Non-falciparum malaria imported mainly from Africa: a review from a Portuguese hospital

Malaria Elimination in Africa: Rethinking Strategies for Plasmodium vivax and Lessons from Botswana

The global malaria community has picked up the theme of malaria elimination in more than 90% of the world's population in the next decade. Recent reports of Plasmodium vivax (P. vivax) in sub-Saharan Africa, including in Duffy-negative individuals, threaten the efforts aimed at achieving elimination. This is not only in view of strategies that are tailored only to P. falciparum elimination but also due to currently revealed biological characteristics of P. vivax concerning the relapse patterns of hypnozoites and conservation of large biomasses in cryptic sites in the bone marrow and spleen. A typical scenario was observed in Botswana between 2008 and 2018, which palpably projects how P. vivax could endanger malaria elimination efforts where the two parasites co-exist. The need for the global malaria community, national malaria programs (NMPs), funding agencies and relevant stakeholders to engage in a forum to discuss and recommend clear pathways for elimination of malaria, including P. vivax, in sub-Saharan Africa is warranted.

Malaria Detection Accelerated: Combing a High-Throughput NanoZoomer Platform with a ParasiteMacro Algorithm

Eradication of malaria, a mosquito-borne parasitic disease that hijacks human red blood cells, is a global priority. Microscopy remains the gold standard hallmark for diagnosis and estimation of parasitemia for malaria, to date. However, this approach is time-consuming and requires much expertise especially in malaria-endemic countries or in areas with low-density malaria infection. Thus, there is a need for accurate malaria diagnosis/parasitemia estimation with standardized, fast, and more reliable methods. To this end, we performed a proof-of-concept study using the automated imaging (NanoZoomer) platform to detect the malarial parasite in infected blood. The approach can be used as a steppingstone for malaria diagnosis and parasitemia estimation. Additionally, we created an algorithm (ParasiteMacro) compatible with free online imaging software (ImageJ) that can be used with low magnification objectives (e.g., 5×, 10×, and 20×) both in the NanoZoomer and routine microscope. The novel approach to estimate malarial parasitemia based on modern technologies compared to manual light microscopy demonstrated 100% sensitivity, 87% specificity, a 100% negative predictive value (NPV) and a 93% positive predictive value (PPV). The manual and automated malaria counts showed a good Pearson correlation for low- (R2 = 0.9377, r = 0.9683 and p < 0.0001) as well as high- parasitemia (R2 = 0.8170, r = 0.9044 and p < 0.0001) with low estimation errors. Our robust strategy that identifies and quantifies malaria can play a pivotal role in disease control strategies.

Molecular identification and anti-malarial drug resistance profile of Plasmodium falciparum from patients attending Kisoro Hospital, southwestern Uganda

Background

The evolution of malaria infection has necessitated the development of highly sensitive diagnostic assays, as well as the use of dried blood spots (DBS) as a potential source of deoxyribonucleic acid (DNA) yield for polymerase chain reaction (PCR) assays. This study identified the different Plasmodium species in malaria-positive patients, and the anti-malarial drug resistance profile for Plasmodium falciparum using DBS samples collected from patients attending Kisoro Hospital in Kisoro district, Southwestern Uganda.

Methods

The blood samples were prospectively collected from patients diagnosed with malaria to make DBS, which were then used to extract DNA for real-time PCR and high-resolution melting (HRM) analysis. Plasmodium species were identified by comparing the control and test samples using HRM-PCR derivative curves. Plasmodium falciparum chloroquine (CQ) resistance transporter (pfcrt) and kelch13 to screen the samples for anti-malarial resistance markers. The HRM-PCR derivative curve was used to present a summary distribution of the different Plasmodium species as well as the anti-malarial drug profile.

Results

Of the 152 participants sampled, 98 (64.5%) were females. The average age of the participants was 34.9 years (range: 2 months–81 years). There were 134 samples that showed PCR amplification, confirming the species as Plasmodium. Plasmodium falciparum (N = 122), Plasmodium malariae (N = 6), Plasmodium ovale (N = 4), and Plasmodium vivax (N = 2) were the various Plasmodium species and their proportions. The results showed that 87 (71.3%) of the samples were sensitive strains/wild type (CVMNK), 4 (3.3%) were resistant haplotypes (SVMNT), and 31 (25.4%) were resistant haplotypes (CVIET). Kelch13 C580Y mutation was not detected.

