Molecular malaria diagnostics: A systematic review and meta-analysis

Molecular tools are crucial for malaria elimination

The eradication of Plasmodium parasites, responsible for malaria, is a daunting global public health task. It requires a comprehensive approach that addresses symptomatic, asymptomatic, and submicroscopic cases. Overcoming this challenge relies on harnessing the power of molecular diagnostic tools, as traditional methods like microscopy and rapid diagnostic tests fall short in detecting low parasitaemia, contributing to the persistence of malaria transmission. By precisely identifying patients of all types and effectively characterizing malaria parasites, molecular tools may emerge as indispensable allies in the pursuit of malaria elimination. Furthermore, molecular tools can also provide valuable insights into parasite diversity, drug resistance patterns, and transmission dynamics, aiding in the implementation of targeted interventions and surveillance strategies. In this review, we explore the significance of molecular tools in the pursuit of malaria elimination, shedding light on their key contributions and potential impact on public health.

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.

Development and evaluation of PlasmoPod: A cartridge-based nucleic acid amplification test for rapid malaria diagnosis and surveillance

Malaria surveillance is hampered by the widespread use of diagnostic tests with low sensitivity. Adequate molecular malaria diagnostics are often only available in centralized laboratories. PlasmoPod is a novel cartridge-based nucleic acid amplification test for rapid, sensitive, and quantitative detection of malaria parasites. PlasmoPod is based on reverse-transcription quantitative polymerase chain reaction (RT-qPCR) of the highly abundant Plasmodium spp. 18S ribosomal RNA/DNA biomarker and is run on a portable qPCR instrument which allows diagnosis in less than 30 minutes. Our analytical performance evaluation indicates that a limit-of-detection as low as 0.02 parasites/μL can be achieved and no cross-reactivity with other pathogens common in malaria endemic regions was observed. In a cohort of 102 asymptomatic individuals from Bioko Island with low malaria parasite densities, PlasmoPod accurately detected 83 cases, resulting in an overall detection rate of 81.4%. Notably, there was a strong correlation between the Cq values obtained from the reference RT-qPCR assay and those obtained from PlasmoPod. In an independent cohort, using dried blood spots from malaria symptomatic children living in the Central African Republic, we demonstrated that PlasmoPod outperforms malaria rapid diagnostic tests based on the PfHRP2 and panLDH antigens as well as thick blood smear microscopy. Our data suggest that this 30-minute sample-to-result RT-qPCR procedure is likely to achieve a diagnostic performance comparable to a standard laboratory-based RT-qPCR setup. We believe that the PlasmoPod rapid NAAT could enable widespread accessibility of high-quality and cost-effective molecular malaria surveillance data through decentralization of testing and surveillance activities, especially in elimination settings.

Laboratory evaluation of the miniature direct-on-blood PCR nucleic acid lateral flow immunoassay (mini-dbPCR-NALFIA), a simplified molecular diagnostic test for Plasmodium

BACKGROUND

Point-of-care diagnosis of malaria is currently based on microscopy and rapid diagnostic tests. However, both techniques have their constraints, including poor sensitivity for low parasitaemias. Hence, more accurate diagnostic tests for field use and routine clinical settings are warranted. The miniature direct-on-blood PCR nucleic acid lateral flow immunoassay (mini-dbPCR-NALFIA) is an innovative, easy-to-use molecular assay for diagnosis of malaria in resource-limited settings. Unlike traditional molecular methods, mini-dbPCR-NALFIA does not require DNA extraction and makes use of a handheld, portable thermal cycler that can run on a solar-charged power pack. Result read-out is done using a rapid lateral flow strip enabling differentiation of Plasmodium falciparum and non-falciparum malaria infections. A laboratory evaluation was performed to assess the performance of the mini-dbPCR-NALFIA for diagnosis of pan-Plasmodium and P. falciparum infections in whole blood.

METHODS

Diagnostic accuracy of the mini-dbPCR-NALFIA was determined by testing a set of Plasmodium-positive blood samples from returned travellers (n = 29), and Plasmodium-negative blood samples from travellers with suspected malaria (n = 23), the Dutch Blood Bank (n = 19) and intensive care patients at the Amsterdam University Medical Centers (n = 16). Alethia Malaria (LAMP) with microscopy for species differentiation were used as reference. Limit of detection for P. falciparum was determined by 23 measurements of a dilution series of a P. falciparum culture. A fixed sample set was tested three times by the same operator to evaluate the repeatability, and once by five different operators to assess the reproducibility.

RESULTS

Overall sensitivity and specificity of the mini-dbPCR-NALFIA were 96.6% (95% CI, 82.2%-99.9%) and 98.3% (95% CI, 90.8%-100%). Limit of detection for P. falciparum was 10 parasites per microlitre of blood. The repeatability of the assay was 93.7% (95% CI, 89.5%-97.8%) and reproducibility was 84.6% (95% CI, 79.5%-89.6%).

CONCLUSIONS

Mini-dbPCR-NALFIA is a sensitive, specific and robust method for molecular diagnosis of Plasmodium infections in whole blood and differentiation of P. falciparum. Incorporation of a miniature thermal cycler makes the assay well-adapted to resource-limited settings. A phase-3 field trial is currently being conducted to evaluate the potential implementation of this tool in different malaria transmission areas.

A rapid multiplex assay of human malaria parasites by digital PCR

BACKGROUND

Blood smear examination through traditional optical microscopy is the gold standard for malaria diagnosis. However, it imposes strict requirements for operational staff and its sensitivity cannot perfectly satisfy the needs of clinical requirements. More sensitive and accurate modern technologies should be applied to this field. Digital PCR (dPCR), as an absolute quantification detection method, can serve as an effective tool to facilitate the diagnosis and classification of different malaria species.

OBJECTIVE

We aimed to establish a new multiplex dPCR detection system for four main Plasmodium species: P. vivax, P. falciparum, P. ovale and P. malariae, which can distinguish exact species of malaria by one PCR reaction.

METHODS

A total of 39 patients were identified as malaria-positive by microscopic examination in Huashan Hospital from 2016 to 2021; seventy blood samples from these patients were collected. Additionally, 20 healthy individuals, 20 patients with fever and 6 patients with other types of blood parasites infection were also included in this study. Each blood sample was subjected to examination by both blood smears and dPCR. By optimizing four different fluorescence-labeled probes in one reaction system, dPCR permitted the performance of accurate quantitation and working out the exact number of copies of malaria DNA per microliter in whole blood. Rapid diagnostic tests were also conducted to verify part of the results obtained by dPCR.

RESULTS

The dPCR system was able to make rapid diagnosis and quantification of malaria DNA samples. The analytical sensitivity of multiplex dPCR was as low as 0.557 copies/μL (95% CI 0.521 to 0.607), and it had a sensitivity of 98.0% and a specificity of 100% in clinical samples. Additionally, three multiple malaria co-infection samples have been detected by this dPCR system, including one triple malaria infection case. By testing consecutive daily blood samples of Patient 39, dPCR facilitated monitoring the efficacy of drug treatment. It showed that the DNA concentrations of P. falciparum ranged from 5474 copies/μL to 0 copies/μL, which can reflect the efficacy of antimalarials in real time. This study also found that haemocyte samples (plasma removed) rather than whole blood had higher malaria detection capability and an enhanced positive rate.

CONCLUSION

The multiplex dPCR system newly established here made a substantial contribution in detecting malaria infection at low concentrations. It is suitable for mixed-infection diagnosis and multi-sample continuous monitoring, and presents a promising candidate as an absolute quantitative tool in clinical practice.

Application of a low-cost, specific, and sensitive loop-mediated isothermal amplification (LAMP) assay to detect Plasmodium falciparum imported from Africa

BACKGROUND

Chinese citizens traveling abroad bring back imported malaria cases to China. Current malaria diagnostic tests, including microscopy and antigen-detecting rapid tests, cannot reliably detect low-density infections. To complement existing diagnostic methods, we aimed to develop a new loop-mediated isothermal amplification (LAMP) assay to detect and identify Plasmodium falciparum in Chinese travelers returning from Africa.

METHODS

We developed a miniaturized LAMP assay to amplify the actin I gene of P. falciparum. Each reaction consumed only 25% of the reagents used in a conventional LAMP assay and the same amount of DNA templates used in nested PCR. We evaluated this LAMP assay's performance and compared it to microscopy and a nested PCR assay using 466 suspected malaria cases imported from Africa. We assessed the sensitivity of the new LAMP assay using cultured P. falciparum, clinical samples, and a plasmid construct, allowing unprecedented precision when quantifying the limit of detection.

RESULTS

The new LAMP assay was highly sensitive and detected two more malaria cases than nested PCR. Compared to nested PCR, the sensitivity and specificity of the novel LAMP assay were 100% [95% confidence interval (CI) 98.5-100%] and 99.1% (95% CI 96.7-99.9%), respectively. When evaluated using serial dilutions of the plasmid construct, the detection limit of the new LAMP was as low as 10² copies/μL, 10-fold lower than PCR. The LAMP assay detected 0.01 parasites/μL of blood (equal to 0.04 parasites/μL of DNA) using cultured P. falciparum and 1-7 parasites/μL of blood (4-28 parasites/μL of DNA) in clinical samples, which is as good as or better than previously reported and commercially licensed assays.

CONCLUSION

The novel LAMP assay based on the P. falciparum actin I gene was specific, sensitive, and cost-effective, as it consumes 1/4 of the reagents in a typical LAMP reaction.

