Accuracy of PfHRP2 versus Pf-pLDH antigen detection by malaria rapid diagnostic tests in hospitalized children in a seasonal hyperendemic malaria transmission area in Burkina Faso

Defining a malaria diagnostic pathway from innovation to adoption: Stakeholder perspectives on data and evidence gaps

Malaria, a major global health concern, requires effective diagnostic tools for patient care, disease control, and elimination. The pathway from concept to the adoption of diagnostic products is complex, involving multiple steps and stakeholders. To map this process, our study introduces a malaria-specific diagnostic pathway, synthesising existing frameworks with expert insights. Comprising six major stages and 31 related activities, the pathway retains the core stages from existing frameworks and integrates essential malaria diagnostic activities, such as WHO prequalification processes, global stakeholder involvement, and broader health systems considerations. To understand the scope and availability of evidence guiding the activities along this pathway, we conducted an online survey with 113 participants from various stages of the malaria diagnostic pathway. The survey assessed perceptions on four critical attributes of evidence: clear requirements, alignment with user needs, accuracy and reliability, and public and free availability. It also explored the types of evidence used and the challenges and potential solutions related to evidence generation and use. Respondents reported using a broad range of formal and informal data sources. Findings indicated differing levels of agreement on the attributes across pathway stages, with notable challenges in the Approvals and Manufacturing stage and consistent concerns regarding the public availability of data/evidence. The study offers valuable insights for optimising evidence generation and utilisation across the malaria diagnostic pathway. It highlights the need for enhanced stakeholder collaboration, improved data availability, and increased funding to support effective evidence generation, sharing, and use. We propose actionable solutions, including the use of public data repositories, progressive data sharing policies, open-access publishing, capacity-building initiatives, stakeholder engagement forums, and innovative funding solutions. The developed framework and study insights have broader applications, offering a model adaptable for other diseases, particularly for neglected tropical diseases, which face similar diagnostic challenges.

Health itinerary-related survival of children under-five with severe malaria or bloodstream infection, DR Congo

BACKGROUND

Prompt appropriate treatment reduces mortality of severe febrile illness in sub-Saharan Africa. We studied the health itinerary of children under-five admitted to the hospital with severe febrile illness in a setting endemic for Plasmodium falciparum (Pf) malaria and invasive non-typhoidal Salmonella infections, identified delaying factors and assessed their associations with in-hospital death.

METHODOLOGY

Health itinerary data of this cohort study were collected during 6 months by interviewing caretakers of children (>28 days - <5 years) admitted with suspected bloodstream infection to Kisantu district hospital, DR Congo. The cohort was followed until discharge to assess in-hospital death.

PRINCIPAL FINDINGS

From 784 enrolled children, 36.1% were admitted >3 days after fever onset. This long health itinerary was more frequent in children with bacterial bloodstream infection (52.9% (63/119)) than in children with severe Pf malaria (31.0% (97/313)). Long health itinerary was associated with in-hospital death (OR = 2.1, p = 0.007) and two thirds of deaths occurred during the first 3 days of admission. Case fatality was higher in bloodstream infection (22.8% (26/114)) compared to severe Pf malaria (2.6%, 8/309). Bloodstream infections were mainly (74.8% (89/119)) caused by non-typhoidal Salmonella. Bloodstream infections occurred in 20/43 children who died in-hospital before possible enrolment and non-typhoidal Salmonella caused 16 out of these 20 bloodstream infections. Delaying factors associated with in-hospital death were consulting traditional, private and/or multiple providers, rural residence, prehospital intravenous therapy, and prehospital overnight stays. Use of antibiotics reserved for hospital use, intravenous therapy and prehospital overnight stays were most frequent in the private sector.

CONCLUSIONS

Long health itineraries delayed appropriate treatment of bloodstream infections in children under-five and were associated with increased in-hospital mortality. Non-typhoidal Salmonella were the main cause of bloodstream infection and had high case fatality.

TRIAL REGISTRATION

NCT04289688.

Asymptomatic malaria infection, associated factors and accuracy of diagnostic tests in a historically high transmission setting in Northern Uganda

BACKGROUND

Asymptomatic malaria infections are important parasite reservoirs and could sustain transmission in the population, but they are often unreported. A community-based survey was conducted to investigate the prevalence and factors associated with asymptomatic malaria infections in a historically high transmission setting in northern Uganda.

METHODS

Using a cross-sectional design, 288 children aged 2-15 years were enrolled and tested for the presence of malaria parasites using rapid diagnostic tests (RDTs) and blood smear microscopy between January to May 2022. Statistical analysis was performed using the exact binomial and Fisher's exact test with p ≤ 0.05 indicating significance. The logistic regression was used to explore factors associated with asymptomatic malaria infections.

RESULTS

Overall, the prevalence of asymptomatic infection was 34.7% (95% CI 29.2-40.5) with the highest observed in children 5-10 years 45.9% (95% CI 35.0-57.0). Gweri village accounted for 39.1% (95% CI 27.6-51.6) of malaria infections. Median parasite density was 1500 parasites/µl of blood. Plasmodium falciparum was the dominant species (86%) followed by Plasmodium malariae (5%). Factors associated with asymptomatic malaria infection were sleeping under mosquito net (Adjusted Odds Ratio (aOR) 0.27; 95% CI 0.13-0.56), p = 0.001 and presence of village health teams (VHTs) (aOR 0.02; 95% CI 0.01-0.45), p = 0.001. Sensitivity and specificity were higher for the P. falciparum/pLDH RDTs compared to HRP2-only RDTs, 90% (95% CI 86.5-93.5) and 95.2% (95% CI 92.8-97.7), p = 0.001, respectively.

CONCLUSION

Asymptomatic malaria infections were present in the study population and this varied with place and person in the different age groups. Plasmodium falciparum was the dominant parasite species however the presence of P. malariae and Plasmodium ovale was observed, which may have implication for the choice and deployment of diagnostic tools. Individuals who slept under mosquito net or had presence of functional VHTs were less likely to have asymptomatic malaria infection. P.f/pLDH RDTs performed better than the routinely used HRP2 RDTs. In view of these findings, investigation and reporting of asymptomatic malaria reservoirs through community surveys is recommended for accurate disease burden estimate and better targeting of control.

Could combined rapid diagnostic testing for malaria and c-reactive protein be helpful for the diagnosis and management of febrile illnesses in children under-5 years of age in rural Burkina Faso?

BACKGROUND

Febrile illnesses are among the most important reasons for medical consultation in sub-Saharan Africa and are frequently treated with antimicrobials due to the unavailability of appropriate diagnostic tools. This practice leads to antimicrobial resistance, with increasing mortality and morbidity as result. One of the few accessible diagnostic tools available in low resource settings is malaria rapid diagnostic tests (mRDTs) which contributed to reducing the over-prescription of anti-malarials, but cannot guide antibiotic prescriptions. To circumvent this problem, we explored whether combined testing with mRDT and c-reactive protein (CRP) could improve the diagnosis of febrile illnesses and subsequent prescription of antibiotics.

METHODS

Clinical specimens (blood, stool and urine) collected from 396 febrile children (axillary temperature of ≥ 37.5 °C) were analyzed with rapid diagnostic tests (malaria and CRP) and microbiology culture to establish the possible cause of fever. Actual antimicrobial prescriptions given to the children were compared with those that could be given based on combined CRP-malaria testing.