Conclusion

The community served by Kisoro hospital has a high Plasmodium species burden, according to this study. Plasmodium falciparum was the dominant species, and it has shown that resistance to chloroquine is decreasing in the region. Based on this, molecular identification of Plasmodium species is critical for better clinical management. Besides, DBS is an appropriate medium for DNA preservation and storage for future epidemiological studies.

The Pan African Vivax and Ovale Network (PAVON): Refocusing on Plasmodium vivax, ovale and asymptomatic malaria in sub-Saharan Africa

The recent World Malaria report shows that progress in malaria elimination has stalled. Current data acquisition by NMCPs depend on passive case detection and clinical reports focused mainly on Plasmodium falciparum (Pf). In recent times, several countries in sub-Saharan Africa have reported cases of Plasmodium vivax (Pv) with a considerable number being Duffy negative. The burden of Pv and Plasmodium ovale (Po) appear to be more than acknowledged. Similarly, the contribution of asymptomatic malaria in transmission is hardly considered by NMCPs in Africa. Inclusion of these as targets in malaria elimination agenda is necessary to achieve elimination goal, as these harbor hypnozoites. The Pan African Vivax and Ovale Network (PAVON) is a new consortium of African Scientists working in Africa on the transmission profile of Pv and Po. The group collaborates with African NMCPs to train in Plasmodium molecular diagnostics, microscopy, and interpretation of molecular data from active surveys to translate into policy. Details of the mission, rational and modus operandi of the group are outlined.

Malaria Rapid Diagnostic Tests: Literary Review and Recommendation for a Quality Assurance, Quality Control Algorithm

Malaria rapid diagnostic tests (RDTs) have had an enormous global impact which contributed to the World Health Organization paradigm shift from empiric treatment to obtaining a parasitological diagnosis prior to treatment. Microscopy, the classic standard, requires significant expertise, equipment, electricity, and reagents. Alternatively, RDT’s lower complexity allows utilization in austere environments while achieving similar sensitivities and specificities. Worldwide, there are over 200 different RDT brands that utilize three antigens: Plasmodium histidine-rich protein 2 (PfHRP-2), Plasmodium lactate dehydrogenase (pLDH), and Plasmodium aldolase (pALDO). pfHRP-2 is produced exclusively by Plasmodium falciparum and is very Pf sensitive, but an alternative antigen or antigen combination is required for regions like Asia with significant Plasmodium vivax prevalence. RDT sensitivity also decreases with low parasitemia (<100 parasites/uL), genetic variability, and prozone effect. Thus, proper RDT selection and understanding of test limitations are essential. The Center for Disease Control recommends confirming RDT results by microscopy, but this is challenging, due to the utilization of clinical laboratory standards, like the College of American Pathologists (CAP) and the Clinical Lab Improvement Act (CLIA), and limited recourses. Our focus is to provide quality assurance and quality control strategies for resource-constrained environments and provide education on RDT limitations.

Detection of malaria parasites in samples from returning US travelers using the Alethia® Malaria Plus LAMP assay

Objective

In this study, the performance of a commercially available malaria LAMP assay (Alethia® Malaria Plus LAMP) was evaluated using retrospective clinical samples obtained from travelers returning to the United States of America (USA). Recently, several laboratories in non-malaria endemic countries evaluated the use of the loop mediated isothermal amplification (LAMP) assays for the diagnosis of imported malaria cases. These tests are simpler than polymerase-chain reaction (PCR)-based assays and were shown to have high sensitivity. Much of malaria diagnoses in the USA, is undertaken at the state level using mainly microscopy and rapid diagnostic tests (RDTs). However, molecular tools offer greater sensitivity over microscopy and RDTs. A reliable, easy to perform molecular assay can provide a test of choice for the accurate detection of malaria parasites in places where expert microscopy is lacking and/or for the detection of low-parasite density infections.

Results

The Alethia® Malaria Plus LAMP assay was easy to use, had similar test performances as the real-time PCR reference test and results were obtained faster (within 1 h) than the reference test. The sensitivity of the assay was 100% with a kappa score of 1 when compared to the reference PET-PCR assay.

