Malaria rapid diagnostic tests: challenges and prospects

EasyNAT Malaria: a simple, rapid method to detect Plasmodium species using cross-priming amplification technology

Malaria infection remains a serious threat to human health worldwide. Rapid and accurate detection technology is crucial for preventing malaria transmission and minimizing damage. We aimed to establish and validate a new rapid molecular detection method for malaria, called EasyNAT Malaria Assay, targeting Plasmodium vivax, Plasmodium falciparum, Plasmodium ovale, and Plasmodium malariae. The analytical performance of EasyNAT Malaria Assay was determined using positive materials. We identified 42 clinical samples as malaria positive and 95 negative samples. Each sample was examined by four methods: light microscopy, rapid diagnostic test, EasyNAT Malaria Assay, and digital PCR. Diagnostic accuracy and clinical performance were evaluated. The limit of detection (LOD)95% of EasyNAT Malaria was consistently 40 parasites/mL. It specifically amplified Plasmodium and performed with reliable repeatability and reproducibility. In 137 clinical samples, EasyNAT Malaria detected four more positive samples than microscopic examination and two more positive samples than rapid diagnostic test (RDT). One clinical sample was positive only under digital PCR. However, no significant differences statistically in sensitivity or specificity were observed. Compared with microscopy, the total, positive, and negative concordance rates of EasyNAT were 97.08%, 100%, and 95.79%, respectively. Enhanced diagnostic accuracy of EasyNAT Malaria in patients who had taken anti-malarial medication before their clinical appointment was observed. The EasyNAT Malaria Assay has good detection efficiency for clinical samples, presents a promising molecular detection tool in clinical practice, and is particularly suitable for rapid screening of high-risk populations in the emergency room.

IMPORTANCE

This study established and validated EasyNAT Malaria Assay as a promising molecular detection tool for malaria screening of high-risk populations in clinical practice. This novel isothermal amplification method may effectively facilitate the rapid diagnosis of malaria and prevent its transmission.

Evaluation of new haematology analyser, XN-31, for malaria detection in blood donors: A single-centre study from India

BACKGROUND AND OBJECTIVES

Malaria continues to be a significant public health concern in India, with several regions experiencing endemicity and sporadic outbreaks. The prevalence of malaria in blood donors, in India, varies between 0.02% and 0.07%. Common techniques to screen for malaria, in blood donors and patients, include microscopic smear examination and rapid diagnostic tests (RDTs) based on antigen detection. The aim of this study was to evaluate a new fully automated analyser, XN-31, for malaria detection, as compared with current practice of using RDT.

MATERIALS AND METHODS

Cross-sectional analytical study was conducted to evaluate clinical sensitivity and specificity of new automated analyser XN-31 among blood donors' samples and clinical samples (patients with suspicion of malaria) from outpatient clinic collected over between July 2021 and October 2022. No additional sample was drawn from blood donor or patient. All blood donors and patients' samples were processed by malaria rapid diagnostic test, thick-smear microscopy (MIC) and the haematology analyser XN-31. Any donor blood unit incriminated for malaria was discarded. Laboratory diagnosis using MIC was considered the 'gold standard' in the present study. Clinical sensitivity and specificity of XN-31 were compared with the gold standard.

RESULTS

Fife thousand and five donor samples and 82 diagnostic samples were evaluated. While the clinical sensitivity and specificity for donor samples were 100%, they were 72.7% and 100% for diagnostic samples.

CONCLUSION

Automated haematology analysers represent a promising solution, as they can deliver speedy and sensitive donor malaria screening assessments. This method also has the potential to be used for pre-transfusion malaria screening along with haemoglobin estimation.

A digital microscope for the diagnosis of Plasmodium falciparum and Plasmodium vivax, including P. falciparum with hrp2/hrp3 deletion

Sensitive and accurate malaria diagnosis is required for case management to accelerate control efforts. Diagnosis is particularly challenging where multiple Plasmodium species are endemic, and where P. falciparum hrp2/3 deletions are frequent. The Noul miLab is a fully automated portable digital microscope that prepares a blood film from a droplet of blood, followed by staining and detection of parasites by an algorithm. Infected red blood cells are displayed on the screen of the instrument. Time-to-result is approximately 20 minutes, with less than two minutes hands-on time. We evaluated the miLab among 659 suspected malaria patients in Gondar, Ethiopia, where P. falciparum and P. vivax are endemic, and the frequency of hrp2/3 deletions is high, and 991 patients in Ghana, where P. falciparum transmission is intense. Across both countries combined, the sensitivity of the miLab for P. falciparum was 94.3% at densities >200 parasites/μL by qPCR, and 83% at densities >20 parasites/μL. The miLab was more sensitive than local microscopy, and comparable to RDT. In Ethiopia, the miLab diagnosed 51/52 (98.1%) of P. falciparum infections with hrp2 deletion at densities >20 parasites/μL. Specificity of the miLab was 94.0%. For P. vivax diagnosis in Ethiopia, the sensitivity of the miLab was 97.0% at densities >200 parasites/μL (RDT: 76.8%, microscopy: 67.0%), 93.9% at densities >20 parasites/μL, and specificity was 97.6%. In Ethiopia, where P. falciparum and P. vivax were frequent, the miLab assigned the wrong species to 15/195 mono-infections at densities >20 parasites/μL by qPCR, and identified only 5/18 mixed-species infections correctly. In conclusion, the miLab was more sensitive than microscopy and thus is a valuable addition to the toolkit for malaria diagnosis, particularly for areas with high frequencies of hrp2/3 deletions.

Comparative evaluation of the diagnostic accuracies of four different malaria rapid diagnostic test kits available in Ghana

Malaria rapid diagnostic test (mRDT) kit is one of the techniques for diagnosing malaria. Due to its inherent advantages over the microscopy technique, several brands of the kit have flooded malaria endemic countries, without prior in-country evaluation. Two of such mRDT kits are Oscar (India) and Standard Q (Korea Republic). In this study, the performance of Oscar and Standard Q mRDT kits were compared to First Response (India) and CareStart (USA) mRDTs, which have been evaluated and deployed for use approved by the Ministry of Health (MOH). In this comparative study, whole blood samples were collected from patients suspected of malaria. Plasmodium falciparum was detected in each sample using nested polymerase chain reaction (nPCR), microscopy and the four mRDTs. The sensitivities, specificities, accuracies, positive and negative predictive values and accuracies of the mRDTs were determined using nPCR as a reference technique. Kappa statistic was used to determine the level of agreement among the techniques. Two hundred (200) blood samples were analyzed in this study. The overall detection rates of P. falciparum by microscopy, First Response, CareStart, Oscar-PfHRP2, Standard Q mRDT kits and nPCR were 31.5%, 34.5%, 33.5%, 32%, 31% and 43% (x2 = 6.1, p = 0.046), respectively. The accuracies of CareStart and First Response were comparable (90.5% vs. 89.5%). Further, comparing their sensitivities, Oscar-PfHRP2 was 74.4% (95% confidence interval (CI): 63.9-83.2) while that of Standard Q was 72.1% (95% CI: 61.4-81.2), with comparable accuracies (Oscar-PfHRP2-89% and Standard Q -88%). Apart from First Response that was 98.3% specific, the others were 100% specific. Kappa test revealed perfect diagnostic agreement (κ = 0.90-0.98) among the four mRDTs. That notwithstanding, Oscar-PfHRP2 agreed better with CareStart (κ = 0.94) and First Response (κ = 0.92) compared to the agreement between Standard Q and, CareStart (κ = 0.92) and First Response (κ = 0.90). Taken together, the diagnostic performance of the four mRDT kits were statistically similar. That notwithstanding, new mRDT kits should be evaluated prior to deployment for use.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

Evaluation of the Performance of Rapid Diagnostic Tests for Malaria Diagnosis and Mapping of Different Plasmodium Species in Mali

BACKGROUND

The first-line diagnosis of malaria in Mali is based on the use of rapid diagnostic tests (RDT) that detect the Histidin Rich Protein 2 (HRP2) antigen specific to Plasmodium falciparum. Our study, based on a real-time polymerase chain reaction (qPCR) gold standard, aimed to describe the distribution of the Plasmodium species in each administrative region of Mali and to assess the performance of RDTs.

METHODS

We randomly selected 150 malaria-negative and up to 30 malaria-positive RDTs in 41 sites distributed in 9 regions of Mali. DNA extracted from the RDT nitrocellulose strip was assayed with a pan-Plasmodium qPCR. Positive samples were then analyzed with P. falciparum-, P. malariae-, P. vivax-, or P. ovale-specific qPCRs.