RESULTS

In total, 68.7% (272/396) of malaria cases were diagnosed by mRDT-Pf-HRP-2. CRP test was positive in 84.3% (334/396) of the children, but bacterial infections were confirmed in 12.4% (49/396) of them. A possible cause of fever could not be established in 20.5% (81/396) of cases. Based on the diagnostic practice in place, 265 of the children with a positive mRDT-Pf-HRP-2 received anti-malarial treatment. Furthermore, 89.5% (111/124) of negative mRDT results received antibiotic treatment and 37.1% (46/124) received antimalarial treatment. Of these 124 cases, 80 had positive CRP tests and 44 negative CRP tests. If the results of CRP testing are considered, 44 CRP/mRDT negative children would not get antibiotic treatment, resulting in a 35.5% reduction in antibiotic prescriptions. However, 2 cases with a bacterial infection would be denied appropriate treatment.

CONCLUSION

Combining mRDT-PfHRP2 with CRP testing is particularly useful in children for whom both tests are negative as it results in a reduction of antibiotics prescriptions. However, there is a risk to miss potential severe bacterial infections and a close follow-up of these cases is strongly recommended.

Diagnostic Performance of Plasmodium falciparum Histidine-Rich Protein-2 Antigen-Specific Rapid Diagnostic Test in Children at the Peripheral Health Care Level in Nanoro (Burkina Faso)

(1) Background: Malaria control has strongly benefited from the implementation of rapid diagnostic tests (RDTs). The malaria RDTs used in Burkina Faso, as per the recommendation of the National Malaria Control Program, are based on the detection of histidine-rich protein-2 (PfHRP2) specific to Plasmodium falciparum, which is the principal plasmodial species causing malaria in Burkina Faso. However, there is increasing concern about the diagnostic performance of these RDTs in field situations, and so constant monitoring of their accuracy is warranted. (2) Methods: A prospective study was performed in the health district of Nanoro, where 391 febrile children under 5 years with an axillary temperature ≥37.5 °C presenting at participating health facilities were subjected to testing for malaria. The HRP2-based RDT and expert microscopy were used to determine the diagnostic performance of the former. Retrospectively, the correctness of the antimalaria prescriptions was reviewed. (3) Results: Taking expert malaria microscopy as the gold standard, the sensitivity of the employed RDT was 98.5% and the specificity 40.5%, with a moderate agreement between the RDT testing and microscopy. In total, 21.7% of cases received an inappropriate antimalarial treatment based on a retrospective assessment with expert microscopy results. (4) Conclusion: Malaria remains one of the principal causes of febrile illness in Burkina Faso. Testing with HRP2-based RDTs is inaccurate, in particular, due to the low specificity, which results in an over-prescription of antimalarials, with emerging antimalarial drug resistance as an important risk and many children not being treated for potential other causes of fever.

Comparative Assessment of the Sensitivity of Ten Commercial Rapid Diagnostic Test Kits for the Detection of Plasmodium

Malaria is one of the most common tropical diseases encountered by members of the French military who are deployed in operations under constrained conditions in malaria-endemic areas. Blood smear microscopy—the gold standard for malaria diagnosis—is often not available in such settings, where the detection of malaria relies on rapid diagnostic tests (RDTs). Ten RDTs (from Biosynex, Carestart, Humasis, SD Bioline, and CTK Biotech), based on the detection of the Plasmodium falciparum histidine-rich protein 2 (HRP2) or lactate dehydrogenase (pLDH, PfLDH, or PvLDH), were assessed against 159 samples collected from imported malaria cases, including 79 P. falciparum, 37 P. vivax, 22 P. ovale, and 21 P. malariae parasites. Samples had been previously characterised using microscopy and real-time PCR. The overall sensitivities for the Plasmodium test ranged from 69.8% (111/159) to 95% (151/159). There was no significant difference for the specific detection of P. falciparum (96.2% to 98.7%, p = 0.845). No significant difference was found between sensitivities to P. vivax by pan LDH or pvLDH (81.1% (30/37) to 94.6% (35/37) (p = 0.845)). Some of the RDTs missed most of P. ovale and P. malariae, with sensitivities for all RDTs ranging respectively from 4.5% (1/22) to 81.8% (18/22) and 14.3% (3/21) to 95.2% (20/21). Carestart Malaria Pf/Pan (pLDH) Ag G0121, a pLDH-based RDT (PfLDH and pLDH), showed the highest sensitivities to P. falciparum (98.7%, 78/79), P. vivax (94.6%, 35/37), P. ovale (81.8%, 18/22), and P. malariae (95.2%, 20/21) and meets the requirements for military deployments in malaria-endemic areas.

Development and evaluation of an electronic algorithm using a combination of a two-step malaria RDT and other rapid diagnostic tools for the management of febrile illness in children under 5 attending outpatient facilities in Burkina Faso

Background

In Sub-Saharan Africa (SSA), febrile illnesses remain a major public health problem in children. However, the persistence of hrp2 antigen and the low sensitivity of pLDH RDT negatively affect antimalarials and antibiotics prescription practices. These limitations lead to poor management of febrile diseases and antimicrobial resistance (AMR). To improve the diagnosis of these febrile diseases and subsequent prescription of antimicrobials, it is hypothesized that the implementation of an algorithm including a two-step malaria RDT PfHRP2/pLDH supported by point-of-care (PoC) tests for bacterial infections could significantly improve the management of febrile diseases and thereby tackling AMR.

Methods

To assess the value of the proposed algorithm, an open-label randomized controlled trial with three arms, enrolling febrile children from 6 to 59 months is proposed.

In the control arm, febrile children will be managed according to the Integrated Management of Childhood Illnesses (IMCI), which is part of the standard of care in Burkina Faso. Treatment will be done according to national guidelines.

In the RDT decisional algorithm (RDT-DA) arm (intervention), the clinical examination based on IMIC will be supported by a two-step malaria RDT and bacterial infections RDTs. Prescription will be left to the discretion of the healthcare workers based on clinical examination and PoC test results.

In the e-algorithm arm (intervention), artificial intelligence integrating multiple layers of clinical information such as clinical examination, signs/symptoms and medical history, and biological information such as biomarkers (CRP and WBC) and pathogen-specific PoC tests, and oximetry will be developed. The e-algorithm will serve to guide the diagnostic and management of febrile infections in children.

In the 3 arms, the case report forms will be digitalized. A final follow-up visit (day 7) will be scheduled for all participants. Patients will be asked to come back to the health facilities before the scheduled visit if the symptoms persist or in case of health condition worsening.

Discussion

If successful, this study could contribute to improve the management of febrile diseases and reduce inappropriate use of antimicrobials.

Trial registration

The trial is registered at ClinicalTrial.gov, NCT05285657. Enrolment started on 4 March 2022 with long-term outcome being assessed completely by 2023.

Evaluation of HRP2 and pLDH-based rapid diagnostic tests for malaria and prevalence of pfhrp2/3 deletions in Aweil, South Sudan

BACKGROUND

Rapid diagnostic tests (RDT) for malaria are the primary tool for malaria diagnosis in sub-Saharan Africa but the utility of the most commonly used histidine-rich protein 2 (HRP2) antigen-based tests is limited in high transmission settings due to the long duration of positivity after successful malaria treatment. HRP2 tests are also threatened by the emergence of Plasmodium that do not carry pfhrp2 or pfhrp 3 genes. Plasmodium lactate dehydrogenase (pLDH)-based tests are promising alternatives, but less available. This study assessed the performances of HRP2 and pLDH(pan) tests under field conditions.

METHODS

The study performed a prospective facility-based diagnostic evaluation of two malaria RDTs in Aweil, South Sudan, during the high transmission season. Capillary blood by fingerprick was collected from 800 children under 15 years of age with fever and no signs of severity. SD Bioline HRP2 and CareStart pLDH(pan) RDTs were performed in parallel, thick and thin smears for microscopy were examined, and dried blood was used for PCR testing.

