Contribution of real-time PCR to Plasmodium species identification and to clinical decisions: a nationwide study in a non-endemic setting

Epidemiological characteristics and molecular identification of Plasmodium species among cases of imported malaria in Kuwait during the COVID-19 pandemic

Cases of imported malaria are reported each year in several malaria non-endemic countries, including Kuwait. PCR testing is the ideal method for identification of the infecting Plasmodium spp. The present study documented the epidemiologic characteristics of molecularly confirmed cases of imported malaria in Kuwait during the first year of COVID-19 pandemic. During the period from February 2020 to February 2021, 100 travelers with suspected malaria who had come from malaria-endemic countries of Africa (n = 60) and Asia (n = 40) were examined. Malaria diagnosis was made by microscopy of blood-stained smears and confirmed by a multiplex real-time PCR assay. Samples with discordant species identification results were sequenced. A total of 27 cases (27%) [P. falciparum, 14; P. vivax, 11; P. ovale, 1; mixed P. falciparum and P. malariae, 1] were detected, of whom 12 came to Kuwait for the first time and 15 were returning after visiting their home countries. Most of the returning travelers (12 out of 15 cases, 80%) had not received malaria chemoprophylaxis. Most cases of falciparum malaria (13/15) were Africans while most of the vivax cases (9/11) were Asians. Malaria was more common among subjects entering Kuwait for the first time (OR = 4.025, CI 1.07,15.1) and illiterates (OR = 13.8, CI 1.8,101.4). In conclusion, imported malaria caused mainly by P. falciparum and P. vivax was an ongoing problem during the COVID-19 pandemic. Travel history and education level were significant predictors of malaria among suspected cases.

Emergence of artemisinin-based combination treatment failure in patients returning from sub-Saharan Africa with P. falciparum malaria

BACKGROUND

Artemisinin-based combination therapies (ACTs) are recommended as first-line treatment against uncomplicated Plasmodium falciparum infection. Mutations in the PfKelch13 (PF3D7_1343700) gene led to resistance to artemisinin in Southeast Asia. Mutations in the Pfcoronin (PF3D7_1251200) gene confer reduced artemisinin susceptibility in vitro to an African Plasmodium strain, but their role in clinical resistance has not been established.

METHODS

We conducted a retrospective observational study of Israeli travellers returning from sub-Saharan Africa with P. falciparum malaria, including patients with artemether-lumefantrine (AL) failure. Blood samples from all malaria-positive patients are delivered to the national Parasitology Reference Laboratory along with personal information. Confirmation of malaria, species identification and comparative parasite load analysis were performed using real-time PCR. DNA extractions from stored leftover samples were analysed for the presence of mutations in Pfkelch13 and Pfcoronin. Age, weight, initial parasitaemia level and Pfcoronin status were compared in patients who failed treatment vs responders.

RESULTS

During 2009-2020, 338 patients had P. falciparum malaria acquired in Africa. Of those, 15 (24-69 years old, 14 males) failed treatment with AL. Four were still parasitemic at the end of treatment, and 11 had malaria recrudescence. Treatment failure rates were 0% during 2009-2012, 9.1% during 2013-2016 and 17.4% during 2017-2020. In all patients, the Pfkelch13 propeller domain had a wild-type sequence. We did find the P76S mutation in the propeller domain of Pfcoronin in 4/15 (28.6%) of the treatment-failure cases compared to only 3/56 (5.5%) in the successfully treated patients (P = 0.027).

CONCLUSION

AL treatment failure emergence was not associated with mutations in Pfkelch13. However, P76S mutation in the Pfcoronin gene was more frequently present in the treatment-failure group and merits further investigation. The increase of malaria incidence in sub-Saharan-Africa partly attributed to the COVID-19 pandemic might also reflect a wider spread of ACT resistance.