RESULTS

Of the 1496 RDTs, 258 (18.6%) were positive for Plasmodium spp., of which 96.9% were P. falciparum. The P. vivax prevalence reached 21.1% in the north. RDT displayed acceptable diagnostic indices; the lower CI95% bounds of Youden indices were all ≥0.50, except in the north (Youden index 0.66 (95% CI [0.44-0.82]) and 0.63 (95% CI [0.33-0.83].

CONCLUSIONS

Overall, RDT diagnostic indices are adequate for the biological diagnosis of malaria in Mali. We recommend the use of RDTs detecting P. vivax-specific antigens in the north.

Malaria elimination in Ghana: recommendations for reactive case detection strategy implementation in a low endemic area of Asutsuare, Ghana

BACKGROUND

Progress toward malaria elimination is increasing as many countries near zero indigenous malaria cases. In settings nearing elimination, interventions will be most effective at interrupting transmission when targeted at the residual foci of transmission. These foci may be missed due to asymptomatic infections. To solve this problem, the World Health Organization recommends reactive case detection (RACD). This case study was conducted to identify individuals with asymptomatic malaria, their predisposing risk factors and recommend RACD in Asutsuare, Ghana based on literature review and a cross sectional study.

METHODS

The study involved a search on PubMed and Google Scholar of literature published between 1st January, 2009-14th August, 2023 using the search terms "malaria" in "Asutsuare". Furthermore, structured questionnaires were administered to one hundred individuals without symptoms of malaria and screened using rapid diagnostic test (RDT) kits, microscopy and real-time polymerase chain reaction (rt-PCR). Malaria prevalence based on the three diagnostic techniques as well as potential malaria risk factors were assessed through questionnaires in a cross-sectional study.

RESULTS

Cumulatively, sixty-four (64) studies (Google Scholar, 57 and PubMed, 7) were reviewed and 22 studies included in the literature on malaria in Asutsuare, Ghana. Significant risk factors were occupation, distance from a house to a waterbody, age group and educational level. Out of the 100 samples, 3 (3%) were positive by RDT, 6 (6%) by microscopy and 9 (9%) by rt-PCR. Ages 5-14.9 years had the highest mean malaria parasite densities of 560 parasites/µl with Plasmodium falciparum as the dominant species in 4 participants. Moreover, in the age group ≥ 15, 2 participants (1 each) harboured P. falciparum and Plasmodium malariae parasites. RDT had a higher sensitivity (76.54%; CI95 66.82-85.54) than rt-PCR (33.33%; CI95 4.33-77.72), while both rt-PCR and RDT were observed to have a higher specificity (92.55; CI95 85.26-96.95) and (97.30; CI95 93.87-99.13), respectively in the diagnosis of malaria.

CONCLUSION

In Asutsuare, Ghana, a low endemic area, the elimination of malaria may require finding individuals with asymptomatic infections. Given the low prevalence of asymptomatic individuals identified in this study and as repleted in the literature review, which favours RACD, Asutsuare is a possible setting receptive for RACD implementation.

Diagnosis and management of malaria in the intensive care unit

Malaria is responsible for approximately three-quarters of a million deaths in humans globally each year. Most of the morbidity and mortality reported are from Sub-Saharan Africa and Asia, where the disease is endemic. In non-endemic areas, malaria is the most common cause of imported infection and is associated with significant mortality despite recent advancements and investments in elimination programs. Severe malaria often requires intensive care unit admission and can be complicated by cerebral malaria, respiratory distress, acute kidney injury, bleeding complications, and co-infection. Intensive care management includes prompt diagnosis and early initiation of effective antimalarial therapy, recognition of complications, and appropriate supportive care. However, the lack of diagnostic capacities due to limited advances in equipment, personnel, and infrastructure presents a challenge to the effective diagnosis and management of malaria. This article reviews the clinical classification, diagnosis, and management of malaria as relevant to critical care clinicians, highlighting the role of diagnostic capacity, treatment options, and supportive care.

Rapid diagnostic tests for malaria diagnosis in Cameroon: impact of histidine rich protein 2/3 deletions and lactate dehydrogenase gene polymorphism

Malaria rapid diagnostic tests (mRDT) play a vital role in malaria control in endemic areas. In this study, histidine-rich protein (hrp) and lactate dehydrogenase (ldh) genes were genotyped in Plasmodium falciparum (Pf) and Plasmodium ovale (Po) spp. isolates. Deletions in P. falciparum hrp2/3 (pfhrp2/3) proteins and single nucleotide polymorphisms (SNPs) were analyzed. Twenty-four samples were analyzed for pfhrp2/3 gene deletions and 25 for SNPs in ldh gene (18 Pf and 7 Po spp.). Deletions in pfhrp2/3 genes were observed in 1.9% malaria positive isolates. The pfldh gene sequences showed one SNP at codon 272 (D272N) in 22.2% of samples while in Po spp., sequences were 100% similar to P. ovale curtisi but when compared to P. ovale wallikeri reference sequence, SNPs at positions 143 (P143S), 168 (K168N), 204 (V204I) were found. Findings suggest low prevalence in pfhrp2/3 genes and highlight the circulation of P. ovale curtisi in the studies areas.

Diagnostic value of rapid test for malaria among febrile neonates in a tertiary hospital in North-East Nigeria: a prospective cross-sectional study

OBJECTIVE

The WHO recommends testing using microscopy or rapid diagnostic test (RDT) before treatment for malaria. However, the use of RDT to diagnose neonatal malaria has not been widely validated with most studies limited to the first week of life. Thus, we conducted this study to determine the utility of RDT in the diagnosis of congenital and acquired malaria in febrile neonates in Nigeria.

DESIGN

This prospective cross-sectional descriptive study consecutively recruited 131 febrile neonates at the Special Care Baby Unit (SCBU) of the Federal Teaching Hospital Gombe, Nigeria. All study participants concurrently had RDT (HRP2, LDH) and malaria microscopy. The performance of both methods was then compared.

RESULT

Seventy-eight of 131 neonates tested for malaria by blood smear microscopy demonstrated malaria parasites; a prevalence of 59.5%. Parasite count ranged from 16 to 520 /μL and the median parasite count was 81.0 /μL with IQR (40.0-134.5). The majority of patients (93.5%) had low-density parasitaemia (≤2+). All species identified were Plasmodium falciparum. None of the 131 neonates tested positive on RDT. The sensitivity and positive predictive value of RDT for neonatal malaria was zero. Congenital malaria was the most common form of neonatal malaria, accounting for 75.6%, while acquired and transfusion-related malaria were estimated at 12.8% and 11.6%, respectively.

CONCLUSION

The RDT used in this study was not sensitive in the diagnosis of congenital or acquired neonatal malaria; therefore, microscopy remains the preferred method of diagnosis of neonatal malaria.

Evaluation of the performance of advantage P.f. malaria Card® and advantage malaria Pan + Pf Card®, two rapid diagnostic tests for parasitological confirmation of malaria cases in field situation in Togo

BACKGROUND

In Togo, malaria remains a major public health problem, and the management of suspected cases requires confirmation with appropriate biological methods. Malaria diagnosis has been improved by the introduction of rapid diagnostic tests (RDTs), recommended by the World Health Organization (WHO) for areas where microscopy is not available. To be used, these RDTs must meet performance criteria defined by the WHO. This study was conducted to evaluate the diagnostic performance of two RDTs: Advantage P.f. Malaria Card® detecting HRP2 antigen and Advantage Malaria Pan + Pf Card® detecting both HRP2 and pLDH antigens.

METHODS

This was a cross-sectional analytical study conducted from December 2019 to February 2020 on malaria-suspected cases received in three sentinel sites in Togo and from whom capillary blood was collected to perform the two RDTs according to the manufacturer's instructions. Sensitivity and specificity were estimated by comparing to thick/thin blood smear, the gold standard, and to PCR, which is a more sensitive.

RESULTS

A total of 390 participants (54.9% female) with a median age of 18 (± 0.8) years were included in the study. The sensitivity of both Advantage P.f. Malaria Card® and Advantage Malaria Pan + Pf Card® compared to thick/thin blood smear was 91.8% and 91.3%, respectively, and for both the specificity was 94.7%. Compared to PCR, the sensitivity was 84.2% and 83.8%, respectively, and the specificity 96.5%.

CONCLUSIONS

The performances of the Advantage P.f. Malaria Card® and Advantage Malaria PAN + Pf Card® compared to microscopy, considered the gold standard, were acceptable under the field conditions found in Togo. They can therefore be used for the biological diagnosis of malaria.