Predicting Plasmodium falciparum infection status in blood using a multiplexed bead-based antigen detection assay and machine learning approaches

Background

Plasmodium blood-stage infections can be identified by assaying for protein products expressed by the parasites. While the binary result of an antigen test is sufficient for a clinical result, greater nuance can be gathered for malaria infection status based on quantitative and sensitive detection of Plasmodium antigens and machine learning analytical approaches.

Methods

Three independent malaria studies performed in Angola and Haiti enrolled persons at health facilities and collected a blood sample. Presence and parasite density of P. falciparum infection was determined by microscopy for a study in Angola in 2015 (n = 193), by qRT-PCR for a 2016 study in Angola (n = 208), and by qPCR for a 2012–2013 Haiti study (n = 425). All samples also had bead-based detection and quantification of three Plasmodium antigens: pAldolase, pLDH, and HRP2. Decision trees and principal component analysis (PCA) were conducted in attempt to categorize P. falciparum parasitemia density status based on continuous antigen concentrations.

Results

Conditional inference trees were trained using the known P. falciparum infection status and corresponding antigen concentrations, and PCR infection status was predicted with accuracies ranging from 73–96%, while level of parasite density was predicted with accuracies ranging from 59–72%. Multiple decision nodes were created for both pAldolase and HRP2 antigens. For all datasets, dichotomous infectious status was more accurately predicted when compared to categorization of different levels of parasite densities. PCA was able to account for a high level of variance (>80%), and distinct clustering was found in both dichotomous and categorical infection status.

Conclusions

This pilot study offers a proof-of-principle of the utility of machine learning approaches to assess P. falciparum infection status based on continuous concentrations of multiple Plasmodium antigens.

Phase 3 Evaluation of an Innovative Simple Molecular Test for the Diagnosis of Malaria and Follow-Up of Treatment Efficacy in Pregnant Women in Sub-Saharan Africa (Preg-Diagmal)

The malaria parasite Plasmodium falciparum (Pf) can sequester in the placenta resulting in low density of peripheral parasitemia and consequently in false negative malaria diagnosis (by microscopy) in pregnant women. Moreover, the use of rapid diagnostic tests (RDTs) in diagnostic strategies, including those for the detection of a malaria infection during pregnancy, is constrained by either persistent malaria antigen (histidine-rich protein 2; HRP2) after successful treatment, leading to false positive test results, or by false negative results as previously mentioned due to parasite sequestration (which is further exacerbated due to the low limited of detection [LoD] of conventional RDTs) or to HRP2 deletion. Recently, a direct blood polymerase chain reaction combined with a nucleic acid lateral flow immunoassay (dbPCR-NALFIA) has been developed, which circumvents these challenges and has demonstrated its diagnostic potential in phase 1 and 2 studies. The PREG-DIAGMAL trial presented in this manuscript will assess the diagnostic performance of dbPCR-NALFIA for the diagnostic of malaria in pregnant women and its potential to monitor treatment efficacy in these subjects. The work is ancillary embedded in an ongoing EDCTP funded trial, the PyraPreg project (PACTR202011812241529) in which the safety and efficacy of a newly registered Artemisinin-Based Combination (Pyronaridine-Artesunate) is being evaluated in pregnant women. This is a Phase 3 diagnostic evaluation conducted in 2 African countries: Democratic Republic of the Congo (DRC) and Burkina Faso. Pregnant women fulfilling the inclusion criteria of the PyraPreg study will be also invited to participate in the PREG-DIAGMAL study. Diagnostic accuracy will be assessed following the WHO/TDR guidelines for the evaluation of diagnostics and reported according to STARD principles. Due to the lack of a 100% specific and sensitive standard diagnostic test for malaria, the sensitivity and specificity of the new test will be compared to the available diagnostic practice in place at the selected settings (microscopy and/or RDT) and to quantitative PCR as the reference test. This phase 3 diagnostic study is designed towards the evaluation of the performance of a new diagnostic tool for the screening of malaria and the monitoring of treatment in pregnant women under real conditions life. If successful, the dbPCR-NALFIA could be a valuable tool to add to the diagnostic arsenal for malaria, in particular during pregnancy. Trial registration: Pan African Clinical Trial Registry database (PACTR202203780981413). Registered on 17 March 2022.

Phase 3 evaluation of an innovative simple molecular test for the diagnosis of malaria in different endemic and health settings in sub-Saharan Africa (DIAGMAL)

Background

Rapid Diagnostic Tests (RDTs) have become the cornerstone for the management of malaria in many endemic settings, but their use is constrained for several reasons: (i) persistent malaria antigen (histidine-rich protein 2; HRP2) leading to false positive test results; (ii) hrp2 deletions leading to false negative PfHRP2 results; and (iii) limited sensitivity with a detection threshold of around 100 parasites/μl blood (pLDH- and HRP2-based) leading to false negative tests. Microscopy is still the gold standard for malaria diagnosis, and allows for species determination and quantitation, but requires trained microscopists, maintained microscopes and has detection limit issues. Consequently, there is a pressing need to develop and evaluate more sensitive and accurate diagnostic tests. To address this need we have developed a direct on blood mini PCR-NALFIA test that combines the benefits of molecular biology with low infrastructural requirements and extensive training.

Methods

This is a Phase 3 diagnostic evaluation in 5 African countries. Study sites (Sudan, Ethiopia, Burkina, Kenya and Namibia) were selected to ensure wide geographical coverage of Africa and to address various malaria epidemiological contexts ranging from high transmission to near elimination settings with different clinical scenarios and diagnostic challenges. Study participants will be enrolled at the study health facilities after obtaining written informed consent. Diagnostic accuracy will be assessed following the WHO/TDR guidelines for the evaluation of diagnostics and reported according to STARD principles. Due to the lack of a 100% specific and sensitive standard diagnostic test for malaria, the sensitivity and specificity of the new test will be compared to the available diagnostic practices in place at the selected sites and to quantitative PCR as the reference test.

Discussion

This phase 3 study is designed to validate the clinical performance and feasibility of implementing a new diagnostic tool for the detection of malaria in real clinical settings. If successful, the proposed technology will improve the diagnosis of malaria. Enrolment started in November 2022 (Kenya) with assessment of long term outcome to be completed by 2023 at all recruitment sites.

Trial registration

Pan African Clinical Trial Registry (www.pactr.org) PACTR202202766889963 on 01/02/2022 and ISCRTN (www.isrctn.com/) ISRCTN13334317 on 22/02/2022.

Malaria diagnostic update: From conventional to advanced method

BACKGROUND

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

AIM

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

RESULTS

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

CONCLUSION

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

Malaria in Haiti: A descriptive study on spatial and temporal profile from 2009 to 2018

Background:

Haiti is one of the Caribbean countries where malaria persists. More than 99% of malaria cases are caused by Plasmodium falciparum, the main vector being the mosquito Anopheles albimanus. In this paper, we describe the epidemiological profile of malaria in Haiti between 2009 and 2018.

Methods

We analyzed information on cases reported by the Ministry of Health of Haiti and the World Health Organization (WHO).

Results:

Between 2009 and 2018, 232,479 malaria cases were reported by the Ministry of Public Health and Population (MSPP); an increase in the incidence of malaria in the country in 2010, followed by a decrease in 2011, was primarily observed. Due to recent efforts to reduce malaria by 2020, its incidence declined from 60,130 cases in 2010 to 8,978 cases in 2018. Controversially, in terms of the number of reported cases, the MSPP and WHO report conflicting data. However, the results from both datasets present the same trend in Haiti from 2009 to 2018. The results also illustrate the endemicity of the disease throughout Haiti, both in rural and urban areas, especially along the coast.

Conclusions:

This study emphasizes the need to promote official data collection and analyses, as well as the application of epidemiological surveillance of malaria at the municipal level, for a better understanding of the real impact of malaria on the Haitian population and to create more appropriate interventions.

Comparison of diagnostic performance between conventional and ultrasensitive rapid diagnostic tests for diagnosis of malaria: A systematic review and meta-analysis

Background

Successful malaria treatment, control and elimination programs require accurate, affordable, and field-deployable diagnostic tests. A number of studies have directly compared diagnostic performance between the new ultrasensitive rapid diagnostic test (us-RDT) and conventional rapid diagnostic test (co-RDT) for detecting malaria. Thus, we undertook this review to directly compare pooled diagnostic performance of us-RDT and co-RDT for detection of malaria.

Methods

PubMed, Web of Science, Scopus, Embase, and ProQuest were searched from their inception until 31 January 2021 accompanied by forward and backward citations tracking. Two authors independently assessed the quality of included studies by RevMan5 software (using the QUADAS-2 checklist). Diagnostic accuracy estimates (sensitivity and specificity and others) were pooled using a random-effect model and 95% confidence interval (CI) in Stata 15 software.

Results

Fifteen studies with a total of 20,236 paired co-RDT and us-RDT tests were included in the meta-analysis. Molecular methods (15 studies) and immunoassay test (one study) were used as standard methods for comparison with co-RDT and us-RDT tests. The pooled sensitivity for co-RDT and us-RDT were 42% (95%CI: 25–62%) and 61% (95%CI: 47–73%), respectively, with specificity of 99% (95%CI: 98–100%) for co-RDT, and 99% (95%CI: 96–99%) for us-RDT. In asymptomatic individuals, the pooled sensitivity and specificity of co-RDT were 27% (95%CI: 8–58%) and 100% (95%CI: 97–100%), respectively, while us-RDT had a sensitivity of 50% (95%CI: 33–68%) and specificity of 98% (95%CI: 94–100%). In low transmission settings, pooled sensitivity for co-RDT was 36% (95%CI: 9 76%) and 62% (95%CI: 44 77%) for us RDT, while in high transmission areas, pooled sensitivity for co RDT and us RDT were 62% (95%CI: 39 80%) and 75% (95%CI: 57–87%), respectively.