Metagenomic Sequencing for the Diagnosis of Plasmodium spp. with Different Levels of Parasitemia in EDTA Blood of Malaria Patients—A Proof-of-Principle Assessment

Molecular diagnostic approaches are increasingly included in the diagnostic workup and even in the primary diagnosis of malaria in non-endemic settings, where it is difficult to maintain skillful microscopic malaria detection due to the rarity of the disease. Pathogen-specific nucleic acid amplification, however, bears the risk of overlooking other pathogens associated with febrile illness in returnees from the tropics. Here, we assessed the discriminatory potential of metagenomic sequencing for the identification of different Plasmodium species with various parasitemia in EDTA blood of malaria patients. Overall, the proportion of Plasmodium spp.-specific sequence reads in the assessed samples showed a robust positive correlation with parasitemia (Spearman r = 0.7307, p = 0.0001) and a robust negative correlation with cycle threshold (Ct) values of genus-specific real-time PCR (Spearman r = −0.8626, p ≤ 0.0001). Depending on the applied bioinformatic algorithm, discrimination on species level was successful in 50% (11/22) to 63.6% (14/22) instances. Limiting factors for the discrimination on species level were very low parasitemia, species-depending lacking availability of reliable reference genomes, and mixed infections with high variance of the proportion of the infecting species. In summary, metagenomic sequencing as performed in this study is suitable for the detection of malaria in human blood samples, but the diagnostic detection limit for a reliable discrimination on species level remains higher than for competing diagnostic approaches like microscopy and PCR.

A nationwide study of imported Plasmodium ovale and mixed infections in Israel 2008-2020

BACKGROUND

Plasmodium ovale is a rather neglected plasmodium. Rarity, a milder disease, and diagnostic difficulties compared with P. falciparum and P. vivax have led to this situation. This study's objective is to present the epidemiological and diagnostical characteristics of imported P. ovale malaria in Israel.

METHODS

Malaria is a reportable disease in Israel. All highly suspected cases are sent to the Ministry of Health central parasitology laboratory for molecular verification. We retrieved epidemiological and diagnostic data on all polymerase chain reaction (PCR)-proven P. ovale infections imported to between 2008 and 2020.

RESULTS

In total, 508 malaria cases were identified, 489 monoinfections and 19 (3.7%) mixed. Fifty-one (10%) were due to P. ovale, among them 13 (25%) were mixed, comprising 68% of all mixed infections. Forty-eight of 51 (94%) underwent blood microscopy, with a sensitivity of 94% (45/48) for genus identification and 15% (7/48) for P. ovale identification. Only 8% (1/12) of mixed infections were identified as such by microscopy. Forty-two (82%) patients underwent RDTs, with a sensitivity of 69% (29/42) for genus identification, and 62% (26/42) for identifying non-falciparum infections. Cycle threshold (Ct) values of P. ovale were significantly higher compared with P. falciparum and P. vivax in both mono and mixed infections (P < 0.05, P < 0.005). Ct levels in RDT positive vs negative infections differed significantly (P < 0.05).

CONCLUSIONS

P. ovale is commonly imported to Israel from Africa, with a high rate of mixed infections. The use of RDTs and microscopy is insufficient for the species-specific diagnosis of P. ovale, and must be complemented by PCR.

Limited Reliability of the Molecular Detection of Plasmodium spp. from Incubated Blood Culture Samples for Forensic Purposes