A novel duplex qualitative real-time PCR assay for the detection and differentiation of Plasmodium ovale curtisi and Plasmodium ovale wallikeri malaria

Background

P. ovale spp. infections are endemic across multiple African countries and are caused by two distinct non-recombining species, P. ovale curtisi (Poc) and P. ovale wallikeri (Pow). These species are thought to differ in clinical symptomatology and latency, but existing diagnostic assays have limited ability to detect and distinguish them. In this study, we developed a new duplex assay for the detection and differentiation of Poc and Pow that can be used to improve our understanding of these parasites.

Methods

Repetitive sequence motifs were identified in available Poc and Pow genomes and used for assay development and validation. We evaluated the analytical sensitivity and specificity of the best-performing assay using a panel of samples from Tanzania and the Democratic Republic of the Congo (DRC), then validated its performance using 55 P. ovale spp. samples and 40 non-ovale Plasmodium samples from the DRC. Poc and Pow prevalence among symptomatic individuals sampled across three provinces of the DRC were estimated.

Results

The best-performing Poc and Pow targets had 9 and 8 copies within the reference genomes, respectively. Our duplex assay had 100% specificity and 95% confidence lower limits of detection of 4.2 and 41.2 parasite genome equivalents/μl for Poc and Pow, respectively. Species was determined in 80% of all P. ovale spp.-positive field samples and 100% of those with >10 parasites/μl. Most P. ovale spp. field samples from the DRC were found to be Poc infections.

Conclusions

We identified promising multi-copy targets for molecular detection and differentiation of Poc and Pow and used them to develop a new duplex real-time PCR assay that performed well when applied to diverse field samples. Though low-density Pow infections are not reliably detected, the assay is highly specific and can be used for high-throughput studies of P. ovale spp. epidemiology among symptomatic cases in malaria-endemic countries like the DRC.

AIDMAN: An AI-based object detection system for malaria diagnosis from smartphone thin-blood-smear images

Malaria is a significant public health concern, with ∼95% of cases occurring in Africa, but accurate and timely diagnosis is problematic in remote and low-income areas. Here, we developed an artificial intelligence-based object detection system for malaria diagnosis (AIDMAN). In this system, the YOLOv5 model is used to detect cells in a thin blood smear. An attentional aligner model (AAM) is then applied for cellular classification that consists of multi-scale features, a local context aligner, and multi-scale attention. Finally, a convolutional neural network classifier is applied for diagnosis using blood-smear images, reducing interference caused by false positive cells. The results demonstrate that AIDMAN handles interference well, with a diagnostic accuracy of 98.62% for cells and 97% for blood-smear images. The prospective clinical validation accuracy of 98.44% is comparable to that of microscopists. AIDMAN shows clinically acceptable detection of malaria parasites and could aid malaria diagnosis, especially in areas lacking experienced parasitologists and equipment.

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

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

coiaf: Directly estimating complexity of infection with allele frequencies

In malaria, individuals are often infected with different parasite strains. The complexity of infection (COI) is defined as the number of genetically distinct parasite strains in an individual. Changes in the mean COI in a population have been shown to be informative of changes in transmission intensity with a number of probabilistic likelihood and Bayesian models now developed to estimate the COI. However, rapid, direct measures based on heterozygosity or FwS do not properly represent the COI. In this work, we present two new methods that use easily calculated measures to directly estimate the COI from allele frequency data. Using a simulation framework, we show that our methods are computationally efficient and comparably accurate to current approaches in the literature. Through a sensitivity analysis, we characterize how the distribution of parasite densities, the assumed sequencing depth, and the number of sampled loci impact the bias and accuracy of our two methods. Using our developed methods, we further estimate the COI globally from Plasmodium falciparum sequencing data and compare the results against the literature. We show significant differences in the estimated COI globally between continents and a weak relationship between malaria prevalence and COI.

CRISPR/Cas advancements for genome editing, diagnosis, therapeutics, and vaccine development for Plasmodium parasites, and genetic engineering of Anopheles mosquito vector

Malaria as vector-borne disease remains important health concern with over 200 million cases globally. Novel antimalarial medicines and more effective vaccines must be developed to eliminate and eradicate malaria. Appraisal of preceding genome editing approaches confirmed the CRISPR/Cas nuclease system as a novel proficient genome editing system and a tool for species-specific diagnosis, and drug resistance researches for Plasmodium species, and gene drive to control Anopheles population. CRISPR/Cas technology, as a handy tool for genome editing can be justified for the production of transgenic malaria parasites like Plasmodium transgenic lines expressing Cas9, chimeric Plasmodium transgenic lines, knockdown and knockout transgenic parasites, and transgenic parasites expressing alternative alleles, and also mutant strains of Anopheles such as only male mosquito populations, generation of wingless mosquitoes, and creation of knock-out/ knock-in mutants. Though, the incorporation of traditional methods and novel molecular techniques could noticeably enhance the quality of results. The striking development of a CRISPR/Cas-based diagnostic kit that can specifically diagnose the Plasmodium species or drug resistance markers is highly required in malaria settings with affordable cost and high-speed detection. Furthermore, the advancement of genome modifications by CRISPR/Cas technologies resolves contemporary restrictions to culturing, maintaining, and analyzing these parasites, and the aptitude to investigate parasite genome functions opens up new vistas in the better understanding of pathogenesis.

A simple alkali lysis method for Plasmodium falciparum DNA extraction from filter paper blood samples

A fast, simple, easy, efficient, and inexpensive method for DNA extraction from malaria parasites collected on filter paper would be very useful for molecular surveillance. The quality and quantity of DNA are critical to molecular diagnosis and analysis. Here, we developed a simple alkali lysis method for DNA extraction from blood samples on filter paper. The results showed that 10-50 mM NaOH and deionized water all effectively isolated parasite DNA at higher parasitemia, as witnessed by successful PCR amplification, while at a parasitemia of 0.01%, the 10 mM NaOH lysis condition generated the best results. Furthermore, DNA extracted by this method was successfully used to amplify a fragment of > 2000 bp. This method successfully extracted DNA from 1 µl of blood at a parasitemia as low as 0.0001% (equivalent to 5 parasites /µl). The DNA isolated by the 10 mM NaOH lysis method was stable to yield PCR products after storage at 4 °C or - 20 °C for 12 months. These results indicate that this alkali lysis method is simple, effective, sensitive, and inexpensive for isolating stable Plasmodium DNA from dried blood spots on filter paper.

Characterizing human movement patterns using GPS data loggers in an area of persistent malaria in Zimbabwe along the Mozambique border

BACKGROUND

Human mobility is a driver for the reemergence or resurgence of malaria and has been identified as a source of cross-border transmission. However, movement patterns are difficult to measure in rural areas where malaria risk is high. In countries with malaria elimination goals, it is essential to determine the role of mobility on malaria transmission to implement appropriate interventions.

METHODS

A study was conducted in Mutasa District, Zimbabwe, to investigate human movement patterns in an area of persistent transmission along the Mozambique border. Over 1 year, a convenience sample of 20 participants/month was recruited from active malaria surveillance cohorts to carry an IgotU^® GT-600 global positioning system (GPS) data logger during all daily activities. Consenting participants were tested for malaria at data logger distribution using rapid antigen diagnostic tests and completed a survey questionnaire. GPS data were analyzed using a trajectory analysis tool, and participant movement patterns were characterized throughout the study area and across the border into Mozambique using movement intensity maps, activity space plots, and statistical analyses.

RESULTS

From June 2016-May 2017, 184 participants provided movement tracks encompassing > 350,000 data points and nearly 8000 person-days. Malaria prevalence at logger distribution was 3.7%. Participants traveled a median of 2.8 km/day and spent a median of 4.6 h/day away from home. Movement was widespread within and outside the study area, with participants traveling up to 500 km from their homes. Indices of mobility were higher in the dry season than the rainy season (median km traveled/day = 3.5 vs. 2.2, P = 0.03), among male compared to female participants (median km traveled/day = 3.8 vs. 2.0, P = 0.0008), and among adults compared to adolescents (median total km traveled = 104.6 vs. 59.5, P = 0.05). Half of participants traveled outside the study area, and 30% traveled into Mozambique, including 15 who stayed in Mozambique overnight.

CONCLUSIONS

Study participants in Mutasa District, Zimbabwe, were highly mobile throughout the year. Many participants traveled long distances from home, including overnight trips into Mozambique, with clear implications for malaria control. Interventions targeted at mobile populations and cross-border transmission may be effective in preventing malaria introductions in this region.

