Sensitivity and specificity for malaria classification of febrile persons by rapid diagnostic test, microscopy, parasite DNA, histidine-rich protein 2, and IgG: Dakar, Senegal 2015

Hematology thin smears perform equally to parasitology thick and thin blood smears for the diagnosis of Plasmodium and Babesia infections in a low prevalence setting

Malaria and babesiosis are significant parasitic infections, requiring timely diagnosis to avoid severe complications. This study retrospectively compared hematology thin smears (HS) with parasitology thick and thin blood smears (PS), the gold standard for diagnosis, to evaluate HS's performance in detecting Plasmodium and Babesia infections. Of 529 cases with paired HS and PS testing, HS demonstrated 93.3% sensitivity and 99.8% specificity, with 97.7% positive and 99.4% negative predictive values. When only considering new diagnoses, HS and PS were 100% concordant. No significant difference was found in percent parasitemia between HS and PS, highlighting HS as a reliable diagnostic tool in settings where PS or other diagnostic modalities may not be readily available.IMPORTANCEThis study demonstrates that hematology thin smears-often available in laboratories that may not have other means of diagnosing blood parasite infections such as parasitology thick and thin smears, rapid diagnostics tests, or polymerase chain reaction-are an accurate and reliable way to diagnose Plasmodium and Babesia infections in a low prevalence setting.

Assessment of Malaria Rapid Diagnostic Tests and Histidine-Rich Protein 2 Deletions among Asymptomatic Children and Adults in Bagamoyo, Tanzania

Malaria rapid diagnostic tests (mRDTs) that detect histidine-rich protein 2 (HRP2) remain the mainstay of falciparum malaria diagnosis in Sub-Saharan Africa. Understanding their test characteristics when used for surveillance in asymptomatic populations is important. We explored the rate of false-positive and false-negative mRDT results among asymptomatic persons >5 years old screened for malaria at schools and clinics in the rural Bagamoyo District using 18S ribosomal RNA real-time polymerase chain reaction (qPCR) as the reference test. Among 5,966 persons screened using mRDTs, microscopy, and qPCR tests from 2018 to 2021, 14% (832) were mRDT-positive. Twelve percent of these (98/832) were negative by both microscopy and qPCR, with children overrepresented among those with false-positive mRDTs. Among those who were mRDT-negative, 22% (1,136/5,134) tested qPCR-positive, predominantly because of low-density parasitemia (92% had <100 p/µL by qPCR). Among mRDT-negative samples with >100 p/µL, we looked for evidence of hrp2 or histidine-rich protein 3 (hrp3) deletion using two methods, multiplexed qPCR and multiplex bead-based immunoassay. When sufficient parasite material existed for a reliable deletion assessment, 12/34 (35%) had evidence of hrp2/3 deletion by qPCR (nine hrp2-/3+ and three hrp2-/3-), and 20/52 (38%) had evidence of deletion by immunoassay. Only three isolates showed evidence of hrp2 deletion by both assays. In an area of low to moderate transmission in Tanzania, false-positive mRDTs are relatively common (12% of positive tests), and false-negative mRDTs are even more common (22% of negative tests), but hrp2/3 deletion causing false-negative mRDTs remains rare (<1% of negative tests).

Congenital malaria in newborns of mothers living in highly endemic parts of Kinshasa, Democratic Republic of Congo

BACKGROUND

Congenital malaria, characterised by low parasitaemia in newborns' peripheral blood, is difficult to diagnose by conventional techniques. Owing to its high sensitivity, polymerase chain reaction (PCR) allows for effective detection of low-density plasmodium infections. This study determined the prevalence of congenital malaria by PCR in newborns of mothers living in a malaria-endemic area of Kinshasa, Democratic Republic of Congo (DRC).

METHODS

A total of 576 mother-newborn pairs were enrolled in two clinical trials in Kinshasa. Maternal peripheral blood was collected at enrolment. At delivery, samples were taken from maternal and newborn peripheral blood, placental blood and placental imprints.

RESULTS

The prevalence of congenital malaria detected by PCR was 2.4% (14/576) compared with 0.9% (5/576) by microscopy. The prevalence of malaria at delivery was 8.9% (51/570), and placental malaria was 10.6% (59/556) by microscopy. At delivery, maternal malaria was significantly associated with congenital malaria [adjusted odds ratio (aOR) 16.06, 95% CI 2.6-98.5, p < 0.01). Placental malaria also increased the risk of congenital malaria (aOR 5.77, 95% CI 0.9-35.2, p = 0.05). Although 10 of 72 women (16.7%) with placental malaria gave birth to low-weight infants, the association was not statistically significant.