The suitability of incubated blood culture material for forensic molecular malaria diagnosis was assessed for non-endemic settings for cases in which the differential diagnosis malaria was initially overlooked. For the proof-of-principle assessment, residual blood culture materials from febrile patients from tropical Ghana were investigated by real-time PCR and compared with available historic microscopic results. In 2114 samples, for which microscopical results and real-time PCR results were available, microscopical results comprised 711 P. falciparum detections, 7 P. malariae detections, 1 microscopically not-further-discriminable Plasmodium spp. detection as well as 13 detections of mixed infections comprising 12 cases of P. falciparum/P. malariae co-infections and 1 case of a P. falciparum/P. ovale complex co-infection, while real-PCR indicated 558 P. falciparum detections, 95 P. malariae detections, 10 P. ovale complex detections, 1 P. vivax detection and 4 detected P. falciparum/P. malariae co-infections. Concordance of routine microscopy and real-time PCR was imperfect. Using routine microscopy as reference was associated with a seemingly low agreement of positive real-time PCR results of 90.9%. However, if positive samples, either by routine microscopy or real-time PCR or both, were applied as a combined reference, the agreement of positive results obtained with real-time PCR was increased from 74.0% to 77.9%, while the agreement of positive results obtained with routine microscopy was decreased from 100% to 85.3%. The predictive value of routine microscopy for negative results in the reference was slightly better with 90.9% compared to real-time PCR with 86.9%; the concordance between routine microscopy and real-time PCR was imperfect. In conclusion, even suboptimal sample materials such as incubated blood culture materials can be applied for forensic malaria diagnosis, if more suitable sample materials are not available, but the molecular detection rate of positive results in routine microscopy is much lower than previously reported for non-incubated blood.

Evaluating performance of multiplex real time PCR for the diagnosis of malaria at elimination targeted low transmission settings of Ethiopia

BACKGROUND

Malaria incidence has declined in Ethiopia in the past 10 years. Current malaria diagnostic tests, including light microscopy and rapid antigen-detecting diagnostic tests (RDTs) cannot reliably detect low-density infections. Studies have shown that nucleic acid amplification tests are highly sensitive and specific in detecting malaria infection. This study took place with the aim of evaluating the performance of multiplex real time PCR for the diagnosis of malaria using patient samples collected from health facilities located at malaria elimination targeted low transmission settings in Ethiopia.

METHODS

A health facility-based, cross-sectional survey was conducted in selected malaria sentinel sites. Malaria-suspected febrile outpatients referred to laboratory for malaria testing between December 2019 and March 2020 was enrolled into this study. Sociodemographic information and capillary blood samples were collected from the study participants and tested at spot with RDTs. Additionally, five circles of dry blood spot (DBS) samples on Whatman filter paper and thick and thin smear were prepared for molecular testing and microscopic examination, respectively. Multiplex real time PCR assay was performed at Ethiopian Public Health Institute (EPHI) malaria laboratory. The performance of multiplex real time PCR assay, microscopy and RDT for the diagnosis of malaria was compared and evaluated against each other.

RESULTS

Out of 271 blood samples, multiplex real time PCR identified 69 malaria cases as Plasmodium falciparum infection, 16 as Plasmodium vivax and 3 as mixed infections. Of the total samples, light microscopy detected 33 as P. falciparum, 18 as P. vivax, and RDT detected 43 as P. falciparum, 17 as P. vivax, and one mixed infection. Using light microscopy as reference test, the sensitivity and specificity of multiplex real time PCR were 100% (95% CI (93-100)) and 83.2% (95% CI (77.6-87.9)), respectively. Using multiplex real time PCR as a reference, light microscopy and RDT had sensitivity of 58% (95% CI 46.9-68.4) and 67% (95% CI 56.2-76.7); and 100% (95% CI 98-100) and 98.9% (95% CI 96-99.9), respectively. Substantial level of agreement was reported between microscopy and multiplex real time PCR results with kappa value of 0.65.

CONCLUSIONS

Multiplex real-time PCR had an advanced performance in parasite detection and species identification on febrile patients' samples than did microscopy and RDT in low malaria transmission settings. It is highly sensitive malaria diagnostic method that can be used in malaria elimination programme, particularly for community based epidemiological samples. Although microscopy and RDT had reduced performance when compared to multiplex real time PCR, still had an acceptable performance in diagnosis of malaria cases on patient samples at clinical facilities.

