Malaria rapid diagnostic tests: challenges and prospects

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.

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.

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.

Keep the quality high: the benefits of lot testing for the quality control of malaria rapid diagnostic tests

Background

The production and use of malaria rapid diagnostic tests (RDTs) has risen dramatically over the past 20 years. In view of weak or non-existing in vitro diagnostics (IVD) regulations and post-marketing surveillance (PMS) systems in malaria endemic countries, the World Health Organization, later joined by the Foundation for Innovative New Diagnostics, established an independent, centralized performance evaluation and Lot Testing (LT) programme to safeguard against poor quality of RDTs being distributed through the public health sector of malaria endemic countries. RDT performances and manufacturer quality management systems have evolved over the past decade raising questions about the future need for a centralized LT programme.

Results

Between 2007 and 2017, 6056 lots have been evaluated, representing approximately 1.6 Billion RDTs. A total of 69 lots (1.1%) failed the quality control. Of these failures, 26 were detected at receipt of the RDT lot in the LT laboratory, representing an estimated 7.9 million poor quality RDTs, and LT requesters were advised that RDTs were not of sufficient quality for use in patient management. Forty-three were detected after long-term storage in the laboratory, of which 24 (56%) were found to be due to a major issue with insufficient buffer volume in single use buffer vials, others predominantly showing loss of sensitivity. The annual cost of running the programme, based on expenses recorded in years 2014–2016, an estimated volume of 700 lots per year and including replenishment of quality control samples, was estimated at US$ 178,500 ($US 255 per lot tested).

Conclusions

Despite the clear benefits of the centralized LT programme and its low cost compared with the potential costs of each country establishing its own PMS system for RDTs, funding concerns have made its future beyond 2020 uncertain. In order to manage the risks of misdiagnosis due to low quality RDTs, and to ensure the continued safety and reliability of malaria case management, there is a need to ensure that an effective and implementable approach to RDT quality control continues to be available to programmes in endemic countries.

Capture and Detection of Plasmodium vivax Lactate Dehydrogenase in a Bead-Based Multiplex Immunoassay

Laboratory detection of malaria antigens has proved valuable for research and epidemiological purposes. We recently developed a bead-based multiplex antigen assay for pan-Plasmodium and Plasmodium falciparum targets. Here, we report integration of a Plasmodium vivax-specific target to this multiplex panel: P. vivax lactate dehydrogenase (PvLDH). Within the multiplex panel, assay signal for purified PvLDH antigen titrated into the single-digit picogram range. Against a panel of polymerase chain reaction (PCR)-confirmed samples from acute P. vivax infections (n = 36), sensitivity was 91.7% in using PvLDH detection for identifying the presence of parasites. Specificity against a panel of persons with no Plasmodium infection (n = 44) was 100%, and specificity against a panel of PCR-confirmed P. falciparum, Plasmodium malariae, or Plasmodium ovale infections (n = 164) was 90.2%. Addition of this PvLDH capture and detection system into the multiplex antigen panel will now allow for sensitive screening for species identification of both P. falciparum and P. vivax in the laboratory.

Dysregulation of angiopoietin-Tie-2 axis in ugandan children hospitalized with pneumonia

OBJECTIVE

Pneumonia is the leading cause of death in children under 5, with the highest burden in resource-limited countries. Endothelial activation occurs in pneumonia and can be assessed using quantitative levels of biomarkers angiopoietin (Ang)-1 and Ang-2. We examined admission levels of Ang-1 and Ang-2 in pediatric pneumonia and their association with disease severity and outcome.

METHODS

Prospective cohort study of children with hypoxemic pneumonia admitted to two hospitals in Uganda. Clinical, radiographic, and microbiologic characteristics were measured at admission. Disease severity was assessed using the Respiratory Index of Severity in Children (RISC). Plasma levels of Ang-1 and Ang-2 were quantified by enzyme-linked immunosorbent assay. Vital signs, oxygen supplementation, and mortality were assessed prospectively.

RESULTS

We included 65 patients (43% female) with median age 19 months (IQR 8-24). Admission Ang-2/Ang-1 ratio directly correlated with RISC (ρ = 0.32, p = 0.008) and lactate level (ρ = 0.48, p < 0.001). Ang-2/Ang-1 ratio was higher in pneumococcal pneumonia than viral RTI (0.19 [IQR: 0.076-0.54] vs. 0.078 [IQR: 0.027-0.11]; p = 0.03). Elevated Ang-2/Ang-1 ratio (>0.084) was associated with prolonged tachypnea (HR 0.50 (95%CI 0.29-0.87), p = 0.02), fever (HR 0.56 (95%CI 0.33 to 0.96), p = 0.02), longer duration of oxygen therapy (HR 0.59 (95%CI 0.35-0.99), p = 0.04), and hospital stay (HR 0.43 (95%CI 0.25-0.74), p = 0.001). The Ang-2/Ang-1 ratio at admission was higher in fatal cases relative to survivors (0.36 [IQR: 0.17-0.58] vs. 0.077 [IQR: 0.025-0.19]; p = 0.05) CONCLUSION: Endothelial activation in hypoxemic pediatric pneumonia, reflected by high plasma Ang-2/Ang-1 ratio, is associated with disease severity, prolonged recovery time, and mortality.

Evaluation of Malaria Diagnostic Methods as a Key for Successful Control and Elimination Programs

Malaria is one of the leading causes of death worldwide. According to the World Health Organization's (WHO's) world malaria report for 2018, there were 228 million cases and 405,000 deaths worldwide. This paper reviews and highlights the importance of accurate, sensitive and affordable diagnostic methods in the fight against malaria. The PubMed online database was used to search for publications that examined the different diagnostic tests for malaria. Currently used diagnostic methods include microscopy, rapid diagnostic tests (RDT), and polymerase chain reaction (PCR). Upcoming methods were identified as loop-mediated isothermal amplification (LAMP), nucleic acid sequence-based amplification (NASBA), isothermal thermophilic helicase-dependent amplification (tHDA), saliva-based test for nucleic-acid amplification, saliva-based test for Plasmodium protein detection, urine malaria test (UMT), and transdermal hemozoin detection. RDT, despite its increasing false negative, is still the most feasible diagnostic test because it is easy to use, fast, and does not need expensive equipment. Noninvasive tests that do not require a blood sample, but use saliva or urine, are some of the recent tests under development that have the potential to aid malaria control and elimination. Emerging resistance to anti-malaria drugs and to insecticides used against vectors continues to thwart progress in controlling malaria. Therefore, future innovation will be required to enable the application of more sensitive and affordable methods in resource-limited settings.

Sensitivity and specificity of malaria rapid diagnostic test (mRDT CareStatTM) compared with microscopy amongst under five children attending a primary care clinic in southern Nigeria

BACKGROUND

Malaria diagnosis using microscopy is currently the gold standard. However, malaria rapid diagnostic tests (mRDTs) were developed to simplify the diagnosis in regions without access to functional microscopy.

AIM

The objective of this study was to compare the diagnostic accuracy of mRDT CareStatTM with microscopy.

SETTING

This study was conducted in the paediatric primary care clinic of the Federal Medical Centre, Asaba, Nigeria.

METHODS

A cross-sectional study for diagnostic accuracy was conducted from May 2016 to October 2016. Ninety-eight participants were involved to obtain a precision of 5%, sensitivity of mRDT CareStatTM of 95% from published work and 95% level of confidence after adjusting for 20% non-response rate or missing data. Consecutive participants were tested using both microscopy and mRDT. The results were analysed using EPI Info Version 7.

RESULTS

A total of 98 children aged 3-59 months were enrolled. Malaria prevalence was found to be 53% (95% confidence interval [CI] = 46% - 60%), whilst sensitivity and specificity were 29% (95% CI = 20% - 38%) and 89% (95% CI = 83% - 95%), respectively. The positive and negative predictive values were 75% (95% CI = 66.4% - 83.6%) and 53% (95% CI = 46% - 60%), respectively.

CONCLUSION

Agreement between malaria parasitaemia using microscopy and mRDT positivity increased with increase in the parasite density. The mRDT might be negative when malaria parasite density using microscopy is low.

Utility of Plasmodium falciparum DNA from rapid diagnostic test kits for molecular analysis and whole genome amplification

Background

Rapid diagnostic tests (RDTs) have become the most common diagnostic tool for detection of Plasmodium falciparum malaria, in particular in remote areas. RDT blood spots provide a source of parasite DNA for molecular analysis. In this study, the utility of RDTs for molecular analysis and the performance of different methods for whole genome amplification were investigated.

Methods

Positive P. falciparum RDTs were collected from Kayin, Myanmar from August 2014 to January 2016. The RDT samples were stored for 6 months, 9 months, 20 months, 21 months, and 32 months before DNA extraction and subsequent molecular analysis of P. falciparum kelch 13 (pfkelch13) mutations, P. falciparum multidrug resistance 1 (pfmdr1), and P. falciparum plasmepsin 2 (pfplasmepsin2) gene amplification. In addition, performance of four whole genome amplification (WGA) kits were compared, including REPLI-g^®, MALBAC^TM, PicoPLEX^®, and GenomePlex^®, for which DNA quantity and quality were compared between original DNA and post-WGA products.