High prevalence of asymptomatic Plasmodium falciparum malaria in Makenene, a locality in the forest-savannah transition zone, Centre Region of Cameroon

Malaria transmission and prevalence is still not well documented across Cameroon particularly in medium-sized cities or localities representing high transit zone. Different risk factors could be associated with persistence malaria transmission such as population movement from high to low transmission settings. A cross-sectional community-based study was carried out to determine malaria prevalence and risk factors in Makenene, a small city in a forest-savannah which is a crossroads between different parts of the country where travellers usually stop-over day and night to rest. Using malaria diagnostic test (mRDTs from SD-BIOLINE) and microscopy (thin and thick blood smears), 406 participants from 237 households were tested for malaria infection. The prevalence of malaria was high irrespective of the detection method: mRDT (41.87%) or microscopy (38.42%). At household level, 46.41% of households had at least one case of malaria with an average of 1.41 infected individuals per household. Parasite density was also high with the majority of infected individuals (64.74%) bearing more than 500 parasites/μl. Only Plasmodium falciparum was found. The chances of being infected with malaria parasites was almost the same for all participants irrespective of the sleeping behavior, bednet usage, house type and environmental factors. The study supports high malaria transmission in the locality and the need for additional studies on vectors bionomics and transmission patterns.

Factors Affecting the Performance of HRP2-Based Malaria Rapid Diagnostic Tests

The recent COVID-19 pandemic has profoundly impacted global malaria elimination programs, resulting in a sharp increase in malaria morbidity and mortality. To reduce this impact, unmet needs in malaria diagnostics must be addressed while resuming malaria elimination activities. Rapid diagnostic tests (RDTs), the unsung hero in malaria diagnosis, work to eliminate the prevalence of Plasmodium falciparum malaria through their efficient, cost-effective, and user-friendly qualities in detecting the antigen HRP2 (histidine-rich protein 2), among other proteins. However, the testing mechanism and management of malaria with RDTs presents a variety of limitations. This paper discusses the numerous factors (including parasitic, host, and environmental) that limit the performance of RDTs. Additionally, the paper explores outside factors that can hinder RDT performance. By understanding these factors that affect the performance of HRP2-based RDTs in the field, researchers can work toward creating and implementing more effective and accurate HRP2-based diagnostic tools. Further research is required to understand the extent of these factors, as the rapidly changing interplay between parasite and host directly hinders the effectiveness of the tool.

Magnetic Bead Handling Using a Paper-Based Device for Quantitative Point-of-Care Testing

Microfluidic paper-based analytical devices (μPADs) have been extensively proposed as ideal tools for point-of-care (POC) testing with minimal user training and technical requirements. However, most μPADs use dried bioreagents, which complicate production, reduce device reproducibility and stability, and require transport and storage under temperature and humidity-controlled conditions. In this work, we propose a μPAD produced using an affordable craft-cutter and stored at room temperature, which is used to partially automate a single-step colorimetric magneto-immunoassay. As a proof-of-concept, the μPAD has been applied to the quantitative detection of Plasmodium falciparum lactate dehydrogenase (Pf-LDH), a biomarker of malaria infection. In this system, detection is based on a single-step magneto-immunoassay that consists of a single 5-min incubation of the lysed blood sample with immuno-modified magnetic beads (MB), detection antibody, and an enzymatic signal amplifier (Poly-HRP). This mixture is then transferred to a single-piece paper device where, after on-chip MB magnetic concentration and washing, signal generation is achieved by adding a chromogenic enzyme substrate. The colorimetric readout is achieved by the naked eye or using a smartphone camera and free software for image analysis. This μPAD afforded quantitative Pf-LDH detection in <15 min, with a detection limit of 6.25 ng mL−1 when the result was interpreted by the naked eye and 1.4 ng mL−1 when analysed using the smartphone imaging system. Moreover, the study of a battery of clinical samples revealed concentrations of Pf-LDH that correlated with those provided by the reference ELISA and with better sensitivity than a commercial rapid diagnostic test (RDT). These results demonstrate that magneto-immunoassays can be partly automated by employing a μPAD, achieving a level of handling that approaches the requirements of POC testing.

Comparison of two malaria multiplex immunoassays that enable quantification of malaria antigens

Background

Immunoassay platforms that simultaneously detect malaria antigens including histidine-rich protein 2 (HRP2)/HRP3 and Plasmodium lactate dehydrogenase (pLDH), are useful epidemiological tools for rapid diagnostic test evaluation. This study presents the comparative evaluation of two multiplex platforms in identifying Plasmodium falciparum with presence or absence of HRP2/HRP3 expression as being indicative of hrp2/hrp3 deletions and other Plasmodium species. Moreover, correlation between the malaria antigen measurements performed at these platforms is assessed after calibrating with either assay standards or international standards and the cross-reactivity among Plasmodium species is examined.

Methods

A 77-member panel of specimens composed of the World Health Organization (WHO) international Plasmodium antigen standards, cultured parasites for P. falciparum and Plasmodium knowlesi, and clinical specimens with mono-infections for P. falciparum, Plasmodium vivax, and Plasmodium malariae was generated as both whole blood and dried blood spot (DBS) specimens. Assays for HRP2, P. falciparum–specific pLDH (PfLDH), P. vivax–specific pLDH (PvLDH), and all human Plasmodium species Pan malaria pLDH (PanLDH) on the Human Malaria Array Q-Plex and the xMAP platforms were evaluated with these panels.

Results

The xMAP showed a higher percent positive agreement for identification of hrp2-deleted P. falciparum and Plasmodium species in whole blood and DBS than the Q-Plex. For whole blood samples, there was a highly positive correlation between the two platforms for PfLDH (Pearson r = 0.9926) and PvLDH (r = 0. 9792), moderate positive correlation for HRP2 (r = 0.7432), and poor correlation for PanLDH (r = 0.6139). In Pearson correlation analysis between the two platforms on the DBS, the same assays were r = 0.9828, r = 0.7679, r = 0.6432, and r = 0.8957, respectively. The xMAP HRP2 assay appeared to cross-react with HRP3, while the Q-Plex did not. The Q-Plex PfLDH assay cross-reacted with P. malariae, while the xMAP did not. For both platforms, P. knowlesi was detected on the PvLDH assay. The WHO international standards allowed normalization across both platforms on their HRP2, PfLDH, and PvLDH assays in whole blood and DBS.

Conclusions

Q-Plex and xMAP show good agreement for identification of P. falciparum mutants with hrp2/hrp3 deletions, and other Plasmodium species. Quantitative results from both platforms, normalized into international units for HRP2, PfLDH, and PvLDH, showed good agreement and should allow comparison and analysis of results generated by either platform.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04203-9.

Diagnostic performance of a 5-plex malaria immunoassay in regions co-endemic for Plasmodium falciparum, P. vivax, P. knowlesi, P. malariae and P. ovale

Commercial point-of-care tests remain insufficient for accurately detecting and differentiating low-level malaria infections in regions co-endemic with multiple non-falciparum species, including zoonotic Plasmodium knowlesi (Pk). A 5-plex chemiluminescent assay simultaneously measures pan-Plasmodium lactate dehydrogenase (pLDH), P. falciparum (Pf)-LDH, P. vivax (Pv)-LDH, Pf-histidine-rich protein-2 (HRP2), and C-reactive protein. We assessed its diagnostic performance on whole blood (WB) samples from 102 healthy controls and 306 PCR-confirmed clinical cases of Pf, Pv, Pk, P. malariae (Pm) and P. ovale (Po) mono-infections from Southeast-Asia. We confirm its excellent HRP2-based detection of Pf. Cross-reactivity of Pf-LDH with all non-falciparum species tested was observed (specificity 57.3%). Pv-LDH performance was suboptimal for Pv (93.9% sensitivity and 73.9% specificity). Poor specificity was driven by strong Pk cross-reactivity, with Pv-LDH detecting 93.9% of Pk infections. The pan-LDH-to-Pf-LDH ratio was capable of discerning Pv from Pk, and robustly differentiated Pf from Pm or Po infection, useful in regions with hrp2/3 deletions. We tested the platform’s performance in plasma for the first time, with WB outperforming plasma for all analytes except Pv-LDH for Pk. The platform is a promising tool for WB malaria diagnosis, although further development is warranted to improve its utility in regions co-endemic for multiple non-falciparum species.