Conclusion

The us-RDT test showed better performance than co-RDT test, and this characteristic is more evident in asymptomatic individuals and low transmission areas; nonetheless, additional studies integrating a range of climate, geography, and demographics are needed to reliably understand the potential of the us-RDT.

Development of a new peptide-bead coupling method for an all peptide-based Luminex multiplexing assay for detection of Plasmodium falciparum antibody responses

Using a recombinant protein antigen for antibody testing shows a sum of antibody responses to multiple different immune epitopes existing in the protein antigen. In contrast, the antibody testing to an immunogenic peptide epitope reflects a singular antibody response to the individual peptide epitope. Therefore, using a panel of peptide epitopes provides an advantage for profiling multiple singular antibody responses with potential to estimate recent malaria exposure in human infections. However, transitioning from malaria immune epitope peptide-based ELISA to an all peptide bead-based multiplex Luminex assay presents some challenges including variation in the ability of different peptides to bind beads. The aim of this study was to develop a peptide coupling method while demonstrating the utility of these peptide epitopes from multiple stage antigens of Plasmodium falciparum for measuring antibodies. Successful coupling of peptide epitopes to beads followed three steps: 1) development of a peptide tag appended to the C-terminus of each peptide epitope consisting of beta-alanine-lysine (x 4)--cysteine, 2) bead modification with a high concentration of adipic acid dihydrazide, and 3) use of the peptide epitope as a blocker in place of the traditional choice, bovine serum albumin (BSA). This new method was used to couple 12 peptide epitopes from multiple stage specific antigens of P. falciparum, 1 Anopheles mosquito salivary gland peptide, and 1 Epstein-Barr virus peptide as an assay control. The new method was applied to testing of IgG in pooled samples from 30 individuals with previously repeated malaria exposure in western Kenya and IgM and IgG in samples from 37 U.S. travelers with recent exposure to malaria. The new peptide-bead coupling method and subsequent multiplex Luminex assay showed reliable detection of IgG to all 14 peptides in Kenyan samples. Among 37 samples from U.S. travelers recently diagnosed with malaria, IgM and IgG to the peptide epitopes were detected with high sensitivity and variation. Overall, the U.S. travelers had a much lower positivity rates of IgM than IgG to different peptide epitopes, ranging from a high of 62.2% positive for one epitope to a low of only 5.4% positive for another epitope. In contrast, the travelers had IgG positive rates from 97.3% to 91.9% to various peptide epitopes. Based on the different distribution in IgM and IgG positivity to overall number of peptide epitopes and to the number of pre-erythrocytic, erythrocytic, gametocytic, and salivary stage epitopes at the individual level, four distinct patterns of IgM and IgG responses among the 37 samples from US travelers were observed. Independent peptide-bead coupling and antibody level readout between two different instruments also showed comparable results. Overall, this new coupling method resolves the peptide-bead coupling challenge, is reproducible, and can be applied to any other immunogenic peptide epitopes. The resulting all peptide bead-based multiplex Luminex assay can be expanded to include other peptide epitopes of P. falciparum, different malaria species, or other diseases for surveillance, either in US travelers or endemic areas.

Towards the use of a smartphone imaging-based tool for point-of-care detection of asymptomatic low-density malaria parasitaemia

BACKGROUND

Globally, there are over 200 million cases of malaria annually and over 400,000 deaths. Early and accurate detection of low-density parasitaemia and asymptomatic individuals is key to achieving the World Health Organization (WHO) 2030 sustainable development goals of reducing malaria-related deaths by 90% and eradication in 35 countries. Current rapid diagnostic tests are neither sensitive nor specific enough to detect the low parasite concentrations in the blood of asymptomatic individuals.

METHODS

Here, an imaging-based sensing technique, particle diffusometry (PD), is combined with loop mediated isothermal amplification (LAMP) on a smartphone-enabled device to detect low levels of parasitaemia often associated with asymptomatic malaria. After amplification, PD quantifies the Brownian motion of fluorescent nanoparticles in the solution during a 30 s video taken on the phone. The resulting diffusion coefficient is used to detect the presence of Plasmodium DNA amplicons. The coefficients of known negative samples are compared to positive samples using a one-way ANOVA post-hoc Dunnett's test for confirmation of amplification.

RESULTS

As few as 3 parasite/µL of blood was detectable in 45 min without DNA extraction. Plasmodium falciparum parasites were detected from asymptomatic individuals' whole blood samples with 89% sensitivity and 100% specificity when compared to quantitative polymerase chain reaction (qPCR).

CONCLUSIONS

PD-LAMP is of value for the detection of low density parasitaemia especially in areas where trained personnel may be scarce. The demonstration of this smartphone biosensor paired with the sensitivity of LAMP provides a proof of concept to achieve widespread asymptomatic malaria testing at the point of care.

Molecular Identification and Characterization of Plasmodium ovale curtisi in Field Isolates from Symptomatic Children in North-Central Nigeria

PURPOSE

Plasmodium ovale is not usually the focus of most malaria research or intervention programmes and has lately been termed the neglected human malaria parasites. The parasite exists as two genetically distinct sympatric species namely P. ovale curtisi and P. ovale wallikeri but information on the distribution of P. ovale sub-species is lacking in Nigeria. The objective of this study, therefore, was aimed at characterizing the P. ovale sub-species in isolates from symptomatic individuals in North-central Nigeria.

METHODS

Parasites were identified by light microscopy of Giemsa stained thick and thin blood films. Molecular characterization and confirmation of P. ovale sub-species were done by species-specific nested PCR and sequencing of the small subunit ribosomal RNA (SSUrRNA) gene.

RESULTS

A total of 412 children were enrolled into this study of which 88.6% (n = 365) were positive for Plasmodium species by nested PCR and P. falciparum was predominant. Of the 365 isolates, 4 (1.1%) had P. ovale infections and of these, 3 (0.8%) were mixed species infections of P. ovale with P. falciparum. DNA sequence analysis confirmed that all the four P. ovale parasites were P. ovale curtisi as their sequences were 99-100% identical to previously published P. ovale curtisi sequences in the GenBank and they cluster with the P. ovale curtisi sequences by phylogeny.

CONCLUSION

Our findings demonstrate the occurrence of P. ovale curtisi in the study area. This has implications for public health and malaria elimination programmes, since they also serve as potential risk to travellers from malaria-free regions.

Accuracy of malaria diagnostic tests performed on non-invasively collected samples: a systematic review and meta-analysis

Background

During the last decade, many studies have assessed the performance of malaria tests on non-invasively collected specimens, but no systematic review has hitherto estimated the overall performance of these tests. We report here the first meta-analysis estimating the diagnostic performance of malaria diagnostic tests performed on saliva, urine, faeces, skin odour (‘sniff and tell’) and hair, using either microscopy or PCR on blood sample as reference test.

Methods

We searched on PubMed, EMBASE, African Journals Online and Cochrane Infectious Diseases from inception until 19 January 2021 for relevant primary studies. A random effects model was used to estimate the overall performance of various diagnostic methods on different types of specimen.

Results

Eighteen studies providing 30 data sets were included in the meta-analysis. The overall sensitivity, specificity and diagnostic OR (DOR) of PCR were 84.5% (95% CI 79.3% to 88.6%), 97.3% (95% CI 95.3% to 98.5%) and 184.9 (95% CI 95.8 to 356.9) in saliva, respectively; 57.4% (95% CI 41.4% to 72.1%), 98.6% (95% CI 97.3% to 99.3%) and 47.2 (95% CI 22.1 to 101.1) in urine, respectively. The overall sensitivity, specificity and DOR of rapid diagnostic test for malaria in urine was 59.8% (95% CI 40.0% to 76.9%), 96.9% (95% CI 91.0% to 99.0%) and 30.8 (95% CI:23.5 to 40.4).

Conclusion

In settings where PCR is available, saliva and urine samples should be considered for PCR-based malaria diagnosis only if blood samples cannot be collected. The performance of rapid diagnostic testing in the urine is limited, especially its sensitivity. Malaria testing on non-invasively collected specimen still needs substantial improvement.

An Automated Microscopic Malaria Parasite Detection System Using Digital Image Analysis

Rapid diagnosis and parasitemia measurement is crucial for management of malaria. Microscopic examination of peripheral blood (PB) smears is the gold standard for malaria detection. However, this method is labor-intensive. Here, we aimed to develop a completely automated microscopic system for malaria detection and parasitemia measurement. The automated system comprises a microscope, plastic chip, fluorescent dye, and an image analysis program. Analytical performance was evaluated regarding linearity, precision, and limit of detection and was compared with that of conventional microscopic PB smear examination and flow cytometry. The automated microscopic malaria parasite detection system showed a high degree of linearity for Plasmodium falciparum culture (R² = 0.958, p = 0.005) and Plasmodium vivax infected samples (R² = 0.931, p = 0.008). Precision was defined as the %CV of the assay results at each level of parasitemia and the %CV value for our system was lower than that for microscopic examination for all densities of parasitemia. The limit of detection analysis showed 95% probability for parasite detection was 0.00066112%, and a high correlation was observed among all three methods. The sensitivity and specificity of the system was both 100% (n = 21/21) and 100% (n = 50/50), respectively, and the system correctly identified all P. vivax and P. falciparum samples. The automated microscopic malaria parasite detection system offers several advantages over conventional microscopy for rapid diagnosis and parasite density monitoring of malaria.