CONCLUSIONS

Although this first assessment of congenital malaria by PCR in DRC found a low prevalence, maternal and placental malaria at delivery were still associated with congenital malaria, highlighting the importance of maternal health in preventing neonatal infections.Abbreviations: Aor adjusted odds ratio; CI confidence interval; cOR crude odds ratio; DNA de-oxyribonucleic acid; GAPDH glyceraldehyde-3-posphate dehydrogenase; g/dL grams per decilitre; Hb haemoglobin; IQR interquartile range; IPTp-SP Intermittent Preventive Treatment in pregnancy with sulfadoxine-pyrimethamine; ITN insecticide-treated nets; PA pyronaridine-artesunate; PCR polymerase chain reaction; RDT rapid diagnostic tests; SD; standard deviation; uRDTs ultra-sensitive rapid diagnostic tests; WHO World Health Organization; µL microlitre.

Real-time PCR for malaria diagnosis and identification of Plasmodium species in febrile patients in Cubal, Angola

BACKGROUND

Malaria is the parasitic disease with the highest morbimortality worldwide. The World Health Organization (WHO) estimates that there were approximately 249 million cases in 2022, of which 3.4% were in Angola. Diagnosis is based on parasite identification by microscopy examination, antigen detection, and/or molecular tests, such as polymerase chain reaction (PCR). This study aimed to evaluate the usefulness of real-time PCR as a diagnostic method for malaria in an endemic area (Cubal, Angola).

METHODS

A cross-sectional study was carried out at the Hospital Nossa Senhora da Paz in Cubal, Angola, including 200 patients who consulted for febrile syndrome between May and July 2022. From each patient, a capillary blood sample was obtained by finger prick for malaria field diagnosis [microscopy and rapid diagnostic test (RDT)] and venous blood sample for real-time PCR performed at the Hospital Universitario Vall d'Hebron in Barcelona, Spain. Any participant with a positive result from at least one of these three methods was diagnosed with malaria.

RESULTS

Of the 200 participants included, 54% were female and the median age was 7 years. Malaria was diagnosed by at least one of the three techniques (microscopy, RDT, and/or real-time PCR) in 58% of the participants, with RDT having the highest percentage of positivity (49%), followed by real-time PCR (39.5%) and microscopy (33.5%). Of the 61 discordant samples, 4 were only positive by microscopy, 13 by real-time PCR, and 26 by RDT. Plasmodium falciparum was the most frequent species detected (90.63%), followed by P. malariae (17.19%) and P. ovale (9.38%). Coinfections were detected in ten participants (15.63%): six (60%) were caused by P. falciparum and P. malariae, three (30%) by P. falciparum and P. ovale, and one (10%) triple infection with these three species. In addition, it was observed that P. falciparum and P. malariae coinfection significantly increased the parasite density of the latter.

CONCLUSIONS

RDT was the technique with the highest positivity rate, followed by real-time PCR and microscopy. The results of the real-time PCR may have been underestimated due to suboptimal storage conditions during the transportation of the DNA eluates. However, real-time PCR techniques have an important role in the surveillance of circulating Plasmodium species, given the epidemiological importance of the increase in non-falciparum species in the country, and can provide an estimate of the intensity of infection.

Advances in Malaria Diagnostic Methods in Resource-Limited Settings: A Systematic Review

Malaria continues to pose a health challenge globally, and its elimination has remained a major topic of public health discussions. A key factor in eliminating malaria is the early and accurate detection of the parasite, especially in asymptomatic individuals, and so the importance of enhanced diagnostic methods cannot be overemphasized. This paper reviewed the advances in malaria diagnostic tools and detection methods over recent years. The use of these advanced diagnostics in lower and lower-middle-income countries as compared to advanced economies has been highlighted. Scientific databases such as Google Scholar, PUBMED, and Multidisciplinary Digital Publishing Institute (MDPI), among others, were reviewed. The findings suggest important advancements in malaria detection, ranging from the use of rapid diagnostic tests (RDTs) and molecular-based technologies to advanced non-invasive detection methods and computerized technologies. Molecular tests, RDTs, and computerized tests were also seen to be in use in resource-limited settings. In all, only twenty-one out of a total of eighty (26%) low and lower-middle-income countries showed evidence of the use of modern malaria diagnostic methods. It is imperative for governments and other agencies to direct efforts toward malaria research to upscale progress towards malaria elimination globally, especially in endemic regions, which usually happen to be resource-limited regions.