RESULTS

Using microscopy as the gold standard, the sensitivity of both tests was estimated at  > 99%, but the specificity of each was lower: 55.0% for the pLDH test and 61.7% for the HRP2 test. When using PCR as the gold standard, the sensitivity of both tests was lower than the values assessed using microscopy (97.0% for pLDH and 96.5% for HRP2), but the specificity increased (65.1% for pLDH and 72.9% for HRP2). Performance was similar across different production lots, sex, and age. Specificity of both the pLDH and HRP2 tests was significantly lower in children who reported taking a therapeutic course of anti-malarials in the 2 months prior to enrollment. The prevalence of pfhrp2/3 deletions in the study population was 0.6%.

CONCLUSIONS

The low specificity of the pLDH RDT in this setting confirms previous results and suggests a problem with this specific test. The prevalence of pfhrp2/3 deletions in the study area warrants continued monitoring and underscores the relevance of assessing deletion prevalence nationally. Improved malaria RDTs for high-transmission environments are needed.

Malaria diagnostic methods with the elimination goal in view

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

Impact of Plasmodium falciparum pfhrp2 and pfhrp3 gene deletions on malaria control worldwide: a systematic review and meta-analysis

Background

Deletion of pfhrp2 and/or pfhrp3 genes cause false negatives in malaria rapid diagnostic test (RDT) and threating malaria control strategies. This systematic review aims to assess the main methodological aspects in the study of pfhrp2 and pfhrp3 gene deletions and its global epidemiological status, with special focus on their distribution in Africa; and its possible impact in RDT.

Methods

The systematic review was conducted by examining the principal issues of study design and methodological workflow of studies addressing pfhrp2 deletion. Meta-analysis was applied to represent reported prevalences of pfhrp2 and pfhrp3 single and double deletion in the World Health Organization (WHO) region. Pooled-prevalence of deletions was calculated using DerSimonnian-Laird random effect model. Then, in-deep analysis focused on Africa was performed to assess possible variables related with these deletions. Finally, the impact of these deletions in RDT results was analysed combining reported information about RDT sensitivity and deletion prevalences.

Results

49 articles were included for the systematic review and 37 for the meta-analysis, 13 of them placed in Africa. Study design differs significantly, especially in terms of population sample and information reported, resulting in high heterogeneity between studies that difficulties comparisons and merged conclusions. Reported prevalences vary widely in all the WHO regions, significantly higher deletion were reported in South-Central America, following by Africa and Asia. Pfhrp3 deletion is more prevalent (43% in South-Central America; 3% in Africa; and 1% in Asia) than pfhrp2 deletion (18% in South-Central America; 4% in Africa; and 3% in Asia) worldwide. In Africa, there were not found differences in deletion prevalence by geographical or population origin of samples. The prevalence of deletion among false negatives ranged from 0 to 100% in Africa, but in Asia and South-Central America was only up to 90% and 48%, respectively, showing substantial relation between deletions and false negatives.

Conclusion

The concerning prevalence of pfhrp2, pfhrp3 and pfhrp2/3 gene deletions, as its possible implications in malaria control, highlights the importance of regular and systematic surveillance of these deletions. This review has also outlined that a standardized methodology could play a key role to ensure comparability between studies to get global conclusions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03812-0.

Social perceptions of malaria and diagnostic-driven malaria treatment in Burkina Faso

Malaria is a parasitic disease, endemic in many tropical and sub-tropical countries. Malaria is a well-known disease, familiar to almost all people in endemic regions, as they or their family are regularly confronted with it; everyone in these regions has probably experienced the disease, at least once in their life. To investigate the social perceptions of malaria in Burkina Faso, including its diagnosis-driven treatment, we have conducted a survey in both urban (Saint Camille Hospital, Ouagadougou HOSCO) and rural (Boussé Hospital) areas. Fifty-six individuals, mostly representatives of the society variability, were surveyed by questionnaires and 2 focus groups were organized with traditional healers. In general, populations seem to have grasped the causes, symptoms and means of preventing the disease. However, the majority of interviewees make a marked confusion between malaria and dengue; dengue fever is considered like a severe form of malaria. The care modalities (modern and/or traditional medicine) are plural and the choice of therapeutic practice depends on both the socio-economic conditions and education level of the patient. Whereas some patients mark preferences for one type of medicine, others simultaneously recourse to both; for these, a medicine does not outperform the other and their combination multiplies the chances of a quick recovery. Whether for modern or traditional medicine, the diagnosis is considered very important for effective disease management. Modern medicine uses diagnostic tools based on light microscopy and immunochromatography (rapid diagnostic tests; RDT); traditional medicine has its own diagnostic logic but nevertheless recognizes modern medicine diagnosis to guide its therapy.

90 % of those interviewed first use modern medicine to seek an accurate diagnosis of their disease and thus to receive adequate treatment. Presumptive treatments are still widely prescribed and accepted by most patients who trust the judgment of their caregiver, not perceiving any benefit to an objective diagnosis. In front of a negative diagnosis, patient reactions are diverse, some accepting investigations for other diseases (45 %), others opting for self-medication (15 %), others resorting to traditional medicine (20 %).

All are unanimous in the importance of diagnosis and are in favor of in-development diagnostic technologies, provided these obviously meet the features of reliability, ease of use, availability and, of course, economical accessibility.

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

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

Clinical diagnostic evaluation of HRP2 and pLDH-based rapid diagnostic tests for malaria in an area receiving seasonal malaria chemoprevention in Niger

Background

Rapid diagnostic tests (RDT) for malaria are common, but their performance varies. Tests using histidine-rich protein 2 (HRP2) antigen are most common, and many have high sensitivity. HRP2 tests can remain positive for weeks after treatment, limiting their specificity and usefulness in high-transmission settings. Tests using Plasmodium lactate dehydrogenase (pLDH) have been less widely used but have higher specificity, mostly due to a much shorter time to become negative.

Methods

A prospective, health centre-based, diagnostic evaluation of two malaria RDTs was performed in rural Niger during the high malaria transmission season (3–28 October, 2017) and during the low transmission season (28 January–31 March, 2018). All children under 5 years of age presenting with fever (axillary temperature > 37.5 °C) or history of fever in the previous 24 h were eligible. Capillary blood was collected by finger prick. The SD Bioline HRP2 (catalog: 05FK50) and the CareStart pLDH(pan) (catalog: RMNM-02571) were performed in parallel, and thick and thin smears were prepared. Microscopy was performed at Epicentre, Maradi, Niger, with external quality control. The target sample size was 279 children with microscopy-confirmed malaria during each transmission season.

Results

In the high season, the sensitivity of both tests was estimated at > 99%, but the specificity of both tests was lower: 58.0% (95% CI 52.1–63.8) for the pLDH test and 57.4% (95% CI 51.5–63.1) for the HRP2 test. The positive predictive value was 66.3% (95% CI 61.1–71.2) for both tests. In the low season, the sensitivity of both tests dropped: 91.0% (95% CI 85.3–95.0) for the pLDH test and 85.8% (95% CI 79.3–90.9) for the HRP2 test. The positive predictive value remained low for both tests in the low season: 60.5% (95% CI 53.9–66.8) for the pLDH test and 61.9% (55.0–68.4) for the HRP2 test. Performance was similar across different production lots, gender, age of the children, and, during the high season, time since the most recent distribution of seasonal malaria chemoprevention.

Conclusions

The low specificity of the pLDH RDT in this setting was unexpected and is not easily explained. As the pLDH test continues to be introduced into new settings, the questions raised by this study will need to be addressed.

