Comparison of PCR and microscopy for the detection of asymptomatic malaria in a Plasmodium falciparum/vivax endemic area in Thailand

Usefulness of serial testing for the diagnosis of malaria in cases of fever upon return from travel

BACKGROUND

When malaria is suspected in case of fever after travel in endemic areas, the current recommendation is to repeat the malaria test at 24-hour intervals, with up to two additional tests, as long as the test result is negative. A retrospective analysis was conducted to investigate the appropriateness of this recommendation by determining the proportion of tests with negative result at first and subsequently with a positive one at second or third attempt.

METHODS

A retrospective study was conducted at the Centre for Primary Care and Public Health, Lausanne, covering a period of 15 years. All patients tested once for malaria were included. Testing included microscopy thick and thin films as well as malaria rapid diagnostic test used in combination. The main outcome measure was the proportion of patients with a first negative test result, subsequently positive on second or third test over the total patients with suspected malaria assessed. Demographic, travel, clinical, and laboratory variables were collected from patients' records to identify potential predictors of an initially negative and then positive test result.

RESULTS

Four thousand nine hundred seventy-two patients were included. Of those, 4557 (91.7%) had definitive negative test results, and 415 (8.3%) had a positive result on the first test [332/415 (80%) Plasmodium falciparum, 40/415 (9.6%) P. vivax, 21/415 (5.1%) P. ovale, 12/415 (2.9%) P. vivax/ovale, 9/415 (2.2%) P. malariae and 1/415 (0.2%) P. knowlesi], and 3/4972 (0.06%) had a positive result on the second test after a first negative result, 1/4972(0.02%) had a positive test result after 2 negative results, all with P. falciparum. One of the four patients that were positive after their initial negative test was pregnant. The very small number of patients with an initially negative test result and secondarily positive did not allow for risk factor analysis.

CONCLUSIONS

The current recommendation of serial malaria testing is not supported by the present study, a fortiori for those who do not present with a strong clinical or laboratory predictor of malaria.

Comparison of Three Methods to Extract Plasmodium falciparum DNA from Whole Blood and Dried Blood Spots

This study aimed to compare the effectiveness of three DNA extraction methods: the GF-1 Blood DNA Extraction Kit (GF-1 BD Kit), which employs a spin column along with lysing and washing buffers; the tris-ethylenediaminetetraacetic acid and proteinase K (TE-pK) method, which utilizes a combination of TE buffer and proteinase K for cell lysis; and DNAzol® Direct (DN 131), a single reagent combined with heating for the extraction process. Plasmodium falciparum DNA was extracted from both whole blood and dried blook spots (DBSs), with consideration of DNA concentration, purity, cost, time requirement, and limit of parasite detection (LOD) for each method. The target gene in this study was 18S rRNA, resulting in a 395-bp product using specific primers. In the comparative analysis, the DN 131 method yielded significantly higher DNA quantities from whole blood and DBSs than the GF-1 BD Kit and TE-pK methods. In addition, the DNA purity obtained from whole blood and DBSs using the GF-1 BD Kit significantly exceeded that obtained using the TE-pK and DN 131 methods. For LOD, the whole blood extracted using the DN 131, GF-1 BD Kit, and TE-pK methods revealed 0.012, 0.012, and 1.6 parasites/µL, respectively. In the case of DBSs, the LODs for the DN 131, GF-1 BD Kit, and TE-pK methods were 1.6, 8, and 200 parasites/µL, respectively. The results revealed that the TE-pK method was the most cost-effective, whereas the DN 131 method showed the simplest protocol. These findings offer alternative approaches for extracting Plasmodium DNA that are particularly well-suited for large-scale studies conducted in resource-limited settings.

Molecular detection of Babesia vesperuginis in bats from Lithuania

Babesia vesperuginis is an intraerythrocytic protozoan parasite that circulates among bats and ticks in many countries worldwide. However, the distribution of B. vesperuginis in the Baltic region has not been studied. A total of 86 dead bats from eight different species were collected and screened for Babesia spp. using real-time PCR. Overall, 52.3% (45/86) of the bats were found positive for Babesia spp. The prevalence of Babesia spp. in different organs varied, with the highest prevalence observed in heart tissues (37.0%) and the lowest in liver tissues (22.2%). However, the observed differences in prevalence among organs were not statistically significant. Blood samples from 125 bats of nine different species were also analyzed for Babesia spp. prevalence using real-time PCR and nested PCR. The results showed a prevalence of 35.2% and 22.4%, respectively. Moreover, 28.3% (17/60) of the examined blood samples were confirmed positive for Babesia spp. through blood smear analysis. The total of 32 partial sequences of the 18S rRNA gene derived in this study were 100% identical to B. vesperuginis sequences from GenBank. In eight species of bats, Pipistrellus nathusii, Pipistrellus pipistrellus, Pipistrellus pygmaeus, Vespertilio murinus, Eptesicus nilssonii, Eptesicus serotinus, Myotis daubentonii and Nyctalus noctula, Babesia parasites were identified. In E. nilssonii, Babesia spp. was identified for the first time.

Rapid, sensitive, and convenient detection of Plasmodium falciparum infection based on CRISPR and its application in detection of asymptomatic infection

Rapid and convenient detection of the Plasmodium in clinically diagnosed individuals and asymptomatically infected populations is essential for global malaria eradication, especially in malaria-endemic African countries where medical equipment and professionals are relatively deficient. Here, we described a CRISPR-based diagnostic for the detection of Plasmodium falciparum, the deadliest and most prevalent species of malaria parasite in Africa, via lateral flow strip readout without the need of nucleic acid extraction. The assay exhibited 100% sensitivity on clinical samples (5 P falciparum) and significant consistency with qPCR test on asymptomatic infection samples (49 P falciparum and 51 non-P. falciparum, Kappa=0.839). An artemisinin-resistant P. falciparum strain and 4 other laboratory-cultured strains can also be detected through this assay, whereas no cross-reactivity with Plasmodium vivax was observed. A 0.001% parasitaemia (corresponding to ∼60 parasites/μL) below the "low parasite density" test threshold (200 parasites/µL) is detectable. Our study demonstrated that direct malaria detection using whole blood on the spot and the detection of both clinical and asymptomatic infections of P. falciparum are feasible. This method is expected to be employed for clinical testing and large-scale community screening in Africa and possibly other places, contributing to the accurate diagnosis and control of malaria.

A Novel Nested Multiplex Polymerase Chain Reaction Assay for Malaria Diagnosis Using the Hydroxymethyl Dihydropterin Pyrophosphokinase-Dihydropteroate Synthase (hppk-dhps) Gene

There are many techniques for malaria diagnosis. Currently, the nested polymerase chain reaction (PCR) method based on a small subunit ribosomal RNA gene (18S rRNA) has been used as a confirmatory method. However, this method is time-consuming, laborious, and costly. Therefore, the objective of this study was to develop nested multiplex PCR for Plasmodium species identification using the dihydropterin pyrophosphokinase-dihydropteroate synthase (hppk-dhps) gene. Genus- and species-specific primers for the hppk-dhps gene were designed. The performance of the novel nested multiplex PCR was compared with 18S rRNA nested PCR. A total of 115 blood samples were used in this study, including 84 infected samples and 31 uninfected samples. Analysis of the blood samples by nested multiplex PCR targeting the hppk-dhps gene identified 81 infected cases. The level of agreement between this novel method and 18S rRNA nested PCR was 97.4%. Further, the novel method successfully detected all human malaria parasites except Plasmodium ovale and detected mixed Plasmodium falciparum/Plasmodium vivax infections. The sensitivity and specificity obtained from this novel method were 96.4% and 100%, respectively. The limit of detection of the hppk-dhps nested multiplex PCR for P. falciparum and P. vivax was 500 parasites/µL and 4 parasites/µL, respectively. The lowest parasite gDNA detected by this method was 0.5 ng/µL for P. falciparum and 0.1 ng/µL for P. vivax. These results corroborate that the hppk-dhps gene is a novel amplification target for the detection of human malaria. This novel target PCR-based method is a beneficial approach for malaria diagnosis, as well as species identification and differentiation.

Sunflower plantings reduce a common gut pathogen and increase queen production in common eastern bumblebee colonies

Community diversity can reduce the prevalence and spread of disease, but certain species may play a disproportionate role in diluting or amplifying pathogens. Flowers act as both sources of nutrition and sites of pathogen transmission, but the effects of specific plant species in shaping bee disease dynamics are not well understood. We evaluated whether plantings of sunflower (Helianthus annuus), whose pollen reduces infection by some pathogens when fed to bees in captivity, lowered pathogen levels and increased reproduction in free-foraging bumblebee colonies (Bombus impatiens). Sunflower abundance reduced the prevalence of a common gut pathogen, Crithidia bombi, and reduced infection intensity, with an order of magnitude lower infection intensity at high sunflower sites compared with sites with little to no sunflower. Sunflower abundance was also positively associated with greater queen production in colonies. Sunflower did not affect prevalence of other detected pathogens. This work demonstrates that a single plant species can drive disease dynamics in foraging B. impatiens, and that sunflower plantings can be used as a tool for mitigating a prevalent pathogen while also increasing reproduction of an agriculturally important bee species.