Results

The proportion of successful amplification of the different molecular markers was similar between blood spots analysed from RDTs stored for 6, 9, 20, 21, or 32 months. Successful amplification was dependent on the molecular markers fragment length (p value < 0.05): 18% for a 1245 bp fragment of pfkelch13, 71% for 364 bp of pfkelch13, 81% for 87 bp of pfmdr1, 81% for 108 bp of pfplasmepsin2. Comparison of the four WGA assay kits showed that REPLI-g^®, MALBAC^TM, and PicoPLEX^® increased the quantity of DNA 60 to 750-fold, whereas the ratio of parasite DNA amplification over human DNA was most favourable for MALBAC^®. Sequencing results of pfkelch13, P. falciparum chloroquine resistance transporter (pfcrt), P. falciparum dihydrofolate reductase (pfdhfr) and six microsatellite markers assessed from the post-WGA product was the same as from the original DNA.

Conclusions

Blood spots from RDTs are a good source for molecular analysis of P. falciparum, even after storage up to 32 months. WGA of RDT-derived parasite DNA reliably increase DNA quantity with sufficient quality for molecular analysis of resistance markers.

Performance evaluation of a popular malaria RDT in Nigeria compared with microscopy

Malaria remains a public health problem in Sub-Saharan Africa. Prompt diagnosis and effective treatment are important in reducing morbidity and mortality associated with malaria especially among high-risk groups. This study evaluated the diagnostic performance of one of the popular malaria rapid diagnostic test (RDT) kit in Nigerian market which has not been investigated before in field-condition compared with microscopy as the gold standard. A total number of 250 children of 10 years and below were examined for malaria parasites using both microscopy and RDT in Uhogua community in Edo state and data were analysed using SPSS version 22. The prevalence of malaria by microscopy was 99.2% while only 55.2% were positive by RDT. Majority of the study populations were asymptomatic for malaria infection. RDT sensitivity and specificity compared to light microscopy was 69.08% and 66.67% respectively while the positive predictive value and negative predictive value were 99.6% and 1.77% respectively. The RDT accuracy was less than 70%. RDT cannot be relied upon alone for malaria diagnosis. Microscopy remains the gold standard for malaria diagnosis.

Use of real-time multiplex PCR, malaria rapid diagnostic test and microscopy to investigate the prevalence of Plasmodium species among febrile hospital patients in Sierra Leone

Background

Malaria continues to affect over 200 million individuals every year, especially children in Africa. Rapid and sensitive detection and identification of Plasmodium parasites is crucial for treating patients and monitoring of control efforts. Compared to traditional diagnostic methods such as microscopy and rapid diagnostic tests (RDTs), DNA based methods, such as polymerase chain reaction (PCR) offer significantly higher sensitivity, definitive discrimination of Plasmodium species, and detection of mixed infections. While PCR is not currently optimized for routine diagnostics, its role in epidemiological studies is increasing as the world moves closer toward regional and eventually global malaria elimination. This study demonstrates the field use of a novel, ambient temperature-stabilized, multiplexed PCR assay in a small hospital setting in Sierra Leone.

Methods

Blood samples from 534 febrile individuals reporting to a hospital in Bo, Sierra Leone, were tested using three methods: a commercial RDT, microscopy, and a Multiplex Malaria Sample Ready (MMSR) PCR designed to detect a universal malaria marker and species-specific markers for Plasmodium falciparum and Plasmodium vivax. A separate PCR assay was used to identify species of Plasmodium in samples in which MMSR detected malaria, but was unable to identify the species.

Results

MMSR detected the presence of any malaria marker in 50.2% of all tested samples with P. falciparum identified in 48.7% of the samples. Plasmodium vivax was not detected. Testing of MMSR P. falciparum-negative/universal malaria-positive specimens with a panel of species-specific PCRs revealed the presence of Plasmodium malariae (n = 2) and Plasmodium ovale (n = 2). The commercial RDT detected P. falciparum in 24.6% of all samples while microscopy was able to detect malaria in 12.8% of tested specimens.

Conclusions

Wider application of PCR for detection of malaria parasites may help to fill gaps existing as a result of use of microscopy and RDTs. Due to its high sensitivity and specificity, species coverage, room temperature stability and relative low complexity, the MMSR assay may be useful for detection of malaria and epidemiological studies especially in low-resource settings.

Old and Recent Advances in Life Cycle, Pathogenesis, Diagnosis, Prevention, and Treatment of Malaria Including Perspectives in Ethiopia

Malaria, caused by apicomplexan parasite, is an old disease and continues to be a major public health threat in many countries. This article aims to present different aspects of malaria including causes, pathogenesis, prevention, and treatment in an articulate and comprehensive manner. Six Plasmodium species are recognized as the etiology of human malaria, of which Plasmodium falciparum is popular in East and Southern Africa. Malaria is transmitted mainly through Anopheles gambiae and Anopheles funestus, the two most effective malaria vectors in the world. Half of the world’s population is at risk for malaria infection. Globally, the morbidity and mortality rates of malaria have become decreased even though few reports in Ethiopia showed high prevalence of malaria. The malaria parasite has a complex life cycle that takes place both inside the mosquito and human beings. Generally, diagnosis of malaria is classified into clinical and parasitological diagnoses. Lack of clear understanding on the overall biology of Plasmodium has created a challenge in an effort to develop new drugs, vaccines, and preventive methods against malaria. However, three types of vaccines and a lot of novel compounds are under perclinical and clinical studies that are triggered by the occurrence of resistance among commonly used drugs and insecticides. Antiadhesion adjunctive therapies are also under investigation in the laboratory. In addition to previously known targets for diagnostic tool, vaccine and drug discovery scientists from all corner of the world are in search of new targets and chemical entities.

Recent Advances in the Development of Biosensors for Malaria Diagnosis

The impact of malaria on global health has continually prompted the need to develop more effective diagnostic strategies that could overcome deficiencies in accurate and early detection. In this review, we examine the various biosensor-based methods for malaria diagnostic biomarkers, namely; Plasmodium falciparum histidine-rich protein 2 (PfHRP-2), parasite lactate dehydrogenase (pLDH), aldolase, glutamate dehydrogenase (GDH), and the biocrystal hemozoin. The models that demonstrate a potential for field application have been discussed, looking at the fabrication and analytical performance characteristics, including (but not exclusively limited to): response time, sensitivity, detection limit, linear range, and storage stability, which are first summarized in a tabular form and then described in detail. The conclusion summarizes the state-of-the-art technologies applied in the field, the current challenges and the emerging prospects for malaria biosensors.

Plasmodium falciparum Parasitemia and Band Sensitivity of the SD Bioline Malaria Ag P.f/Pan Rapid Diagnostic Test in Madagascar

Current malaria rapid diagnostic tests (RDTs) contain antibodies against Plasmodium falciparum-specific histidine-rich protein 2 (PfHRP2), Plasmodium lactate dehydrogenase (pLDH), and aldolase in various combinations. Low or high parasite densities/target antigen concentrations may influence the accuracy and sensitivity of PfHRP2-detecting RDTs. We analyzed the SD Bioline Malaria Ag P.f/Pan RDT performance in relation to P. falciparum parasitemia in Madagascar, where clinical Plasmodium vivax malaria exists alongside P. falciparum. Nine hundred sixty-three samples from patients seeking care for suspected malaria infection were analyzed by RDT, microscopy, and Plasmodium species-specific, ligase detection reaction-fluorescent microsphere assay (LDR-FMA). Plasmodium infection positivity by these diagnostics was 47.9%, 46.9%, and 58%, respectively. Plasmodium falciparum-only infections were predominant (microscopy, 45.7%; LDR-FMA, 52.3%). In all, 16.3% of P. falciparum, 70% of P. vivax, and all of Plasmodium malariae, Plasmodium ovale, and mixed-species infections were submicroscopic. In 423 P. falciparum mono-infections, confirmed by microscopy and LDR-FMA, the parasitemia in those who were positive for both the PfHRP2 and pan-pLDH test bands was significantly higher than that in those who were positive only for the PfHRP2 band (P < 0.0001). Plasmodium falciparum parasitemia in those that were detected as P. falciparum-only infections by microscopy but P. falciparum mixed infections by LDR-FMA also showed similar outcome by the RDT band positivity. In addition, we used varying parasitemia (3-0.0001%) of the laboratory-maintained 3D7 strain to validate this observation. A positive pLDH band in high P. falciparum-parasitemic individuals may complicate diagnosis and treatment, particularly when the microscopy is inconclusive for P. vivax, and the two infections require different treatments.