Enhanced In-Vitro Hemozoin Polymerization by Optimized Process using Histidine-Rich Protein II (HRPII)

Conductive biopolymers, an important class of functional materials, have received attention in various fields because of their unique electrical, optical, and physical properties. In this study, the polymerization of heme into hemozoin was carried out in an in vitro system by the newly developed heme polymerase (histidine-rich protein 2 (HRP-II)). The HRP-II was produced by recombinant E. coli BL21 from the Plasmodium falciparum gene. To improve the hemozoin production, the reaction conditions on the polymerization were investigated and the maximum production was achieved after about 790 μM at 34 °C with 200 rpm for 24 h. As a result, the production was improved about two-fold according to the stepwise optimization in an in vitro system. The produced hemozoin was qualitatively analyzed using the Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Finally, it was confirmed that the enzymatically polymerized hemozoin had similar physical properties to chemically synthesized hemozoin. These results could represent a significant potential for nano-biotechnology applications, and also provide guidance in research related to hemozoin utilization.

The XN-30 hematology analyzer for rapid sensitive detection of malaria: a diagnostic accuracy study

BACKGROUND

Accurate and timely diagnosis of malaria is essential for disease management and surveillance. Thin and thick blood smear microscopy and malaria rapid diagnostic tests (RDTs) are standard malaria diagnostics, but both methods have limitations. The novel automated hematology analyzer XN-30 provides standard complete blood counts (CBC) as well as quantification of malaria parasitemia at the price of a CBC. This study assessed the accuracy of XN-30 for malaria detection in a controlled human malaria infection (CHMI) study and a phase 3 diagnostic accuracy study in Burkina Faso.

METHODS

Sixteen healthy, malaria-naive CHMI participants were challenged with five Plasmodium falciparum-infected mosquitoes. Blood was sampled daily for XN-30, blood smear microscopy, and malaria qPCR. The accuracy study included patients aged > 3 months presenting with acute febrile illness. XN-30, microscopy, and rapid diagnostic tests (HRP-2/pLDH) were performed on site; qPCR was done in retrospect. The malaria reference standard was microscopy, and results were corrected for sub-microscopic cases.

RESULTS

All CHMI participants became parasitemic by qPCR and XN-30 with a strong correlation for parasite density (R² = 0.91; p < .0001). The XN-30 accurately monitored treatment and allowed detection of recrudescence. Out of 908 patients in the accuracy study, 241 had microscopic malaria (density 24-491,802 parasites/μL). The sensitivity and specificity of XN-30 compared to microscopy were 98.7% and 99.4% (PPV = 98.7%, NPV = 99.4%). Results were corrected for qPCR-confirmed sub-microscopic cases. Three microscopy-confirmed cases were not detected by XN-30. However, XN-30 detected 19/134 (14.2%) qPCR-confirmed cases missed by microscopy. Among qPCR-confirmed cases, XN-30 had a higher sensitivity (70.9% versus 66.4%; p = .0009) and similar specificity (99.6% versus 100%; p = .5) as microscopy. The accuracy of XN-30 for microscopic malaria was equal to or higher than HRP-2 and pLDH RDTs, respectively.

CONCLUSIONS

The XN-30 is a novel, automated hematology analyzer that combines standard hemocytometry with rapid, objective, and robust malaria detection and quantification, ensuring prompt treatment of malaria and malaria anemia and follow-up of treatment response.

TRIAL REGISTRATION

Both trials were registered on clinicaltrials.gov with respective identifiers NCT02836002 (CHMI trial) and NCT02669823 (diagnostic accuracy study).

Concurrence of CareStart™ Malaria HRP2 RDT with microscopy in population screening for Plasmodium falciparum infection in the Mount Cameroon area: predictors for RDT positivity

Background

Malaria remains a diagnostic challenge in many endemic communities. Although rapid diagnostic tests (RDTs) are presently widely used for malaria diagnosis, there is a dearth of information on post-marketing surveillance on its efficacy in Cameroon. The present study evaluated the performance characteristics of CareStart™ Malaria HRP2 (histidine-rich protein 2) antigen (Ag) RDT in diagnosing Plasmodium falciparum infection in the Mount Cameroon area and predictors associated with RDT positivity.

Methods

The CareStart™ Malaria HRP2 Plasmodium falciparum (G0141) Ag RDT was evaluated in a cross-sectional community-based survey involving 491 children of both sexes aged 6 months to 14 years between April and May 2018. Malaria parasitaemia was confirmed by light microscopy. Sensitivity (Se), specificity (Sp), positive (PPV) and negative (NPV) predictive values of the RDT, and the corresponding accuracy and Kappa value (κ) were determined using microscopy as the gold standard. Haemoglobin (Hb) concentration was obtained using an auto-haematology analyser. Results were compared using the chi-square test and associations between predictor variables, and RDT results were assessed using logistic regression analysis.

Results

Microscopically confirmed malaria parasite prevalence was 27.7%, and geometric mean density was 187 parasites/μL of blood (range 70-1162). Se, Sp, PPV, NPV and accuracy were 82.4, 76.6, 57.4, 91.9 and 78.2%, respectively. Sensitivity depended on parasitaemia and reached 96.1% at densities ≥ 200 parasites/μL of blood. The accuracy of malaria parasitaemia (as assessed by the area under the receiver operating characteristic curve) to predict malaria by RDT was 75.4% (95% CI 70.6-80.1). The agreement between microscopy and RDT was moderate (κ = 0.52). RDT positivity was significantly associated with fever (P < 0.001), children less than 5 years (P = 0.02), history of fever within a month (P < 0.001) and anaemia (P = 0.002).

Conclusion

The overall concurrence of CareStart™ Malaria HRP2 pf Ag RDT with microscopy in the detection of P. falciparum infection is moderate and is most useful at parasitaemia ≥ 200 parasites/μL of blood and presentation with fever. While RDT is effective as a diagnostic test for confirmation of clinical cases of malaria, its applications in population screening with a higher proportion of asymptomatic cases are limited.

Algorithms for sequential interpretation of a malaria rapid diagnostic test detecting two different targets of Plasmodium species to improve diagnostic accuracy in a rural setting (Nanoro, Burkina Faso)

Background

Malaria rapid diagnostic tests (RDT) have limitations due to the persistence of histidine-rich protein 2 (HRP2) antigen after treatment and low sensitivity of Plasmodium lactate dehydrogenase (pLDH) based RDTs. To improve the diagnosis of malaria in febrile children, two diagnostic algorithms, based on sequential interpretation of a malaria rapid diagnostic test detecting two different targets of Plasmodium species and followed by expert microscopy, were evaluated.

Methods

Two diagnostic algorithms were evaluated using 407 blood samples collected between April and October 2016 from febrile children and the diagnostic accuracy of both algorithms was determined. Algorithm 1: The result of line T1-HRP2 were read first; if negative, malaria infection was considered to be absent. If positive, confirmation was done with the line T2-pLDH. If T2-pLDH test was negative, the malaria diagnosis was considered as “inconclusive” and microscopy was performed; Algorithm 2: The result of line T2-pLDH were read first; if positive, malaria infection was considered to be present. If negative, confirmation was done with the line T1-HRP2. If T1-HRP2 was positive the malaria diagnosis was considered as “inconclusive” and microscopy was performed. In absence of malaria microscopy, a malaria infection was ruled out in children with an inconclusive diagnostic test result when previous antimalarial treatment was reported.