Survey of malaria vectors on the Cambodia, Thailand and China-Laos Borders

BACKGROUND

Anopheles maculatus, Anopheles minimus and Anopheles dirus are the major vectors of malaria transmission in the Greater Mekong Subregion (GMS). The malaria burden in this region has decreased significantly in recent years as all GMS countries progress towards malaria elimination. It is necessary to investigate the Anopheles diversity and abundance status and assess the Plasmodium infection rates to understand the malaria transmission potential of these vector species in GMS countries to guide the development of up-to-date vector control strategies and interventions.

METHODS

A survey of mosquitoes was conducted in Stung Treng, Sainyabuli and Phongsaly Provinces on the Cambodia-Laos, Thailand-Laos and China-Laos borders, respectively. Mosquito collection was done by overnight trapping at sentinel sites in each province. After morphological identification, the 18S rRNA-based nested-PCR was performed to detect malaria parasites in the captured Anopheles mosquitoes.

RESULTS

A total of 18 965 mosquitoes comprising of 35 species of 2 subgenera (Subgenus Anopheles and Subgenus Cellia) and 4 tribes (Tribes Culicini, Aedini, Armigerini and Mansoniini) were captured. Tribe Culicini accounted for 85.66% of captures, followed by Subgenus Anopheles (8.15%). Anopheles sinensis dominated the Subgenus Anopheles by 99.81%. Plasmodium-infection was found in 25 out of the 1 683 individual or pooled samples of Anopheles. Among the 25 positive samples, 19, 5 and 1 were collected from Loum, Pangkhom and Siem Pang village, respectively. Eight Anopheles species were found infected with Plasmodium, i.e., An. sinensis, Anopheles kochi, Anopheles vagus, An. minimus, Anopheles annularis, Anopheles philippinensis, Anopheles tessellatus and An. dirus. The infection rates of Plasmodium falciparum, Plasmodium vivax and mixture of Plasmodium parasite species were 0.12% (2/1 683), 1.31% (22/1 683) and 0.06% (1/1 683), respectively.

CONCLUSIONS

Overall, this survey re-confirmed that multiple Anopheles species carry malaria parasites in the international border areas of the GMS countries. Anopheles sinensis dominated the Anopheles collections and as carriers of malaria parasites, therefore may play a significant role in malaria transmission. More extensive investigations of malaria vectors are required to reveal the detailed vector biology, ecology, behaviour, and genetics in GMS regions in order to assist with the planning and implementation of improved malaria control strategies.

Assessing the diagnostic performance of a novel RT-PCR fluorescence method for the detection of human plasmodium species

Background

Malaria elimination effort is hampered not only by the lack of effective medication but also due to the lack of sensitive diagnostic tools to detect infections with low levels of parasitemia. Therefore, more sensitive and specific high-throughput molecular diagnostic approaches are needed for accurate malaria diagnosis.

Methods

In the present study, the performance of a novel single-tube MC004 real-time polymerase chain reaction (PCR) assay (MRC-Holland, Amsterdam, the Netherlands) was assessed for the detection of infection and discrimination of Plasmodium species. Blood samples (n = 150) were collected from malaria suspected patients at Adama malaria diagnosis and treatment centre, Adama, central Ethiopia. The positive predictive value (PPV), negative predictive value (NPV), analytical sensitivity and specificity of the assay were assessed against the conventional microscopic method.

Results

Plasmodium species were detected in 59 (39.3%) of the samples by microscopy and in 62 (41.3%) by the novel MC004 RT-PCR. Plasmodium vivax, Plasmodium falciparum and mixed infections with Plasmodium falciparum & Plasmodium vivax accounted for 47.5%, 40.6% and 11.9% respectively as detected by microscopy. The MC004 RT-PCR assay identified 59.7% and 40.3% of the samples positive for Plasmodium vivax and Plasmodium falciparum respectively. The sensitivity, specificity, PPV, and NPV of the MC004 RT-PCR assay were 95.8%, 97.8%, 92%, and 98.9%, respectively. No mixed infections were detected using the MC004 assay.

Conclusion

The MC004 RT-PCR assay is a useful tool for the early detection of malaria and identification of Plasmodium species with a high degree of sensitivity and specificity. Due to its high sensitivity, and simplicity (being a single-tube assay), the MC004 is suitable for use in clinical settings and epidemiological studies.

Evaluation of Multiplex/Nested Polymerase Chain Reaction and Loop-Mediated Isothermal Amplification for Malaria Diagnosis in Southeastern Iran

Malaria is one of the most serious health problems in many countries, including Iran. Accurate diagnosis is important regardless of the elimination status of a country. A cross-sectional study was performed on 105 people who were suspected to be positive for malaria infection in Sistan and Baluchistan, Iran. Blood smears (thin and thick films) were stained with 10% Giemsa. DNA was extracted from the prepared thin and thick films for molecular methods. Multiplex/nested polymerase chain reaction (mn-PCR), loop-mediated isothermal amplification (LAMP), and light microscopy (LM) were compared with nested PCR (nPCR) as a gold standard. Of 105 subjects, 52 (49.5%), 58 (55.2%), 58 (55.2%), and 63 (60%) were positive for malaria by LM, nPCR, mn-PCR, and LAMP, respectively. The sensitivity, specificity, and kappa were 92.1%, 100%, and 0.9 for LAMP and 100%, 100%, and 1 for mn-PCR, respectively. Eight cases of coinfection (Plasmodium vivax and Plasmodium falciparum) that were not detected by LM method were diagnosed by mn-PCR and LAMP. In the present study, the high sensitivity and specificity of LAMP and mn-PCR indicate that these two tests are good alternatives to nPCR for malaria diagnosis.

Challenges in Laboratory Diagnosis of Malaria in a Low-Resource Country at Tertiary Care in Eastern Nepal: A Comparative Study of Conventional vs. Molecular Methodologies

For ongoing malaria elimination programmes, available methods such as microscopy and rapid diagnostic tests (RDTs) cannot detect all malaria cases in acute febrile illness. These methods are entirely dependent on the course of infection, parasite load, and skilled technical resources. Our study objectives were to estimate the performance of light microscopy and a RDT as well as real-time PCR for the detection of the Plasmodium parasite. Altogether, 52 blood samples collected from patients with acute febrile illness were tested by microscopy, RDT, and real-time PCR. The results were compared in terms of sensitivity and specificity. Microscopy detected the malaria parasite in 5.8% of the blood samples whereas 13.5% were detected by the RDT and 27% by real-time PCR. Considering real-time PCR as the gold standard method, microscopy had a sensitivity of 21.4% and a specificity of 100%, and the RDT had a sensitivity of 28.6% and a specificity of 92.1%. Microscopy together with the RDT successfully detected malaria positive cases in blood samples of Ct value below 20, but both were unable to detect malaria cases between 26-40 Ct value ranges amplified by real-time PCR. Despite various diagnostic tools being available, microscopy still remains the method of choice for diagnosis, while the RDT is user-friendly when applied at the point of care. However, our preliminary results emphasize the need to implement the test with higher sensitivity and specificity in the context of a malaria elimination programme. Such programmes can be a crucial opportunity to understand the species prevalent in a low-endemic region. However, these results should be further verified with a large cohort study to document the submicroscopic infection.

Serology for Plasmodium vivax surveillance: A novel approach to accelerate towards elimination

Plasmodium vivax is the most widespread causative agent of human malaria in the world. Despite the ongoing implementation of malaria control programs, the rate of case reduction has declined over the last 5 years. Hence, surveillance of malaria transmission should be in place to identify and monitor areas that require intensified malaria control interventions. Serological tools may offer additional insights into transmission intensity over parasite and entomological measures, especially as transmission levels decline. Antibodies can be detected in the host system for months to even years after parasite infections have been cleared from the blood, enabling malaria exposure history to be captured. Because the Plasmodium parasite expresses more than 5000 proteins, it is important to a) understand antibody longevity following infection and b) measure antibodies to more than one antigen in order to accurately inform on the exposure and/or immune status of populations. This review summarises current practices for surveillance of P. vivax malaria, the current state of research into serological exposure markers and their potential role for accelerating malaria elimination, and discusses further studies that need to be undertaken to see such technology implemented in malaria-endemic areas.