Misidentification of Plasmodium ovale as Plasmodium vivax malaria by a microscopic method: a meta-analysis of confirmed P. ovale cases

Plasmodium ovale is a benign tertian malaria parasite that morphologically resembles Plasmodium vivax. P. ovale also shares similar tertian periodicity and can cause relapse in patients without a radical cure, making it easily misidentified as P. vivax in routine diagnosis. Therefore, its prevalence might be underreported worldwide. The present study aimed to quantify the prevalence of P. ovale misidentified as P. vivax malaria using data from studies reporting confirmed P. ovale cases by molecular methods. Studies reporting the misidentification of P. ovale as P. vivax malaria were identified from three databases, MEDLINE, Web of Science, and Scopus, without language restrictions, but the publication date was restricted to 1993 and 2020. The quality of the included studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS). The random-effects model was used to estimate the pooled prevalence of the misidentification of P. ovale as P. vivax malaria by the microscopic method when compared to those with the reference polymerase chain reaction method. Subgroup analysis of participants was also performed to demonstrate the difference between imported and indigenous P. ovale cases. The heterogeneity of the included studies was assessed using Cochran's Q and I² statistics. Publication bias across the included studies was assessed using the funnel plot and Egger’s test, and if required, contour-enhanced funnel plots were used to identify the source(s) of funnel plot asymmetry. Of 641 articles retrieved from databases, 22 articles met the eligibility criteria and were included in the present study. Of the 8,297 malaria-positive cases identified by the PCR method, 453 P. ovale cases were confirmed. The pooled prevalence of misidentification of P. ovale as P. vivax malaria by the microscopic method was 11% (95% CI: 7–14%, I²: 25.46%). Subgroup analysis of the participants demonstrated a higher prevalence of misidentification in indigenous cases (13%, 95% CI: 6–21%, I²: 27.8%) than in imported cases (10%, 95% CI: 6–14%, I²: 24.1%). The pooled prevalence of misidentification of P. vivax as P. ovale malaria by the microscopic method was 1%, without heterogeneity (95% CI: 0–3%, I²: 16.8%). PCR was more sensitive in identifying P. ovale cases than the microscopic method (p < 0.00001, OR: 2.76, 95% CI: 1.83–4.15, I²: 65%). Subgroup analysis of participants demonstrated the better performance of PCR in detecting P. ovale malaria in indigenous cases (p: 0.0009, OR: 6.92, 95% CI: 2.21–21.7%, I²: 68%) than in imported cases (p: 0.0004, OR: 2.15, 95% CI: 1.41–3.29%, I²: 63%). P. ovale infections misidentified as P. vivax malaria by the microscopic method were frequent and led to underreported P. ovale cases. The molecular identification of P. ovale malaria in endemic areas is needed because a higher rate of P. ovale misidentification was found in endemic or indigenous cases than in imported cases. In addition, updated courses, enhanced training, and refreshers for microscopic examinations, particularly for P. ovale identification, are necessary to improve the microscopic identification of Plasmodium species in rural health centres where PCR is unavailable.

Case Report: Diagnostic Challenges in the Detection of a Mixed Plasmodium vivax/ovale Infection in a Non-Endemic Setting

In clinical practice, mixed-species malaria infections are often not detected by light microscopy (LM) or rapid diagnostic test, as a low number of parasites of one species may occur. Here, we report the case of an 8-year-old girl migrating with her family from Afghanistan with a two-species mixed infection with Plasmodium vivax and Plasmodium ovale. This case demonstrates the significance of molecular testing in the detection of mixed-species malaria infections and highlights the importance of a detailed data analysis during the medical validation procedure to prevent underestimation of mixed-species infections. To our knowledge, this is the first case report of a two-species mixed infection comprising both P. vivax and P. ovale confirmed by LM and different real-time polymerase chain reaction (PCR) approaches.

Meta-analysis of the diagnostic performance characteristics of three commercial and one in-house nucleic acid amplification tests for malaria screening

Background

A meta-analysis of previously performed evaluation studies of nucleic acid amplification testing (NAT) approaches for the screening for and differentiation of Plasmodium spp. using identical samples was performed to comparatively assess their suitability for the routine diagnostic setting.