Results

For single interpretation, the sensitivity of PfHRP2 was 98.4% and the specificity was 74.2%, and for the pLDH test the sensitivity was 89.3% and the specificity was 98.8%. Malaria was accurately diagnosed using both algorithms in 84.5% children. The algorithms with the two-line malaria RDT classified the test results into two groups: conclusive and inconclusive results. The diagnostic accuracy for conclusive results was 98.3% using diagnostic algorithm 1 and 98.6% using algorithm 2. The sensitivity and specificity for the conclusive results were 98.2% and 98.4% for algorithm 1, and 98.6% and 98.4% for algorithm 2, respectively. There were 63 (15.5%) children who had an “inconclusive” result for whom expert microscopy was needed. In children with inconclusive results (PfHRP2+/pLDH- only) previous antimalarial treatment was reported in 16 children with malaria negative microscopy (16/40; 40%) and 1 child with malaria positive microscopy (1/23; 4.3%).

Conclusion

The strategy of sequential interpretation of two-line malaria RDT can improve the diagnosis of malaria. However, some cases will still require confirmative testing with microscopy or additional investigations on previous antimalarial treatment.

The use of Fionet technology for external quality control of malaria rapid diagnostic tests and monitoring health workers' performance in rural military health facilities in Tanzania

INTRODUCTION

Internal and external quality control (QC) of rapid diagnostic tests (RDTs) is important to increase reliability of RDTs currently used to diagnose malaria. However, cross-checking of used RDTs as part of quality assurance can rarely be done by off-site personnel because there is no guarantee of retaining visible test lines after manufacturers' recommended reading time. Therefore, this study examined the potential of using Fionet™ technology for remote RDT quality monitoring at seven clinics, identifying reasons for making RDT processing and interpretation errors, and taking corrective actions for improvement of diagnosis and consequently improved management of febrile patients.

METHODS

The study was conducted at seven military health facilities in Mainland Tanzania and utilized RDTs capable of detecting Plasmodium falciparum specific Histidine-rich protein 2 (Pf-HRP2) and the genus specific Plasmodium lactate dehydrogenase (pLDH) for other species of plasmodium (P. vivax, P. malariae or P. ovale; pan-pLDH). Patients' data and images of processed RDTs from seven clinics were uploaded on a Fionet web portal and reviewed regularly to monitor preparation procedures and visual interpretation of test results compared to automated analysis using the Deki reader of RDT. Problems detected were rapidly communicated to remote laboratory personnel at the clinic for corrective action and follow-up of patients who were falsely diagnosed as negative and missed treatment. Factors contributing to making errors in visual interpretation of RDT results were analyzed during visits to the health facilities.

RESULTS

A total of 1,367 (1.6%) out of 83,294 RDT test images uploaded to the Fionet portal had discordant test results of which 822 (60.1%) and 545 (39.9%) were falsely reported as negative and positive, respectively. False negative and false positive test results were common for a single test line in 515 (62.7%) and 741 (54.2%) tests, respectively. Out of 1,367 RDT images assessed, 98 (7.2%) had quality problems related to preparation procedures of which 95(96.9%) errors were due to putting too much blood on the sample well or insufficient buffer in the respective wells. The reasons for discrepant results included, false reporting of none existent lines in 526 (38.5%) tests, missing a faint positive line in 493 (36.1%), missing a strong positive line in 248(18.1%) and errors caused by poorly processed RDTs in 96 (7.2%) tests. Among the false negative tests (n = 822), 669 (48.9%) patients were eligible for follow-up and only 339 (48.5%) were reached and 291 (85.8%) received appropriate anti-malaria therapy.

CONCLUSION

Fionet technology enabled remote monitoring of RDT quality issues, identifying reasons contributing to laboratory personnel making errors and provided a rapid method to implement corrective actions at remote sites to improve malaria diagnosis and consequently improved health care management of febrile patients infected with malaria.

Assessing the performance of only HRP2 and HRP2 with pLDH based rapid diagnostic tests for the diagnosis of malaria in middle Ghana, Africa

BACKGROUND

Rapid diagnostic test (RDT) kits have been useful tools to screen for the presence of infection with malaria parasites. Despite the improvement, false results from RDTs present a greater challenge. The need for quality test kits is desirable. We evaluated the diagnostic accuracy of three malaria RDTs.

METHOD

The team consented and enrolled 754 participants from the two major public hospitals in Kintampo districts of Ghana from June 2014 to August 2014. Venous blood samples were obtained by trained personnel and samples were screened for malaria using CareStart and SD Bioline HRP2 and HRP2 with pLDH based RDTs with blood slides for malaria microscopy as "gold standard". Geometric mean parasite densities were estimated and parasite densities were used to estimate the quantitative limits of the RDTs. The sensitivities, specificities and other performance criteria were calculated using statistical analytical software.

RESULT

The median age of participants was 21 (range 5-31) years. There were 28.6% (215/752) were males and 71.4% (537/752) were females. Comparing with microscopy, the sensitivity, specificity, positive predictive value, negative predictive value and the ROC were for CareStart (HRP2), 98.2%, 66.5%, 82.6%, 95.6%, 0.82; for CareStart (HRP2/pLDH) 98.2%, 66.5%, 82.6%, 95.6%, 0.82 and for SD-Bioline (HRP2/pLDH) RDTs 98.2%, 69.2%, 84.2%, 96.0%, 0.84 respectively. The performance for all the kits were acceptable at a cut-off of 25 or more parasites/μl of blood.

CONCLUSIONS

The diagnostic performance of the three malaria RDTs was acceptable, according to the World Health Organisation criteria, to detect densities ≥25 parasite/μl of blood. The RDTs with HRP2/pLDH targets were comparable to those with only HRP2 and could successfully substitute current and commonly used HRP2-based RDTs.

Implementation of a malaria rapid diagnostic test in a rural setting of Nanoro, Burkina Faso: from expectation to reality

Background

Malaria rapid diagnostic tests (RDTs) are nowadays widely used in malaria endemic countries as an alternative to microscopy for the diagnosis of malaria. However, quality control of test performance and execution in the field are important in order to ensure proper use and adequate diagnosis of malaria. The current study compared the performance of a histidine-rich protein 2-based RDT used at peripheral health facilities level in real life conditions with that performed at central reference laboratory level with strict adherence to manufacturer instructions.

Methods

Febrile children attending rural health clinics were tested for malaria with a RDT provided by the Ministry of Health of Burkina Faso as recommended by the National Malaria Control Programme. In addition, a blood sample was collected in an EDTA tube from all study cases for retesting with the same brand of RDT following the manufacturer’s instructions with expert malaria microscopy as gold standard at the central reference laboratory. Fisher exact test was used to compare the proportions by estimating the p-value (p ≤ 0.05) as statistically significant.

Results

In total, 407 febrile children were included in the study and malaria was diagnosed in 59.9% (244/407) of the cases with expert malaria microscopy. The sensitivity of malaria RDT testing performed at health facilities was 97.5% and comparable to that achieved at the laboratory (98.8%). The number of malaria false negatives was not statistically significant between the two groups (p = 0.5209). However, the malaria RDT testing performed at health facilities had a specificity issue (52.8%) and was much lower compared to RDT testing performed at laboratory (74.2%). The number of malaria false positives was statistically significantly different between the two groups (p = 0.0005).

Conclusion

Malaria RDT testing performed at the participating rural health facilities resulted in more malaria false positives compared to those performed at central laboratory. Several factors, including storage and transportation conditions but also training of health workers, are most likely to influence test performance. Therefore, it is very important to have appropriate quality control and training programmes in place to ensure correct performance of RDT testing.

How long do rapid diagnostic tests remain positive after anti-malarial treatment?

BACKGROUND

Rapid diagnostic tests (RDTs) are increasingly becoming a paradigm for both clinical diagnosis of malaria infections and for estimating community parasite prevalence in household malaria indicator surveys in malaria-endemic countries. The antigens detected by RDTs are known to persist in the blood after treatment with anti-malarials, but reports on the duration of persistence (and the effect this has on RDT positivity) of these antigens post-treatment have been variable.