Ultrasensitive and label-free biosensor for the detection of Plasmodium falciparum histidine-rich protein II in saliva

Malaria elimination is a global public health priority. To fulfil the demands of elimination diagnostics, we have developed an interdigitated electrode sensor platform targeting the Plasmodium falciparum Histidine Rich Protein 2 (PfHRP2) protein in saliva samples. A protocol for frequency-specific PfHRP2 detection in phosphate buffered saline was developed, yielding a sensitivity of 2.5 pg/mL based on change in impedance magnitude of the sensor. This protocol was adapted and optimized for use in saliva with a sensitivity of 25 pg/mL based on change in resistance. Further validation demonstrated detection in saliva spiked with PfHRP2 from clinical isolates in 8 of 11 samples. With a turnaround time of ~2 hours, the label-free platform based on impedance sensors has the potential for miniaturization into a point-of-care diagnostic device for malaria elimination.

A multiplex qPCR approach for detection of pfhrp2 and pfhrp3 gene deletions in multiple strain infections of Plasmodium falciparum

The rapid and accurate diagnosis of Plasmodium falciparum malaria infection is an essential factor in malaria control. Currently, malaria diagnosis in the field depends heavily on using rapid diagnostic tests (RDTs) many of which detect circulating parasite-derived histidine-rich protein 2 antigen (PfHRP2) in capillary blood. P. falciparum strains lacking PfHRP2, due to pfhrp2 gene deletions, are an emerging threat to malaria control programs. The novel assay described here, named qHRP2/3-del, is well suited for high-throughput screening of P. falciparum isolates to identify these gene deletions. The qHRP2/3-del assay identified pfhrp2 and pfhrp3 deletion status correctly in 93.4% of samples with parasitemia levels higher than 5 parasites/µL when compared to nested PCR. The qHRP2/3-del assay can correctly identify pfhrp2 and pfhrp3 gene deletions in multiple strain co-infections, particularly prevalent in Sub-Saharan countries. Deployment of this qHRP2/3-del assay will provide rapid insight into the prevalence and potential spread of P. falciparum isolates that escape surveillance by RDTs.

Development of a film-based immunochromatographic microfluidic device for malaria diagnosis

In this study, a novel film-based immunochromatographic microfluidic device (IMD) has been developed for malaria diagnosis. A microfluidic channel was patterned on a polyethylene terephthalate (PET) double-sided adhesive film using a plotting cutter and was assembled with a polycarbonate (PC) film. The PC film used for the probe immobilization layer was activated using oxygen plasma treatment to modify the film surface with avidin-biotin linker to immobilize a capture antibody. A fluorescent labeled Pan type mAb conjugate was prepared for signal indicator after undergoing a sandwich enzyme-linked immunosorbent assay (ELISA). Target antigens include Plasmodium falciparum (P. falciparum) lactate dehydrogenase (LDH) and Plasmodium vivax (P. vivax) LDH which were injected into the sample inlet. Target antigens combined with the conjugate and then flowed to the detection chamber where two test dots and a control dot (Ctrl) exist. In the presence of P. falciparum LDH, three detection dots including test dot 1 (T1), test dot 2 (T2) and Ctrl revealed fluorescence signals where P. falciparum mAb, Pan type pLDH mAb and goat anti-mouse IgG were immobilized, respectively. When P. vivax LDH was present, T2 and Ctrl dots showed fluorescence signals while no signal was detected with the negative control. P. falciparum LDH and P. vivax LDH were successfully detected on the IMD with a detection limit of 50 ng/mL and 100 ng/mL, respectively. The IMD provides a point-of-care diagnosis platform which is able to analyze pathogenic bacteria and viruses that can be applied in the field of clinical diagnosis and food safety testing.

The use of GPS data loggers to describe the impact of spatio-temporal movement patterns on malaria control in a high-transmission area of northern Zambia

Background

Human movement is a driver of malaria transmission and has implications for sustainable malaria control. However, little research has been done on the impact of fine-scale movement on malaria transmission and control in high-transmission settings. As interest in targeted malaria control increases, evaluations are needed to determine the appropriateness of these strategies in the context of human mobility across a variety of transmission settings.

Methods

A human mobility study was conducted in Nchelenge District, a high-transmission setting in northern Zambia. Over 1 year, 84 participants were recruited from active malaria surveillance cohorts to wear a global positioning system data logger for 1 month during all daily activity. Participants completed a survey questionnaire and underwent malaria testing and treatment at the time of logger distribution and at collection 1 month later. Incident malaria infections were identified using polymerase chain reaction. Participant movement was characterized throughout the study area and across areas targeted for an indoor residual spraying (IRS) intervention. Participant movement patterns were compared using movement intensity maps, activity space plots, and statistical analyses. Malaria risk was characterized across participants using spatial risk maps and time spent away from home during peak vector biting hours.

Results

Movement data were collected from 82 participants, and 63 completed a second study visit. Participants exhibited diverse mobility patterns across the study area, including movement into and out of areas targeted for IRS, potentially mitigating the impact of IRS on parasite prevalence. Movement patterns did not differ significantly by season or age, but male participants traveled longer distances and spent more time away from home. Monthly malaria incidence was 22%, and malaria risk was characterized as high across participants. Participants with incident parasitemia traveled a shorter distance and spent more time away from home during peak biting hours; however, these relationships were not statistically significant, and malaria risk score did not differ by incident parasitemia.

Conclusions

Individual movement patterns in Nchelenge District, Zambia have implications for malaria control, particularly the effectiveness of targeted IRS strategies. Large and fine-scale population mobility patterns should be considered when planning intervention strategies across transmission settings.

Electronic supplementary material

The online version of this article (10.1186/s12942-019-0183-y) contains supplementary material, which is available to authorized users.

Infected RBC flag/parameter provided by Mindray BC-6800 haematology analyzer aid the diagnosis of malaria

Background

The Mindray BC-6800 haematology analyzer (BC-6800) provides a dedicated flag ‘Infected RBC’ (InR) and the number of InR (InR#)/the permillage of InR (InR‰) in routine blood testing as a screening tool for malaria in endemic areas. This study sought to evaluate the effectiveness of the BC-6800 flag parameter for aiding the diagnosis of malaria.

Methods

A total of 181 samples were tested using the Mindray BC-6800 haematology analyzer, including 117 malaria-infected samples collected from Yunnan, China, and 64 samples from healthy controls. Microscopy examination was conducted as reference when stained thick blood film revealed the presence of malaria parasites identified as Plasmodium vivax and Plasmodium falciparum. The receiver operating characteristic (ROC) curve analysis was developed using Analyse-it v4.92.3. The Kappa value was determined to evaluate the agreement between BC-6800 and light microscopy.

Results

The sensitivity of InR‰ generated by BC-6800 for P. vivax and P. falciparum was 88.3 and 24.1%, respectively; specificity of InR‰ for malaria parasites was 84.3 and 84.3%, respectively; positive predictive value and negative predictive value was 89.4 and 82.7% for P. vivax, and 52.8 and 60.3% for P. falciparum. There was a strong correlation between ΔWBC and InR‰ (R² = 0.9731 for P. vivax and R² = 0.9757 for P. falciparum). There was also a significant correlation between parasitaemia and InR# in P. vivax-infected samples (R² = 0.734). InR# was evaluated using ROC curve analysis, the area under the ROC curve is 0.95 with a 95% confidence interval of 0.926 to 0.974, and the cut-off value is 0.01 × 10⁹/L for P. vivax. However, the ring stage and the early trophozoite stage of Plasmodium cannot be detected easily on BC-6800, possibly because of the small size and low nucleic acid content of these stages.

Conclusions

The findings suggest that the flag ‘InR’ and the parameters ‘InR#/InR‰’ provided by the BC-6800 haematology analyzer could be used to screen for malaria in a clinical setting.

Blood lead level in infants and subsequent risk of malaria: A prospective cohort study in Benin, Sub-Saharan Africa

Lead and malaria both present significant health risks to children in Sub-Saharan Africa. Previous studies have shown that high blood lead levels in children act as a protective factor against subsequent malaria incidence. The main objective of this study was to investigate associations between blood lead level and malaria outcomes prospectively in Beninese children from 12 to 24 months of age. Two-hundred and four children were assessed for lead at 12 months and closely followed until 24 months for malaria; when symptoms and parasite density were also recorded. Univariate and multivariate negative binomial and linear regression models tested associations between blood lead level quartile and total episodes of malaria (total symptomatic and asymptomatic episodes) and parasite density, respectively. Median blood lead level among children measured at 12 months was 56.50 (4.81-578) μg/L. During the 12-month follow-up, 172 (84.31%) children had at least one malaria episode. Univariate and multivariate negative binomial and linear regressions did not reveal significant associations between blood lead level quartile and malaria outcomes. Iron deficiency was not found to be an effect modifier. Results from this prospective child-cohort study investigating associations between blood lead level and malaria did not confirm results from previous cross-sectional studies. Further research is needed to further explore this relationship and other co-morbidities due to malaria and lead.