Fully automated point-of-care differential diagnosis of acute febrile illness

Background

In this work, a platform was developed and tested to allow to detect a variety of candidate viral, bacterial and parasitic pathogens, for acute fever of unknown origin. The platform is based on a centrifugal microfluidic cartridge, the LabDisk (“FeverDisk” for the specific application), which integrates all necessary reagents for sample-to-answer analysis and is processed by a compact, point-of-care compatible device.

Methodology/Principal findings

A sample volume of 200 μL per FeverDisk was used. In situ extraction with pre-stored reagents was achieved by bind-wash-elute chemistry and magnetic particles. Enzymes for the loop-mediated isothermal amplification (LAMP) were pre-stored in lyopellet form providing stability and independence from the cold chain. The total time to result from sample inlet to read out was 2 h. The proof-of-principle was demonstrated in three small-scale feasibility studies: in Dakar, Senegal and Khartoum, Sudan we tested biobanked samples using 29 and 9 disks, respectively; in Reinfeld, Germany we tested spiked samples and analyzed the limit of detection using three bacteria simultaneously spiked in whole blood using 15 disks. Overall during the three studies, the FeverDisk detected dengue virus (different serotypes), chikungunya virus, Plasmodium falciparum, Salmonella enterica Typhi, Salmonella enterica Paratyphi A and Streptococcus pneumoniae.

Conclusions/Significance

The FeverDisk proved to be universally applicable as it successfully detected all different types of pathogens as single or co-infections, while it also managed to define the serotype of un-serotyped dengue samples. Thirty-eight FeverDisks at the two African sites provided 59 assay results, out of which 51 (86.4%) were confirmed with reference assay results. The results provide a promising outlook for future implementation of the platform in larger prospective clinical studies for defining its clinical sensitivity and specificity. The technology aims to provide multi-target diagnosis of the origins of fever, which will help fight lethal diseases and the incessant rise of antimicrobial resistance.

Infectious diseases in tropical regions may have a variety of viral, bacterial or parasitic origins and a patient may suffer from several diseases simultaneously, each presenting with acute fever as a clinical symptom. This makes it difficult to determine the origin of the pathogen causing the disease(s). In addition to the endemic infectious diseases, outbreaks of epidemics frequently complicate diagnostic demands. Accurate diagnosis for proper patient management requires the utilization of highly sensitive and specific, rapid, easy-to-use diagnostic tools compatible with point-of-care settings. We describe the use of a disk-shaped microfluidic platform, the “FeverDisk”, for differential diagnosis of acute fever. Our FeverDisk platform demonstrated its capability to detect bacteria, viruses and parasites that are typical of tropical single and co-infections from biobanked samples within only 2 hours and in very good agreement with reference method results. This, in combination with its easy-to-use and point-of-care compatible nature, render our platform a promising candidate for detection of tropical diseases and precise identification of the cause of acute fever, in endemic and epidemic settings. Future work will involve extensive clinical characterization of the platform in prospective studies.

Performance and Application of Commercially Available Loop-Mediated Isothermal Amplification (LAMP) Kits in Malaria Endemic and Non-Endemic Settings

Loop-mediated isothermal amplification (LAMP) is a sensitive molecular tool suitable for use as a near point-of-care test for the diagnosis of malaria. Recent meta-analyses have detailed high sensitivity and specificity of malaria LAMP when compared to microscopy, rapid diagnostic tests, and polymerase chain reaction in both endemic and non-endemic settings. Despite this, the use of malaria LAMP has primarily been limited to research settings to date. In this review, we aim to assess to what extent commercially available malaria LAMP kits have been applied in different settings, and to identify possible obstacles that may have hindered their use from being adopted further. In order to address this, we conducted a literature search in PubMed.gov using the search terms (((LAMP) OR (Loop-mediated isothermal amplification)) AND ((Malaria) OR (Plasmodium))). Focusing primarily on studies employing one of the commercially available kits, we then selected three key areas of LAMP application for further review: the performance and application of LAMP in malaria endemic settings including low transmission areas; LAMP for malaria screening during pregnancy; and malaria LAMP in returning travelers in non-endemic settings.

Rapid diagnostic tests for Plasmodium vivax malaria in endemic countries

BACKGROUND

Plasmodium vivax (P vivax) is a focus of malaria elimination. It is important because P vivax and Plasmodium falciparum infection are co-endemic in some areas. There are asymptomatic carriers of P vivax, and the treatment for P vivax and Plasmodium ovale malaria differs from that used in other types of malaria. Rapid diagnostic tests (RDTs) will help distinguish P vivax from other malaria species to help treatment and elimination. There are RDTs available that detect P vivax parasitaemia through the detection of P vivax-specific lactate dehydrogenase (LDH) antigens.

OBJECTIVES

To assess the diagnostic accuracy of RDTs for detecting P vivax malaria infection in people living in malaria-endemic areas who present to ambulatory healthcare facilities with symptoms suggestive of malaria; and to identify which types and brands of commercial tests best detect P vivax malaria.

SEARCH METHODS

We undertook a comprehensive search of the following databases up to 30 July 2019: Cochrane Infectious Diseases Group Specialized Register; Central Register of Controlled Trials (CENTRAL), published in the Cochrane Library; MEDLINE (PubMed); Embase (OVID); Science Citation Index Expanded (SCI-EXPANDED) and Conference Proceedings Citation Index-Science (CPCI-S), both in the Web of Science.

SELECTION CRITERIA

Studies comparing RDTs with a reference standard (microscopy or polymerase chain reaction (PCR)) in blood samples from patients attending ambulatory health facilities with symptoms suggestive of malaria in P vivax-endemic areas.

DATA COLLECTION AND ANALYSIS

For each included study, two review authors independently extracted data using a pre-piloted data extraction form. The methodological quality of the studies were assessed using a tailored Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool. We grouped studies according to commercial brand of the RDT and performed meta-analysis when appropriate. The results given by the index tests were based on the antibody affinity (referred to as the strength of the bond between an antibody and an antigen) and avidity (referred to as the strength of the overall bond between a multivalent antibody and multiple antigens). All analyses were stratified by the type of reference standard. The bivariate model was used to estimate the pooled sensitivity and specificity with 95% confidence intervals (CIs), this model was simplified when studies were few. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 10 studies that assessed the accuracy of six different RDT brands (CareStart Malaria Pf/Pv Combo test, Falcivax Device Rapid test, Immuno-Rapid Malaria Pf/Pv test, SD Bioline Malaria Ag Pf/Pv test, OnSite Pf/Pv test and Test Malaria Pf/Pv rapid test) for detecting P vivax malaria. One study directly compared the accuracy of two RDT brands. Of the 10 studies, six used microscopy, one used PCR, two used both microscopy and PCR separately and one used microscopy corrected by PCR as the reference standard. Four of the studies were conducted in Ethiopia, two in India, and one each in Bangladesh, Brazil, Colombia and Sudan. The studies often did not report how patients were selected. In the patient selection domain, we judged the risk of bias as unclear for nine studies. We judged all studies to be of unclear applicability concern. In the index test domain, we judged most studies to be at low risk of bias, but we judged nine studies to be of unclear applicability concern. There was poor reporting on lot testing, how the RDTs were stored, and background parasitaemia density (a key variable determining diagnostic accuracy of RDTs). Only half of the included studies were judged to be at low risk of bias in the reference standard domain, Studies often did not report whether the results of the reference standard could classify the target condition or whether investigators knew the results of the RDT when interpreting the results of the reference standard. All 10 studies were judged to be at low risk of bias in the flow and timing domain. Only two brands were evaluated by more than one study. Four studies evaluated the CareStart Malaria Pf/Pv Combo test against microscopy and two studies evaluated the Falcivax Device Rapid test against microscopy. The pooled sensitivity and specificity were 99% (95% CI 94% to 100%; 251 patients, moderate-certainty evidence) and 99% (95% CI 99% to 100%; 2147 patients, moderate-certainty evidence) for CareStart Malaria Pf/Pv Combo test. For a prevalence of 20%, about 206 people will have a positive CareStart Malaria Pf/Pv Combo test result and the remaining 794 people will have a negative result. Of the 206 people with positive results, eight will be incorrect (false positives), and of the 794 people with a negative result, two would be incorrect (false negative). For the Falcivax Device Rapid test, the pooled sensitivity was 77% (95% CI: 53% to 91%, 89 patients, low-certainty evidence) and the pooled specificity was 99% (95% CI: 98% to 100%, 621 patients, moderate-certainty evidence), respectively. For a prevalence of 20%, about 162 people will have a positive Falcivax Device Rapid test result and the remaining 838 people will have a negative result. Of the 162 people with positive results, eight will be incorrect (false positives), and of the 838 people with a negative result, 46 would be incorrect (false negative).