Methods

Three commercial NATs for malaria (one loop-mediated isothermal amplification [LAMP] assay, two real-time polymerase chain reactions [PCRs]) and one in-house real-time PCR were comparatively assessed with a collection of 1020 well-characterized ethylenediaminetetraacetic acid (EDTA) blood samples from patients with suspected or confirmed malaria.

Results

Altogether 765 (75%) concordantly negative and 223 (21.9%) concordantly positive results of the four molecular tests were obtained, while discordant results were seen in 32 (3.1%) instances. For genus-specific assays, the observed sensitivity and specificity ranges were 96.4%–98.4% and 99.6%–99.9%, and for species-specific assays, 94.0%–97.6% and 99.6%–100%, respectively. Falsely negative molecular test results comprised microscopically negative samples, samples at the microscopic detection threshold and quantitatively less abundant species in mixed infections.

Conclusions

Excellent test characteristics of all assessed assays with only minor differences encourage molecular malaria screening with genus- and species-specific NAT with discrepancies only within the borderline range of their detection thresholds.

Vivax Malaria Chemoprophylaxis: The Role of Atovaquone-Proguanil Compared to Other Options

Background

Atovaquone-proguanil is considered causal prophylaxis (inhibition of liver-stage schizonts) for Plasmodium falciparum; however, its causal prophylactic efficacy for Plasmodium vivax is not known. Travelers returning to nonendemic areas provide a unique opportunity to study P. vivax prophylaxis.

Methods

In a retrospective observational study, for 11 years, Israeli rafters who had traveled to the Omo River in Ethiopia, a highly malaria-endemic area, were followed for at least 1 year after their return. Malaria prophylaxis used during this period included mefloquine, doxycycline, primaquine, and atovaquone-proguanil. Prophylaxis failure was divided into early (within a month of exposure) and late malaria.

Results

Two hundred fifty-two travelers were included in the study. Sixty-two (24.6%) travelers developed malaria, 56 (91.9%) caused by P. vivax, with 54 (87.1%) cases considered as late malaria. Among travelers using atovaquone-proguanil, there were no cases of early P. falciparum or P. vivax malaria. However, 50.0% of atovaquone-proguanil users developed late vivax malaria, as did 46.5% and 43.5% of mefloquine and doxycycline users, respectively; only 2 (1.4%) primaquine users developed late malaria (P < .0001).

Conclusions

Short-course atovaquone-proguanil appears to provide causal (liver schizont stage) prophylaxis for P. vivax, but is ineffective against late, hypnozoite reactivation-related attacks. These findings suggest that primaquine should be considered as the chemoprophylactic agent of choice for areas with high co-circulation of P. falciparum and P. vivax.

A comparison of two PCR protocols for the differentiation of Plasmodium ovale species and implications for clinical management in travellers returning to Germany: a 10-year cross-sectional study

BACKGROUND

To assess the occurrence of Plasmodium ovale wallikeri and Plasmodium ovale curtisi species in travellers returning to Germany, two real-time PCR protocols for the detection and differentiation of the two P. ovale species were compared. Results of parasite differentiation were correlated with patient data.

METHODS

Residual nucleic acid extractions from EDTA blood samples of patients with P. ovale spp. malaria, collected between 2010 and 2019 at the National Reference Centre for Tropical Pathogens in Germany, were subjected to further parasite discrimination in a retrospective assessment. All samples had been analysed by microscopy and by P. ovale spp.-specific real-time PCR without discrimination on species level. Two different real-time PCR protocols for species discrimination of P. o. curtisi and P. o. wallikeri were carried out. Results were correlated with patient data on gender, age, travel destination, thrombocyte count, and duration of parasite latency.

RESULTS

Samples from 77 P. ovale spp. malaria patients were assessed, with a male:female ratio of about 2:1 and a median age of 30 years. Parasitaemia was low, ranging from few visible parasites up to 1% infected erythrocytes. Discriminative real-time PCRs revealed 41 cases of P. o. curtisi and 36 cases of P. o. wallikeri infections. Concordance of results by the two PCR approaches was 100%. Assessment of travel destinations confirmed co-existence of P. o. curtisi and P. o. wallikeri over a wide range of countries in sub-Saharan Africa. Latency periods for the two P. ovale species were similar, with median values of 56.0 days for P. o. curtisi and 58.0 days for P. o. wallikeri; likewise, there was no statistically significant difference in thrombocyte count with median values of 138.5/µL for patients with P. o. curtisi and 152.0/µL for P. o. wallikeri-infected patients.