Tissue and blood protozoa including toxoplasmosis, Chagas disease, leishmaniasis, Babesia, Acanthamoeba, Balamuthia, and Naegleria in solid organ transplant recipients- Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of tissue and blood protozoal infections in the pre- and post-transplant period. Significant new developments in the field have made it necessary to divide the previous single guideline published in 2013 into two sections, with the intestinal parasites separated from this guideline devoted to tissue and blood protozoa. The current update reflects the increased focus on donor screening and risk-based recipient monitoring for parasitic infections. Increased donor testing has led to new recommendations for recipient management of Toxoplasma gondii and Trypanosoma cruzi. Molecular diagnostics have impacted the field, with access to rapid diagnostic testing for malaria and polymerase chain reaction testing for Leishmania. Changes in Babesia treatment regimens in the immunocompromised host are outlined. The risk of donor transmission of free-living amebae infection is reviewed. Changing immigration patterns and the expansion of transplant medicine in developing countries has contributed to the recognition of parasitic infections as an important threat to transplant outcomes. Medications such as benznidazole and miltefosine are now available to US prescribers as access to treatment of tissue and blood protozoa is increasingly prioritized.

Distribution of Plasmodium species and assessment of performance of diagnostic tools used during a malaria survey in Southern and Western Provinces of Zambia

Background

Zambia continues to make strides in reducing malaria burden through the use of proven malaria interventions and has recently pledged to eliminate malaria by 2021. Case management services have been scaled up at community level with rapid diagnostic tests (RDTs) providing antigen-based detection of falciparum malaria only. Key to national malaria elimination goals is the ability to identify, treat and eliminate all Plasmodium species. This study sought to determine the distribution of non-falciparum malaria and assess the performance of diagnostic tests for Plasmodium falciparum in Western and Southern Provinces of Zambia, two provinces planned for early malaria elimination.

Methods

A sub-set of individuals’ data and samples from a cross-sectional household survey, conducted during peak malaria transmission season in April and May 2017, was used. The survey collected socio-demographic information on household members and coverage of malaria interventions. Malaria testing was done on respondents of all ages using blood smears and RDTs while dried blood spots were collected on filter papers for analysis using photo-induced electron transfer polymerase chain reaction (PET-PCR). Slides were stained using Giemsa stain and examined by microscopy for malaria parasites.

Results

From the 1567 individuals included, the overall prevalence of malaria was 19.4% (CI 17.5–21.4) by PCR, 19.3% (CI 17.4–21.4) by RDT and 12.9% (CI 11.3–14.7) by microscopy. Using PET-PCR as the gold standard, RDTs showed a sensitivity of 75.7% (CI 70.4–80.4) and specificity of 94.2% (CI 92.8–95.4). The positive predictive value (PPV) was 75.9% (CI 70.7–80.6) and negative predictive value (NPV) was 94.1% (CI 92.1–95.4). In contrast, microscopy for sensitivity, specificity, PPV, and NPV values were 56.9% (CI 51.1–62.5), 97.7% (CI 96.7–98.5), 85.6% (CI 80.0–90.2), 90.4% (CI 88.7–91.9), respectively. Non-falciparum infections were found only in Western Province, where 11.6% of P. falciparum infections were co-infections with Plasmodium ovale or Plasmodium malariae.

Conclusion

From the sub-set of survey data analysed, non-falciparum species are present and occurred as mixed infections. As expected, PET-PCR was slightly more sensitive than both malaria RDTs and microscopy to detecting malaria infections.

A comparison of thick-film microscopy, rapid diagnostic test, and polymerase chain reaction for accurate diagnosis of Plasmodium falciparum malaria

Background

Accurate diagnosis of malaria is important for effective disease management and control. In Cameroon, presumptive clinical diagnosis, thick-film microscopy (TFM), and rapid diagnostic tests (RDT) are commonly used to diagnose cases of Plasmodium falciparum malaria. However, these methods lack sensitivity to detect low parasitaemia. Polymerase chain reaction (PCR), on the other hand, enhances the detection of sub-microscopic parasitaemia making it a much-needed tool for epidemiological surveys, mass screening, and the assessment of interventions for malaria elimination. Therefore, this study sought to determine the frequency of cases missed by traditional methods that are detected by PCR.

Methods

Blood samples, collected from 551 febrile Cameroonian patients between February 2014 and February 2015, were tested for P. falciparum by microscopy, RDT and PCR. The hospital records of participants were reviewed to obtain data on the clinical diagnosis made by the health care worker.

Results

The prevalence of malaria by microscopy, RDT and PCR was 31%, 45%, and 54%, respectively. However, of the 92% of participants diagnosed as having clinical cases of malaria by the health care worker, 38% were malaria-negative by PCR. PCR detected 23% and 12% more malaria infections than microscopy and RDT, respectively. A total of 128 (23%) individuals had sub-microscopic infections in the study population. The sensitivity of microscopy, RDT, and clinical diagnosis was 57%, 78% and 100%; the specificity was 99%, 94%, and 17%; the positive predictive values were 99%, 94%, and 59%; the negative predictive values were 66%, 78%, and 100%, respectively. Thus, 41% of the participants clinically diagnosed as having malaria had fever caused by other pathogens.

Conclusions

Malaria diagnostic methods, such as TFM and RDT missed 12–23% of malaria cases detected by PCR. Therefore, traditional diagnostic approaches (TFM, RDT and clinical diagnosis) are not adequate when accurate epidemiological data are needed for monitoring malaria control and elimination interventions.

Development of a Flow-Free Magnetic Actuation Platform for an Automated Microfluidic ELISA

There is a need to create an easily deployable and point-of-care (POC) diagnostic platform for disease outbreaks and for monitoring and maintenance of chronic illnesses. Such platforms are useful in regions where access to clinical laboratories may be limited or constrained using cost-effective solutions to quickly process high numbers of samples. Using oil and water liquid–liquid interphase separation, immunoassays developed for microfluidic chips can potentially meet this need when leveraged with electromagnetic actuation and antibody-coated superparamagnetic beads. We have developed a microfluidic immunoassay detection platform, which enables assay automation and maintains successful liquid containment for future use in the field. The assay was studied through a series of magnetic and fluid simulations to demonstrate these optimizations, and an optimized chip was tested using a target model for HIV-1, the p24 capsid antigen. The use of minimal reagents further lowers the cost of each assay and lowers the required sample volume for testing (<50 μL), that can offer easy turnaround for sample collection and assay results. The developed microfluidic immunoassay platform can be easily scaled for multiplex or multi-panel specific testing at the POC.

A flow-free device is developed for automated and rapid ELISA testing at the point-of-care settings.

On the discriminatory and predictive accuracy of the RDT against the microscopy in the diagnosis of malaria among under-five children in Nigeria

Background

Accurate identification of malaria cases is crucial to the management of cases and the eventual success of malaria eradication agenda. This study is designed to evaluate the discriminatory and predictive accuracy of malaria rapid diagnostic tests (RDTs) in Nigeria.

Methods

The data obtained during the 2015 Nigeria Malaria Indicator Survey was used to quantify the discriminatory accuracy of the RDT against the microscopy through the analysis of its sensitivity, specificity, positive (LR+) and negative (LR−) likelihood ratio. The positive (PPV) and negative (NPV) predictive values, area under the receiver operating characteristic curve, and diagnostic odds ratio were used to assess the predictive accuracy of the RDTs using expert microscopy as a gold standard at p = 0.05. The McNemar paired test and the Kappa statistics were used to assess the level of agreement between the diagnostic tests.

Results

There was a significant but not an excellent agreement between the results of the RDT and microscopy tests (p < 0.001). The overall sensitivity of the RDT was 87.6% (85.9–89.2%), specificity was 75.8% (74.4–77.1%), while the diagnostic accuracy stood at 79.0% (77.9–80.0%). The LR+, LR−, PPV and NPV were 3.6 (3.4–3.8) and 0.16 (0.14–0.19), 57.5% (56.1–58.9%) and 94.2% (93.5–94.9%), respectively. The sensitivity of RDT increased as the age of the children increased, from 85.7% among those aged 0–6 months to 86.1% in 7–23 month olds to 88.1% among those aged 24–59 months, but the reverse was the specificity. For children with severe anaemia, the sensitivity of the RDT was nearly 100% compared with a specificity of 39%. While the sensitivity and the PPV reduced with children’s level of anaemia, the higher the severity of anaemia, the lower the NPV, specificity, the diagnostic accuracy of the RDT. The odds of RDT being sensitive was about 50% [adjusted Odds Ratio (aOR) = 0.52 (95% CI 0.30–0.90)] lower among children aged 7–23 months compared with those aged 24–59 months while the odds of RDT being sensitive was 2 times [aOR = 2.15 (95% CI 1.67–2.77)] higher among those 7–23 months than among those aged 24–59 months.

Conclusions

Although there was a significant agreement in the outcomes of RDT and microscopy tests, the discriminatory accuracy of RDT was weak. Also, the predictive accuracy, especially the PPV of the RDTS, were very low. These measures of accuracies differed across the age of the children, level of anaemia, recent experience of malaria and other characteristics. Without an accurate, efficient and reliable diagnosis of malaria, the goal of eliminating malaria and reduction of malaria-related deaths to zero by 2020 will only remain elusive.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2678-1) contains supplementary material, which is available to authorized users.