AUTHORS' CONCLUSIONS

The CareStart Malaria Pf/Pv Combo test was found to be highly sensitive and specific in comparison to microscopy for detecting P vivax in ambulatory healthcare in endemic settings, with moderate-certainty evidence. The number of studies included in this review was limited to 10 studies and we were able to estimate the accuracy of 2 out of 6 RDT brands included, the CareStart Malaria Pf/Pv Combo test and the Falcivax Device Rapid test. Thus, the differences in sensitivity and specificity between all the RDT brands could not be assessed. More high-quality studies in endemic field settings are needed to assess and compare the accuracy of RDTs designed to detect P vivax.

Ultra-sensitive RDT performance and antigen dynamics in a high-transmission Plasmodium falciparum setting in Mali

BACKGROUND

The recent expansion of tools designed to accurately quantify malaria parasite-produced antigens has enabled us to evaluate the performance of rapid diagnostic tests (RDTs) as a function of the antigens they detect-typically histidine rich protein 2 (HRP2) or lactate dehydrogenase (LDH).

METHODS

For this analysis, whole blood specimens from a longitudinal study in Bancoumana, Mali were used to evaluate the performance of the ultra-sensitive HRP2-based Alere™ Malaria Ag P.f RDT (uRDT). The samples were collected as part of a transmission-blocking vaccine trial in a high transmission region for Plasmodium falciparum malaria. Furthermore, antigen dynamics after successful anti-malarial drug treatment were evaluated in these samples using the Q-Plex Human Malaria Array (4-Plex) to quantify antigen concentrations.

RESULTS

The uRDT had a 50% probability of a positive result at 207 pg/mL HRP2 [95% credible interval (CrI) 160-268]. Individuals with symptomatic infection remained positive by uRDT for a median of 33 days [95% confidence interval (CI) 28-47] post anti-malarial drug treatment. Biphasic exponential decay models accurately captured the population level post-treatment dynamics of both HRP2 and Plasmodium LDH (pLDH), with the latter decaying more rapidly. Motivated by these differences in rates of decay, a novel algorithm that used HRP2:pLDH ratios to predict if an individual had active versus recently cleared P. falciparum infection was developed. The algorithm had 77.5% accuracy in correctly classifying antigen-positive individuals as those with and without active infection.

CONCLUSIONS

These results characterize the performance of the ultra-sensitive RDT and demonstrate the potential for emerging antigen-quantifying technologies in the field of malaria diagnostics to be helpful tools in distinguishing between active versus recently cleared malaria infections.

Diagnosis of clinical malaria in endemic settings

INTRODUCTION

Malaria continues to be a major global health problem, with over 228 million cases and 405,000 deaths estimated to occur annually. Rapid and accurate diagnosis of malaria is essential to decrease the burden and impact of this disease, particularly in children. We aimed to review the main available techniques for the diagnosis of clinical malaria in endemic settings and explore possible future options to improve its rapid recognition.

AREAS COVERED

literature relevant to malaria diagnosis was identified through electronic searches in Pubmed, with no language or date restrictions and limited to humans.

EXPERT OPINION

Light microscopy is still considered the gold standard method for malaria diagnosis and continues to be at the frontline of malaria diagnosis. However, technologies as rapid diagnostic tests, mainly those who detect histidine-rich protein-2, offer an accurate, rapid and affordable alternative for malaria diagnosis in endemic areas. They are now the technique most extended in endemic areas for parasitological confirmation. In these settings, PCR-based assays are usually restricted to research and they are not currently helpful in the management of clinical malaria. Other technologies, such as isothermal methods could be an interesting and alternative approach to PCR in the future.

Method for Malaria Diagnosis Based on Extractions of Samples Using Non-Invasive Techniques: An Opportunity for the Nursing Clinical Practice

Malaria has been for millennia one of the best known and most destructive diseases affecting humans. Its high impact has aroused great interest for the development of new effective and reliable diagnostic techniques. Recently it has been recently published that hairs from mammal hosts are able to capture, hold and finally remove foreign DNA sequences of Leishmania parasites. The aim of this study was to check if Plasmodium falciparum (P. falciparum) DNA remains stable in blood samples deposited in Whatman paper after suffering different transport and storage conditions, and to compare the sensitivity of these results with those offered by thick a smear and Rapid Diagnostic Test, and besides to examine whether P. falciparum DNA would be detected and quantified by Real time quantitative PCR (qPCR) from hairs of people with different types of malaria. P. falciparum Histidine Repeat Protein II (pHRP-II) antigen detection and P. falciparum DNA were detected in 18 of 19 dry blood samples adhered to Whatman paper (94.74%), besides, Plasmodium DNA was also detected in seven out of 19 hair samples analyzed (36.84%), remaining stable until analysis for several months under the exposure to different environmental conditions. Although the sensitivity of PCR for the diagnosis of malaria in hair samples is not as high as blood analysis, the study of Plasmodium DNA presence in blood and hair could constitute a complementary tool with numerous advantages in sample collection, transport and storage. We suggest that the method could be also applied to medical, forensic and paleo-parasitological diagnosis, not only for malaria but also for searching many other pathogens in hair samples.

Systematic review and meta-analysis of diagnostic accuracy of loop-mediated isothermal amplification (LAMP) methods compared with microscopy, polymerase chain reaction and rapid diagnostic tests for malaria diagnosis

BACKGROUND

Diagnosis is a challenging issue for eliminating malaria. Loop-mediated isothermal amplification (LAMP) could be an alternative to conventional methods. This study aimed to evaluate the diagnostic accuracy of LAMP for malaria compared with microscopy, polymerase chain reaction (PCR) and rapid diagnostic tests (RDTs).

METHODS AND DESIGN

MEDLINE, Web of Science and Scopus were searched from inception to 1 July 2019. Prospective and retrospective, randomised and non-randomised, mono-center and multi-center studies, including symptomatic or asymptomatic patients, that reported one LAMP method and one comparator (microscopy, RDT or PCR) were included. PROSPERO registration number: CRD42017075186.

RESULTS

Sixty-six studies published between 2006 and 2019 were included, leading to the analysis of 30,641 LAMP tests. The pooled sensitivity of LAMP remained between 96% and 98%, whichever the comparator. The pooled specificity of LAMP was around 95%, but was a little higher if the best PCR studies were considered. The AUC was found to be >0.98, whichever the subgroup of studies was considered. Diagnostic odds ratio (DOR) was found to be around 1000 for all subgroups, except for Plasmodium vivax.

CONCLUSION

This meta-analysis confirmed that the LAMP method is robust for diagnosing malaria, both in symptomatic and asymptomatic people. Thus, the impact of LAMP for controlling malaria is expected to be important.

Submicroscopic malaria infection is not associated with fever in cross-sectional studies in Malawi

Background

Submicroscopic Plasmodium falciparum infections are widespread in many areas. However, the contribution of these infections to symptomatic malaria is not well understood. This study evaluated whether participants with submicroscopic P. falciparum infections have higher prevalence of fever than uninfected participants in southern Malawi.

Methods

A total of 16,650 children and adults were enrolled in the course of six cross-sectional surveys during the dry season (October–November) and after the rainy season (April–May) between 2012 and 2014 in three districts in southern Malawi. Demographic and socioeconomic data were collected in conjunction with data on clinical histories, use of malaria preventive measures, and anti-malarial medication taken within 2 weeks of the survey. Axillary temperatures were measured, and blood samples were collected for P. falciparum detection by microscopy and PCR. Participants without malaria parasites detected on microscopy but with a positive PCR for P. falciparum were defined as having submicroscopic infection. Fever was defined as having any one of: reported fever in the past 2 weeks, reported fever in the past 48 h, or a temperature of ≥ 37.5 °C measured at the time of interview.

Results

Submicroscopic P. falciparum infections and fever were both detected in 9% of the study population. In the final analysis adjusted for clustering within household and enumeration area, having submicroscopic P. falciparum infection was associated with reduced odds of fever in the dry season (odds ratio = 0.52; 95% CI 0.33–0.82); the association in the rainy season did not achieve statistical significance (odds ratio = 1.20; 95% CI 0.91–1.59). The association between submicroscopic infection and fever was consistent across all age groups. When the definition of fever was limited to temperature of ≥ 37.5 °C measured at the time of interview, the association was not statistically significant in either the rainy or dry season.

Conclusions

In this series of cross-sectional studies in southern Malawi, submicroscopic P. falciparum infection was not associated with increased risk of fever. Submicroscopic detection of the malaria parasite is important in efforts to decrease transmission but is not essential for the clinical recognition of malaria disease.

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.

Loop-mediated isothermal amplification (LAMP) test for diagnosis of uncomplicated malaria in endemic areas: a meta-analysis of diagnostic test accuracy

Background

The global malaria decline has stalled and only a few countries are pushing towards pre-elimination. The aim of the malaria elimination phase is interruption of local transmission of a specified malaria parasite in a defined geographical area. New and improved screening tools and strategies are required for detection and management of very low-density parasitaemia in the field. The objective of this study was to synthesize evidence on the diagnostic accuracy of loop-mediated isothermal amplification (LAMP) test for the detection of malaria parasites among people living in endemic areas.

Methods

This study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis for Diagnostic Test Accuracy (PRISMA-DTA) guideline. Relevant studies in the health-related electronic databases were searched. According to the criteria set for this study, eligible studies were identified. The quality of included studies was evaluated with the use of a quality assessment checklist. A summary performance estimates such as pooled sensitivity and specificity were stratified by type of LAMP. Bivariate model for data analyses was applied. Summary receiver operating characteristics plots were created to display the results of individual studies in a receiver operating characteristics space. Meta-regression analysis was performed to investigate the sources of heterogeneity among individual studies.