An electrochemical aptamer-based biosensor targeting Plasmodium falciparum histidine-rich protein II for malaria diagnosis

Malaria is an infectious disease caused by parasitic protozoans from the genus Plasmodium, with the species P. falciparum causing the highest number of deaths worldwide. Rapid diagnostic tests (RDTs) have become critical in the management of malaria, but current RDTs that detect P. falciparum are primarily antibody-based, which can have drawbacks in cost and robustness. Here, we report the development of an electrochemical aptamer-based (E-AB) biosensing alternative. Through selective evolution of ligands by exponential enrichment, we identify DNA aptamers that bind specifically to P. falciparum histidine-rich protein II (PfHRP2). The aptamer is modified with a methylene blue reporter and attached to a gold sensor surface for square-wave voltammetry interrogation. Through this method we are able to quantify PfHRP2 in human serum with an LOD of 3.73 nM. We further demonstrate the biosensor is stable in serum buffers and reusable for multiple detection rounds. These findings provide a promising alternative to conventional PfHRP2 detection for malaria diagnosis, while also expanding the capabilities of E-AB biosensors.

Analytical validation of a real-time hydrolysis probe PCR assay for quantifying Plasmodium falciparum parasites in experimentally infected human adults

Background

Volunteer infection studies have become a standard model for evaluating drug efficacy against Plasmodium infections. Molecular techniques such as qPCR are used in these studies due to their ability to provide robust and accurate estimates of parasitaemia at increased sensitivity compared to microscopy. The validity and reliability of assays need to be ensured when used to evaluate the efficacy of candidate drugs in clinical trials.

Methods

A previously described 18S rRNA gene qPCR assay for quantifying Plasmodium falciparum in blood samples was evaluated. Assay performance characteristics including analytical sensitivity, reportable range, precision, accuracy and specificity were assessed using experimental data and data compiled from phase 1 volunteer infection studies conducted between 2013 and 2019. Guidelines for validation of laboratory-developed molecular assays were followed.

Results

The reportable range was 1.50 to 6.50 log₁₀ parasites/mL with a limit of detection of 2.045 log₁₀ parasites/mL of whole blood based on a parasite diluted standard series over this range. The assay was highly reproducible with minimal intra-assay (SD = 0.456 quantification cycle (C_q) units [0.137 log₁₀ parasites/mL] over 21 replicates) and inter-assay (SD = 0.604 C_q units [0.182 log₁₀ parasites/mL] over 786 qPCR runs) variability. Through an external quality assurance program, the QIMR assay was shown to generate accurate results (quantitative bias + 0.019 log₁₀ parasites/mL against nominal values). Specificity was 100% after assessing 164 parasite-free human blood samples.

Conclusions

The 18S rRNA gene qPCR assay is specific and highly reproducible and can provide reliable and accurate parasite quantification. The assay is considered fit for use in evaluating drug efficacy in malaria clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03717-y.

Comparison of polymerase chain reaction, microscopy, and rapid diagnostic test in malaria detection in a high burden state (Odisha) of India

Precise identification of Plasmodium species is critical in malaria control and elimination. Despite several shortcomings, microscopy and rapid diagnostic test (RDT) continue to be the leading diagnostic methods. Polymerase chain reaction (PCR) is the most sensitive method but its dependency on advanced laboratory and skilled workers limits its use. Here, we compared the diagnostic performance of microscopy, RDT, and PCR in clinically suspected patients from a high malaria burden state (Odisha) of India. The diagnostic performance (sensitivity, specificity, positive predictive value, and negative predictive value) of all three methods was compared using microscopy and PCR as the gold standard. PCR identified 323 (76.5 %) positive cases out of 422 samples, whereas microscopy and RDT identified only 272 (64.4 %) and 266 (63.0 %) positive cases, respectively. The sensitivity of RDT and microscopy for detecting malaria and P. falciparum cases was >80% compared to that by PCR. However, the sensitivity in identifying P. vivax (57.0 %) and a mixture of P. falciparum and P. vivax (18.0 %) was poor. We highlight application of PCR in malaria diagnosis and its benefits in reducing the transmission. This emphasizes the need for incorporation of molecular diagnostic approaches for effective elimination strategies.

Performance evaluation of the highly sensitive histidine-rich protein 2 rapid test for plasmodium falciparum malaria in North-West Tanzania

Background

Precise detection of Plasmodium infections in community surveys is essential for effective malaria control. Microscopy and rapid diagnostic tests (RDTs) are the major techniques used to identify malaria infections in the field-based surveys. Although microscopy is still considered as the gold standard, RDTs are increasingly becoming versatile due to their rapid and adequate performance characteristics.

Methods

A malaria prevalence cross-sectional survey was carried out in north-western Tanzania in 2016, aimed at appraising the performance of high sensitivity Plasmodium falciparum (HSPf) tests compared to SD Bioline Pf and microscopy in detecting P. falciparum infections. A total of 397 individuals aged five years and above were tested for P. falciparum infections. The sensitivity, specificity, positive, and negative predictive values (PPV and NPV) of microscopy, Pf RDT and HSPf RDT was determined using PCR as the gold standard method.

Results

The prevalence of P. falciparum infections determined by microscopy, SD Bioline Pf, HSPf and PCR was 21.9, 27.7, 33.3 and 43.2%, respectively. The new HSPf RDT had significantly higher sensitivity (98.2%) and specificity (91.6%) compared to the routinely used SD Bioline Pf RDT(P < 0.001). The positive predictive value (PPV) was 81.8% and the negative predictive value (NPV) was 99.2% for the routinely used SD Bioline Pf RDT. Moreover, HSPf RDT had sensitivity of 69% and specificity of 76.8% compared to microscopy. The PPV was 45.5% and the NPV was 89.8% for microscopy. Furthermore, the analytical sensitivity test indicated that the newly developed HSPf RDT had lower detection limits compared to routinely used SD Bioline RDT.

Conclusions

HSPf RDT had better performance when compared to both microscopy and the currently used malaria RDTs. The false negativity could be associated with the low parasite density of the samples. False positivity may be related to the limitations of the expertise of microscopists or persistent antigenicity from previous infections in the case of RDTs. Nevertheless, HS PfRDT performed better compared to routinely used Pf RDT, and microscopy in detecting malaria infections. Therefore, HS Pf RDT presents the best alternative to the existing commercial/regularly available RDTs due to its sensitivity and specificity, and reliability in diagnosing malaria infections.

Application of High-Resolution Melting (HRM) Technique towards the Detection of Asymptomatic Malaria in a Malaria Endemic Area of Southeastern Iran under Elimination Program

Background:

Asymptomatic malaria, which usually exists in low parasitemia, acts as the Plasmodium species reservoirs contributing towards malaria transmission. This situation hinders malaria elimination programs in endemic areas, thus necessitating an active case detection with a high sensitive method and treatment of cases. This is why we used a High Resolution Melting (HRM) assay to monitor the trend of asymptomatic malaria in a malaria endemic area of Iran which is under elimination program.

Methods:

The peripheral blood was sampled from 271 clinically approved non-febrile individuals from a malaria endemic zone of southeastern Iran for asymptomatic malaria prevalence detection by microscopy, Rapid Diagnostic Tests (RDTs) and HRM methods. The HRM assay was done based on the amplification of 18S SSU rRNA gene.

Results:

The HRM assay revealed infections from three individuals out of 271 (1.1% asymptomatic malaria prevalence) from the participants, two Iranian natives with Plasmodium vivax infection and one Pakistani immigrant with P. falciparum infection. Neither microscopy nor RDTs detected Plasmodium spp infections from the 271 non-febrile individuals. The nucleotide sequencing analysis of the positive controls used in this study showed a close homology with the reference gene bank sequences of P. falciparum 3D7 (CPO16995.1) and P. vivax Sal-1(UO3079.1).

Conclusion:

This study revealed a low frequency of asymptomatic malaria trend within malaria endemic areas of southeastern Iran which are under intense elimination program and also the ability of HRM assay in detecting low Plasmodium spp parasitemia beyond the limits of microscopy and RDTs.

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

Background

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

Methods

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

Results

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

Conclusions

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

Implications of asymptomatic infection for the natural history of selected parasitic tropical diseases

Progress has been made in the control or elimination of tropical diseases, with a significant reduction of incidence. However, there is a risk of re-emergence if the factors fueling transmission are not dealt with. Although it is essential to understand these underlying factors for each disease, asymptomatic carriers are a common element that may promote resurgence; their impact in terms of proportion in the population and role in transmission needs to be determined. In this paper, we review the current evidence on whether or not to treat asymptomatic carriers given the relevance of their role in the transmission of a specific disease, the efficacy and toxicity of existing drugs, the Public Health interest, and the benefit at an individual level, for example, in Chagas disease, to prevent irreversible organ damage. In the absence of other control tools such as vaccines, there is a need for safer drugs with good risk/benefit profiles in order to change the paradigm so that it addresses the complete infectious process beyond manifest disease to include treatment of non-symptomatic infected persons.