Genetic variability of Plasmodium falciparum histidine-rich proteins 2 and 3 in Central America

Background

Malaria is an important disease in many tropical countries. Rapid diagnostic tests (RDTs) are valuable tools for diagnosing malaria in remote areas. The majority of RDTs used for the diagnosis of Plasmodium falciparum are based on the detection of the specific histidine-rich proteins (PfHRP2 and PfHRP3). During the last decade, the threat posed by the lack of expression of these antigens and the variability of the proteins on the diagnosis of malaria has been widely discussed. The aim of this study was to evaluate the genetic diversity of pfhrp2 and pfhrp3 of P. falciparum isolates collected in three Central American countries.

Methods

DNA samples were amplified and sequenced to assess the diversity of nucleotides and amino acids. A search for known epitopes within the amino acid sequence was carried out, and the sensitivity of the sequences was evaluated according to a predictive model. A phylogenetic analysis was carried out including homologous sequences from different regions of the world. Protein structures were predicted in silico.

Results

Five different patterns for PfHRP2 and one pattern for PfHRP3 were identified. Isolates from Central America show a high level of genetic diversity in pfhrp2; however, the amino acid sequences seem to contain enough motifs to be detected by the RDTs currently available.

Conclusion

It is unlikely that the variability of the pfhrp2 and pfhrp3 genes has a significant impact on the ability of the RDTs to detect the PfHRP antigens in Central America.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2668-3) contains supplementary material, which is available to authorized users.

Performance of an immuno-rapid malaria Pf/Pv rapid diagnostic test for malaria diagnosis in the Western Brazilian Amazon

INTRODUCTION

Rapid diagnostic tests (RDTs) for detecting Plasmodium antigens have become increasingly common worldwide. We aimed to evaluate the accuracy of the Immuno-Rapid Malaria Pf/Pv RDT in detecting Plasmodium vivax infection compared to standard thick blood smear (TBS) under microscopy.

METHODS

Hundred and eighty-one febrile patients from the hospital's regular admissions were assessed using TBS and RDT in a blinded experiment.

RESULTS

RDT showed a sensitivity of 98.9%, specificity of 100%, and accuracy of 99.5% for P. vivax infection when compared to TBS.

CONCLUSIONS

The RDT is highly accurate, making it a valuable diagnostic tool for P. vivax infection.

Molecular monitoring of the diversity of human pathogenic malaria species in blood donations on Bioko Island, Equatorial Guinea

BACKGROUND

Malaria can be transmitted by blood transfusion from human to human and it is responsible for the majority of transfusion-transmitted infectious diseases worldwide. In sub-Saharan Africa, it had been estimated that almost a quarter of blood donations contain malaria parasites. Since rapid diagnostic tests and thick blood smear microscopy lack sensitivity for low density parasitaemia, particularly in asymptomatic adults, the most reliable method to assess the problem of transfusion-transmitted malaria are nucleic acid-based molecular approaches such as quantitative polymerase chain reaction. The study was undertaken to determine the prevalence of sub-microscopic malaria parasite infection among blood donors in Malabo, Equatorial Guinea.

METHODS

Between July and August 2017, a total of 200 individual blood samples from blood donors at the Malabo Blood Bank were collected and screened by rapid diagnostic tests and thick blood smear microscopy. Retrospectively, the same samples were analysed for the presence of undetected, low-density malaria parasites using quantitative polymerase chain reaction.

RESULTS

In comparison to 6.5% (13/200) by rapid diagnostic test and 2.0% (4/200) by microscopy, the proportion of Plasmodium falciparum positive blood donations analysed by quantitative polymerase chain reaction was significantly higher (26%, 52/200). Densities of P. falciparum positive blood donations were ranging from 0.06 to 3707.0 parasites/µL with 79.6% below 100 parasites/µL and therefore not detectable by non-molecular malaria diagnostic tests. qPCR based species identification revealed that P. falciparum was the dominating species responsible for 88.1% (52/59) of positive blood donations, followed by Plasmodium malariae (15.3%, 9/59) and Plasmodium ovale (3.4%, 2/59).

CONCLUSIONS

This study confirms that in malaria endemic settings, sub-patent malaria infections among blood donors are prevalent. In blood collected from healthy donors living in Malabo, P. falciparum, P. malariae and P. ovale parasites were identified. Currently widely used malaria diagnostic tools have missed more than 75% of P. falciparum containing blood donations, demonstrating the value of quantitative polymerase chain reaction to reliably detect low density P. falciparum infections. Since the availability of molecular diagnostic methods in malaria endemic countries is still limited, the blood recipients living in malaria endemic countries should be treated following WHO recommendations.

Screening for Pfhrp2/3-Deleted Plasmodium falciparum, Non-falciparum, and Low-Density Malaria Infections by a Multiplex Antigen Assay

Background

Detection of Plasmodium antigens provides evidence of malaria infection status and is the basis for most malaria diagnosis.

Methods

We developed a sensitive bead-based multiplex assay for laboratory use, which simultaneously detects pan-Plasmodium aldolase (pAldo), pan-Plasmodium lactate dehydrogenase (pLDH), and P. falciparum histidine-rich protein 2 (PfHRP2) antigens. The assay was validated against purified recombinant antigens, monospecies malaria infections, and noninfected blood samples. To test against samples collected in an endemic setting, Angolan outpatient samples (n = 1267) were assayed.

Results

Of 466 Angolan samples positive for at least 1 antigen, the most common antigen profiles were PfHRP2+/pAldo+/pLDH+ (167, 36%), PfHRP2+/pAldo-/pLDH- (163, 35%), and PfHRP2+/pAldo+/pLDH- (129, 28%). Antigen profile was predictive of polymerase chain reaction (PCR) positivity and parasite density. Eight Angolan samples (1.7%) had no or very low PfHRP2 but were positive for 1 or both of the other antigens. PCR analysis confirmed 3 (0.6%) were P. ovale infections and 2 (0.4%) represented P. falciparum parasites lacking Pfhrp2 and/or Pfhrp3.

Conclusions

These are the first reports of Pfhrp2/3 deletion mutants in Angola. High-throughput multiplex antigen detection can inexpensively screen for low-density P. falciparum, non-falciparum, and Pfhrp2/3-deleted parasites to provide population-level antigen estimates and identify specimens requiring further molecular characterization.

Practice of antimalarial prescription to patients with negative rapid test results and associated factors among health workers in Oyo State, Nigeria

Introduction

Contrary to World Health Organizations recommendations, health workers (HWs) still prescribe antimalarials to malaria rapid diagnostic test (mRDT)-negative patients, thus increasing overuse and the risk of parasite resistance to the antimalarials. The reasons for this are not clear. We identified factors associated with antimalarial prescription to mRDT-negative patients.

Methods

We conducted a cross-sectional study among 423 HWs. Data on socio-demographic characteristics, training, supervision experience and fever management practices were collected. We tested associations between independent variables and prescription of antimalarials to mRDT-negative patients using Chi square and logistic regression at p < 0.05.

Results

The HWs were mostly community health workers (58.6%), with mean age of 41.0 (±8.8) years and 13.6 (± 9.0) years of professional practice. Females were 322 (76.1%) and 368 (87%) were married. Of the 423 HWs interviewed, 329 (77.8%) received training on mRDT use, 329 (80.6%) received supervision and 129 (30.5%) had good knowledge of causes of fever. Overall, 110 (26.0%) of the HWs prescribed antimalarials to mRDT-negative patients. A higher proportion of non-trained vs trained HWs [Adjusted Odds Ratio (aOR) = 4.9; 95% Confidence Interval (CI) (2.5-8.3)], and HWs having poor knowledge vs HWs having good knowledge of causes of fever [aOR = 1.9; 95% CI (1.0-3.5)], prescribed antimalarials to mRDT-negative patients.

Conclusion

HWs' lack of training on mRDT use and poor knowledge of causes of fever were associated with prescription of antimalarials to mRDT-negative patients. We recommend training on management of fever and mRDT use to reduce such inappropriate antimalarial prescriptions.

Wash-free, label-free immunoassay for rapid electrochemical detection of PfHRP2 in whole blood samples

Currently, the diagnosis of many diseases relies on laboratory-based immunoassays (ELISA, Western Blot), which are laborious, time-consuming and expensive. To address these limitations, we report a wash-free and label-free electrochemical immunoassay for rapid measurements of protein biomarkers in blood samples. This immunosensor employs a unique detection scheme based on electrochemical-chemical (EC) redox cycling for signal amplification combined with an affinity-based protein quantification strategy. All of the reagents required for this assay are dried and stored on a stacked membrane assembly, consisting of a Vivid Plasma Separation membrane and two cellulose membranes situated above the sensor, enabling excellent stability at room temperature for up to 2 months. Proof of concept was carried out by performing measurements of Plasmodium falciparum histidine-rich protein 2 (PfHRP2) in whole blood samples, which could be detected from 100 ng/mL to 100 µg/mL with excellent specificity and reproducibility. Each measurement requires only two liquid dispensing steps and can completed in 5 min, making this diagnostic platform promising for point-of-care testing in resource-limited settings.