METHODS

In this review, published studies on the persistence of positivity of RDTs post-treatment are collated, and a bespoke Bayesian survival model is fit to estimate the number of days RDTs remain positive after treatment.

RESULTS

Half of RDTs that detect the antigen histidine-rich protein II (HRP2) are still positive 15 (5-32) days post-treatment, 13 days longer than RDTs that detect the antigen Plasmodium lactate dehydrogenase, and that 5% of HRP2 RDTs are still positive 36 (21-61) days after treatment. The duration of persistent positivity for combination RDTs that detect both antigens falls between that for HRP2- or pLDH-only RDTs, with half of RDTs remaining positive at 7 (2-20) days post-treatment. This study shows that children display persistent RDT positivity for longer after treatment than adults, and that persistent positivity is more common when an individual is treated with artemisinin combination therapy than when treated with other anti-malarials.

CONCLUSIONS

RDTs remain positive for a highly variable amount of time after treatment with anti-malarials, and the duration of positivity is highly dependent on the type of RDT used for diagnosis. Additionally, age and treatment both impact the duration of persistence of RDT positivity. The results presented here suggest that caution should be taken when using RDT-derived diagnostic outcomes from cross-sectional data where individuals have had a recent history of anti-malarial treatment.

Comparison of visual and automated Deki Reader interpretation of malaria rapid diagnostic tests in rural Tanzanian military health facilities

Background

Although microscopy is a standard diagnostic tool for malaria and the gold standard, it is infrequently used because of unavailability of laboratory facilities and the absence of skilled readers in poor resource settings. Malaria rapid diagnostic tests (RDT) are currently used instead of or as an adjunct to microscopy. However, at very low parasitaemia (usually < 100 asexual parasites/µl), the test line on malaria rapid diagnostic tests can be faint and consequently hard to visualize and this may potentially affect the interpretation of the test results. Fio Corporation (Canada), developed an automated RDT reader named Deki Reader™ for automatic analysis and interpretation of rapid diagnostic tests. This study aimed to compare visual assessment and automated Deki Reader evaluations to interpret malaria rapid diagnostic tests against microscopy. Unlike in the previous studies where expert laboratory technicians interpreted the test results visually and operated the device, in this study low cadre health care workers who have not attended any formal professional training in laboratory sciences were employed.

Methods

Finger prick blood from 1293 outpatients with fever was tested for malaria using RDT and Giemsa-stained microscopy for thick and thin blood smears. Blood samples for RDTs were processed according to manufacturers’ instructions automated in the Deki Reader. Results of malaria diagnoses were compared between visual and the automated devise reading of RDT and microscopy.

Results

The sensitivity of malaria rapid diagnostic test results interpreted by the Deki Reader was 94.1% and that of visual interpretation was 93.9%. The specificity of malaria rapid diagnostic test results was 71.8% and that of human interpretation was 72.0%. The positive predictive value of malaria RDT results by the Deki Reader and visual interpretation was 75.8 and 75.4%, respectively, while the negative predictive values were 92.8 and 92.4%, respectively. The accuracy of RDT as interpreted by DR and visually was 82.6 and 82.1%, respectively.

Conclusion

There was no significant difference in performance of RDTs interpreted by either automated DR or visually by unskilled health workers. However, despite the similarities in performance parameters, the device has proven useful because it provides stepwise guidance on processing RDT, data transfer and reporting.

Impact Evaluation of Seasonal Malaria Chemoprevention under Routine Program Implementation: A Quasi-Experimental Study in Burkina Faso

Seasonal malaria chemoprevention (SMC) for children < 5 is a strategy that is gaining popularity in West African countries. Although its efficacy to reduce malaria incidence has been demonstrated in trials, the effects of SMC implemented in routine program conditions, outside of experimental contexts, are unknown. In 2014 and 2015, a survey was conducted in 1,311 households located in Kaya District (Burkina Faso) where SMC had been recently introduced. All children < 72 months were tested for malaria and anemia. A pre–post study with control group was designed to measure SMC impact during high transmission season. A difference-in-differences approach was coupled in the analysis with propensity score weighting to control for observable and time-invariant nonobservable confounding factors. SMC reduced the parasitemia point and period prevalence by 3.3 and 24% points, respectively; this translated into protective effects of 51% and 62%. SMC also reduced the likelihood of having moderate to severe anemia by 32%, and history of recent fever by 46%. Self-reported coverage for children at the first cycle was 83%. The SMC program was successfully added to a package of interventions already in place. To our knowledge, with prevalence < 10% during the peak of the transmission season, this is the first time that malaria can be reported as hypo-endemic in a sub-Sahelian setting in Burkina Faso. SMC has great potential, and along with other interventions, it could contribute to approaching the threshold where elimination strategies will be envisioned in Burkina Faso.

Accuracy of a Plasmodium falciparum specific histidine-rich protein 2 rapid diagnostic test in the context of the presence of non-malaria fevers, prior anti-malarial use and seasonal malaria transmission

Background

It remains challenging to distinguish malaria from other fever causing infections, as a positive rapid diagnostic test does not always signify a true active malaria infection. This study was designed to determine the influence of other causes of fever, prior anti-malarial treatment, and a possible seasonality of the performance of a PfHRP2 RDT for the diagnosis of malaria in children under-5 years of age living in a malaria endemic area.

Methods

A prospective etiology study was conducted in 2015 among febrile children under 5 years of age in Burkina Faso. In order to assess the influence of other febrile illnesses, prior treatment and seasonality on the performance of a PfHRP2 RDT in diagnosing malaria, the RDT results were compared with the gold standard (expert microscopic diagnosis of Plasmodium falciparum) and test results were analysed by assuming that prior anti-malarial use and bacterial/viral infection status would have been known prior to testing. To assess bacterial and viral infection status blood, urine and stool samples were analysed.

Results

In total 683 blood samples were analysed with microscopy and RDT-PfHRP2. Plasmodium falciparum malaria was diagnosed in 49.8% (340/683) by microscopy compared to 69.5% (475/683) by RDT-PfHRP2. The RDT-PfHRP2 reported 29.7% (141/475) false positive results and 1.8% (6/340) false negative cases. The RDT-PfHRP2 had a high sensitivity (98.2%) and negative predictive value (97.1%), but a low specificity (58.9%) and positive predictive value (70.3%). Almost 50% of the alternative cause of fever were diagnosed by laboratory testing in the RDT false positive malaria group.

Conclusions

The use of a malaria RDT-PfHRP2 in a malaria endemic area may cause misdiagnosis of the actual cause of fever due to false positive test results. The development of a practical diagnostic tool to screen for other causes of fever in malaria endemic areas is required to save lives.

Performance of pfHRP2 versus pLDH antigen rapid diagnostic tests for the detection of Plasmodium falciparum: a systematic review and meta-analysis

INTRODUCTION

There have been many inconsistent reports about the performance of histidine-rich protein 2 (HRP2) and lactate dehydrogenase (LDH) antigens as rapid diagnostic tests (RDTs) for the diagnosis of past Plasmodium falciparum infections. This meta-analysis was performed to determine the performance of pfHRP2 versus pLDH antigen RDTs in the detection of P. falciparum.

MATERIAL AND METHODS

After a systematic review of related studies, Meta-DiSc 1.4 software was used to calculate the pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR). Forest plots and summary receiver operating characteristic curve (SROC) analysis were used to summarize the overall test performance.