Results

Twenty-seven studies across 17 endemic countries were identified. The vast majority of studies were with unclear risk of bias in the selection of index test. Overall, the pooled test performances were high for Pan LAMP (sensitivity: 0.95, 95% CI 0.91 to 0.97; specificity: 0.98, 95% CI 0.95 to 0.99), Plasmodium falciparum (Pf) LAMP (sensitivity: 0.96, 95% CI 0.94 to 0.98; specificity: 0.99, 95% CI 0.96 to 1.00) or for Plasmodium vivax (Pv) LAMP from 6 studies (sensitivity: 0.98, 95% CI 0.92 to 0.99; specificity: 0.99, 95% CI 0.72 to 1.00). The area under the curve for Pan LAMP (0.99, 95% CI 0.98–1.00), Pf LAMP (0.99, 95% CI 0.97–0.99) and Pv LAMP was (1.00, 95% CI 0.98–1.00) indicated that the diagnostic performance of these tests were within the excellent accuracy range. Meta-regression analysis showed that sample size had the greatest impact on test performance, among other factors.

Conclusions

The current findings suggest that LAMP-based assays are appropriate for detecting low-level malaria parasite infections in the field and would become valuable tools for malaria control and elimination programmes. Future well-designed larger sample studies on LAMP assessment in passive and active malaria surveillances that use PCR as the reference standard and provide sufficient data to construct 2 × 2 diagnostic table are needed.

Update on the major imported protozoan infections in travelers and migrants

Globalization has contributed to the emergence of specific parasitic diseases in novel geographical areas, and in these regions, these infections in travelers and immigrants may cause a considerable burden of disease. Timely diagnosis and treatment of protozoan infections to decrease mortality and prevent associated complications are essential. In this respect, the increased availability of specific DNA-detection procedures has improved the diagnosis of many imported parasitic infections. Travelers and immigrants with associated comorbidities or immunosuppression may pose a special challenge regarding management. An updated review of the main protozoan infections in mobile populations (malaria, Chagas disease, leishmaniasis, enteric protozoan infections) is provided, focusing on the changing epidemiology of these diseases, recent developments in diagnosis and management and the possibility of local transmission of imported infections.

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.

Beyond Blood Smears: Qualification of Plasmodium 18S rRNA as a Biomarker for Controlled Human Malaria Infections

18S rRNA is a biomarker that provides an alternative to thick blood smears in controlled human malaria infection (CHMI) trials. We reviewed data from CHMI trials at non-endemic sites that used blood smears and Plasmodium 18S rRNA/rDNA biomarker nucleic acid tests (NATs) for time to positivity. We validated a multiplex quantitative reverse transcription–polymerase chain reaction (qRT-PCR) for Plasmodium 18S rRNA, prospectively compared blood smears and qRT-PCR for three trials, and modeled treatment effects at different biomarker-defined parasite densities to assess the impact on infection detection, symptom reduction, and measured intervention efficacy. Literature review demonstrated accelerated NAT-based infection detection compared with blood smears (mean acceleration: 3.2–3.6 days). For prospectively tested trials, the validated Plasmodium 18S rRNA qRT-PCR positivity was earlier (7.6 days; 95% CI: 7.1–8.1 days) than blood smears (11.0 days; 95% CI: 10.3–11.8 days) and significantly preceded the onset of grade 2 malaria-related symptoms (12.2 days; 95% CI: 10.6–13.3 days). Discrepant analysis showed that the risk of a blood smear–positive, biomarker-negative result was negligible. Data modeling predicted that treatment triggered by specific biomarker-defined thresholds can differentiate complete, partial, and non-protective outcomes and eliminate many grade 2 and most grade 3 malaria-related symptoms post-CHMI. Plasmodium 18S rRNA is a sensitive and specific biomarker that can justifiably replace blood smears for infection detection in CHMI trials in non-endemic settings. This study led to biomarker qualification through the U.S. Food and Drug Administration for use in CHMI studies at non-endemic sites, which will facilitate biomarker use for the qualified context of use in drug and vaccine trials.

Evaluation of the multiplex real-time PCR assays RealStar malaria S&T PCR kit 1.0 and FTD malaria differentiation for the differentiation of Plasmodium species in clinical samples

BACKGROUND

Two commercial PCR assays were assessed in a retrospective study to determine their reliability as tools for the differentiation of Plasmodium species in human blood.

METHODS

A total of 1022 blood samples from 817 patients with suspected or confirmed malaria submitted to the German National Reference Centre for Tropical Pathogens were subjected to malaria microscopy using thick and thin blood films as well as to a genus-specific malaria real-time PCR. Parasite-positive samples were analysed by RealStar Malaria S&T PCR Kit 1.0 (altona Diagnostics) and FTD Malaria Differentiation (Fast Track Diagnostics) multiplex real-time PCR assays targeting species-specific Plasmodium DNA.

RESULTS

Out of the 1022 blood samples, 247 (24.2%) tested positive for Plasmodium spp. The two multiplex assays showed rather similar performance characteristics and provided concordant species information in 98.9% of samples positive by malaria microscopy and in 95.1% (RealStar) and 96.8% (FTD) of samples positive by genus-specific PCR. Compared to FTD, RealStar revealed slightly reduced sensitivity for submicroscopic, low-level P. falciparum infections, while FTD was unable to detect P. knowlesi.

CONCLUSIONS

The two commercial malaria PCR assays assessed are suitable for discriminating Plasmodium species in clinical samples, and can provide additional information in cases of microscopically uncertain findings.

Malaria Prevalence in a Low Transmission Area, Jazan District of Southwestern Saudi Arabia

Detailed description of malaria in low transmission areas is crucial for elimination. The current study aimed to provide a comprehensive description for malaria transmission in Jazan, a low transmission district, southwestern Saudi Arabia. Patients at a tertiary care hospital were recruited in our study between August 2016 and September 2018. Malaria diagnosis was performed through a species-specific nested polymerase chain reaction (nested PCR), microscopy and Paramax-3TM rapid detection test (RDT). Malaria was detected in 30 patients by the PCR, with point prevalence of 10.9%. Of these malaria infections, 80% was imported, 26.6% was asymptomatic and 23.3% was sub-microscopic. Malaria was reported throughout the year, with February/March and September/October peaks. Infection was significantly more in males than in females (P=0.01). Likewise, infections were detected more in febrile than in non-febrile patients (P=0.01). Adult aged 15-24 years, fever and travel were identified as high-risk factors. Malaria was primarily attributed to Plasmodium falciparum mono-infections, followed by P. vivax mono-infections and lastly to falciparum/vivax mixed infections accounting 76.6%, 16.6%, and 6.6% of PCR-confirmed malaria cases, respectively. The nested PCR was superior to the smear microscopy (sensitivity 76.6%; specificity 100%) and the RDT (sensitivity 83.3%, specificity 94.2%). The overall percent agreement between microscopy and the RDT was 92.7% (kappa=0.63). High proportion of imported malaria including sub-microscopic and sub-patent cases were described. We suggest that incorporation of molecular tool into the conventional malaria diagnosis is beneficial in Jazan district.

Performance evaluation of different strategies based on microscopy techniques, rapid diagnostic test and molecular loop-mediated isothermal amplification assay for the diagnosis of imported malaria

OBJECTIVES

Malaria is one of most common tropical diseases encountered in travellers and migrants. It requires an urgent and reliable diagnosis considering its potential severity. In this study, performance of five diagnostic assays were evaluated in a nonendemic region and compared prospectively to quantitative PCR (qPCR).

METHODS

A prospective study was conducted at Toulouse Hospital from August 2017 to January 2018 and included all patients with initial Plasmodium screening. Thin and thick blood smears (TnS, TkS), quantitative buffy coat (QBC), rapid diagnostic tests (RDTs) and commercial loop-mediated isothermal amplification (LAMP) were independently performed on each blood sample and compared to our qPCR reference standard.

RESULTS

The study encompassed 331 patients, mainly returning from Africa. qPCR detected 73 Plasmodium-positive samples (including 58 falciparum). Individually, LAMP had a 97.3% (71/73) sensitivity, far ahead of TnS (84.9%, 62/73), TkS (86.3%, 63/73), QBC (86.3%, 63/73) and RDT (86.3%, 63/73). RDT demonstrated a high sensitivity for falciparum (98.3%, 57/58) but missed all ovale, malariae and knowlesi infections. Specificity was excellent for all techniques (99.6-100%). The most sensitive diagnosis strategies were TnS + RDT (95.9%, 70/73), TnS + LAMP (97.3%, 71/73) and TnS + RDT + LAMP (100%, 73/73), about 10% higher than strategies using exclusively microscopy, TkS + TnS (87.7%, 64/73) or QBC + TnS (87.7%, 64/73). TnS remains necessary for Plasmodium species identification and quantification. Adding sequentially TnS only on LAMP-positive samples did not decrease TnS + LAMP strategy sensitivity.

CONCLUSIONS

In nonendemic countries, the currently recommended microscopy-based strategies seem unsatisfactory for malaria diagnosis considering RDT and LAMP performance, two rapid and sensitive assays that require limited training.