Performance of antigen detection for HRP2-based malaria rapid diagnostic tests in community surveys: Tanzania, July-November 2017

BACKGROUND

Malaria rapid diagnostic tests (RDTs) based on the detection of the Plasmodium falciparum histidine-rich protein 2 (HRP2) antigen are widely used for detection of active infection with this parasite and are the only practical malaria diagnostic test in some endemic settings. External validation of RDT results from field surveys can confirm appropriate RDT performance.

METHODS

A community-based cross-sectional survey was conducted between July and November 2017 enrolling participants of all ages in households from 15 villages in four border regions of Tanzania: Geita, Kigoma, Mtwara and Ruvuma. All participants had an RDT performed in the field and provided a blood sample for later laboratory multiplex antigen detection of HRP2. In assessing the continuous HRP2 levels in participant blood versus RDT result, dose-response logistic regression provided quantitative estimates for HRP2 limit of detection (LOD).

RESULTS

From the 15 study villages, 6941 persons were enrolled that had a RDT at time of enrollment and provided a DBS for later laboratory antigen detection. RDT positive prevalence for the HRP2 band by village ranged from 20.0 to 43.6%, but the magnitude of this prevalence did not have an effect on the estimated LOD of RDTs utilized in different villages. Overall, HRP2 single-target tests had a lower LOD at the 95% probability of positive RDT (4.3 ng/mL; 95% CI 3.4-5.4) when compared to pLDH/HRP2 dual target tests (5.4 ng/mL; 4.5-6.3), though this difference was not significant. With the exception of one village, all other 14 villages (93.3%) showed RDT LOD estimates at 90% probability of positive RDT between 0.5 and 12.0 ng/mL.

CONCLUSIONS

Both HRP2-only and pLDH/HRP2 combo RDTs utilized in a 2017 Tanzania cross-sectional survey of border regions generally performed well, and reliably detected HRP2 antigen in the low ng/mL range. Though single target tests had lower levels of HRP2 detection, both tests were within similar ranges among the 15 villages. Comparison of quantitative HRP2 detection limits among study sites can help interpret RDT testing results when generating population prevalence estimates for malaria infection.

Enzyme-linked aptamer-based sandwich assay (ELASA) for detecting Plasmodium falciparum lactate dehydrogenase, a malarial biomarker

Herein, we report a sensitive and selective enzyme-linked aptamer-based sandwich assay (ELASA) to detect Plasmodium falciparum lactate dehydrogenase (PfLDH), which is an attractive biomarker for malaria diagnosis and antimalarial medication. We performed the sandwich assay with a single aptamer sequence, called 2008s, owing to the structural properties of the PfLDH tetramer instead of using a conventional sandwich assay with two different aptamers (or antibodies) for capturing and probing a target molecule. First, the biotinylated PfLDH aptamer was linked with immobilized streptavidin on a microwell plate for binding flexibility, and then PfLDH was bound to the aptamer. Next, a horseradish peroxidase-conjugated aptamer of the same sequence was used to analyze PfLDH quantitatively. Using this approach, the limit of detection (LOD) of PfLDH with the naked eye was 100 ng mL^-1, and the LOD and limit of quantification from the absorbance measurements were 34.9 ng mL^-1 and 95.5 ng mL^-1, respectively, based on PfLDH spiked blood samples. Our proposed method selectively binds PfLDH, not human lactate dehydrogenase. Therefore, this method may be a valuable tool for diagnosing, monitoring, and quarantining malaria cases easily and rapidly.

Antimicrobial Stewardship in Tropical Infectious Diseases: Focusing on Dengue and Malaria

Acute undifferentiated febrile illness (AUFI) is the presenting symptom of various tropical and infectious diseases. Viral infection is generally the most common cause of AUFI, accounting for 8–11.8% of cases; thus, antibiotics might be unnecessary. Dengue and malaria are common tropical infectious diseases requiring effective supportive treatment and antimalarial agents, respectively. The uncertainty of early diagnosis results in widespread empirical antimicrobial treatment in high -income as well as in low-and middle-income countries. Although rapid diagnostic tests (RDTs) have been shown to limit antibiotic prescriptions in dengue and malaria, we observed a wide range of antibiotic prescriptions for 13–92.7% of cases in previous literature, particularly in RDT-negative malaria cases. Given several RDT limitations, antimicrobial stewardship (AMS) appears to be an effective strategy for controlling unnecessary antibiotic use and antimicrobial resistance (AMR) prevention. This program should be endorsed by a multidisciplinary team in tropical diseases to control collateral damage of inappropriate antimicrobial use. Empirical antibiotic treatment should be administered based on clinical judgement, microbiological evidence, and local epidemiological data. Rapid termination of antibiotic therapy, including disease control or elimination, is the mainstay of AMS in tropical diseases. Local and international sectors should implement an AMS programme to reduce AMR in the Tropics.