Malaria diagnostic methods with the elimination goal in view

Malaria control measures have been in use for years but have not completely curbed the spread of infection. Ultimately, global elimination is the goal. A major playmaker in the various approaches to reaching the goal is the issue of proper diagnosis. Various diagnostic techniques were adopted in different regions and geographical locations over the decades, and these have invariably produced diverse outcomes. In this review, we looked at the various approaches used in malaria diagnostics with a focus on methods favorably used during pre-elimination and elimination phases as well as in endemic regions. Microscopy, rapid diagnostic testing (RDT), loop-mediated isothermal amplification (LAMP), and polymerase chain reaction (PCR) are common methods applied depending on prevailing factors, each with its strengths and limitations. As the drive toward the elimination goal intensifies, the search for ideal, simple, fast, and reliable point-of-care diagnostic tools is needed more than ever before to be used in conjunction with a functional surveillance system supported by the ideal vaccine.

Deletions of the Plasmodium falciparum histidine-rich protein 2/3 genes are common in field isolates from north-eastern Tanzania

Plasmodium falciparum parasites lacking histidine-rich protein 2 and 3 (pfhrp2/3) genes have been reported in several parts of the world. These deletions are known to compromise the effectiveness of HRP2-based malaria rapid diagnostic tests (HRP2-RDT). The National Malaria Control Programme (NMCP) in Tanzania adopted HRP2-RDTs as a routine tool for malaria diagnosis in 2009 replacing microscopy in many Health facilities. We investigated pfhrp2/3 deletions in 122 samples from two areas with diverse malaria transmission intensities in Northeastern Tanzania. Pfhrp2 deletion was confirmed in 1.6% of samples while pfhrp3 deletion was confirmed in 50% of samples. We did not find parasites with both pfhrp2 and pfhrp3 deletions among our samples. Results from this study highlight the need for systematic surveillance of pfhrp2/3 deletions in Tanzania to understand their prevalence and determine their impact on the performance of mRDT.

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.

Detecting asymptomatic carriage of Plasmodium falciparum in southern Ghana: utility of molecular and serological diagnostic tools

Background

Asymptomatic malaria infections can serve as potential reservoirs for malaria transmission. The density of parasites contained in these infections range from microscopic to submicroscopic densities, making the accurate detection of asymptomatic parasite carriage highly dependent on the sensitivity of the tools used for the diagnosis. This study sought to evaluate the sensitivities of a variety of molecular and serological diagnostic tools at determining the prevalence of asymptomatic Plasmodium falciparum parasite infections in two communities with varying malaria parasite prevalence.

Methods

Whole blood was collected from 194 afebrile participants aged between 6 and 70 years old living in a high (Obom) and a low (Asutsuare) malaria transmission setting of Ghana. Thick and thin blood smears, HRP2 based malaria rapid diagnostic test (RDT) and filter paper dried blood spots (DBS) were prepared from each blood sample. Genomic DNA was extracted from the remaining blood and used in Plasmodium specific photo-induced electron transfer polymerase chain reaction (PET-PCR) and Nested PCR, whilst the HRP2 antigen content of the DBS was estimated using a bead immunoassay. A comparison of malaria parasite prevalence as determined by each method was performed.

Results

Parasite prevalence in the high transmission site of Obom was estimated at 71.4%, 61.9%, 60%, 37.8% and 19.1% by Nested PCR, the HRP2 bead assay, PET-PCR, HRP2-RDT and microscopy respectively. Parasite prevalence in the low transmission site of Asutsuare was estimated at 50.1%, 11.2%, 5.6%, 0% and 2.2% by Nested PCR, the HRP2 bead assay, PET-PCR, RDT and microscopy, respectively. The diagnostic performance of Nested PCR, PET-PCR and the HRP2 bead assay was similar in Obom but in Asutsuare, Nested PCR had a significantly higher sensitivity than PET-PCR and the HRP2 bead assay, which had similar sensitivity.

Conclusions

Nested PCR exhibited the highest sensitivity by identifying the highest prevalence of asymptomatic P. falciparum in both the high and low parasite prevalence settings. However, parasite prevalence estimated by the HRP2 bead assay and PET-PCR had the highest level of inter-rater agreement relative to all the other tools tested and have the advantage of requiring fewer processing steps relative to Nested PCR and producing quantitative results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04078-w.

Analysis of nucleic acids extracted from rapid diagnostic tests reveals a significant proportion of false positive test results associated with recent malaria treatment

BACKGROUND

Surveillance programmes often use malaria rapid diagnostic tests (RDTs) to determine the proportion of the population carrying parasites in their peripheral blood to assess the malaria transmission intensity. Despite an increasing number of reports on false-negative and false-positive RDT results, there is a lack of systematic quality control activities for RDTs deployed in malaria surveillance programmes.

METHODS

The diagnostic performance of field-deployed RDTs used for malaria surveys was assessed by retrospective molecular analysis of the blood retained on the tests.

RESULTS

Of the 2865 RDTs that were collected in 2018 on Bioko Island and analysed in this study, 4.7% had a false-negative result. These false-negative RDTs were associated with low parasite density infections. In 16.6% of analysed samples, masked pfhrp2 and pfhrp3 gene deletions were identified, in which at least one Plasmodium falciparum strain carried a gene deletion. Among all positive RDTs analysed, 28.4% were tested negative by qPCR and therefore considered to be false-positive. Analysing the questionnaire data collected from the participants, this high proportion of false-positive RDTs could be explained by P. falciparum histidine rich protein 2 (PfHRP2) antigen persistence after recent malaria treatment.

CONCLUSION

Malaria surveillance depending solely on RDTs needs well-integrated quality control procedures to assess the extent and impact of reduced sensitivity and specificity of RDTs on malaria control programmes.

A Dual, Systematic Approach to Malaria Diagnostic Biomarker Discovery

Background

The emergence and spread of Plasmodium falciparum parasites that lack HRP2/3 proteins and the resulting decreased utility of HRP2-based malaria rapid diagnostic tests (RDTs) prompted the World Health Organization and other global health stakeholders to prioritize the discovery of novel diagnostic biomarkers for malaria.

Methods

To address this pressing need, we adopted a dual, systematic approach by conducting a systematic review of the literature for publications on diagnostic biomarkers for uncomplicated malaria and a systematic in silico analysis of P. falciparum proteomics data for Plasmodium proteins with favorable diagnostic features.

Results

Our complementary analyses led us to 2 novel malaria diagnostic biomarkers compatible for use in an RDT format: glyceraldehyde 3-phosphate dehydrogenase and dihydrofolate reductase-thymidylate synthase.

Conclusions

Overall, our results pave the way for the development of next-generation malaria RDTs based on new antigens by identifying 2 lead candidates with favorable diagnostic features and partially de-risked product development prospects.

Purification of native histidine-rich protein 2 (nHRP2) from Plasmodium falciparum culture supernatant, infected RBCs, and parasite lysate

Background

Despite the widespread use of histidine-rich protein 2 (HRP2)-based rapid diagnostic tests (RDTs), purified native HRP2 antigen is not standardly used in research applications or assessment of RDTs used in the field.

Methods

This report describes the purification of native HRP2 (nHRP2) from the HB3 Plasmodium falciparum culture strain. As this culture strain lacks pfhrp3 from its genome, it is an excellent source of HRP2 protein only and does not produce the closely-related HRP3. The nHRP2 protein was isolated from culture supernatant, infected red blood cells (iRBCs), and whole parasite lysate using nickel-metal chelate chromatography. Biochemical characterization of nHRP2 from HB3 culture was conducted by SDS-PAGE and western blotting, and nHRP2 was assayed by RDT, ELISA, and bead-based immunoassay.

Results

Purified nHRP2 was identified by SDS-PAGE and western blot as a − 60 kDa protein that bound anti-HRP-2 monoclonal antibodies. Mouse anti-HRP2 monoclonal antibody was found to produce high optical density readings between dilutions of 1:100 and 1:3,200 by ELISA with assay signal observed up to a 1:200,000 dilution. nHRP2 yield from HB3 culture by bead-based immunoassay revealed that both culture supernatant and iRBC lysate were practical sources of large quantities of this antigen, producing a total yield of 292.4 µg of nHRP2 from two pooled culture preparations. Assessment of nHRP2 recognition by RDTs revealed that Carestart Pf HRP2 and HRP2/pLDH RDTs detected purified nHRP2 when applied at concentrations between 20.6 and 2060 ng/mL, performing within a log-fold dilution of commercially-available recombinant HRP2. The band intensity observed for the nHRP2 dilutions was equivalent to that observed for P. falciparum culture strain dilutions of 3D7 and US06 F Nigeria XII between 12.5 and 1000 parasites/µL.