Comparing drug regimens for clearance of malaria parasites in asymptomatic adults using PCR in Kilifi County, Kenya: an open-label randomised controlled clinical trial (MalPaC)

Background: To restrict trial endpoints to infections acquired after vaccination in Phase IIb trials of candidate malaria vaccines, participants are treated with anti-malarial drugs to clear existing infections. Anti-malarial drugs with a long half-life may inhibit the acquisition of new infections. This study evaluated the effects of three anti-malarial drug regimens on the clearance of existing infections and acquisition of new infections. Methods: An open-label randomised controlled trial (MalPaC) was conducted between November 2013 and February 2014. Ninety adults were randomised 1:1:1 to receive one of three treatments: atovaquone/proguanil and artesunate (AP+AS); artesunate (AS); or sulphadoxine-pyrimethamine, artesunate, and primaquine (SP+AS+PQ). Parasite monitoring was determined over 84-day follow-up by assessing Plasmodium falciparum positivity by 18s qPCR, live and sexual stage parasites by RT-PCR, and recrudescence of infections by msp2 genotyping. Results: At enrolment, parasite prevalence by qPCR was 44% (40/90, day 0), which fell to 10% (9/90, day 16), then rose to almost the initial rates by day 84 (39%, 35/90). Individuals treated with AS and SP+AS+PQ were more likely to have higher qPCR positive rates compared to participants treated with AP+AS in the immediate post-treatment phase (days 16-28) (OR=7.7 [95%CI 4.6-12.8] p<0.0005 and OR=4.2 [95%CI 2.6-6.8] p<0.0005, respectively). In the immediate post-treatment phase, qPCR positivity was less likely associated with evidence of live parasites and gametocytaemia. Prevalence of “old”, “new” or “undetectable” infections did not differ significantly over time or drug regimen. However, participants on the AP+AS drug regimen were less likely to have parasite infection recrudescence compared to participants treated with AS and SP+AS+PQ. Conclusion: Falciparum DNA remained detectable by PCR post-treatment with incomplete parasite clearance regardless of drug regimen. Though AP+AS drug regimen may also have partially suppressed the acquisition of new infections during post-treatment follow-up. Trial registration: Pan African Clinical Trials Registry, 22nd of August 2013, PACTR201309000625311.

Performance Outcomes from Africa-Based Malaria Diagnostic Competency Assessment Courses

The U.S. President's Malaria Initiative-funded MalariaCare project implemented an external quality assurance scheme to support malaria diagnostics and case management across a spectrum of health facilities in participating African countries. A component of this program was a 5-day, malaria diagnostic competency assessment (MDCA) course for health facility laboratory staff conducting malaria microscopy. The MDCA course provided a method to quantify participant skill levels in microscopic examination of malaria across three major diagnosis areas: parasite detection, species identification, and parasite quantification. A total of 817 central-, regional-, and peripheral-level microscopists from 45 MDCA courses across nine African countries were included in the analysis. Differences in mean scores with respect to daily marginal performance were positive and statistically significant (P < 0.001) for each challenge type across all participants combined. From pretest to assessment day 4, mean scores for parasite detection, species identification, and parasite quantification increased by 19.1, 34.9, and 38.2 percentage points, respectively. In addition, sensitivity and specificity increased by 20.8 and 13.8 percentage points, respectively, by assessment day 4. Furthermore, the ability of MDCA participants to accurately report Plasmodium falciparum species when present increased from 44.5% at pretest to 67.1% by assessment day 4. The MDCA course rapidly improved the microscopy performance of participants over a short period of time. Because of its rigor, the MDCA course could serve as a mechanism for measuring laboratory staff performance against country-specific minimum competency standards and could easily be adapted to serve as a national certification course.

Novel molecular diagnostic technique for detecting the different species of Plasmodium

BACKGROUND

Sensitive diagnostic techniques are needed for timely detection of malaria parasite and disease control. Molecular diagnostic techniques involving Polymerase chain reaction (PCR) with 18 s rRNA as a known diagnostic target with an overall sensitivity of 10 parasites per microliter is used as a gold standard. Till date, no attempt has been undertaken to develop a technique for the identification of four Plasmodium species in a single step PCR combined with restriction digestion with enzymes.

METHOD

Plasmodium species-specific polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays have been developed, based on RFLP of amplified PCR product of mitochondrial gene as a target. This approach identifies Plasmodium species in two steps involving amplification of mitochondrial (Mt) gene by PCR followed by digestion with restriction enzymes.

RESULT

A total of 36 clinical samples were subjected to PCR-RFLP for the diagnosis and detection of malaria parasites targeting mitochondrial gene (Mt). The findings of the method were compared with gold standard methods (Microscopy, RDTs and Nested PCR) and was able to detect mixed infection with a sensitivity of 100% and specificity of 93.8% with respect to nested PCR. The results obtained by PCR-RFLP were validated with Sanger sequencing (n = 32) and were found to be consistent with the method.

CONCLUSION

This method identifies and distinguishes four species of human malaria parasite namely P. falciparum (Pf), P. vivax (Pv), P. malariae (Pm) and P. ovale (Po) in approximately 4 h. To overcome and address PCR difficulties, continuous efforts are needed for the development of newer diagnostic techniques.

The diagnostic performance of rapid diagnostic tests and microscopy for malaria diagnosis in eastern Sudan using a nested polymerase chain reaction assay as a reference standard

Background

Accurate diagnosis of malaria infection is essential for successful control and management of the disease. Both microscopy and rapid diagnostic tests (RDTs) are recommended for malaria diagnosis, however, RDTs are more commonly used. The aim of the current study was to assess the performance of microscopy and RDTs in the diagnosis of Plasmodium falciparum infection using a nested polymerase chain reaction (PCR) assay as the gold standard.

Methods

A cross-sectional study was carried out in Kassala Hospital, eastern Sudan. A total of 341 febrile participants of all ages were recruited. Blood specimens were collected and malaria testing was performed using an RDT (SD Bioline Malaria Ag Pf), microscopy and nested PCR. The sensitivity, specificity, positive and negative predictive values (PPV and NPV, respectively) of microscopy and the RDT were investigated.

Results

The prevalence of P. falciparum malaria infections in this study was 22.9%, 24.3% and 26.7% by PCR, microscopy and RDT, respectively. Compared with microscopy, the RDT had slightly higher sensitivity (80.7% vs 74.3%; p=0.442), equivalent specificity (89.3% vs 90.4%), a similar PPV (69.2% vs 69.8%) and a higher NPV (94.0% vs 92.2%).

Conclusions

The diagnostic performance of the RDT was better than that of microscopy in the diagnosis of P. falciparum malaria when nested PCR was used as the gold standard.

Malaria epidemiology and comparative reliability of diagnostic tools in Bannu; an endemic malaria focus in south of Khyber Pakhtunkhwa, Pakistan

The present study was aimed at elucidation of malaria epidemiology and comparing performance of several diagnostic procedures in Bannu, a highly endemic district of Khyber Pakhtunkhwa, Pakistan. Dried blood spots were collected from patients suspected of malaria visiting a hospital and two private laboratories in district Bannu and processed for species-specific PCR (rRNA). Patients were also screened for malaria through microscopy and RDT. A well-structured questionnaire was used to collect patient information to assess risk factors for malaria. Of 2033 individuals recruited, 21.1% (N = 429) were positive for malaria by at least one method. Overall, positivity detected by PCR was 30.5% (95/311) followed by 17.7% by microscopy (359/2033) and 16.4% by RDT (266/1618). Plasmodium vivax (16.9%, N = 343) was detected as the dominant species followed by Plasmodium falciparum (2.3%, N = 47) and mixed infections (1.2%, N = 39). Microscopy and RDT (Cohen's kappa k = 0.968, p = <0.0001, McNemar test p = 0.069) displayed significant agreement with each other. Satisfactory health, sleeping indoors, presence of health-care facility in vicinity (at an accessible range from home), living in upper middle class and in concrete houses significantly reduced malaria risk; whereas, low literacy level, presence of domestic animals indoors and malaria diagnosis recommended by clinician increased the disease risk. Overall, findings from the study provide reasonable basis for use of RDT as a cost-effective screening tool in field and for clinicians who can proceed with timely treatment of malaria patients. Appropriate management of identified risk factors could contribute to reduction of malaria prevalence in Bannu and its peripheries.

Evaluation of automated malaria diagnosis using the Sysmex XN-30 analyser in a clinical setting

BACKGROUND

Early and accurate diagnosis of malaria is a critical aspect of efforts to control the disease, and several diagnostic tools are available. Microscopic assessment of a peripheral blood smear enables direct visualization of parasites in infected red blood cells and is the clinical diagnostic gold standard. However, it is subjective and requires a high level of skill. Numerous indirect detection methods are in use, but are not ideal since surrogate markers of infection are measured. This study describes the first clinical performance evaluation of the automated Sysmex XN-30 analyser, which utilizes fluorescence flow cytometry to directly detect and quantitate parasite-infected red blood cells.