Prevalence of Plasmodium parasitaemia in blood donors and a survey of the knowledge, attitude and practices of transfusion malaria among health workers in a hospital in Kumasi, Ghana

Malaria is one of the transfusion transmissible infections in malaria endemic countries such as Ghana. Healthy blood donors may harbour Plasmodium parasites without showing signs of malaria. Blood from such donors constitutes a risk to transfusion recipients and the recipients of this blood may go on to develop transfusion transmitted malaria (TTM). In many malaria endemic countries, blood donors are not screened for Plasmodium parasites. We investigated the prevalence of Plasmodium in blood donors in a hospital in Ghana as well as evaluate health workers knowledge, attitude and practices towards TTM. The study was carried out at the Kwadaso Seventh Day Adventist Hospital in Kumasi, Ghana from September 2016 to May 2017. Blood samples from 100 blood donors and 100 non-donors were examined for Plasmodium using microscopy and a rapid diagnostic test (RDT). In addition the blood groups of participants were determined. To obtain information concerning knowledge, attitude and practices of transfusion transmitted malaria, questionnaires were administered to 100 health workers including doctors, nurses and laboratory technicians. The prevalence rate of Plasmodium parasitaemia in blood donors by RDT and microscopy was 8% and 3% respectively, compared to non-donors who had a prevalence of 5% and 2% by RDT and microscopy respectively. Out of 100 health workers surveyed, 26% (26/100) had never heard of transfusion transmitted malaria. In an emergency situation, 41% health workers were willing to transfuse malaria positive blood but only 2%, 4% and 8% were willing to transfuse blood that was positive for HIV, Hepatitis B and Syphilis respectively. Regular training workshops may help improve the knowledge of health workers as a quarter of workers had not heard about transfusion transmitted malaria and 6.8% did not know that malaria was transmissible by transfusion.

High proportions of pfhrp2 gene deletion and performance of HRP2-based rapid diagnostic test in Plasmodium falciparum field isolates of Odisha

BACKGROUND

With the documentation of cases of falciparum malaria negative by rapid diagnostic tests (RDT), though at low frequency from natural isolates in a small pocket of Odisha, it became absolutely necessary to investigate the status of HRP-2 based RDT throughout the state and in different seasons of the year.

METHODS

Suspected individuals were screened for malaria infection by microscopy and RDT in 25/30 districts of Odisha, India. Discrepancies in results were confirmed by PCR. False negative RDT samples for Plasmodium falciparum mono-infection were evaluated for detection of HRP2 antigen in ELISA and genotyped for pfhrp2, pfhrp3 and their flanking genes. Multiplicity of infection was ascertained based on msp1 and msp2 genotyping and parasitaemia level was determined by microscopy.

RESULTS

Of the total 1058 patients suspected for malaria, 384 were microscopically confirmed for P. falciparum mono-infection and RDT failure was observed in 58 samples at varying proportion in different regions of the state. The failure in detection was due to undetectable level of HRP-2. Although most of these samples were screened during rainy season (45/345), significantly high proportion (9/17) of RDT negative samples were obtained during the summer compared to rainy season (P = 0.0002; OR = 7.5). PCR genotyping of pfhrp2 and pfhrp3 in RDT negative samples showed 38/58 (65.5) samples to be pfhrp2 negative and 24/58 (41.4) to be pfhrp3 negative including dual negative in 17/58 (29.3). Most of the RDT negative samples (39/58) were with single genotype infection and high proportions of pfhrp2 deletion (7/9) was observed in summer. No difference in parasitaemia level was observed between RDT positive and RDT negative patients.

CONCLUSION

High prevalence of parasites with pfhrp2 deletion including dual deletions (pfhrp2 and pfhrp3) is a serious cause of concern, as these patients could not be given a correct diagnosis and treatment. Therefore, HRP2-based RDT for diagnosing P. falciparum infection in Odisha is non-reliable and must be performed in addition to or replaced by other appropriate diagnostic tools for clinical management of the disease.

An Update on Malaria Rapid Diagnostic Tests

PURPOSE OF REVIEW

Modern advances in malaria rapid diagnostic test (RDT) technology have increased demand for low-cost, easy-to-use assays in areas endemic for malaria. Substantial developments in diagnostic sensitivity and specificity, improvements in non-falciparum RDTs, and novel biotechnological innovations are gradually aligning the performance of RDTs with reference-level diagnostics including PCR and expert microscopy gold standards.

RECENT FINDINGS

Trends have emerged in recent malaria RDT literature: (1) improvements in the sensitivity and specificity of RDTs for Plasmodium falciparum diagnosis, making them comparable to expert microscopic examination; (2) reduced false-positive and false-negative reactions with novel antibody development; (3) improved sensitivity and specificity capabilities of Plasmodium vivax-specific RDTs; (4) developing RDTs for co-endemic mixed infection differentiation; (5) significant improvements of RDTs for Plasmodium knowlesi; (6) a global push towards assessing and confronting the growing concerns of widespread pfhrp2 gene deletions; and (7) original innovation in loop-mediated isothermal amplification (LAMP) biotechnological RDT-like platforms that demonstrate promising performance characteristics for P. falciparum, P. vivax, and P. knowlesi infections. The past 5 years have been characterized by increasing demand for malaria RDTs, translating into meaningful improvements in performance and novel biotechnological innovation. Future work should facilitate the development of improved RDT platforms for Plasmodium ovale, P. knowlesi, and Plasmodium malariae, and surmount the issue of pfhrp2 gene deletions, while maintaining comparable performance to both PCR and expert microscopy reference standards.

Can malaria rapid diagnostic tests by drug sellers under field conditions classify children 5 years old or less with or without Plasmodium falciparum malaria? Comparison with nested PCR analysis

Background

Malaria rapid diagnostic tests (RDTs) available as dipsticks or strips, are simple to perform, easily interpretable and do not require electricity nor infrastructural investment. Correct interpretation of and compliance with the RDT results is a challenge to drug sellers. Thus, drug seller interpretation of RDT strips was compared with laboratory scientist re-reading, and PCR analysis of Plasmodium DNA extracted from RDT nitrocellulose strips and fast transient analysis (FTA) cards. Malaria RDT cassettes were also assessed as a potential source of Plasmodium DNA.

Methods

A total of 212 children aged between 2 and 60 months, 199 of whom had complete records at two study drug shops in south western Uganda participated in the study. Duplicate 5 μL samples of capillary blood were picked from the 212 children, dispensed onto the sample well of the CareStart™ Pf-HRP2 RDT cassette and a FTA, Whatman™ 3MM filter paper in parallel. The RDT strip was interpreted by the drug seller within 15–20 min, visually re-read centrally by laboratory scientist and from it; Plasmodium DNA was recovered and detected by PCR, and compared with FTA recovered P. falciparum DNA PCR detection.

Results

Malaria positive samples were 62/199 (31.2%, 95% CI 24.9, 38.3) by drug seller interpretation of RDT strip, 59/212 (27.8%, 95% CI 22.2, 34.3) by laboratory scientist, 55/212 (25.9%, 95% CI 20.0, 32.6) by RDT nitrocellulose strip PCR and 64/212 (30.2%, 95% CI 24.4, 37.7). The overall agreement between the drug seller interpretation and laboratory scientist re-reading of the RDT strip was 93.0% with kappa value of 0.84 (95% CI 0.75, 0.92). The drug seller compliance with the reported RDT results was 92.5%. The performance of the three diagnostic strategies compared with FTA-PCR as the gold standard had sensitivity between 76.6 and 86.9%, specificity above 90%, positive predictive values ranging from 79.0 to 89.8% and negative predictive values above 90%.

Conclusion

Drug sellers can use RDTs in field conditions and achieve acceptable accuracy for malaria diagnosis, and they comply with the RDT results. Plasmodium DNA can be recovered from RDT nitrocellulose strips even in the context of drug shops. Future malaria surveillance and diagnostic quality control studies with RDT cassette as a source of Plasmodium DNA are recommended.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2508-x) contains supplementary material, which is available to authorized users.