Use cases for genetic epidemiology in malaria elimination

Background

While traditional epidemiological approaches have supported significant reductions in malaria incidence across many countries, higher resolution information about local and regional malaria epidemiology will be needed to efficiently target interventions for elimination. The application of genetic epidemiological methods for the analysis of parasite genetics has, thus far, primarily been confined to research settings. To illustrate how these technical methods can be used to advance programmatic and operational needs of National Malaria Control Programmes (NMCPs), and accelerate global progress to eradication, this manuscript presents seven use cases for which genetic epidemiology approaches to parasite genetic data are informative to the decision-making of NMCPs.

Methods

The use cases were developed through a highly iterative process that included an extensive review of the literature and global guidance documents, including the 2017 World Health Organization’s Framework for Malaria Elimination, and collection of stakeholder input. Semi-structured interviews were conducted with programmatic and technical experts about the needs and opportunities for genetic epidemiology methods in malaria elimination.

Results

Seven use cases were developed: Detect resistance, Assess drug resistance gene flow, Assess transmission intensity, Identify foci, Determine connectivity of parasite populations, Identify imported cases, and Characterize local transmission chains. The method currently used to provide the information sought, population unit for implementation, the pre-conditions for using these approaches, and post-conditions intended as a product of the use case were identified for each use case.

Discussion

This framework of use cases will prioritize research and development of genetic epidemiology methods that best achieve the goals of NMCPs, and ultimately, inform the establishment of normative policy guidance for their uses. With significant engagement of stakeholders from malaria endemic countries and collaboration with local programme experts to ensure strategic implementation, genetic epidemiological approaches have tremendous potential to accelerate global malaria elimination efforts.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2784-0) contains supplementary material, which is available to authorized users.

Diagnostic performance of CellaVision DM96 for Plasmodium vivax and Plasmodium falciparum screening in peripheral blood smears

Microscopic examination of blood smears is the standard method for malaria diagnosis but is labor-intensive and requires expert staff. CellaVision DM96 (CellaVision, Lund, Sweden) is a digital hematology analyzer available for advanced morphological analysis of blood films including intracellular parasites. Here, we evaluated the CellaVision DM96 Advanced RBC Application for malaria detection in stained peripheral blood (PB) smears. Two hundred and twenty thin PB smear slides (84 P. vivax, 14 P. falciparum, 122 negative controls) were stained with Wright-Giemsa using automated slidemaker/strainers of Beckman Coulter hematology systems (LH780, Beckman Coulter Inc., Miami, FL). The slides were automatically analyzed by CellaVision, and images were manually reviewed by experts. The results of automatic and manual detection by CellaVision were compared to those of microscopic examination. The sensitivity and specificity of automatic detection by CellaVision were 23.5% (23/98) and 81.1% (99/122), respectively. When CellaVision images were manually reviewed, the sensitivity and specificity increased to 65.3% (64/98) and 90.2% (110/122), respectively. The detection of P. falciparum showed the highest sensitivity by both the automated (33.3%) and the manual (85.7%) method. CellaVision misinterpreted malaria parasites as Howell-Jolly bodies in 57.1%, as Pappenheimer bodies in 84.7%, and as basophilic stipplings in 75.5% of the slides. Malaria diagnosis using CellaVision DM96 requires further improvements. Manual review improves CellaVision performance, but confirmation by conventional microscopy remains essential.

The temporal dynamics and infectiousness of subpatent Plasmodium falciparum infections in relation to parasite density

Malaria infections occurring below the limit of detection of standard diagnostics are common in all endemic settings. However, key questions remain surrounding their contribution to sustaining transmission and whether they need to be detected and targeted to achieve malaria elimination. In this study we analyse a range of malaria datasets to quantify the density, detectability, course of infection and infectiousness of subpatent infections. Asymptomatically infected individuals have lower parasite densities on average in low transmission settings compared to individuals in higher transmission settings. In cohort studies, subpatent infections are found to be predictive of future periods of patent infection and in membrane feeding studies, individuals infected with subpatent asexual parasite densities are found to be approximately a third as infectious to mosquitoes as individuals with patent (asexual parasite) infection. These results indicate that subpatent infections contribute to the infectious reservoir, may be long lasting, and require more sensitive diagnostics to detect them in lower transmission settings.

The role of subpatent infections for malaria transmission and elimination is unclear. Here, Slater et al. analyse several malaria datasets to quantify the density, detectability, course of infection and infectiousness of subpatent infections.

Field evaluation of malaria malachite green loop-mediated isothermal amplification in health posts in Roraima state, Brazil

Background

Microscopic detection of malaria parasites is the standard method for clinical diagnosis of malaria in Brazil. However, malaria epidemiological surveillance studies specifically aimed at the detection of low-density infection and asymptomatic cases will require more sensitive and field-usable tools. The diagnostic accuracy of the colorimetric malachite green, loop-mediated, isothermal amplification (MG-LAMP) assay was evaluated in remote health posts in Roraima state, Brazil.

Methods

Study participants were prospectively enrolled from health posts (healthcare-seeking patients) and from nearby villages (healthy participants) in three different study sites. The MG-LAMP assay and microscopy were performed in the health posts. Two independent readers scored the MG-LAMP tests as positive (blue/green) or negative (clear). Sensitivity and specificity of local microscopy and MG-LAMP were calculated using results of PET-PCR as a reference.

Results

A total of 91 participants were enrolled. There was 100% agreement between the two MG-LAMP readers (Kappa = 1). The overall sensitivity and specificity of MG-LAMP were 90.0% (95% confidence interval (CI) 76.34–97.21%) and 94% (95% CI 83.76–98.77%), respectively. The sensitivity and specificity of local microscopy were 83% (95% CI 67.22–92.66%) and 100% (95% CI 93.02–100.00%), respectively. PET-PCR detected six mixed infections (infection with both Plasmodium falciparum and Plasmodium vivax); two of these were also detected by MG-LAMP and one by microscopy. Microscopy did not detect any Plasmodium infection in the 26 healthy participants; MG-LAMP detected Plasmodium in five of these and PET-PCR assay detected infection in three. Overall, performing the MG-LAMP in this setting did not present any particular challenges.

Conclusion

MG-LAMP is a sensitive and specific assay that may be useful for the detection of malaria parasites in remote healthcare settings. These findings suggest that it is possible to implement simple molecular tests in facilities with limited resources.

Clinical Validation of a Commercial LAMP Test for Ruling out Malaria in Returning Travelers: A Prospective Diagnostic Trial

The mainstay of malaria diagnosis relies on rapid diagnostic tests (RDTs) and microscopy, both of which lack analytical sensitivity. This leads to repeat testing to rule out malaria. A prospective diagnostic trial of the Meridian illumigene Malaria assay (loop-mediated isothermal amplification [LAMP]) was conducted comparing it with reference microscopy and RDTs (BinaxNOW Malaria) in returning travelers between June 2017 and January 2018. Returning travelers with signs and symptoms of malaria were enrolled in the study. RDTs, microscopy, and LAMP assays were performed simultaneously. A total of 298 patients (50.7% male; mean age, 32.5 years) were enrolled, most visiting friends and relatives (43.3%), presenting with fever (88.9%), not taking prophylaxis (82.9%), and treated as outpatients (84.1%). In the prospective arm (n = 348), LAMP had a sensitivity of 98.1% (95% confidence interval [CI], 90.0%–100%) and a specificity of 97.6% (95% CI, 95.2%–99.1%) vs microscopy. After discrepant resolution with real-time polymerase chain reaction, LAMP had a sensitivity of 100% (95% CI, 93.7%–100%) and a specificity of 100% (95% CI, 98.7%–100%) vs microscopy. After discrepant resolution, RDTs had a sensitivity of 83.3% (95% CI, 58.6%–96.4%) and a specificity of 96.2% (95% CI, 93.2%–98.1%) vs microscopy. When including retrospective specimens (n = 377), LAMP had a sensitivity of 98.8% (95% CI, 93.2%–100%) and a specificity of 97.6% (95% CI, 95.2%–99.1%) vs microscopy, and after discrepant resolution of this set, LAMP had a sensitivity of 100% (95% CI, 95.8%–100%) and a specificity of 100% (95% CI, 98.7%–100%). A cost-benefit analysis of reagents and labor suggests savings of up to USD$13 per specimen using a novel algorithm with LAMP screening.

Poor Diagnostic Performance of a Species-Specific Loop-Mediated Isothermal Amplification (LAMP) Platform for Malaria

Background

The objective of this study was to assess an in-house loop-mediated isothermal amplification (LAMP) platform for malaria parasite detection and identification on species level.

Methods

LAMP primers specific for the human Plasmodium spp., namely, P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi, as well as genus-specific primers, were tested against a composite gold standard comprising microscopy from thick and thin blood films, commercial genus-specific Meridian illumigene Malaria LAMP, in-house real-time polymerase chain reaction (PCR), and commercial fast-track diagnostics (FTD) Malaria differentiation PCR.

Results

Of the 523 blood samples analyzed, the composite gold standard indicated 243 Plasmodium-species-DNA-containing samples (46.5%). Sensitivity and specificity of the analyzed genus- and species-specific LAMP primers were 71.0%–100.0% and 90.8%–100.0%, respectively. The influence of parasitemia was best documented for P. falciparum-specific LAMP with sensitivity values of 35.5% (22/62) for microscopically negative samples containing P. falciparum DNA, 50% (19/38) for parasitemia ≤50/μL, 84% (21/25) for parasitemia ≤500/μL, and 100% (92/92) for parasitemia >500/μL.