First evidence of local circulation of Plasmodium ovale curtisi and reliability of a malaria rapid diagnostic test among symptomatic outpatients in Douala, Cameroon

The performances of a commonly used Plasmodium falciparum-detecting rapid diagnostic test (RDT) were determined in symptomatic individuals living in Cameroon. Discrepancies between RDT and light microscopy (LM) results were further investigated, with a focus on non-falciparum malaria (NFM) which are still largely understudied in sub-Saharan Africa (sSA) countries. In the present study, a total of 355 individuals aged 1-65 years were enrolled in the study. Their signs/symptoms and sociodemographic characteristics were documented. The RDT reliability was evaluated using LM as gold standard method. Polymerase chain reaction (PCR) of Plasmodium 18S gene was performed for samples with discordant results between LM and RDT (i.e., RDT-/LM+, and RDT+/LM-). The PCR amplicons of NFM species were sequenced and BLASTed. The prevalence of malaria infection by LM was 95.7% (95% CI: 93.1-97.4%). The sensitivity and specificity of RDT for P. falciparum detection was 94.0% and 66.7%, respectively. By PCR assay, P. ovale curtisi (PoC) was found in 5 of the 30 discordant samples, and on sequence analysis these isolates were found to be phylogenetically closer to sequences reported from China-Myanmar border and Malaysia. This is the first report on molecular characterization of P. ovale subspecies in Cameroon. The study also outlines the good diagnostic performances of the RDT for detection of P. falciparum. Though, the presence of PoC indicated the importance of having RDTs targeting the NFM species in malaria diagnosis and treatment, which is presently limited in the country.

A powerful qPCR-high resolution melting assay with taqman probe in plasmodium species differentiation

BACKGROUND

The use of highly sensitive molecular tools in malaria diagnosis is currently largely restricted to research and epidemiological settings, but will ultimately be essential during elimination and potentially eradication. Accurate diagnosis and differentiation down to species levels, including the two Plasmodium ovale species and zoonotic variants of the disease, will be important for the understanding of changing epidemiological patterns of the disease.

METHODS

A qPCR-high resolution melting (HRM) method was to detect and differentiate all human Plasmodium species with one forward and one reverse primer set. The HRM detection method was further refined using a hydrolysis probe to specifically discriminate Plasmodium falciparum.

RESULTS

Out of the 113 samples tested with the developed HRM-qPCR- P. falciparum probe assay, 96 (85.0 %) single infections, 12 (10.6 %) mixed infections, and 5 (4.4 %) were Plasmodium negative. The results were concordant with those of the nested PCR at 98.2 %. The assay limit of detection was varied from 21.47 to 46.43 copies /µl, equivalent to 1-2.11 parasites/µl. All P. falciparum infections were confirmed with the associated Taqman probe.

CONCLUSIONS

Although the dependence on qPCR currently limits its deployment in resource-limited environments, this assay is highly sensitive and specific, easy to perform and convenient for Plasmodium mono-infection and may provide a novel tool for rapid and accurate malaria diagnosis also in epidemiological studies.

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

BACKGROUND

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

METHODS AND DESIGN

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

RESULTS

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

CONCLUSION

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

A Systematic Review: Performance of Rapid Diagnostic Tests for the Detection of Plasmodium knowlesi, Plasmodium malariae, and Plasmodium ovale Monoinfections in Human Blood

Background

Despite the increased use and worldwide distribution of malaria rapid diagnostic tests (RDTs) that distinguish between Plasmodium falciparum and non-falciparum species, little is known about their performance detecting Plasmodium knowlesi (Pk), Plasmodium malariae (Pm), and Plasmodium ovale (Po). This review seeks to analyze the results of published studies evaluating the diagnostic accuracy of malaria RDTs in detecting Pk, Pm, and Po monoinfections.

Methods

MEDLINE, EMBASE, Web of Science, and CENTRAL databases were systematically searched to identify studies that reported the performance of RDTs in detecting Pk, Pm, and Po monoinfections.

Results

Among 40 studies included in the review, 3 reported on Pk, 8 on Pm, 5 on Po, 1 on Pk and Pm, and 23 on Pm and Po infections. In the meta-analysis, estimates of sensitivities of RDTs in detecting Pk infections ranged 2%-48%. Test performances for Pm and Po infections were less accurate and highly heterogeneous, mainly because of the small number of samples tested.