Conclusions

Purified nHRP2 could be a valuable reagent for laboratory applications as well as assessment of new and existing RDTs prior to their use in clinical settings. These results establish that it is possible to extract microgram quantities of the native HRP2 antigen from HB3 culture and that this purified protein is well recognized by existing monoclonal antibody lines and RDTs.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03946-1.

Performance of rapid diagnostic tests, microscopy, loop-mediated isothermal amplification (LAMP) and PCR for malaria diagnosis in Ethiopia: a systematic review and meta-analysis

Background

Rapid accurate diagnosis followed by effective treatment is very important for malaria control. Light microscopy remains the “golden standard” method for malaria diagnosis. Diagnostic test method must have sufficient level of accuracy for detecting malaria parasites. Therefore, this study aimed to investigate the diagnostic accuracy of rapid diagnostic tests (RDTs), microscopy, loop-mediated isothermal amplification (LAMP) and/or polymerase chain reaction (PCR) for the malaria diagnosis in Ethiopia.

Methods

Data bases such as PubMed, PubMed central, Science direct databases, Google scholar, and Scopus were searched from September to October, 2020 for studies assessing the diagnostic accuracy of RDTs, microscopy, LAMP and PCR methods for malaria diagnosis.

Results

A total of 29 studies published between 2001 and 2020 were analysed using review manager, Midas (Stata) and Meta-disc. The sensitivity and specificity of studies comparing RDT with microscopy varies from 79%–100% to 80%–100%, respectively. The sensitivity of LAMP (731 tests) was 100% and its specificity was varies from 85 to 99% when compared with microscopy and PCR. Considerable heterogeneity was observed between studies included in this meta-analysis. Meta-regression showed that blinding status and target antigens were the major sources of heterogeneity (P < 0.05). RDT had an excellent diagnostic accuracy (Area under the ROC Curve = 0.99) when compared with microscopy. Its specificity was quite good (93%–100%) except for one outlier (28%), but lower “sensitivity” was observed when PCR is a reference test. This indicates RDT had a good diagnostic accuracy (AUC = 0.83). Microscopy showed a very good diagnostic accuracy when compared with PCR.

Conclusions

The present study showed that microscopy and RDTs had high efficiency for diagnosing febrile malaria patients. The diagnostic accuracy of RDT was excellent when compared with microscopy. This indicates RDTs have acceptable sensitivities and specificities to be used in resource poor settings as an alternative for microscopy. In this study, LAMP showed an excellent sensitivities and specificities. Furthermore, the need of minimum equipment and relatively short time for obtaining results can made LAMP one of the best alternatives especially for accurate diagnosis of asymptomatic malaria.

Accuracy of SD Malaria Ag P.f/Pan® as a rapid diagnostic test in French Amazonia

Background

French Guiana (FG) is a French overseas territory where malaria is endemic. The current incidence rate is 0.74‰ inhabitants, and Plasmodium vivax is widely predominating even though Plasmodium falciparum is still present due to imported cases mainly from Africa. In FG, rapid diagnostic test (SD Malaria Ag P.f/Pan®) is based on the detection of pan-pLDH, PfHRP2, and PfHRP3 antigens, while in South America, the share of deletion of PfHRP2 gene is significantly increasing. Accordingly, the study questions the reliability of RDTs in the Amazonian context.

Methods

The study is retrospective. It is conducted over 4 years and analysed 12,880 rapid diagnostic tests (RDTs) compared to concomitant Blood Film Tests (BFTs) sampled for malaria diagnosis.

Results

The global assessment of the accuracy of SD Malaria Ag P.f/Pan® in the diagnostic of malaria shows both Positive and Negative Predictive Values (PPV and NPV) higher than 95%, except for PPV in the diagnosis of malaria to P. falciparum (88%). Overall, the concordance rate between RDT and BFT (positive/positive; negative/negative) was 99.5%. The PPV of the RDT in the follow-up of patients diagnosed with P. falciparum was the lowest during the first 28 days. The PPV of the RDT in the follow-up of patients diagnosed with P. vivax was the lowest during the first 21 days. The global sensitivity of SD Malaria Ag P.f/Pan® test was, on average, 96% (88.2–100) for P. falciparum and 93% (90.6–94.2) for P. vivax. The global specificity was 99.8% (99.5–100) for all included species.

Conclusion

SD Malaria Ag P.f/Pan® is a reliable rapid test used for the first-line diagnosis in remote healthcare centres. The test results should be interpreted in the light of patient’s recent medical history and the date of arrival to FG.

Evaluating the dual reactivity on SD bioline malaria rapid diagnosis tests as a potential indicator of high parasitemia due to Plasmodium falciparum

The co-reactivity of the Plasmodium histidine-rich protein 2 (HRP2) and lactate dehydrogenase (pLDH) in malaria rapid diagnosis tests (mRDTs) as a potential indicator of high parasitemia linked to Plasmodium falciparum was evaluated in the reported study from Cameroon. The samples were screened for malaria using both mRDTs (SD bioline HRP2/pLDH), light microscopy and further confirmed by Plasmodium species-specific PCR assay. Of the 483 patients enrolled, 161 (33.3%) showed a reactive mRDTs amongst which 70 patients were positive by both microscopy and mRDTs with 30.0% (21/70) positive for HRP2 alone, while 70.0% (49/70) showed a dual reaction to HRP2 and pLDH parasite antigens. P. falciparum parasitemia was found to be significantly high among patients with both reactive antigens, (p < 0.0001) suggesting that mRDTs reactivity is influenced by parasite load which could be used as a diagnostic marker for therapeutic management of patients with high parasitemia in field conditions.

Considerations for quality assurance of multiplex malaria antigen detection assays with large sample sets

Multiplex assays for malaria antigen detection can gather data from large sample sets, but considerations for the consistency and quality assurance (QA) of mass testing lack evaluation. We present a QA framework for a study occurring November 2019 to March 2020 involving 504 assay plates detecting four Plasmodium antigens: pan-Plasmodium aldolase and lactate dehydrogenase (LDH), histidine-rich protein 2 (HRP2), P. vivax LDH (PvLDH). Controls on each plate included buffer blank, antigen negative blood, and 4-point positive dilution curve. The blank and negative blood provided consistently low signal for all targets except for pAldolase, which showed variability. Positive curve signals decreased throughout the 5-month study duration but retained a coefficient of variation (CV) of < 5%, with the exception of HRP2 in month 5 (CV of 11%). Regression fittings for inter-plate control signals provided mean and standard deviations (SDs), and of 504 assay plates, 6 (1.2%) violated the acceptable deviation limits and were repeated. For the 40,272 human blood samples assayed in this study, of 161,088 potential data points (each sample × 4 antigens), 160,641 (99.7%) successfully passed quality checks. The QA framework presented here can be utilized to ensure quality of laboratory antigen detection for large sample sets.

No evidence of false-negative Plasmodium falciparum rapid diagnostic results in Monrovia, Liberia

Background

Malaria diagnosis in many malaria-endemic countries relies mainly on the use of rapid diagnostic tests (RDTs). The majority of commercial RDTs used in Africa detect the Plasmodium falciparum histidine-rich protein 2 (PfHRP2). pfhrp2/3 gene deletions can therefore lead to false-negative RDT results. This study aimed to evaluate the frequency of PCR-confirmed, false-negative P. falciparum RDT results in Monrovia, Liberia.

Methods

PfHRP2-based RDT (Paracheck Pf®) and microscopy results from 1038 individuals with fever or history of fever (n = 951) and pregnant women at first antenatal care (ANC) visit (n = 87) enrolled in the Saint Joseph’s Catholic Hospital (Monrovia) from March to July 2019 were used to assess the frequency of false-negative RDT results. True–false negatives were confirmed by detecting the presence of P. falciparum DNA by quantitative PCR in samples from individuals with discrepant RDT and microscopy results. Samples that were positive by 18S rRNA qPCR but negative by PfHRP2-RDT were subjected to multiplex qPCR assay for detection of pfhrp2 and pfhrp3.

Results

One-hundred and eighty-six (19.6%) and 200 (21.0%) of the 951 febrile participants had a P. falciparum-positive result by RDT and microscopy, respectively. Positivity rate increased with age and the reporting of joint pain, chills and shivers, vomiting and weakness, and decreased with the presence of coughs and nausea. The positivity rate at first ANC visit was 5.7% (n = 5) and 8% (n = 7) by RDT and microscopy, respectively. Out of 207 Plasmodium infections detected by microscopy, 22 (11%) were negative by RDT. qPCR confirmed absence of P. falciparum DNA in the 16 RDT-negative but microscopy-positive samples which were available for molecular testing. Among the 14 samples that were positive by qPCR but negative by RDT and microscopy, 3 only amplified pfldh, and among these 3 all were positive for pfhrp2 and pfhrp3.

