametocytemia persisted from days 0 to 7 and from days 0 to 21 for AL and PA. When the alleles of day 3 versus day 0 were compared according to base pair sizes, 59% of parasites shared identical alleles for glurp, 36% each for 3D7 and FC27, while K1 was 77%, RO33 64%, and MAD20 23%, respectively. Similarly, day 14 versus day 0 was 36% (glurp), 64% (3D7), and 32% (FC27), while 73% (K1), 77% (RO33), and 41% (MAD20), respectively.

CONCLUSION

The occurrence of residual parasitemia on days 3 and 14 following AL or PA treatment may be attributable to the presence of either viable asexual, gametocytes, or dead parasite DNAs, which requires further investigation.

Longitudinal and Cross-sectional Analyses of Asymptomatic HIV-1/Malaria Co-infection in Kisumu County, Kenya

Individuals infected with HIV-1 experience more frequent and more severe episodes of malaria and are likely to harbor asymptomatic parasitemia, thus potentially making them more efficient reservoirs of malaria. Two studies (cross-sectional and longitudinal) were designed in sequence between 2015-2018 and 2018-2020, respectively, to test the hypothesis that HIV-1 infected individuals have higher prevalence of asymptomatic parasitemia and gametocytemia than the HIV-1 negatives. This article describes the overall design of the two studies, encompassing data for the longitudinal study and additional data to the previously published baseline data for the cross-sectional study. In the cross-sectional study, HIV-1 positive participants were significantly older, more likely to be male, and more likely to have parasitemia relative to HIV-1 negatives (P < 0.01). In the longitudinal study, 300 participants were followed for 6 months. Of these, 102 were HIV-1 negative, 106 were newly diagnosed HIV-1 positive, and 92 were HIV-1 positive and on antiretroviral therapy, including antifolates, at enrollment. Overall parasitemia positivity at enrollment was 17.3% (52/300). Of these, 44% (23/52) were HIV-1 negative, 52% (27/52) were newly diagnosed HIV-1 positives, and only 4% (2/52) were HIV-1 positive and on treatment. Parasitemia for those on stable antiretroviral therapy was significantly lower (hazard ratio: 0.51, P < 0.001), compared with the HIV-1-negatives. On follow-up, there was a significant decline in parasitemia prevalence (hazard ratio: 0.74, P < 0.001) among the HIV patients newly initiated on antiretroviral therapy including trimethoprim-sulfamethoxasole. These data highlight the impact of HIV-1 and HIV treatment on asymptomatic parasitemia over time.

Field evaluation of the diagnostic performance of EasyScan GO: a digital malaria microscopy device based on machine-learning

BACKGROUND

Microscopic examination of Giemsa-stained blood films remains the reference standard for malaria parasite detection and quantification, but is undermined by difficulties in ensuring high-quality manual reading and inter-reader reliability. Automated parasite detection and quantification may address this issue.

METHODS

A multi-centre, observational study was conducted during 2018 and 2019 at 11 sites to assess the performance of the EasyScan Go, a microscopy device employing machine-learning-based image analysis. Sensitivity, specificity, accuracy of species detection and parasite density estimation were assessed with expert microscopy as the reference. Intra- and inter-device reliability of the device was also evaluated by comparing results from repeat reads on the same and two different devices. This study has been reported in accordance with the Standards for Reporting Diagnostic accuracy studies (STARD) checklist.

RESULTS

In total, 2250 Giemsa-stained blood films were prepared and read independently by expert microscopists and the EasyScan Go device. The diagnostic sensitivity of EasyScan Go was 91.1% (95% CI 88.9-92.7), and specificity 75.6% (95% CI 73.1-78.0). With good quality slides sensitivity was similar (89.1%, 95%CI 86.2-91.5), but specificity increased to 85.1% (95%CI 82.6-87.4). Sensitivity increased with parasitaemia rising from 57% at < 200 parasite/µL, to ≥ 90% at > 200-200,000 parasite/µL. Species were identified accurately in 93% of Plasmodium falciparum samples (kappa = 0.76, 95% CI 0.69-0.83), and in 92% of Plasmodium vivax samples (kappa = 0.73, 95% CI 0.66-0.80). Parasite density estimates by the EasyScan Go were within ± 25% of the microscopic reference counts in 23% of slides.

CONCLUSIONS

The performance of the EasyScan Go in parasite detection and species identification accuracy fulfil WHO-TDR Research Malaria Microscopy competence level 2 criteria. In terms of parasite quantification and false positive rate, it meets the level 4 WHO-TDR Research Malaria Microscopy criteria. All performance parameters were significantly affected by slide quality. Further software improvement is required to improve sensitivity at low parasitaemia and parasite density estimations. Trial registration ClinicalTrials.gov number NCT03512678.

Impact of Malaria Diagnostic Technologies on the Disease Burden in the Sub-Saharan Africa