RESULTS

Residual EDTA blood samples from suspected malaria cases referred for routine diagnosis were analysed on the XN-30. Parasitaemia was reported as a percentage, as well as absolute numbers of infected red blood cells, and scattergrams provided a visual image of the parasitized red blood cell clusters. The results reported by the XN-30 correlated with microscopy and the analyser demonstrated 100% sensitivity and specificity. Measurements were reproducible and storage of samples at room temperature did not affect the parameters. Several Plasmodium species were detected, including Plasmodium falciparum, Plasmodium vivax and Plasmodium ovale. The XN-30 also identified the transmissible gametocytes as a separate cluster on the scattergrams. Abnormal red blood cell indices (low haemoglobin and raised reticulocyte counts), haemoglobinopathies and thrombocytopenia did not interfere with the detection of parasites. The XN-30 also generated a concurrent full blood count for each sample.

CONCLUSIONS

The novel technology of the Sysmex XN-30 provides a robust, rapid, automated and accurate platform for diagnosing malaria in a clinical setting. The objective enumeration of red blood cells infected with Plasmodium species makes it suitable for global use and allows monitoring of the parasite load once therapy has been initiated, thereby providing an early marker of drug resistance. The automated generation of a full blood count for each sample provides an opportunity for detecting unsuspected cases. Asymptomatic carriers can also be identified, which will be useful in blood transfusion centres, and will enable treatment of these individuals to prevent the spread of the disease.

Evaluation of malaria multiplex/nested PCR performance at low parasite densities and mixed infection in Iran: A country close to malaria elimination

BACKGROUND

Malaria is still a major public health problem in subtropical and tropical regions. The rapid and accurate diagnosis of malaria remains a challenge in most of the endemic areas. The primary objective of the present study was to evaluate the performance of multiplex/nested PCR in detecting Plasmodium falciparum at low parasite densities and mixed infection.

METHODS

The study was performed in the Sistan-Baluchestan province of the southeastern Iran, from May 2015 to July 2016. A total of 105 patients suspected to malaria infection were enrolled in the study. The obtained DNA products, extracted from the thick/thin films, were analyzed by multiplex/nested PCR using genus-specific primers and compared with light microscopy.

RESULTS

43 samples were confirmed to be infected by microscopic examination. Among 43 microscopically diagnosed P. falciparum cases, 11.4% (12/105) were confirmed by multiplex/nested PCR, 36.2% (38/105) were confirmed as P. vivax, 1.9% (2/105) had mixed infections with P. falciparum and P. vivax. Among microscopy-negative samples, 10 samples turned malaria-positive in nPCR. In multiplex/nested PCR, the rate of mixed infections was 8.6% (9/105). When compared to LM, the sensitivity, specificity, positive predictive value and negative predictive value of multiplex/nested PCR were calculated to be 82.8, 91.5, 92.3 and 81.1%, respectively.

CONCLUSION

In this study, we showed that microscopic examination of blood smears does not reliably distinguish Plasmodium species in the case of mixed infections. Therefore, it seems that multiplex/nested PCR is a good candidate for examining the presence of malaria parasites in clinically suspected but microscopically negative cases.

Serological and molecular techniques applied for identification of Plasmodium spp. in blood samples from nonhuman primates

The aim of this study was to identify Plasmodium spp. in blood samples from nonhuman primates (NHPs) in the state of Maranhão, using classical and alternative techniques for examination of human malaria. A total of 161 blood samples from NHPs were analyzed: 141 from captive animals at a Wildlife Screening Center (CETAS) and 20 from free-living animals in a private reserve. The techniques used were microscopy, rapid diagnostic test (RDT), Indirect fluorescent antibody test (IFAT) and molecular techniques (semi-nested PCR, quantitative real-time PCR and LAMP). Two serological methods (dot-ELISA and indirect ELISA) were also standardized with rhoptry protein-soluble antigen of P. falciparum and P. berghei. Trophozoite forms of Plasmodium sp. were identified on slides from five different animals. No samples were positive through RDT and LAMP. Four samples were seropositive for P. malariae through IFAT. The samples showed low reactivity to ELISA. Plasmodium sp. was detected in 34.16% (55/161) of the samples using qPCR based on the 18S rRNA gene. After sequencing, two samples showed 100% identityl to P. malariae, one showed 97% identity to Plasmodium sp. ZOOBH and one showed 99% identity to P. falciparum . PCR was shown to be the most sensitive technique for diagnosing Plasmodium in NHP samples.

Field evaluation of a real time loop-mediated isothermal amplification assay (RealAmp) for malaria diagnosis in Cruzeiro do Sul, Acre, Brazil

Conventional molecular methods, such as nested polymerase chain reaction (PCR), are very sensitive for detection of malaria parasites, but require advanced laboratory equipment and trained personnel. Real-time loop-mediated isothermal amplification (RealAmp), a loop-mediated isothermal amplification-based molecular tool (LAMP), facilitates rapid target amplification at a single temperature setting, reducing the need for sophisticated equipment. We evaluated the performance of a field-adapted RealAmp assay for malaria diagnosis in Cruzeiro do Sul, Acre State, Brazil, a remote area in Brazil with limited laboratory capabilities. We enrolled 1,000 patients with fever (axillary temperature ≥ 37.5 C) or history of fever in last 24 h presenting for malaria diagnosis from February through June 2015. DNA was extracted from dried blood spots using a boil and spin method (heat treatment) at the sample processing site, and also using commercial kits at a Brazilian national reference laboratory. RealAmp was performed for Plasmodium genus, P. falciparum, and P. vivax identification. In addition, Giemsa-stained blood smears were prepared and examined by two independent well-trained study microscopists. A combination of Real-time PCR and nested PCR was used as reference test. The sensitivity and specificity of RealAmp in the field site laboratory were 94.1% (95% confidence interval [CI]: 90.1–96.8) and 83.9% (95% CI: 81.1–86.4), respectively. The sensitivity and specificity of local microscopy were 87.7% (95% CI: 82.6–91.7) and 98.9% (95% CI: 97.8–99.4), respectively, while study microscopy showed sensitivity of 96.4% (95% CI: 93.0–98.4) and specificity of 98.2% (95% CI: 97.0–99.0). None of the three tests detected 20 P. falciparum and P. vivax mixed infections identified by the reference test. Our findings highlight that it is possible to implement simple molecular tests in facilities with limited resources such as Cruzeiro do Sul in Brazil. RealAmp sensitivity was similar to that of microscopy performed by skilled professionals; both RealAmp and study microscopy performed poorly in detection of mixed infection. Attempts to develop and evaluate simpler molecular tools should continue, especially for the detection of malaria infection in remote areas.

Epidemiology of Malaria in Yulin, South China 1999-2016: Imported Malaria Threatens Zero Local Case Status

OBJECTIVES

This article describes the epidemiology of malaria in Yulin, 1999-2016. We review also malaria control strategy in Yulin in the posteradication phase.

MATERIALS AND METHODS

We examined all malaria case records from Yulin prefecture reported to the Ministry of Health since 1999 and extracted malaria data between 1999 and 2003, the stage of malaria eradication, from the notifiable disease reporting records and case records of Guangxi. Malaria data between 2004 and 2016, the stage of malaria elimination, was obtained from the National Notifiable Disease Reporting System and National Malaria Reporting System. We collected mosquitoes with light traps in the vector-breeding seasons and did the distinguished work with optical microscope.

RESULTS

Malaria average incidence decreased to 0.085/100,000, peaking of 0.263/100,000 in 2006, and no cases in years 2001, 2009, and 2010. Peak seasons are in November and June with proportions of 16.48% and 14.29%, respectively. Pathogenic parasites differed in the two stages; Plasmodium vivax was prevalent between 1999 and 2010, and Plasmodium falciparum between 2011 and 2015. Most malaria cases in the last 18 years occurred in males between 20 and 50 years of age. Of the 91 malaria cases acquired outside Yulin between 1999 and 2016, 31.87% were acquired in other provinces of China, and 68.13% were acquired in foreign countries. Sporozoite-positive vectors were zero between 1999 and 2016.

CONCLUSION

In Yulin, between 1999 and 2016, autochthonous malaria cases decreased to zero. The personal preventative measures of surveillance-treatment-follow-up have been demonstrated to be effective in the Yulin malaria elimination campaign between 1999 and 2016. The major threat of malaria reintroduction to Yulin lies in imported malaria, especially by returning employees working in epidemic areas such as Africa and Southeast Asia. Data concerning employees who have worked abroad should be gathered to enable the construction of a mathematic model to forecast future trends of malaria in Yulin. The antimalaria campaign has to work closely with local authorities.