RESULTS

Fourteen studies which met the inclusion criteria were included in the meta-analysis. The summary performances for pfHRP2- and pLDH-based tests in the diagnosis of P. falciparum infections were as follows: pooled sensitivity, 96.3% (95.8-96.7%) vs. 82.6% (81.7-83.5%); specificity, 86.1% (85.3-86.8%) vs. 95.9% (95.4-96.3%); diagnostic odds ratio (DOR), 243.31 (97.679-606.08) vs. 230.59 (114.98-462.42); and area under ROCs, 0.9822 versus 0.9849 (all p < 0.001).

CONCLUSIONS

The two RDTs performed satisfactorily for the diagnosis of P. falciparum, but the pLDH tests had higher specificity, whereas the pfHRP2 tests had better sensitivity. The pfHRP2 tests had slightly greater accuracy compared to the pLDH tests. A combination of both antigens might be a more reliable approach for the diagnosis of malaria.

A Systematic Review of the Incidence, Risk Factors and Case Fatality Rates of Invasive Nontyphoidal Salmonella (iNTS) Disease in Africa (1966 to 2014)

This study systematically reviews the literature on the occurrence, incidence and case fatality rate (CFR) of invasive nontyphoidal Salmonella (iNTS) disease in Africa from 1966 to 2014. Data on the burden of iNTS disease in Africa are sparse and generally have not been aggregated, making it difficult to describe the epidemiology that is needed to inform the development and implementation of effective prevention and control policies. This study involved a comprehensive search of PubMed and Embase databases. It documents the geographical spread of iNTS disease over time in Africa, and describes its reported incidence, risk factors and CFR. We found that Nontyphoidal Salmonella (NTS) have been reported as a cause of bacteraemia in 33 out of 54 African countries, spanning the five geographical regions of Africa, and especially in sub-Saharan Africa since 1966. Our review indicates that NTS have been responsible for up to 39% of community acquired blood stream infections in sub-Saharan Africa with an average CFR of 19%. Salmonella Typhimurium and Enteritidis are the major serovars implicated and together have been responsible for 91%% of the cases of iNTS disease, (where serotype was determined), reported in Africa. The study confirms that iNTS disease is more prevalent amongst Human Immunodeficiency Virus (HIV)-infected individuals, infants, and young children with malaria, anaemia and malnutrition. In conclusion, iNTS disease is a substantial cause of community-acquired bacteraemia in Africa. Given the high morbidity and mortality of iNTS disease in Africa, it is important to develop effective prevention and control strategies including vaccination.

Multicenter Pivotal Clinical Trial of Urine Malaria Test for Rapid Diagnosis of Plasmodium falciparum Malaria

The need to expand malaria diagnosis capabilities alongside policy requirements for mandatory testing before treatment motivates exploration of noninvasive rapid diagnostic tests (RDTs). We report the outcome of the first cross-sectional, single-blind clinical performance evaluation of a urine malaria test (UMT) for diagnosis of Plasmodium falciparum malaria in febrile patients. Matched urine and finger-prick blood samples from participants ≥2 years of age with fever (axillary temperature of ≥37.5°C) or with a history of fever in the preceding 48 h were tested with UMT and microscopy (as the gold standard). BinaxNOW (Pf and Pan versions) blood RDTs were done to assess relative performance. Urinalysis and rheumatoid factor (RF) tests were conducted to evaluate possible interference. Diagnostic performance characteristics were computed at 95% confidence intervals (CIs). Of 1,800 participants screened, 1,691 were enrolled; of these 566 (34%) were febrile, and 1,125 (66%) were afebrile. Among enrolled participants, 341 (20%) tested positive by microscopy, 419 (25%) were positive by UMT, 676 (40%) were positive by BinaxNOW Pf, and 368 (22%) were positive by BinaxNow Pan. UMT sensitivity among febrile patients (for whom the test was indicated) was 85%, and specificity was 84%. Among febrile children ≤5 years of age, UMT sensitivity was 93%, and specificity was 83%. The area under the receiver-operator characteristic curve (AUC) of UMT (0.84) was not significantly different from that of BinaxNOW Pf (0.86) or of BinaxNOW Pan (0.87), indicating that the tests do not differ in overall performance. Gender, seasons, and RF did not impact UMT performance. Leukocytes, hematuria, and urobilinogen concentrations in urine were associated with lower UMT specificities. UMT performance was comparable to that of the BinaxNOW Pf/Pan tests, making UMT a promising tool to expand malaria testing in public and private health care settings where there are challenges to blood-based malaria diagnosis testing.

Spatial heterogeneity can undermine the effectiveness of country-wide test and treat policy for malaria: a case study from Burkina Faso

BACKGROUND

Considerable debate has arisen regarding the appropriateness of the test and treat malaria policy broadly recommended by the World Health Organization. While presumptive treatment has important drawbacks, the effectiveness of the test and treat policy can vary considerably across regions, depending on several factors such as baseline malaria prevalence and rapid diagnostic test (RDT) performance.

METHODS

To compare presumptive treatment with test and treat, generalized linear mixed effects models were fitted to data from 6510 children under five years of age from Burkina Faso's 2010 Demographic and Health Survey.

RESULTS

The statistical model results revealed substantial regional variation in baseline malaria prevalence (i.e., pre-test prevalence) and RDT performance. As a result, a child with a positive RDT result in one region can have the same malaria infection probability as a demographically similar child with a negative RDT result in another region. These findings indicate that a test and treat policy might be reasonable in some settings, but may be undermined in others due to the high proportion of false negatives.

CONCLUSIONS

High spatial variability can substantially reduce the effectiveness of a national level test and treat malaria policy. In these cases, region-specific guidelines for malaria diagnosis and treatment may need to be formulated. Based on the statistical model results, proof-of-concept, web-based tools were created that can aid in the development of these region-specific guidelines and may improve current malaria-related policy in Burkina Faso.

Deformability based sorting of red blood cells improves diagnostic sensitivity for malaria caused by Plasmodium falciparum

The loss of red blood cell (RBC) deformability is part of the pathology of many diseases. In malaria caused by Plasmodium falciparum infection, metabolism of hemoglobin by the parasite results in progressive reduction in RBC deformability that is directly correlated with the growth and development of the parasite. The ability to sort RBCs based on deformability therefore provides a means to isolate pathological cells and to study biochemical events associated with disease progression. Existing methods have not been able to sort RBCs based on deformability or to effectively enrich for P. falciparum infected RBCs at clinically relevant concentrations. Here, we develop a method to sort RBCs based on deformability and demonstrate the ability to enrich the concentration of ring-stage P. falciparum infected RBCs (Pf-iRBCs) by >100× from clinically relevant parasitemia (<0.01%). Deformability based sorting of RBCs is accomplished using ratchet transport through asymmetrical constrictions using oscillatory flow. This mechanism provides dramatically improved selectivity over previous biophysical methods by preventing the accumulation of cells in the filter microstructure to ensure that consistent filtration forces are applied to each cell. We show that our approach dramatically improves the sensitivity of malaria diagnosis performed using both microscopy and rapid diagnostic test by converting samples with difficult-to-detect parasitemia (<0.01%) into samples with easily detectable parasitemia (>0.1%).

Genetic diversity of Plasmodium falciparum histidine-rich protein 2 in the China-Myanmar border area

Deletion of the Plasmodium falciparum histidine-rich protein 2 (pfhrp2) gene may affect the performance of PfHRP2-based rapid diagnostic tests (RDTs). Here we investigated the genetic diversity of the pfhrp2 gene in clinical parasite isolates collected in recent years from the China-Myanmar border area. Deletion of pfhrp2 has been identified in 4 out of 97 parasite isolates. Sequencing of the pfhrp2 exon2 from 67 isolates revealed a high level of genetic diversity in pfhrp2, which is reflected in the presence of many repeat types and their variants, as well as variable copy numbers and different arrangements of these repeats in parasite isolates. In addition, we observed pfhrp3 deletion in three of the four parasites harboring pfhrp2 deletion, suggesting of double deletions of both genes in these three isolates. Analysis of two cases, which were P. falciparum-positive by microscopy and PCR but failed by two PfHRP2-based RDTs, did not find pfhrp2 deletion. Further correlational studies of pfhrp2 polymorphisms with detection sensitivity are needed to identify factors influencing the performance of RDTs in malaria-endemic areas.