Conclusions

In our hands, performance characteristics of species-specific in-house LAMP for malaria lack reliability required for diagnostic laboratories. The use of the easy-to-apply technique for surveillance purposes may be considered.

Commit, hide and escape: the story of Plasmodium gametocytes

Malaria is the major cause of mortality and morbidity in tropical countries. The causative agent, Plasmodium sp., has a complex life cycle and is armed with various mechanisms which ensure its continuous transmission. Gametocytes represent the sexual stage of the parasite and are indispensable for the transmission of the parasite from the human host to the mosquito. Despite its vital role in the parasite's success, it is the least understood stage in the parasite's life cycle. The presence of gametocytes in asymptomatic populations and induction of gametocytogenesis by most antimalarial drugs warrants further investigation into its biology. With a renewed focus on malaria elimination and advent of modern technology available to biologists today, the field of gametocyte biology has developed swiftly, providing crucial insights into the molecular mechanisms driving sexual commitment. This review will summarise key current findings in the field of gametocyte biology and address the associated challenges faced in malaria detection, control and elimination.

Diagnostic accuracy of loop-mediated isothermal amplification (LAMP) for screening malaria in peripheral and placental blood samples from pregnant women in Colombia

Background

Pregnant women frequently show low-density Plasmodium infections that require more sensitive methods for accurate diagnosis and early treatment of malaria. This is particularly relevant in low-malaria transmission areas, where intermittent preventive treatment is not recommended. Molecular methods, such as polymerase chain reaction (PCR) are highly sensitive, but require sophisticated equipment and advanced training. Instead, loop mediated isothermal amplification (LAMP) provides an opportunity for molecular detection of malaria infections in remote endemic areas, outside a reference laboratory. The aim of the study is to evaluate the performance of LAMP for the screening of malaria in pregnant women in Colombia.

Methods

This is a nested prospective study that uses data and samples from a larger cross-sectional project conducted from May 2016 to January 2017 in three Colombian endemic areas (El Bagre, Quibdó, and Tumaco). A total of 531 peripheral and placental samples from pregnant women self-presenting at local hospitals for antenatal care visits, at delivery or seeking medical care for suspected malaria were collected. Samples were analysed for Plasmodium parasites by light microscopy (LM), rapid diagnostic test (RDT) and LAMP. Diagnostic accuracy endpoints (sensitivity, specificity, predictive values, and kappa scores) of LM, RDT and LAMP were compared with nested PCR (nPCR) as the reference standard.

Results

In peripheral samples, LAMP showed an improved sensitivity (100.0%) when compared with LM 79.5% and RDT 76.9% (p < 0.01), particularly in afebrile women, for which LAMP sensitivity was two-times higher than LM and RDT. Overall agreement among LAMP and nPCR was high (kappa value = 1.0). Specificity was similar in all tests (100%). In placental blood, LAMP evidenced a four-fold improvement in sensitivity (88.9%) when compared with LM and RDT (22.2%), being the only method, together with nPCR, able to detect placental infections in peripheral blood.

Conclusions

LAMP is a simple, rapid and accurate molecular tool for detecting gestational and placental malaria, being able to overcome the limited sensitivity of LM and RDT. These findings could guide maternal health programs in low-transmission settings to integrate LAMP in their surveillance systems for the active detection of low-density infections and asymptomatic malaria cases.

Donor-derived multiorgan transmission of mixed P. malariae and P. ovale infection: Impact of globalization on post-transplant infections

A 57-year-old man was admitted with fever and thrombocytopenia 1 month after renal transplantation. He had never received a blood transfusion or travelled outside Spain. A peripheral blood smear revealed Plasmodium malariae and P. ovale parasites, diagnosis confirmed later by malaria PCR. The donor, from Equatorial Guinea, had negative thick and thin blood smears and rapid malaria antigen test prior to organ donation. Peripheral blood malaria PCR was not performed during donor screening. The second renal recipient and the liver recipient were evaluated and were found to be asymptomatic. Thick and thin films and rapid malaria diagnostic tests were negative for both patients and blood for malaria PCR was sent to the referral laboratory. The index patient was treated with oral chloroquine diphosphate, with a favorable outcome and was considered cured. Malaria PCR was negative for the other renal recipient and positive for P. malariae and P. ovale curtisi for the liver transplant patient. Both were treated with oral chloroquine and the liver recipient also completed treatment with primaquine phosphate. This reported case of multiorgan transmission of mixed malaria infection highlights the importance of PCR-based tests for Plasmodium in the screening of donors from endemic areas.

Elimination or more accurate estimation? Investigation of trends in malaria diagnoses in the Ouest Department of Haiti from 2008 to 2017

Background

According to the 2016 World Malaria Report, the malaria incidence in Haiti declined by > 40% between 2010 and 2015. Though elimination efforts have likely contributed, this time period also corresponded to a national change in diagnostic methods.

Methods

Monthly reports of aggregated patient data were acquired from five clinics in the Ouest Department of Haiti. Generalized linear models were used to compare the number of febrile patients tested, the number of positive tests, and the proportion of tests that were positive (TRP) before and after the national adoption of rapid diagnostic tests (RDTs).

Results

Prior to the earthquake when microcopy was used for diagnosis, a total of 1,727 patients with 557 (32.3%) positive; post-earthquake testing was reduced and the TPR was variable; during the post recovery period when RDTs were used exclusivly, a total of 5,132 patients were tested using RDTs, only 83 (1.62%) were positive. Compared to the pre-earthquake period, there was a 69% increase in the number of patients tested (IRR: 1.69; 95% CI IRR 1.59, 2.79), and a 97.0% decrease in the proportion of patients with a positive test result (IRR: 0.03; 95% CI IRR 0.02, 0.04) in the post-recovery period.

Conclusions

While the decline in malaria indicators between 2010 and 2015 has been cited as evidence of progress towards elimination, these reports derived estimates of the malaria burden in Haiti using two different diagnostic tests. Thus, comparison of these periods in the context of malaria elimination should be made with caution.

Limitations of Rapid Diagnostic Testing in Patients with Suspected Malaria: A Diagnostic Accuracy Evaluation from Swaziland, a Low-Endemicity Country Aiming for Malaria Elimination

Background.

The performance of Plasmodium falciparum–specific histidine-rich protein 2–based rapid diagnostic tests (RDTs) to evaluate suspected malaria in low-endemicity settings has not been well characterized.

Methods.

Using dried blood spot samples from patients with suspected malaria at 37 health facilities from 2012 to 2014 in the low-endemicity country of Swaziland, we investigated the diagnostic accuracy of histidine-rich protein 2–based RDTs using qualitative polymerase chain reaction (PCR) (nested PCR targeting the cytochrome b gene) and quantitative PCR as reference standards. To explore reasons for false-negative and/or false-positive results, we used pfhrp2/3-specific PCR and logistic regression analyses of potentially associated epidemiological factors.

Results.

From 1353 patients, 93.0% of RDT-positive (n = 185) and 31.2% of RDT-negative samples (n = 340) were available and selected for testing. Compared with nested PCR, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of RDTs were 51.7%, 94.1%, 67.3%, and 89.1%, respectively. After exclusion of samples with parasite densities <100/μL, which accounted for 75.7% of false-negative results and 33.3% of PCR-detectable infections, the sensitivity, specificity, PPV, and NPV were 78.8%, 93.7%, 62.3%, and 97.1%. Deletions of pfhrp2 were not detected. False-positivity was more likely during the second year and was not associated with demographics, recent malaria, health facility testing characteristics, or potential DNA degradation.

Conclusions.

In the low-transmission setting of Swaziland, we demonstrated low sensitivity of RDT for malaria diagnosis, owing to an unexpectedly high proportion of low-density infection among symptomatic subjects. The PPV was also low, requiring further investigation. A more accurate point-of-care diagnostic may be needed to support malaria elimination efforts.

Diagnostic accuracy of loop-mediated isothermal amplification (LAMP) for screening patients with imported malaria in a non-endemic setting

BACKGROUND

Sensitive and easy-to-perform methods for the diagnosis of malaria are not yet available. Improving the limit of detection and following the requirements for certification are issues to be addressed in both endemic and non-endemic settings. The aim of this study was to test whether loop-mediated isothermal amplification of DNA (LAMP) may be an alternative to microscopy or real-time PCR for the screening of imported malaria cases in non-endemic area.

RESULTS

310 blood samples associated with 829 suspected cases of imported malaria were tested during a one year period. Microscopy (thin and thick stained blood slides, reference standard) was used for the diagnosis. Real-time PCR was used as a standard of truth, and LAMP (Meridian Malaria Plus) was used as an index test in a prospective study conducted following the Standards for Reporting Diagnosis Accuracy Studies. In the 83 positive samples, species identification was P. falciparum (n = 66), P. ovale (n = 9), P. vivax (n = 3) P. malariae (n = 3) and 2 co-infections with P. falciparum + P.malariae. Using LAMP methods, 93 samples gave positive results, including 4 false-positives. Sensitivity, specificity, positive predictive value and negative predictive value for LAMP tests were 100%, 98.13%, 95.51%, and 100% compared to PCR.

CONCLUSION

High negative predictive value, and limit of detection suggest that LAMP can be used for screening of imported malaria cases in non-endemic countries when expert microscopists are not immediately available. However, the rare occurrence of non-valid results and the need for species identification and quantification of positive samples preclude the use of LAMP as a single reference method.