Worldwide, transmission of emerging and reemerging malaria infections poses a significant threat to human health in the Sub-Saharan Africa, one that can quickly overwhelm public health resources. While the disease burden of malaria in the Sub-Saharan Africa appears to be on a gradual decline, it is characterized by spatial and temporal variability occasioning a sorry state for the Global South Countries. New evidence on long-term complications of malaria heightens our awareness of its public health impact. Given the likelihood of misdiagnosis, and the unknown levels of malaria transmission across different landscapes, many missed opportunities for prevention occur. Africa's population growth, unplanned urbanization, habitat destruction, and trans-border travel are contributing to a rise in the calamitous epidemiology of malaria. Despite empirical statistics demonstrating a downward trend in the malaria disease burden attributable to the scale-up of multiple control strategies, including new diagnostic technologies, malaria remains a global threat to human health in Sub-Sahara Africa. Malaria is a severe public health threat globally, despite several advancements and innovations in its control. Six species of the genus Plasmodium including Plasmodium malariae, Plasmodium falciparum, Plasmodium cynomolgi, Plasmodium knowlesi, Plasmodium ovale, and Plasmodium vivax are known to infect humans. However, greatest disease burden and fatalities are caused by Plasmodium falciparum. Globally, about 3 billion individuals are at risk of contracting malaria disease every year, with over 400,000 fatalities reported in the Sub-Saharan Africa. World Health Organization (WHO) 2018 malaria report indicated that approximately 405,000 mortalities and 228 million cases were reported worldwide, with Africa carrying the highest disease burden. Over the last decade, there has been a significant decline in malaria deaths and infections, which may be related to the availability of effective diagnostic techniques. However, in certain areas, the rate of decline has slowed or even reversed the gains made so far. Accurate diagnosis, adequate treatment, and management of the disease are critical WHO-set goals of eliminating malaria by 2030. Microscopy, rapid diagnostic tests (RDTs), nucleic acid amplification tests (NAATs), and biosensors are all currently accessible diagnostic methods. These technologies have substantial flaws and triumphs that could stymie or accelerate malaria eradication efforts. The cost, ease, accessibility, and availability of skilled persons all influence the use of these technologies. These variables have a direct and indirect ramification on the entire management portfolio of patients. Despite the overall decline in the malaria disease burden driven partly by new diagnostic technologies, a sobering pattern marked by limited number of studies and spatial as well as temporal heterogeneity remains a concern. This review summarizes the principle, performance, gaps, accomplishments, and applicability of numerous malaria diagnostic techniques and their potential role in reducing the malaria disease burden in Sub-Saharan Africa.

Automated detection and staging of malaria parasites from cytological smears using convolutional neural networks

Microscopic examination of blood smears remains the gold standard for laboratory inspection and diagnosis of malaria. Smear inspection is, however, time-consuming and dependent on trained microscopists with results varying in accuracy. We sought to develop an automated image analysis method to improve accuracy and standardization of smear inspection that retains capacity for expert confirmation and image archiving. Here, we present a machine learning method that achieves red blood cell (RBC) detection, differentiation between infected/uninfected cells, and parasite life stage categorization from unprocessed, heterogeneous smear images. Based on a pretrained Faster Region-Based Convolutional Neural Networks (R-CNN) model for RBC detection, our model performs accurately, with an average precision of 0.99 at an intersection-over-union threshold of 0.5. Application of a residual neural network-50 model to infected cells also performs accurately, with an area under the receiver operating characteristic curve of 0.98. Finally, combining our method with a regression model successfully recapitulates intraerythrocytic developmental cycle with accurate lifecycle stage categorization. Combined with a mobile-friendly web-based interface, called PlasmoCount, our method permits rapid navigation through and review of results for quality assurance. By standardizing assessment of Giemsa smears, our method markedly improves inspection reproducibility and presents a realistic route to both routine lab and future field-based automated malaria diagnosis.

Assessment of Microscopic Detection of Malaria with Nested Polymerase Chain Reaction in War-Torn Federally Administered Tribal Areas of Pakistan

INTRODUCTION

Diagnostic accuracy of malaria is critical for early treatment, control, and elimination of malaria, especially in war-affected malaria-endemic areas. Microscopic detection of Plasmodium species has been the gold standard in remote malaria-endemic regions. However, the diagnostic accuracy is still questioned, especially in discriminating mixed and submicroscopic parasitic levels. This study was designed to evaluate the diagnostic performance of microscopic examination against nested PCR analysis in war-torn malaria-endemic Federally Administered Tribal Areas (FATA) of Pakistan.

METHODS

Venous blood samples were collected from symptomatic patients for microscopic examination and nested PCR analysis from January 2016-December 2016 from five Agencies (Bajaur, Mohmand, Khyber, Orakzai and Kurram Agency) and four Frontier Regions (Peshawar, Kohat, Bannu, and Dera Ismail Khan Frontier Region) of FATA. Malaria-positive isolates were confirmed by nested PCR (targeting Plasmodium small subunit ribosomal ribonucleic acid (ssrRNA) genes) for speciation.

RESULTS

Among enrolled participants, 762 were found positive for malaria parasite on microscopic examination of the blood film. Plasmodium vivax was found in 623, Plasmodium falciparum in 132 and 7 were diagnosed with mixed infection (P. vivax and P. falciparum coinfection). Nested PCR detected Plasmodium infection in 679 samples (523 P. vivax, 121 P. falciparum, and 35 mixed infections). Compared with microscopy, the sensitivity of nested PCR was 98.94%, and specificity was 98.27%, while the sensitivity and specificity of slide microscopy 89.34% and 87.99% respectively.

CONCLUSION

The conventional microscopy method has low sensitivity to detect the mixed infection as compared to nested PCR. High sensitivity and specificity observed in nested PCR make this molecular tool a useful technique for monitoring, controlling, and eliminating malaria-endemic regions.

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.

A Systematic Literature Review of Microscopy Methods Reported in Malaria Clinical Trials

Microscopy of stained blood films is essential for the diagnosis of malaria, differentiation of parasite species, and estimation of parasite density performed for assessments of antimalarial drug efficacy. The accuracy and comparability of these measures over time and space are vital to discern the emergence or spread of antimalarial drug resistance. Although evidence-based guidelines for malaria microscopy methods exist, the age-old microscopy techniques for parasitological assessments are subject to considerable methodological variations. The purpose of this review was to explore critically how microscopy methods were reported in published malarial studies between 2013 and 2017 with the focus on outlining the methodological differences and improving reporting standards in practice.