Multiplex real-time PCR for diagnosing malaria in a non-endemic setting: a prospective comparison to conventional methods

Almost a decade ago our diagnostic laboratory implemented an in-house real-time PCR for the detection of Plasmodium DNA to diagnose malaria in parallel with conventional diagnostics, i.e., microscopy (thick and thin smears), quantitative buffy coat microscopy (QBC), and a rapid diagnostic test (RDT). Here we report our experiences and make a comparison between the different diagnostic procedures used in this non-endemic setting. All patients during the period February 2009-December 2017 suspected of malaria were prospectively tested at the moment of sample collection. Both PCR and conventional malaria diagnostics were carried out on a total of 839 specimens from 825 patients. In addition, three Plasmodium falciparum (Pf) patients were closely followed by real-time PCR and microscopy after treatment. Overall, 56 samples (55 patients) tested positive by real-time PCR, of which six were missed by microscopy and seven by QBC. RDT showed fairly good results in detecting Pf, whereas specificity was not optimal. RDT failed to detect 10 of 17 non-Pf PCR positive specimens. One Plasmodium malariae patient would have been missed if only conventional diagnostic tests had been used. The high sensitivity of the PCR was confirmed by the number of PCR positive, microscopy negative post-treatment samples. In conclusion, within our routine diagnostic setting, malaria real-time PCR not only showed a high level of agreement with the conventional methods used, but also showed higher sensitivity and better specificity. Still, for complete replacement of the conventional procedures in a non-endemic setting, the time-to-results of the real-time PCR is currently too long.

Deletions of pfhrp2 and pfhrp3 genes of Plasmodium falciparum from Honduras, Guatemala and Nicaragua

Background

Malaria remains a public health problem in some countries of Central America. Rapid diagnostic tests (RDTs) are one of the most useful tools to assist in the diagnosis of malaria in remote areas. Since its introduction, a wide variety of RDTs have been developed for the detection of different parasite antigens. PfHRP2 is the most targeted antigen for the detection of Plasmodium falciparum infections. Genetic mutations and gene deletions are important factors influencing or affecting the performance of rapid diagnostic tests.

Methods

In order to demonstrate the presence or absence of the pfhrp2 and pfhrp3 genes and their flanking regions, a total of 128 blood samples from patients with P. falciparum infection from three Central American countries were analysed through nested or semi-nested PCR approaches.

Results

In total, 25.8 and 91.4% of the isolates lacked the region located between exon 1 and exon 2 of pfhrp2 and pfhrp3 genes, respectively. Parasites from the three countries showed deletions of one or both genes. The highest proportion of pfhrp2 deletions was found in Nicaragua while the isolates from Guatemala revealed the lowest number of pfhrp2 deletions. Parasites collected from Honduras showed the highest proportion of phfrp3 absence (96.2%). Twenty-one percent of isolates were double negative mutants for the exon 1–2 segment of both genes, and 6.3% of isolates lacked the full-length coding region of both genes.

Conclusions

This study provides molecular evidence of the existence of P. falciparum isolates lacking the pfhrp2 and pfhrp3 genes, and their flanking regions, in Honduras, Guatemala and Nicaragua. This finding could hinder progress in the control and elimination of malaria in Central America. Continuous evaluation of RDTs and molecular surveillance would be recommended.

Developments in the Diagnostic Techniques of Infectious Diseases: Rural and Urban Prospective

Objectives:

Diagnostics is the first step for the treatment and eradication of infectious microbial diseases. Due to ever evolving pathogens and emerging new diseases, there is an urgent need to identify suitable diagnostic techniques for better management of each disease. The success rate of specific diagnostic technique in any population depends on various factors including type of the microbial pathogen, availability of resources, technical expertise, disease severity and degree of epidemic of disease in the area. One of the important tasks of the policy makers is to identify and implement suitable diagnostic techniques for specific regions based on their specific requirements. In this review we have discussed various techniques available in the literature and their suitability for the target population based on above mentioned criteria.

Methods:

Diagnostic techniques evaluation of well documented representative microbial diseases; Tuberculosis (bacterial), Malaria (parasitic) and HIV (viral) were included in the study. Identification and collection of information and data was performed focusing on the diagnostic techniques used from the scientific publications from Pubmed, Science Access, Scopus, EMBASE and several regional databases. WHO and CDC database for Tuberculosis, Malaria and HIV were also included. These techniques were compared with respect to the financial resource availability, expertise and management, functional capacity, pathogen virulence and degree of epidemic in the population.

Results and Conclusion:

In case of Tuberculosis, ELISA and colorimetric techniques are successful in rural and urban communities with 80% – 90% sensitivity. Genotyping and SNP analysis are useful in drug resistant strains. Parasitic disease Malaria also follows the same trend with diagnostic techniques like RDTs being common in both population with fast results and around 90% sensitivity. STD disease like HIV however shows slight different trends due to urgent need of interference in rural epidemics of the disease. Rapid and sensitive immunotechniques like dipsticks and agglutination with almost 100% sensitivity are used in both rural and urban areas. For the confirmation further tests are done like protein Western and NAAT. Advance techniques could be the option for higher epidemic area, drug resistance and disease research, while rapid techniques would be suitable for low income areas and POC facilities. Therefore, suitability of the diagnostic techniques for better management depends not only on the financial resources and assessment skills of a community but sometimes on the disease itself. We have further discussed the technological improvements for specific settings (rural/urban) based on the past research for better management of diseases, which could be implemented for the understanding of understudied and newly emerging diseases.

Performance of a highly sensitive rapid diagnostic test (HS-RDT) for detecting malaria in peripheral and placental blood samples from pregnant women in Colombia

BACKGROUND

Pregnancy poses specific challenges for the diagnosis of Plasmodium falciparum infection due to parasite sequestration in the placenta, which translates in low circulation levels in peripheral blood. The aim of this study is to assess the performance of a new highly sensitive rapid diagnostic test (HS-RDT) for the detection of malaria in peripheral and placental blood samples from pregnant women in Colombia.

METHODS

This is a retrospective study using 737 peripheral and placental specimens collected from pregnant women in Colombian malaria-endemic regions. Light microscopy (LM), conventional rapid diagnostic tests (Pf/Pv RDT and Pf RDT), and HS-RDT testing were performed. Diagnostic accuracy endpoints of LM, HS-RDT and RDTs were compared with nested polymerase chain reaction (nPCR) as the reference test.

RESULTS

In comparison with nPCR, the sensitivity of HS-RDT, Pf RDT, Pf/Pv RDT and LM to detect infection in peripheral samples was 85.7% (95% CI = 70.6-93.7), 82.8% (95% CI = 67.3-91.9), 77.1% (95% CI = 61.0-87.9) and 77.1% (95% CI = 61.0-87.9) respectively. The sensitivity to detect malaria in asymptomatic women, was higher with HS-RDT, where LM and Pf/Pv RDT missed half of infections detected by nPCR, but differences were not significant. Overall, specificity was similar for all tests (>99.0%). In placental blood, the prevalence of infection by P. falciparum by nPCR was 2.8% (8/286), by HS-RDT was 1% and by conventional RDTs (Pf RDT and Pf/Pv RDT) and LM was 0.7%. The HS-RDT detected placental infections in peripheral blood that were negative by LM and Pf/Pv RDT, however the number of positive placentas was low.

CONCLUSIONS

The sensitivity of HS-RDT to detect P. falciparum infections in peripheral and placental samples from pregnant women was slightly better compared to routinely used tests during ANC visits and at delivery. Although further studies are needed to guide recommendations on the use of the HS-RDT for malaria case management in pregnancy, this study shows the potential value of this test to diagnose malaria in pregnancy in low-transmission settings.

Accuracy, Ease of Use, Safety, and Acceptability of a 23-μL Conical Cup Blood Transfer Device for Use with Rapid Diagnostic Tests

Devices to safely transfer fixed amounts of finger prick blood to rapid diagnostic tests (RDTs) pose a significant challenge, especially in non-laboratory settings. Following the success of an “inverted cup device” for transfer of 5 μL blood, a prototype with a conical cup shape was developed for transfer of 20 μL blood, the amount needed for human immunodeficiency virus or human African trypanosomiasis (HAT) RDTs. This study determined the volume of blood transferred by this new blood transfer device (BTD) and compared its ease of use, safety, and acceptability with that of a plastic pipette when used by health workers (HWs) for HAT RDTs in northwestern Uganda. After a half-day training, 48 HWs had used the two BTDs with at least 10 patients. The conical cup BTD effectively transferred a mean of 22.76 μL of blood (standard deviation 3.31 μL). A significantly higher proportion of HWs were able to collect the full amount of blood using the conical cup BTD, as compared with the pipette (92.4% versus 74.2%, P < 0.001). In HW questionnaires, the conical cup BTD scored higher than the pipette in various aspects of ease of use and safety. In addition, HWs preferred the conical cup BTD (79%), indicating that it was easy to handle, made work faster, and increased their confidence in front of the patient. These findings suggest that the design of the conical cup BTD may be adapted for RDTs requiring 20 μL of blood to facilitate safe and accurate blood transfer.