SD Bioline malaria antigen Pf (HRP-2/pLHD) for assessing efficacy of artemisinin combination therapy against Plasmodium falciparum in pediatric patients in the Democratic Republic of the Congo

Introduction

The emergence of Plasmodium falciparum resistance to artemisinin combination therapy (ACT) is a worrying development. It calls for close surveillance to monitor the efficacy of the drugs. The objectives of this study were to determine the performance of SD Bioline malaria AgPf(HRP-2/pLDH) 3 band Rapid Diagnostic Test (RDT) against Giemsa-stained blood smear and evaluate the suitability of this test in assessing the therapeutic efficacy of ACT in pediatric malaria patients in the Democratic Republic of the Congo (DRC).

Methods

Five hundred and one patients with malaria symptoms were screened for P. falciparum in Kinshasa, DRC. Of the 166 patients who tested positive for P. falciparum at recruitment (day 0), 103 consented to participate in this study and were followed up and retested for P. falciparum on day 3, day 7, day 14, day 21 and day 28.

Results

Sensitivity and specificity of the test were significantly high on day 0 and so were their positive and negative predictive values. Higher proportions of false positive cases were observed on the HRP-2 band irrespective of patient parasite densities during the follow up but these were barely seen on the pLDH band. Some patients turned positive during follow up but pLDH readings remained consistent with blood smear readings.

Conclusion

SD Bioline malaria AgPf(HRP-2/pLDH) RDT demonstrated high performance in DRC. Thus, the test can be employed to assess the efficacy of ACT in pediatric malaria patients and prioritize areas that require the deployment of advanced testing like polymerase chain reaction (PCR).

Malaria Diagnosis Across the International Centers of Excellence for Malaria Research: Platforms, Performance, and Standardization

Diagnosis is “the act of identifying a disease, illness, or problem by examining someone or something.” When an individual with acute fever presents for clinical attention, accurate diagnosis leading to specific, prompt treatment often saves lives. As applied to malaria, not only individual patient diagnosis is important but also assessing population-level malaria prevalence using appropriate diagnostic methods is essential for public health purposes. Similarly, identifying (diagnosing) fake antimalarial medications prevents the use of counterfeit drugs that can have disastrous effects. Therefore, accurate diagnosis in broad areas related to malaria is fundamental to improving health-care delivery, informing funding agencies of current malaria situations, and aiding in the prioritization of regional and national control efforts. The International Centers of Excellence for Malaria Research (ICEMR), supported by the U.S. National Institute of Allergy and Infectious Diseases, has collaborated on global efforts to improve malaria diagnostics by working to harmonize and systematize procedures across different regions where endemicity and financial resources vary. In this article, the different diagnostic methods used across each ICEMR are reviewed and challenges are discussed.

Comparison of rapid diagnostic test Plasmotec Malaria-3, microscopy, and quantitative real-time PCR for diagnoses of Plasmodium falciparum and Plasmodium vivax infections in Mimika Regency, Papua, Indonesia

BACKGROUND

The World Health Organization recommends malaria be diagnosed by standard microscopy or rapid diagnostic test (RDT) before treatment. RDTs have been used with greater frequency in the absence of matching blood slide confirmation in the majority of RDT reported cases in Mimika Regency, Papua Province, Indonesia. Given the importance of RDT in current health system as point-of-care tool, careful validation of RDT product performance for providing accurate malaria diagnosis is critical.

METHODS

Plasmotec Malaria-3 (XW-P07) performance was evaluated by comparing it with paired blood film microscopy and quantitative real-time PCR (qPCR). Consecutive whole blood samples were derived from one clinic in Mimika as part of routine passive malaria case detection. RDT results were read by two trained technicians and interpreted by consensus. Expert microscopic examination of blood slides was cross-checked by observer-blinded second reader and a third examiner if discordant between examinations. qPCR was used as the 'gold standard', followed by microscopy for the outcome/disease variable. Comparison analysis included sensitivity (Sn), specificity (Sp), positive and negative predictive values (PPV & NPV), and other diagnostic screening performance measures for detecting Plasmodium falciparum and Plasmodium vivax infections.

RESULTS

Overall malaria positive samples from qPCR was 42.2% (175/415 samples); and from matching blood slides 40.5% (168/415) of which those infections with relatively low parasite densities ≤100/μl blood was 5.7% of P. falciparum and 16.5% of P. vivax samples examined. Overall RDT performance when compared with microscopy for detecting P. falciparum was Sn:92%, Sp:96.6%, PPV:88%, NPV:97.8%, Kappa:0.87; and for P. vivax Sn:72.9%, Sp:99.1%, PPV:95.4%, NPV:93.4%, Kappa:0.79. Overall RDT performance when compared with qPCR for detecting P. falciparum was Sn:92%, Sp:96.6%, PPV:88%, NPV:97.8%, Kappa:0.87; and for P. vivax Sn:66%, Sp:99.1%, PPV:95.4%, NPV:90.9%, Kappa:0.73.

CONCLUSIONS

Plasmotec Malaria-3 test showed good overall performance scores in precision for detecting P. falciparum, but lower values regarding sensitivity and negative likelihood ratio for detecting P. vivax, a finding partly associated with greater frequency of lower density P. vivax infections compared to P. falciparum in this study. In particular, the negative likelihood ratio (>0.1) for P. vivax detection indicates RDT lacked sufficient discriminating exclusion power falling below general acceptance criteria.

Paracheck® rapid diagnostic test for detecting malaria infection in under five children: a population-based survey in Burkina Faso

BACKGROUND

Over the past ten years, Rapid Diagnostic Tests (RDT) played a major role in improving the use of biological malaria diagnosis, in particular in poor-resources settings. In Burkina Faso, a recent Demography and Health Survey (DHS) gave the opportunity to assess the performance of the Paracheck® test in under five children nationwide at community level.

METHODS

A national representative sample of 14,947 households was selected using a stratified two-stage cluster sampling. In one out of two households, all under five children were eligible to be tested for malaria using both RDT and microscopy diagnosis. Paracheck® performance was assessed using miscroscopy as the gold standard. Sensitivity and specificity were calculated as well as the diagnosis accuracy (DA) and the Youden index.

RESULTS

The malaria infection prevalence was estimated at 66% (95% CI: 64.8-67.2) according to microscopy and at 76.2% (95% CI: 75.1-77.3) according to Paracheck®. The sensitivity and specificity were estimated at 89.9% (95% CI: 89.0-90.8) and 50.4% (95% CI: 48.3-52.6) respectively with a Diagnosis Accuracy of 77% and a Youden index of 40%. The positive predictive value for malaria infection was 77.9% (95% CI: 76.7-79.1) and the negative predictive value was 72.1% (95% CI: 69.7-74.3). Variations were found by age group, period of the year and urban and rural areas, as well as across the 13 regions of the country.

CONCLUSION

While the sensitivity of the Paracheck® test was high, its specificity was poor in the general under five population of Burkina Faso. These results suggest that Paracheck® is not suitable to assess malaria infection prevalence at community level in areas with high malaria transmission. In such settings, malaria prevalence in the general population could be estimated using microscopy.