An Alternative Method for Extracting Plasmodium DNA from EDTA Whole Blood for Malaria Diagnosis

Molecular techniques have been introduced for malaria diagnosis because they offer greater sensitivity and specificity than microscopic examinations. Therefore, DNA isolation methods have been developed for easy preparation and cost effectiveness. The present study described a simple protocol for Plasmodium DNA isolation from EDTA-whole blood. This study demonstrated that after heating infected blood samples with Tris–EDTA buffer and proteinase K solution, without isolation and purification steps, the supernatant can be used as a DNA template for amplification by PCR. The sensitivity of the extracted DNA of Plasmodium falciparum and Plasmodium vivax was separately analyzed by both PCR and semi-nested PCR (Sn-PCR). The results revealed that for PCR the limit of detection was 40 parasites/μl for P. falciparum and 35.2 parasites/μl for P. vivax, whereas for Sn-PCR the limit of detection was 1.6 parasites/μl for P. falciparum and 1.4 parasites/μl for P. vivax. This new method was then verified by DNA extraction of whole blood from 11 asymptomatic Myanmar migrant workers and analyzed by Sn-PCR. The results revealed that DNA can be extracted from all samples, and there were 2 positive samples for Plasmodium (P. falciparum and P. vivax). Therefore, the protocol can be an alternative method for DNA extraction in laboratories with limited resources and a lack of trained technicians for malaria diagnosis. In addition, this protocol can be applied for subclinical cases, and this will be helpful for epidemiology and control.

A case of blackwater fever with persistent Plasmodium falciparum parasitaemia detected by PCR after artemether-lumefantrine treatment

Background

Blackwater fever is a complication of malaria infection consisting of a syndrome of febrile intra-vascular haemolysis with severe anaemia and intermittent passage of dark-red to black colour urine. Despite numerous reports and studies of this condition, its pathogenesis remains incompletely understood.

Case presentation

This report describes a case of classic blackwater fever in a returning traveller, without prior history of malaria infection nor usage of anti-malarial prophylaxis, treated with two courses of oral artemether–lumefantrine combination therapy. Unusual persistence of submicroscopic Plasmodium falciparum parasitaemia was detected by PCR for 18 days after initiation of treatment.

Conclusion

To the authors’ knowledge this is the first reported occurrence of a case of blackwater fever associated with prolonged submicroscopic parasitaemia. This unusual case challenges the current knowledge of the pathogenesis of this condition and opens questions that may have important diagnostic and treatment implications.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2180-1) contains supplementary material, which is available to authorized users.

Submicroscopic malaria cases play role in local transmission in Trenggalek district, East Java Province, Indonesia

Background

Trenggalek district is a hypoendemic malaria area with mainly imported cases brought by migrant workers from islands outside Java. During malaria surveillance in 2015, no malaria cases were found microscopically, but some cases were positive by PCR. Therefore, a study was conducted to prove that local malaria transmission still occur.

Methods

The adult villagers were invited to the house of the head of this village to be screened for malaria using aseptic venipuncture of 1 mL blood upon informed consent. Thin and thick blood films as well as blood spots on filter paper were made for each subject. The blood films were stained with Giemsa and the blood spots were used to extract DNA for polymerase chain reaction (PCR) amplification to determine the malaria infection. In addition, the history of malaria infection and travel to malaria endemic areas were recorded. Entomologic survey to detect the existence of anopheline vector was also conducted.

Results

Of the total 64 subjects that participated in the survey, no malaria parasites were found through microscopic examination of the blood films. The PCR analysis found six positive cases (two Plasmodium falciparum, one Plasmodium vivax and two mixed infection of both species), and two of them had no history of malaria and have never travelled to malaria endemic area. Entomologic survey using human bait trap detected the existence of Anopheles indefinitus that was found to be positive for P. vivax by PCR.

Conclusions

The results indicated that although we did not find any microscopically slide positive cases, six PCR positive subjects were found. The fact that 2 of the 6 malaria positive subjects have never travelled to malaria endemic area together with the existence of the vector confirm the occurence of local transmission of malaria in the area.

Comparative evaluation of a rapid diagnostic test, an antibody ELISA, and a pLDH ELISA in detecting asymptomatic malaria parasitaemia in blood donors in Buea, Cameroon

BACKGROUND

In malaria endemic areas, infected blood donors serve as a source of infection to blood recipients, which may adversely affect their prognosis. This necessitates the proper screening of blood to be used for transfusion in these areas. The purpose of this study was to determine the prevalence of malaria parasitaemia in blood donors in Buea, Cameroon, and to evaluate the performance of a rapid diagnostic test (RDT), a malaria antibody enzyme-linked immunosorbent assay (ELISA), and a Plasmodium lactate dehydrogenase (pLDH) ELISA in the detection of asymptomatic malaria parasitaemia in the target population.

METHODS

In a prospective study conducted between September 2015 and June 2016, 1 240 potential blood donors were enrolled. The donors were screened for malaria parasites using Giemsa microscopy (GM) and a RDT. A sub-sample of 184 samples, comprising 88 positive and 96 negative samples, were selected for the evaluation of the pLDH ELISA and the antibody ELISA. The chi-square test and correlation analysis were performed as part of the statistical analyses. The statistical significance cut-off was set at P < 0.05.

RESULTS

The prevalence of malaria parasitaemia in this study was found to be 8.1% (95% CI: 6.6 - 9.7). The prevalence was not observed to be dependent on the age or sex of the participants. The RDT had a sensitivity (88.0%), specificity (99.1%), and negative predictive value (99.0%) higher than the ELISAs. The performance of the pLDH ELISA, which demonstrated the highest positive predictive value (91.6%), was generally comparable to the RDT. The sensitivity was lowest with the antibody ELISA (69.9%), which also demonstrated the highest false positive and false negative rates. The detection threshold for the pLDH (three parasites/μl) was lower compared to the RDT (50 - 60 parasites/μl). Non-significant positive correlations were observed between the parasite density and the pLDH titers and malaria antibody titers.

CONCLUSIONS

Overall, the RDT and the pLDH ELISA demonstrated a perfectly correlated agreement with GM, meanwhile the antibody ELISA demonstrated a substantially correlated agreement with GM. The pLDH is therefore recommended for mass screening of blood (to detect malaria parasitaemia) for transfusions in the study area. However, where this is not feasible, an RDT will suffice.

Estimating age-time-dependent malaria force of infection accounting for unobserved heterogeneity

Despite well-recognized heterogeneity in malaria transmission, key parameters such as the force of infection (FOI) are generally estimated ignoring the intrinsic variability in individual infection risks. Given the potential impact of heterogeneity on the estimation of the FOI, we estimate this quantity accounting for both observed and unobserved heterogeneity. We used cohort data of children aged 0·5-10 years evaluated for the presence of malaria parasites at three sites in Uganda. Assuming a Susceptible-Infected-Susceptible model, we show how the FOI relates to the point prevalence, enabling the estimation of the FOI by modelling the prevalence using a generalized linear mixed model. We derive bounds for varying parasite clearance distributions. The resulting FOI varies significantly with age and is estimated to be highest among children aged 5-10 years in areas of high and medium malaria transmission and highest in children aged below 1 year in a low transmission setting. Heterogeneity is greater between than within households and it increases with decreasing risk of malaria infection. This suggests that next to the individual's age, heterogeneity in malaria FOI may be attributed to household conditions. When estimating the FOI, accounting for both observed and unobserved heterogeneity in malaria acquisition is important for refining malaria spread models.

Imported Plasmodium falciparum and locally transmitted Plasmodium vivax: cross-border malaria transmission scenario in northwestern Thailand

BACKGROUND

Cross-border malaria transmission is an important problem for national malaria control programmes. The epidemiology of cross-border malaria is further complicated in areas where Plasmodium falciparum and Plasmodium vivax are both endemic. By combining passive case detection data with entomological data, a transmission scenario on the northwestern Thai-Myanmar border where P. falciparum is likely driven by importation was described, whereas P. vivax is also locally transmitted. This study highlights the differences in the level of control required to eliminate P. falciparum and P. vivax from the same region.

METHODS

Malaria case data were collected from malaria clinics in Suan Oi village, Tak Province, Thailand between 2011 and 2014. Infections were diagnosed by light microscopy. Demographic data, including migrant status, were correlated with concomitantly collected entomology data from 1330 mosquito trap nights using logistic regression. Malaria infection in the captured mosquitoes was detected by ELISA.

RESULTS

Recent migrants were almost four times more likely to be infected with P. falciparum compared with Thai patients (OR 3.84, p < 0.001) and cases were significantly associated with seasonal migration. However, P. falciparum infection was not associated with the Anopheles mosquito capture rates, suggesting predominantly imported infections. In contrast, recent migrants were equally likely to present with P. vivax as mid-term migrants. Both migrant groups were twice as likely to be infected with P. vivax in comparison to the resident Thai population (OR 1.96, p < 0.001 and OR 1.94, p < 0.001, respectively). Plasmodium vivax cases were strongly correlated with age and local capture rates of two major vector species Anopheles minimus and Anopheles maculatus (OR 1.23, p = 0.020 and OR 1.33, p = 0.046, respectively), suggesting that a high level of local transmission might be causing these infections.