Conclusions

Limited data available suggest that malaria RDTs show suboptimal performance for detecting Pk, Pm, and Po infections. New improved RDTs and appropriately designed cross-sectional studies to demonstrate the usefulness of RDTs in the detection of neglected Plasmodium species are urgently needed.

Malaria burden and pre-hospital medication among subjects with malaria in Maiduguri, Northeast Nigeria

The study re-visited malaria burden and pre-hospital medication among malarious subjects in Maiduguri, Northeast Nigeria. A total of 1,657 febrile subjects were screened for malaria by microscopy at two health institutions. Giemsa-stained blood smears were examined for parasitaemia and gametocytaemia; and parasite density (PD), gametocyte density (GD) and gametocyte sex ratio (GSR) were determined. The mean age of the 1,657 subjects was 27.5 ± 12.2 years and 7.8% (130/1,657) of the subjects aged <5 years. Sex distribution showed 47.0% (778/1,657) males and 53.0% (879/1657) females. Parasitaemia was recorded in 22.6% (375/1,657) with geometric mean PD of 8,925 (320–275,000) parasites/μl blood. The prevalence of parasitaemia was highest among subjects <5 years (χ² = 401.1; df = 5; p < 0.0001) and in August and September (χ² = 406.9; df = 11; p < 0.0001). Prevalence of gametocytaemia was 12.8% (48/375) with geometric mean GD of 109 (8–464) gametocytes/μl blood. The prevalence was higher in dry (16.5%, 29/176) than wet (9.5%, 19/199) months (χ² = 4.0; df = 1; p = 0.045). The weighted mean GSR was 0.4 ± 0.1 with highest value in March (0.7 ± 0.2). Pre-hospital medication was recorded in 74.1% (278/375) of the subjects with parasitaemia. Analgesics (51.7%; 194/375) accounted for the highest proportion of drug consumed while 9.3% (35/375) of the subjects took antimalarial drugs. Malaria persisted in Maiduguri especially among subjects <5 years during wet months and pre-hospital medication is a common practice. These findings could serve as guide for policy decision that could contribute to effective treatment and control of malaria in the region.

A cluster of the first reported Plasmodium ovale spp. infections in Peru occuring among returning UN peace-keepers, a review of epidemiology, prevention and diagnostic challenges in nonendemic regions

BACKGROUND

Plasmodium ovale curtisi and Plasmodium ovale wallikeri are regarded as less virulent forms of malaria with a geographic distribution including Southeast Asia, Central and West Africa, and is increasingly reported as an infection in returning travellers. A species of malaria that may have delayed or relapsing presentations similar to Plasmodium vivax, the clinical presentation of P. ovale spp. has been described to have prepatent periods of 2 weeks or slightly longer with reports of relapse following primary infection out to 8-9 months. This presentation may be obscured further in the setting of anti-malarial exposure, with report of delayed primary infection out to 4 years. Presented is a cluster of 4 imported P. ovale spp. cases in returning Peruvian military personnel assigned to United Nations peace-keeping operations in the Central African Republic.

CASE PRESENTATION

From January to December 2016, Peruvian peace-keepers were deployed in support of United Nations (UN) operations in the Central African Republic (CAR). While serving abroad, Navy, Army, and Air Force members experienced 223 episodes of Plasmodium falciparum malaria following interruption of prophylaxis with mefloquine. Diagnosis was made using rapid diagnostics tests (RDTs) and/or smear with no coinfections identified. Cases of malaria were treated with locally-procured artemether-lumefantrine. Returning to Peru in January 2017, 200 peace-keepers were screened via thick and thin smear while on weekly mefloquine prophylaxis with only 1 showing nucleic acid within red blood cells consistent with Plasmodium spp. and 11 reporting syndromes of ill-defined somatic complaints. Between a period of 5 days to 11 months post return, 4 cases of P. ovale spp. were diagnosed using smear and polymerase chain reaction (PCR) following febrile complaints. All cases were subsequently treated with chloroquine and primaquine, with cure of clinical disease and documented clearance of parasitaemia.

CONCLUSION

These patients represent the first imported cases in Peru of this species of malaria as well as highlight the challenges in implementing population level prophylaxis in a deployed environment, and the steps for timely diagnosis and management in a non-endemic region where risk of introduction for local transmission exists.

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

Background

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

Methods

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

Results

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

Conclusions

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