CONCLUSIONS

Two different real-time PCR protocols were found to be suitable for the discrimination of P. o. curtisi and P. o. wallikeri with only minor differences in sensitivity. Due to the overall low parasitaemia and the lack of differences in severity-related aspects like parasite latency periods or thrombocyte counts, this study supports the use of P. ovale spp. PCR without discrimination on species level to confirm the diagnosis and to inform clinical management of malaria in these patients.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Multiplex real-time PCR for diagnosing malaria in a non-endemic setting: a prospective comparison to conventional methods

Almost a decade ago our diagnostic laboratory implemented an in-house real-time PCR for the detection of Plasmodium DNA to diagnose malaria in parallel with conventional diagnostics, i.e., microscopy (thick and thin smears), quantitative buffy coat microscopy (QBC), and a rapid diagnostic test (RDT). Here we report our experiences and make a comparison between the different diagnostic procedures used in this non-endemic setting. All patients during the period February 2009-December 2017 suspected of malaria were prospectively tested at the moment of sample collection. Both PCR and conventional malaria diagnostics were carried out on a total of 839 specimens from 825 patients. In addition, three Plasmodium falciparum (Pf) patients were closely followed by real-time PCR and microscopy after treatment. Overall, 56 samples (55 patients) tested positive by real-time PCR, of which six were missed by microscopy and seven by QBC. RDT showed fairly good results in detecting Pf, whereas specificity was not optimal. RDT failed to detect 10 of 17 non-Pf PCR positive specimens. One Plasmodium malariae patient would have been missed if only conventional diagnostic tests had been used. The high sensitivity of the PCR was confirmed by the number of PCR positive, microscopy negative post-treatment samples. In conclusion, within our routine diagnostic setting, malaria real-time PCR not only showed a high level of agreement with the conventional methods used, but also showed higher sensitivity and better specificity. Still, for complete replacement of the conventional procedures in a non-endemic setting, the time-to-results of the real-time PCR is currently too long.

Plasmodium malariae in Israeli Travelers: A Nationwide Study

Background

Little is known about Plasmodium malariae, a relatively rare cause of malaria in returned travelers. Recently, polymerase chain reaction (PCR) use for malaria diagnosis has enhanced specificity of P. malariae detection. The study objective was to describe the unique aspects of P. malariae diagnosis and clinical course in travelers.

Methods

Malaria is a reportable disease in Israel. All PCR-proven P. malariae monoinfections in Israeli travelers between January 2008 and January 2017 were retrieved from the Ministry of Health Reference Parasitology Laboratory. Data regarding method and timing of diagnosis, clinical characteristics, and laboratory testing were collected from patient charts.

Results

Eighteen patients with P. malariae were included. All cases were acquired in Africa. During the study period, the relative proportion of P. malariae increased (2%-10% of all malaria cases). Malaria was identified by blood smear in 10 of 18 patients (56%) on admission, and by rapid antigen test in 5 of 18 (29%) patients only, while P. malariae speciation was correctly identified by smear in 2 of 18 (11%) patients. Though all patients reported fever, only 4 of 18 (22%) described a quartan fever course. In 7 of 18 (39%) patients, malaria was contracted despite prophylactic treatment. Five patients had prolonged prepatent periods (median, 55 days), all of whom received prior prophylaxis.

Conclusions

The relative proportion of P. malariae is on the rise. Diagnosis in routine clinical settings is inadequate due to the low sensitivity and specificity of blood smears. PCR should be considered when clinical suspicion is high. Prophylaxis failure, which caused delayed clinical presentation, was documented.