CONCLUSIONS

On the Thai-Myanmar border, P. falciparum infections occur mostly in the recent migrant population with a seasonality reflecting that of agricultural activity, rather than that of the local mosquito population. This suggests that P. falciparum was mostly imported. In contrast, P. vivax cases were significantly associated with mosquito capture rates and less with migrant status, indicating local transmission. This highlights the different timelines and requirements for P. falciparum and P. vivax elimination in the same region and underlines the importance of multinational, cross-border malaria control.

Identification of the Plasmodium species in clinical samples from children residing in five epidemiological strata of malaria in Cameroon

Background

Malaria in Cameroon was previously known to be caused solely by Plasmodium falciparum but today, evidence points to other Plasmodium species including P. vivax, P. ovale and P. malariae. The purpose of this study was to identify the Plasmodium species in clinical samples from children residing in five epidemiological strata of malaria in Cameroon, so as to advise control policies.

Methods

One thousand six hundred nine febrile children (≤15 years) were recruited from five epidemiological strata of malaria including the Sudano-sahelian (SS) strata, the High inland plateau (HIP) strata, the South Cameroonian Equatorial forest (SCEF) strata, the High western plateau (HWP) strata and the Coastal (C) strata. Malaria parasites were detected by Giemsa microscopy (GM) while a multiplex polymerase chain reaction (PCR) was used to identify the Plasmodium species. Statistical analysis performed included the Pearson chi-square test, and statistical significance was set at p < 0.05.

Results

The PCR-adjusted prevalence of malaria was 17.6%. The detection rate of PCR was higher than GM (p = 0.05). However, GM demonstrated a high sensitivity (85.5%) and specificity (100%) and, overall, a perfectly correlated agreement with PCR (97.5%). The prevalence of malaria was significantly higher in children between 60 and 119 months (p < 0.001) and in Limbe (in the Coastal strata) (p < 0.001). Contrariwise, the prevalence of malaria was not associated with gender (p = 0.239). P. falciparum was identified in all (100%) the cases of malaria; P. ovale, P. vivax, P. malariae and P. knowlesi were all absent. No case of mixed infection was identified.

Conclusions

P. falciparum was the only species causing clinical malaria in the target population, which is contrary to studies that have reported P. vivax, P. malariae and P. ovale as causing clinical malaria in Cameroon.

Use of malaria RDTs in various health contexts across sub-Saharan Africa: a systematic review

BACKGROUND

The World Health Organization recommends parasitological confirmation of malaria prior to treatment. Malaria rapid diagnostic tests (RDTs) represent one diagnostic method that is used in a variety of contexts to overcome limitations of other diagnostic techniques. Malaria RDTs increase the availability and feasibility of accurate diagnosis and may result in improved quality of care. Though RDTs are used in a variety of contexts, no studies have compared how well or effectively RDTs are used across these contexts. This review assesses the diagnostic use of RDTs in four different contexts: health facilities, the community, drug shops and schools.

METHODS

A comprehensive search of the Pubmed database was conducted to evaluate RDT execution, test accuracy, or adherence to test results in sub-Saharan Africa. Original RDT and Plasmodium falciparum focused studies conducted in formal health care facilities, drug shops, schools, or by CHWs between the year 2000 and December 2016 were included. Studies were excluded if they were conducted exclusively in a research laboratory setting, where staff from the study team conducted RDTs, or in settings outside of sub-Saharan Africa.

RESULTS

The literature search identified 757 reports. A total of 52 studies were included in the analysis. Overall, RDTs were performed safely and effectively by community health workers provided they receive proper training. Analogous information was largely absent for formal health care workers. Tests were generally accurate across contexts, except for in drug shops where lower specificities were observed. Adherence to RDT results was higher among drug shop vendors and community health workers, while adherence was more variable among formal health care workers, most notably with negative test results.

CONCLUSIONS

Malaria RDTs are generally used well, though compliance with test results is variable - especially in the formal health care sector. If low adherence rates are extrapolated, thousands of patients may be incorrectly diagnosed and receive inappropriate treatment resulting in a low quality of care and unnecessary drug use. Multidisciplinary research should continue to explore determinants of good RDT use, and seek to better understand how to support and sustain the correct use of this diagnostic tool.

Laboratory Diagnosis of Malaria: Comparison of Manual and Automated Diagnostic Tests

Malaria is the second most prevalent disease in Pakistan resulting in ~30,000 annual deaths. In endemic countries like Pakistan precise and timely diagnosis of malaria is imperative to overcome the associated risks of fatal outcomes. Malarial parasite was screened in 128 malaria suspected patients and 150 healthy controls, by species-specific PCR, microscopy of blood smears, hemoanalyzer Sysmex XE-2100, and rapid test devices (First Response Malaria® and ICT Malaria Combo®). The microscopy detected MP in 126 samples (parasite load/µl 386–53712/µl); 71.094% were infected with Plasmodium vivax and 14.844% with P. falciparum while 14.062% had mixed P. vivax and P. falciparum infection. The mean parasite load for P. vivax and P. falciparum was 14496/µl and 24410/µl, respectively. The abnormal scattergrams of DIFF, WBC/ Baso, IMI channel, and RET-EXT on Sysmex XE-2100 supported 99.2% parasite detection, whereas only 93% of confirmed malaria cases were detected by both rapid tests. About 127 samples were positive by PCR. Since Sysmex XE-2100 automatically detected the presence of malarial parasite with high sensitivity, it can be a good option for presumptive diagnosis in endemic areas. Microscopy remains the gold standard to confirm MP in suspected patients. Rapid diagnostic tests have acceptable sensitivity and specificity.

Asymptomatic and sub-microscopic malaria infection in Kayah State, eastern Myanmar

Background

Myanmar has the heaviest burden of malaria in the Greater Mekong Sub-region. Asymptomatic Plasmodium spp. infections are common in this region and may represent an important reservoir of transmission that must be targeted for malaria elimination.

Methods

A mass blood survey was conducted among 485 individuals from six villages in Kayah State, an area of endemic but low transmission malaria in eastern Myanmar. Malaria infection was screened by rapid diagnostic test (RDT), light microscopy and real-time polymerase chain reaction (PCR), and its association with demographic factors was explored.

Results

The prevalence of asymptomatic Plasmodium spp. infection was 2.3% (11/485) by real-time PCR. Plasmodium vivax accounted for 72.7% (8/11) and Plasmodium falciparum for 27.3% (3/11) of infections. Men were at greater risk of infection by Plasmodium spp. than women. Individuals who worked as farmers or wood and bamboo cutters had an increased risk of infection.

Conclusion

A combination of RDT, light microscopy and PCR diagnostics were used to identify asymptomatic malaria infection, providing additional information on asymptomatic cases in addition to the routine statistics on symptomatic cases, so as to determine the true burden of disease in the area. Such information and risk factors can improve malaria risk stratification and guide decision-makers towards better design and delivery of targeted interventions in small villages, representative of Kayah State.

Global Epidemiology of Plasmodium vivax

Plasmodium vivax is the most widespread human malaria, putting 2.5 billion people at risk of infection. Its unique biological and epidemiological characteristics pose challenges to control strategies that have been principally targeted against Plasmodium falciparum Unlike P. falciparum, P. vivax infections have typically low blood-stage parasitemia with gametocytes emerging before illness manifests, and dormant liver stages causing relapses. These traits affect both its geographic distribution and transmission patterns. Asymptomatic infections, high-risk groups, and resulting case burdens are described in this review. Despite relatively low prevalence measurements and parasitemia levels, along with high proportions of asymptomatic cases, this parasite is not benign. Plasmodium vivax can be associated with severe and even fatal illness. Spreading resistance to chloroquine against the acute attack, and the operational inadequacy of primaquine against the multiple attacks of relapse, exacerbates the risk of poor outcomes among the tens of millions suffering from infection each year. Without strategies accounting for these P. vivax-specific characteristics, progress toward elimination of endemic malaria transmission will be substantially impeded.

Assessing the reliability of microscopy and rapid diagnostic tests in malaria diagnosis in areas with varying parasite density among older children and adult patients in Nigeria

Background:

Current malaria control strategies are based on early diagnosis and appropriate treatment of malaria cases. The study aimed at comparing the performance of blood film microscopy and rapid diagnostic test (RDT) in Plasmodium falciparum detection in patients ≥6 years of age.

Materials and Methods:

A total of 154 consecutive pyretic patients aged 6-62 years were enrolled, sampled, and tested for malaria using RDT (first response) and microscopy by Giemsa staining. Genomic DNA was extracted after saponin hemolysis and nested polymerase chain reaction (PCR) was used to detect Plasmodium falciparum. The endpoints were sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).