Conclusion

There is no qPCR-confirmed evidence of false-negative RDT results due to pfhrp2/pfhrp3 deletions in this study conducted in Monrovia (Liberia). This indicates that these deletions are not expected to affect the performance of PfHRP2-based RDTs for the diagnosis of malaria in Liberia. Nevertheless, active surveillance for the emergence of PfHRP2 deletions is required.

Prevalence of Plasmodium falciparum isolates lacking the histidine rich protein 2 gene among symptomatic malaria patients in Kwilu Province of the Democratic Republic of Congo

Background

Malaria rapid diagnostic tests have become a primary and critical tool for malaria diagnosis in malaria-endemic countries where Plasmodium falciparum Histidine Rich Protein 2-based rapid diagnostic tests (PfHRP2-based RDTs) are widely used. However, in the last decade, the accuracy of PfHRP2-based RDTs has been challenged by the emergence of P. falciparum strains harbouring deletions of the P. falciparum histidine rich protein 2 (pfhrp2) gene, resulting in false-negative results. In the Democratic Republic of Congo (D.R. Congo), little is known about the prevalence of the pfhrp2 gene deletion among P. falciparum isolates infecting symptomatic patients, especially in low to moderate transmission areas where pfhrp2 deletion parasites are assumed to emerge and spread. Here we determine the local prevalence and factors associated with pfhrp2 gene deletions among symptomatic malaria patients in the Kwilu Province of the D.R. Congo.

Methods

We used secondary data from a prospective health facility-based cross-sectional study conducted in 2018. Blood was collected for microscopy, PfHRP2-RDT, and spotted onto Whatman filter paper for downstream genetic analysis. Genomic DNA was extracted and used to perform PCR assays for the detection and confirmation of pfhrp2 gene deletions. Fischer’s exact and the Kruskal–Wallis tests were applied to look for associations between potential explanatory variables and the pfhrp2 gene deletion with a level of statistical significance set at P < 0.05.

Results

Of the 684 enrolled symptomatic patients, 391 (57.7%) were female. The majority (87.7%) reported the presence of mosquito breeding sites within the household’s compound, and fever was the most reported symptom (81.6%). The overall prevalence of the pfhrp2 gene deletion was 9.2% (95% CI: 6.7%–12.1%). The deletion of the pfhrp2 gene was associated with health zone of origin (P = 0.012) and age (P = 0.019). Among false-negative PfHRP2-RDT results, only 9.9% were due to pfhrp2 gene deletion.

Conclusions

P. falciparum isolates with pfhrp2 gene deletions are relatively common among symptomatic patients in Kwilu province. Further investigations are needed to provide enough evidence for policy change. Meanwhile, the use of RDTs targeting PfHRP2 and parasite lactate dehydrogenase (pLDH) antigens could limit the spread of deleted isolates.

Graphic Abstract

Lineage-Specific Expansion of Plasmodium falciparum Parasites With pfhrp2 Deletion in the Greater Mekong Subregion

Deletion of the pfhrp2 gene in Plasmodium falciparum can lead to false-negative rapid diagnostic test (RDT) results, constituting a major challenge for evidence-based malaria treatment. Here we analyzed the whole genome sequences of 138 P. falciparum clinical samples collected from the China-Myanmar boarder for pfhrp2 and pfhrp3 gene deletions. We found pfhrp2 and pfhrp3 deletions in 9.4% and 3.6% of samples, respectively, with no samples harboring deletions of both genes. The pfhrp2 deletions showed 2 distinct breakpoints, representing 2 different chromosomal deletion events. A phylogenetic analysis performed using genome-wide single-nucleotide polymorphisms revealed that the 2 pfhrp2 breakpoint groups as well as all the pfhrp3-negative parasites formed separate clades, suggesting they might have resulted from clonal expansion of pfhrp2- and pfhrp3-negative parasites. These findings highlight the need for urgent surveys to determine the prevalence of pfhrp2-negative parasites causing false-negative RDT results and a plan for switching of RDTs pending the survey results.

Machine learning approaches classify clinical malaria outcomes based on haematological parameters

BACKGROUND

Malaria is still a major global health burden, with more than 3.2 billion people in 91 countries remaining at risk of the disease. Accurately distinguishing malaria from other diseases, especially uncomplicated malaria (UM) from non-malarial infections (nMI), remains a challenge. Furthermore, the success of rapid diagnostic tests (RDTs) is threatened by Pfhrp2/3 deletions and decreased sensitivity at low parasitaemia. Analysis of haematological indices can be used to support the identification of possible malaria cases for further diagnosis, especially in travellers returning from endemic areas. As a new application for precision medicine, we aimed to evaluate machine learning (ML) approaches that can accurately classify nMI, UM, and severe malaria (SM) using haematological parameters.

METHODS

We obtained haematological data from 2,207 participants collected in Ghana: nMI (n = 978), SM (n = 526), and UM (n = 703). Six different ML approaches were tested, to select the best approach. An artificial neural network (ANN) with three hidden layers was used for multi-classification of UM, SM, and uMI. Binary classifiers were developed to further identify the parameters that can distinguish UM or SM from nMI. Local interpretable model-agnostic explanations (LIME) were used to explain the binary classifiers.

RESULTS

The multi-classification model had greater than 85% training and testing accuracy to distinguish clinical malaria from nMI. To distinguish UM from nMI, our approach identified platelet counts, red blood cell (RBC) counts, lymphocyte counts, and percentages as the top classifiers of UM with 0.801 test accuracy (AUC = 0.866 and F1 score = 0.747). To distinguish SM from nMI, the classifier had a test accuracy of 0.96 (AUC = 0.983 and F1 score = 0.944) with mean platelet volume and mean cell volume being the unique classifiers of SM. Random forest was used to confirm the classifications, and it showed that platelet and RBC counts were the major classifiers of UM, regardless of possible confounders such as patient age and sampling location.

CONCLUSION

The study provides proof of concept methods that classify UM and SM from nMI, showing that the ML approach is a feasible tool for clinical decision support. In the future, ML approaches could be incorporated into clinical decision-support algorithms for the diagnosis of acute febrile illness and monitoring response to acute SM treatment particularly in endemic settings.

Conventional and High-Sensitivity Malaria Rapid Diagnostic Test Performance in 2 Transmission Settings: Haiti 2017

Accurate malaria diagnosis is foundational for control and elimination, and Haiti relies on histidine-rich protein 2 (HRP2)-based rapid diagnostic tests (RDTs) identifying Plasmodium falciparum in clinical and community settings. In 2017, 1 household and 2 easy-access group surveys tested all participants (N = 32 506) by conventional and high-sensitivity RDTs. A subset of blood samples (n = 1154) was laboratory tested for HRP2 by bead-based immunoassay and for P. falciparum 18S rDNA by photo-induced electron transfer polymerase chain reaction. Both RDT types detected low concentrations of HRP2 with sensitivity estimates between 2.6 ng/mL and 14.6 ng/mL. Compared to the predicate HRP2 laboratory assay, RDT sensitivity ranged from 86.3% to 96.0% between tests and settings, and specificity from 90.0% to 99.6%. In the household survey, the high-sensitivity RDT provided a significantly higher number of positive tests, but this represented a very small proportion (<0.2%) of all participants. These data show that a high-sensitivity RDT may have limited utility in a malaria elimination setting like Haiti.

Ultrasensitive and Robust Point-of-Care Immunoassay for the Detection of Plasmodium falciparum Malaria

Plasmodium falciparum malaria is widespread in the tropical and subtropical regions of the world. There is ongoing effort to eliminate malaria from endemic regions, and sensitive point-of-care (POC) diagnostic tests are required to support this effort. However, current POC tests are not sufficiently sensitive to detect P. falciparum in asymptomatic individuals. After extensive optimization, we have developed a highly sensitive and robust POC test for the detection of P. falciparum infection. The test is based on upconverting nanophosphor-based lateral flow (UCNP-LF) immunoassay. The developed UCNP-LF test was validated using whole blood reference panels containing samples at different parasite densities covering eight strains of P. falciparum from different geographical areas. The limit of detection was compared to a WHO-prequalified rapid diagnostic test (RDT). The UCNP-LF achieved a detection limit of 0.2-2 parasites/μL, depending on the strain, which is 50- to 250-fold improvement in analytical sensitivity over the conventional RDTs. The developed UCNP-LF is highly stable even at 40 °C for at least 5 months. The extensively optimized UCNP-LF assay is as simple as the conventional malaria RDTs and requires 5 μL of whole blood as sample. Results can be read after 20 min from sample addition, with a simple photoluminescence reader. In the absence of a reader device at the testing site, the strips after running the test can be transported and read at a central location with access to a reader. We have found that the test and control line signals are stable for at least 10 months after running the test. The UCNP-LF has potential for diagnostic testing of both symptomatic and asymptomatic individuals.