Protein-Induced Fluorescence Enhancement Based Detection of Plasmodium falciparum Glutamate Dehydrogenase Using Carbon Dot Coupled Specific Aptamer

A novel 90-mer long ssDNA aptamer (NG3) covering a 40-mer random region targeting Plasmodium falciparum glutamate dehydrogenase ( PfGDH) developed through systematic evolution of ligands by exponential enrichment (SELEX) technique. The binding affinity of the aptamer to PfGDH discerned by circular dichroism (CD) was 0.5 ± 0.04 μM. The specificity of the aptamer toward the target was confirmed by gel electrophoresis and CD studies. The presence of two quadruplex forming regions, two big and four small stem loop structures with a δG of -7.99 kcal mol^-1 for NG3 were deduced by computational studies. The spherical carbon dots (Cdots) of size 2-4 nm, synthesized by pyrolysis method using l-glutamate as a substrate were covalently linked to the amine modified aptamer. The Cdot with a band gap of 2.8 eV and a quantum yield of 34% produced fluorescence at ∼ λ_410 nm when excited at λ_320nm. The quantum yield of Cdot-aptamer assembly was increased up to 40% in the presence of the PfGDH in solution. A linear relationship with a dynamic range of 0.5 nM to 25 nM (R² = 0.98) and a limit of detection (LOD) of 0.48 nM was observed between the fluorescence intensity of the Cdots-aptamer conjugate and the concentration of PfGDH. The method could detect PfGDH with an LOD of 2.85 nM in diluted serum sample. This novel simple, sensitive and specific protein induced fluorescence enhancement based detection of PfGDH has a great potential to develop as a method for malaria detection.

Evaluation of automated loop-mediated amplification (LAMP) for routine malaria detection in blood samples of German travelers - A cross-sectional study

BACKGROUND

We assessed a commercial loop-mediated amplification (LAMP) platform for its reliability as a screening tool for malaria parasite detection.

METHODS

A total of 1000 blood samples from patients with suspected or confirmed malaria submitted to the German National Reference Center for Tropical Pathogens were subjected to LAMP using the Meridian illumigene Malaria platform. Results were compared with microscopy from thick and thin blood films in all cases. In case of discordant results between LAMP and microscopy (n = 60), confirmation testing was performed with real-time PCR. Persistence of circulating parasite DNA was analyzed by serial assessments of blood samples following malaria treatment.

RESULTS

Out of 1000 blood samples analyzed, 238 were positive for malaria parasites according to microscopy (n = 181/1000) or PCR (additional n = 57/60). LAMP demonstrated sensitivity of 98.7% (235/238), specificity of 99.6% (759/762), positive predictive value (PPV) of 98.7% (235/238) and negative predictive value (NPV) of 99.6% (759/762), respectively. For first slides of patients with malaria and for follow-up slides, sensitivity values were 99.1% (106/107) and 98.5% (129/131), respectively.

CONCLUSIONS

The performance of the Meridian illumigene Malaria platform is suitable for initial screening of patients suspected of clinical malaria.

Towards development of aptamers that specifically bind to lactate dehydrogenase of Plasmodium falciparum through epitopic targeting

Background

Early detection is crucial for the effective treatment of malaria, particularly in those cases infected with Plasmodium falciparum. There is a need for diagnostic devices with the capacity to distinguish P. falciparum from other strains of malaria. Here, aptamers generated against targeted species-specific epitopes of P. falciparum lactate dehydrogenase (rPfLDH) are described.

Results

Two classes of aptamers bearing high binding affinity and specificity for recombinant P. falciparum lactate dehydrogenase (rPfLDH) and P. falciparum-specific lactate dehydrogenase epitopic oligopeptide (LDHp) were separately generated. Structurally-relevant moieties with particular consensus sequences (GGTAG and GGCG) were found in aptamers reported here and previously published, confirming their importance in recognition of the target, while novel moieties particular to this work (ATTAT and poly-A stretches) were identified. Aptamers with diagnostically-supportive functions were synthesized, prime examples of which are the aptamers designated as LDHp 1, LDHp 11 and rLDH 4 and rLDH 15 in work presented herein. Of the sampled aptamers raised against the recombinant protein, rLDH 4 showed the highest binding to the target rPfLDH in the ELONA assay, with both rLDH 4 and rLDH 15 indicating an ability to discriminate between rPfLDH and rPvLDH. LDHp 11 was generated against a peptide selected as a unique P. falciparum LDH peptide. The aptamer, LDHp 11, like antibodies against the same peptide, only detected rPfLDH and discriminated between rPfLDH and rPvLDH. This was supported by affinity binding experiments where only aptamers generated against a unique species-specific epitope showed an ability to preferentially bind to rPfLDH relative to rPvLDH rather than those generated against the whole recombinant protein. In addition, rLDH 4 and LDHp 11 demonstrated in situ binding to P. falciparum cells during confocal microscopy.

Conclusions

The utilization and application of LDHp 11, an aptamer generated against a unique species-specific epitope of P. falciparum LDH indicated the ability to discriminate between recombinant P. falciparum and Plasmodium vivax LDH. This aptamer holds promise as a biorecognition element in malaria diagnostic devices for the detection, and differentiation, of P. falciparum and P. vivax malaria infections. This study paves the way to explore aptamer generation against targeted species-specific epitopes of other Plasmodium species.

Phosphoethanolamine-N-methyltransferase is a potential biomarker for the diagnosis of P. knowlesi and P. falciparum malaria

BACKGROUND

Plasmodium knowlesi is recognised as the main cause of human malaria in Southeast Asia. The disease is often misdiagnosed as P. falciparum or P. malariae infections by microscopy, and the disease is difficult to eliminate due to its presence in both humans and monkeys. P. knowlesi infections can rapidly cause severe disease and require prompt diagnosis and treatment. No protein biomarker exists for the rapid diagnostic test (RDT) detection of P. knowlesi infections. Plasmodium knowlesi infections can be diagnosed by PCR.

METHODS AND PRINCIPAL FINDINGS

Phosphoethanolamine-N-methyltransferase (PMT) is involved in malaria lipid biosynthesis and is not found in the human host. The P. falciparum, P. vivax and P. knowlesi PMT proteins were recombinantly expressed in BL21(DE3) Escherichia coli host cells, affinity purified and used to raise antibodies in chickens. Antibodies against each recombinant PMT protein all detected all three recombinant proteins and the native 29 kDa P. falciparum PMT protein on western blots and in ELISA. Antibodies against a PMT epitope (PLENNQYTDEGVKC) common to all three PMT orthologues detected all three proteins. Antibodies against unique peptides from each orthologue of PMT, PfCEVEHKYLHENKE, PvVYSIKEYNSLKDC, PkLYPTDEYNSLKDC detected only the parent protein in western blots and P. falciparum infected red blood cell lysates or blood lysates spiked with the respective proteins. Similar concentrations of PfPMT and the control, PfLDH, were detected in the same parasite lysate. The recombinant PfPMT protein was detected by a human anti-malaria antibody pool.

CONCLUSION

PMT, like the pan-specific LDH biomarker used in RDT tests, is both soluble, present at comparable concentrations in the parasite and constitutes a promising antimalarial drug target. PMT is absent from the human proteome. PMT has the potential as a biomarker for human malaria and in particular as the first P. knowlesi specific protein with diagnostic potential for the identification of a P. knowlesi infection.

High prevalence of malaria in a non-endemic setting: comparison of diagnostic tools and patient outcome during a four-year survey (2013-2017)

Background

Malaria is no longer endemic in Italy since 1970 when the World Health Organization declared Italy malaria-free, but it is now the most commonly imported disease. The aim of the study was to analyse the trend of imported malaria cases in Parma, Italy, during January 2013–June 2017, reporting also the treatment and the outcome of cases, exploring the comparison of the three diagnostic tests used for malaria diagnosis: microscopy, immunochromatographic assay (ICT) (BinaxNOW^®) and Real-time PCR assays detecting Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, Plasmodium ovale curtisi, Plasmodium ovale wallikeri, and Plasmodium knowlesi.

Results

Of the 288 patients with suspected malaria, 87 were positive by microscopy: 73 P. falciparum, 2 P. vivax, 8 P. ovale, 1 P. vivax/P. ovale, 1 P. malariae and 2 Plasmodium sp. All samples were positive by ICT except 6. Plasmodial DNA was revealed in the 87 cases and in 2 additional cases showing P. falciparum-specific bands by ICT, as follows: 75 P. falciparum, 2 P. vivax, 6 P. ovale curtisi, 3 P. ovale wallikeri, 1 P. malariae, and 2 mixed infections. 72 patients were foreigners and 17 Italians travelling for tourism or business. The majority of these patients presented with fever at blood collection and did not have chemoprophylaxis. No fatal cases were observed and the drug mostly used was quinine observing a negative blood smear or a parasitaemia < 0.001% after 48–72 h’ therapy.

Conclusions

The study shows an update and a thorough analysis of imported malaria cases in the area of Parma during 4.5 years from the point of view of the total case management, clinical and diagnostic. The prevalence of malaria in such area in the considered period was especially due to immigrants mostly from Africa. Molecular methods were more sensitive and specific than microscopy and ICT, both detecting additional cases of P. falciparum malaria missed by microscopy and correctly identifying the Plasmodium species of medical interest. The data reported in this study may stimulate the clinicians in non-endemic areas to suspect malaria also in cases, where the most typical symptoms are absent, and the parasitologists to confirm the results of microscopy, remaining the reference method, with molecular methods to avoid misdiagnosis.