Results:

Of the 154 patients, 80 (51.9%) had fever of ≥37.5°C. 106 (68.8%) were positive by First response^®, 132 (85.7%) by microscopy, and 121 (78.6%) by PCR. The sensitivity, specificity, PPV, and NPV of first response compared to microscopic method were 82.2%, 100.0%, 100.0%, and 34.3%, respectively, while it was 75.4%, 75.0%, 95.3%, and 31.2%, respectively, when compared to PCR. The sensitivity, specificity, PPV, and NPV of the microscopic method compared to PCR were 92.3%, 50.0%, 90.91%, and 54.5%, respectively. There was a significant difference in the performance of RDT and film microscopy methods (P ≤ 0.05).

Conclusion:

Microscopy performed better and is more reliable than first response (RDT) in areas with low parasite density among patients ≥6 years of age. Rapid diagnostic tests could be useful in aareas with high parasite density as an alternative to smear microscopy

Evaluation of the Parasight Platform for Malaria Diagnosis

The World Health Organization estimates that nearly 500 million malaria tests are performed annually. While microscopy and rapid diagnostic tests (RDTs) are the main diagnostic approaches, no single method is inexpensive, rapid, and highly accurate. Two recent studies from our group have demonstrated a prototype computer vision platform that meets those needs. Here we present the results from two clinical studies on the commercially available version of this technology, the Sight Diagnostics Parasight platform, which provides malaria diagnosis, species identification, and parasite quantification. We conducted a multisite trial in Chennai, India (Apollo Hospital [n = 205]), and Nairobi, Kenya (Aga Khan University Hospital [n = 263]), in which we compared the device to microscopy, RDTs, and PCR. For identification of malaria, the device performed similarly well in both contexts (sensitivity of 99% and specificity of 100% at the Indian site and sensitivity of 99.3% and specificity of 98.9% at the Kenyan site, compared to PCR). For species identification, the device correctly identified 100% of samples with Plasmodium vivax and 100% of samples with Plasmodium falciparum in India and 100% of samples with P. vivax and 96.1% of samples with P. falciparum in Kenya, compared to PCR. Lastly, comparisons of the device parasite counts with those of trained microscopists produced average Pearson correlation coefficients of 0.84 at the Indian site and 0.85 at the Kenyan site.

Plasmodium malariae in the Colombian Amazon region: you don't diagnose what you don't suspect

Background

Malaria is a worldwide public health problem; parasites from the genus Plasmodium spp. are the aetiological agent of this disease. The parasite is mainly diagnosed by microscope-based techniques. However, these have limited sensitivity. Many asymptomatic infections are sub-microscopic and can only be detected by molecular methods. This study was aimed at comparing nested PCR results to those obtained by microscope for diagnosing malaria and to present epidemiological data regarding malaria in Colombia’s Amazon department.

Methods

A total of 1392 blood samples (taken by venepuncture) from symptomatic patients in Colombia’s Amazon department were analysed in parallel by thick blood smear (TBS) test and nested PCR for determining Plasmodium spp. infection and identifying infecting species, such as Plasmodium vivax, Plasmodium malariae and/or Plasmodium falciparum. Descriptive statistics were used for comparing the results from both tests regarding detection of the disease, typing infecting species and their prevalence in the study region. Bearing the microscope assay in mind as gold standard, PCR diagnosis performance was evaluated by statistical indicators.

Conclusion

The present study revealed great differences between both diagnostic tests, as well as suggesting high P. malariae prevalence from a molecular perspective. This differed profoundly from previous studies in this region of Colombia, usually based on the TBS test, suggesting that diagnosis by conventional techniques could lead to underestimating the prevalence of certain Plasmodium spp. having high circulation in this area. The present results highlight the need for modifying state malaria surveillance schemes for more efficient strategies regarding the detection of this disease in endemic areas. The importance of PCR as a back-up test in cases of low parasitaemia or mixed infection is also highlighted.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1629-3) contains supplementary material, which is available to authorized users.

Characteristics of Imported Malaria and Species of Plasmodium Involved in Shandong Province, China (2012-2014)

Malaria remains a serious public health problem in Shandong Province, China; therefore, it is important to explore the characteristics of the current malaria prevalence situation in the province. In this study, data of malaria cases reported in Shandong during 2012-2014 were analyzed, and Plasmodium species were confirmed by smear microscopy and nested-PCR. A total of 374 malaria cases were reported, 80.8% of which were reported from 6 prefectures. Of all cases, P. falciparum was dominant (81.3%), followed by P. vivax (11.8%); P. ovale and P. malariae together accounted for 6.4% of cases. Notably, for the first time since 2012, no indigenous case had been reported in Shandong Province, a situation that continued through 2014. Total 95.2% of cases were imported from Africa. The ratio of male/female was 92.5:1, and 96.8% of cases occurred in people 20-54 years of age. Farmers or laborers represented 77.5% of cases. No significant trends of monthly pattern were found in the reported cases. All patients were in good condition after treatment, except for 3 who died. These results indicate that imported malaria has increased significantly since 2012 in Shandong Province, especially for P. falciparum, and there is an emergence of species diversity.

The development of malaria diagnostic techniques: a review of the approaches with focus on dielectrophoretic and magnetophoretic methods

The large number of deaths caused by malaria each year has increased interest in the development of effective malaria diagnoses. At the early-stage of infection, patients show non-specific symptoms or are asymptomatic, which makes it difficult for clinical diagnosis, especially in non-endemic areas. Alternative diagnostic methods that are timely and effective are required to identify infections, particularly in field settings. This article reviews conventional malaria diagnostic methods together with recently developed techniques for both malaria detection and infected erythrocyte separation. Although many alternative techniques have recently been proposed and studied, dielectrophoretic and magnetophoretic approaches are among the promising new techniques due to their high specificity for malaria parasite-infected red blood cells. The two approaches are discussed in detail, including their principles, types, applications and limitations. In addition, other recently developed techniques, such as cell deformability and morphology, are also overviewed in this article.

Effective High-Throughput Blood Pooling Strategy before DNA Extraction for Detection of Malaria in Low-Transmission Settings

In the era of (pre) elimination setting, the prevalence of malaria has been decreasing in most of the previously endemic areas. Therefore, effective cost- and time-saving validated pooling strategy is needed for detection of malaria in low transmission settings. In this study, optimal pooling numbers and lowest detection limit were assessed using known density samples prepared systematically, followed by genomic DNA extraction and nested PCR. Pooling strategy that composed of 10 samples in 1 pool, 20 µl in 1 sample, was optimal, and the parasite density as low as 2 p/µl for both falciparum and vivax infection was enough for detection of malaria. This pooling method showed effectiveness for handling of a huge number of samples in low transmission settings (<9% positive rate). The results indicated that pooling of the blood samples before DNA extraction followed by usual nested PCR is useful and effective for detection of malaria in screening of hidden cases in low-transmission settings.

Consistent prevalence of asymptomatic infections in malaria endemic populations in Colombia over time

Background

Malaria control programmes rely on confirmation of parasite presence in patients’ blood prior to treatment administration. Plasmodium parasites are detected mostly by microscopy or rapid diagnostic test (RDT). Although these methods contribute significantly to malaria control/elimination, they are not suitable for detecting the significant proportion of asymptomatic subjects harbouring low levels of parasitaemia, which endure untreated as potential reservoirs for transmission. Malaria prevalence was assessed in endemic regions of Colombia over a 4-year follow-up.

Methods

A series of cross-sectional surveys were conducted between 2011 and 2014 in low to moderate malaria transmission sentinel sites (SS) of Tumaco, Buenaventura and Tierralta municipalities of Colombia. A census was performed and a random sample of houses was selected from each SS prior to each survey. Inhabitants were asked to answer a questionnaire on clinical, epidemiological and demographic aspects, and to provide a blood sample for malaria diagnosis using microscopy and quantitative real time polymerase chain reaction (qPCR).

Results

A total of 3059 blood samples were obtained from all SS, 58.5 % of which were from women and displayed a malaria prevalence ranging from 4 % (95 % CI 3–5 %) to 10 % (95 % CI 8–12 %) in the 4 years’ study period. Almost all malaria cases (n = 220, 97 %) were sub-microscopic and only detectable by qPCR; 90 % of the cases were asymptomatic at the time of blood collection. While Buenaventura and Tierralta had a decreasing tendency during the follow-up, Tumaco had a rise in 2013 and then a decrease in 2014. Plasmodium vivax accounted for the majority (66–100 %) of cases in Tierralta and Buenaventura and for 25–50 % of the cases in Tumaco.

Conclusions

This study demonstrates an important prevalence of asymptomatic malaria cases not detectable by microscopy, which therefore remain untreated representing a parasite pool for malaria transmission. This demands the introduction of alternative strategies for diagnosis and treatment, especially for areas of low transmission to reduce it to appropriate levels for malaria pre-elimination efforts to start.