Large Variations in Malaria Parasite Carriage by Afebrile School Children Living in Nearby Communities in the Central Region of Ghana

Background

Indicators of successful malaria control interventions include a reduction in the prevalence and densities of malaria parasites contained in both symptomatic and asymptomatic infections as well as a reduction in malaria transmission. Individuals harboring malaria parasites in asymptomatic infections serve as reservoirs for malaria transmission. This study determined the prevalence of asymptomatic malaria parasite carriage in afebrile children attending six different schools in two districts, the Cape Coast Metropolitan Assembly (CCMA) and the Komenda Edina Eguafo Abirem (KEEA) of the Central Region of Ghana.

Methods

This cross sectional study recruited afebrile children aged between 3 and 15 years old from six randomly selected schools in the Central Region of Ghana. Finger-pricked blood was collected and used to prepare thick and thin blood smears as well as spot a strip of filter paper (Whatman #3). Nested PCR was used to identify Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, and Plasmodium vivax in DNA extracted from the filter paper spots. The multiplicity of P. falciparum infection was determined using merozoite surface protein 2 genotyping.

Results

Out of the 528 children sampled, PCR identified 27.1% to harbor Plasmodium parasites in asymptomatic infections, whilst microscopy identified malaria parasites in 10.6% of the children. The overall PCR estimated prevalence of P. falciparum and P. malariae was 26.6% and 1.3%, respectively, with no P. ovale or P. vivax identified by PCR or microscopy. The RDT positivity rate ranged from 55.8% in Simiw to 4.5% in Kuful. Children from the Simiw Basic School accounted for 87.5% of all the asymptomatic infections. The multiplicity of P. falciparum infection was predominantly monoclonal and biclonal.

Conclusions

The low prevalence of asymptomatic malaria parasite carriage by the children living in the Cape Coast Metropolis suggests that the malaria control interventions in place in CCMA are highly effective and that additional malaria control interventions are required for the KEEA district to reduce the prevalence of asymptomatic malaria parasite carriers. No molecular evidence of P. ovale and P. vivax was identified in the afebrile children sampled from the selected schools.

Performance Evaluation of Malaria Pf/Pv Combo Test Kit at Highly Malaria-Endemic Area, Southern Ethiopia: A Cross-Sectional Study

Background

Malaria rapid diagnostic tests (RDTs) are alternative diagnostic methods that have enabled reliable biological diagnostic testing in all situations where previously only clinical diagnosis was available. Varying diagnostic accuracy of malaria RDTs makes policymakers confused while choosing malaria test kits for their country.

Objective

The aim of this study was to evaluate the diagnostic performance of currently being used malaria RDT in Southern Ethiopia.

Methods

A cross-sectional study design was conducted from October 1 to December 15, 2016. A total of 160 patients were included in the study. Finger-prick blood sample was obtained from study subjects for the RDT test and microscopic examination. Collected data were entered and analyzed using SPSS version 20.0.

Result

The test kit evaluated had an overall sensitivity, specificity, PPV, and NPV of 97.44%, 93.67%, 93.83%, and 97.37%, respectively, to detect the presence or absence of malaria. Sensitivity and specificity of the kit for P. falciparum detection were 63.27% and 94.3% and for P. vivax detection were 86.96% and 95.62%, respectively. The agreement between microscopy and RDT for specific identification of malaria species was moderate with a kappa value of 0.568.

Conclusion

The overall performance of the kit was below the WHO standard. Further study on a large sample size is recommended to be carried out in the study area to use the test kit instead of microscopy for malaria diagnosis. Providing training on quality malaria laboratory diagnosis and availing necessary supplies for malaria diagnosis shall also be considered.

Evaluation of PfHRP2 and PfLDH Malaria Rapid Diagnostic Test Performance in Assosa Zone, Ethiopia

In malaria-endemic countries, rapid diagnostic tests (RDTs) targeting Plasmodium falciparum histidine-rich protein 2 (PfHRP2) and lactate dehydrogenase (PfLDH) have been widely used. However, little is known regarding the diagnostic performances of these RDTs in the Assosa zone of northwest Ethiopia. The objective of this study was to determine the diagnostic performances of PfHRP2 and PfLDH RDTs using microscopy and quantitative PCR (qPCR) as a reference test. A health facility-based cross-sectional study design was conducted from malaria-suspected study participants at selected health centers from November to December 2018. Finger-prick blood samples were collected for microscopy, RDTs, and qPCR method. The prevalence of P. falciparum was 26.4%, 30.3%, and 24.1% as determined by microscopy, PfHRP2 RDT, and PfLDH RDT, respectively. Compared with microscopy, the sensitivity and specificity of the PfHRP2 RDT were 96% and 93%, respectively, and those of the PfLDH RDT were 89% and 99%, respectively. Compared with qPCR, the specificity of the PfHRP2 RDT (93%) and PfLDH RDT (98%) was high, but the sensitivity of the PfHRP2 RDT (77%) and PfLDH RDT (70%) was relatively low. These malaria RDTs and reference microscopy methods showed reasonable agreement with a kappa value above 0.85 and provided accurate diagnosis of P. falciparum malaria. Thus, the current malaria RDT in the Ministry of Health program can be used in the Assosa zone of Ethiopia. However, continuous monitoring of the performance of PfHRP2 RDT is important to support control and elimination of malaria in Ethiopia.

Multiplex Human Malaria Array: Quantifying Antigens for Malaria Rapid Diagnostics

Malaria antigen detection through rapid diagnostic tests (RDTs) is widely used to diagnose malaria and estimate prevalence. To support more sensitive next-generation RDT development and screen asymptomatic malaria, we developed and evaluated the Q-Plex^™ Human Malaria Array (Quansys Biosciences, Logan, UT), which quantifies the antigens commonly used in RDTs—Plasmodium falciparum–specific histidine-rich protein 2 (HRP2), P. falciparum-specific lactate dehydrogenase (Pf LDH), Plasmodium vivax–specific LDH (Pv LDH), and Pan malaria lactate dehydrogenase (Pan LDH), and human C-reactive protein (CRP), a biomarker of severity in malaria. At threshold levels yielding 99.5% or more diagnostic specificity, diagnostic sensitivities against polymerase chain reaction–confirmed malaria for HRP2, Pf LDH, Pv LDH, and Pan LDH were 92.7%, 71.5%, 46.1%, and 83.8%, respectively. P. falciparum culture strains and samples from Peru indicated that HRP2 and Pf LDH combined improves detection of P. falciparum parasites with hrp2 and hrp3 deletions. This array can be used for antigen-based malaria screening and detecting hrp2/3 deletion mutants of P. falciparum.

A secreted fungal histidine- and alanine-rich protein regulates metal ion homeostasis and oxidative stress

Like pathogens, beneficial endophytic fungi secrete effector proteins to promote plant colonization, for example, through perturbation of host immunity. The genome of the root endophyte Serendipita indica encodes a novel family of highly similar, small alanine- and histidine-rich proteins, whose functions remain unknown. Members of this protein family carry an N-terminal signal peptide and a conserved C-terminal DELD motif. Here we report on the functional characterization of the plant-responsive DELD family protein Dld1 using a combination of structural, biochemical, biophysical and cytological analyses. The crystal structure of Dld1 shows an unusual, monomeric histidine zipper consisting of two antiparallel coiled-coil helices. Similar to other histidine-rich proteins, Dld1 displays varying affinity to different transition metal ions and undergoes metal ion- and pH-dependent unfolding. Transient expression of mCherry-tagged Dld1 in barley leaf and root tissue suggests that Dld1 localizes to the plant cell wall and accumulates at cell wall appositions during fungal penetration. Moreover, recombinant Dld1 enhances barley root colonization by S. indica, and inhibits H₂ O₂ -mediated radical polymerization of 3,3'-diaminobenzidine. Our data suggest that Dld1 has the potential to enhance micronutrient accessibility for the fungus and to interfere with oxidative stress and reactive oxygen species homeostasis to facilitate host colonization.