Submicroscopic Malaria in Migrants from Sub-Saharan Africa, Spain

Imported malaria in a non-endemic country: sixteen years of cases in a hospital in the South of Madrid, Spain

PURPOSE

Malaria keeps on being a serious global health threat, especially in many tropical countries, where it is endemic. Also in non-endemic countries, like Spain, malaria is an issue that requires attention due to the presence of imported cases.

METHODS

This is a retrospective study, including all patients diagnosed with malaria at Severo Ochoa University Hospital from 2006 to 2022, being classified according to: (I) their type of stay in an endemic area as visiting friends and relatives (VFR), migrants of recent arrival (MRA), or tourism and business (T&B), and (II) the mode of presentation as microscopic (MM) or submicroscopic (SMM) malaria.

RESULTS

In this study, 132 patients (23.7% of all suspected) were diagnosed with malaria. The PCR was the most sensitive technique (99.2%), followed by antigen detection (78.8%) and microscopy (75%), with Plasmodium falciparum being the predominant species (94.7%). VFR was the largest group infected with malaria (69.7%), mostly symptomatic (98.2%) and presenting MM (90.2%). Instead, MRA patients (25%) presented milder (47.4%) or no symptoms (31.6%) and higher cases of SMM (42.4%). Coinfection with another imported pathogen was present in 19 patients (14.4%), being MRA more frequently coinfected (30.3%) CONCLUSION: This study shows the need for establishing systems for VFRs to attend pre-travel consultations to reduce malaria imported risk. In the case of MRA, screening for imported diseases should be conducted upon their arrival. Finally, we highlight two cases of co-infection with imported viruses, showing that presence of symptoms resembling malaria from another imported pathogen does not exclude malaria.

Malaria diagnosis using a combined system of a simple and fast extraction method with a lyophilised Dual-LAMP assay in a non-endemic setting

Malaria is a parasitic disease distributed in tropical areas but with a high number of imported cases in non-endemic countries. The most specific and sensitive malaria diagnostic methods are PCR and LAMP. However, both require specific equipment, extraction procedures and a cold chain. This study aims to solve some limitations of LAMP method with the optimization and validation of six LAMP assays, genus and species-specific, using an easy and fast extraction method, the incorporation of a reaction control assay, two ways (Dual) of result reading and reagent lyophilization. The Dual-LAMP assays were validated against the Nested-Multiplex Malaria PCR. A conventional column and saline extraction methods, and the use of lyophilized reaction tubes were also assessed. A new reaction control Dual-LAMP-RC assay was designed. Dual-LAMP-Pspp assay showed no cross-reactivity with other parasites, repeatability and reproducibility of 100%, a significant correlation between parasite concentration and time to amplification and a LoD of 1.22 parasites/µl and 5.82 parasites/µl using column and saline extraction methods, respectively. Sensitivity and specificity of the six Dual-LAMP assays reach values of 100% or close to this, being lower for the Dual-LAMP-Pm. The Dual-LAMP-RC assay worked as expected. Lyophilized Dual-LAMP results were concordant with the reference method. Dual-LAMP malaria assays with the addition of a new reaction control LAMP assay and the use of a fast and easy saline extraction method, provided low limit of detection, no cross-reactivity, and good sensitivity and specificity. Furthermore, the reagent lyophilization and the dual result reading allow their use in most settings.

Malaria parasite prevalence among migrants: a systematic review and meta-analysis

BACKGROUND

Asymptomatic malaria infections are highly prevalent in endemic areas.

OBJECTIVES

This systematic review aimed to estimate the pooled prevalence of malaria parasites in migrants screened in non-endemic areas.

DATA SOURCES

MEDLINE-Ovid, EMBASE, Web of Science, Global Health, Lilacs, Cochrane, and MedRxiv.

STUDY ELIGIBILITY CRITERIA

Cross-sectional studies and observational prospective or retrospective cohort studies conducted in Europe, USA, Canada, Australia, or New Zealand regardless of language or publication status. Studies should include prevalence data on malaria in migrants that were recruited through a systematic screening approach. We excluded studies where people were tested because of malaria symptoms.

PARTICIPANTS

Migrant individuals exposed to malaria infection ASSESSMENT OF RISK OF BIAS: A standardized and validated appraisal instrument was used for studies reporting prevalence data (Joanna Briggs Institute Manual for Evidence Synthesis).

METHODS OF DATA SYNTHESIS

Pooled estimates of the parasite prevalence by PCR, microscopy, and rapid diagnostic test (RDT) were calculated with a random-effects model. Heterogeneity was explored by stratification by age, region of origin, period of study, and quality of studies.

RESULTS

Of 1819 studies retrieved, 23 studies were included with in total 4203 participant PCR data, 3186 microscopy and 4698 RDT data, respectively. Migrants from sub-Saharan Africa had a malaria parasite prevalence of 8.3% (95% CI 5.1-12.2) by PCR, 4.3% (1.5-8.2) by RDT, and 3.1% (0.7-6.8) by microscopy. For migrants from Asia and Latin America, the prevalence with PCR was 0% (0.0-0.08) and 0.4% (0.0-1.8), respectively. Migrants from the Central African Region had the highest PCR prevalence (9.3% [6.0-13.0]), followed by West African migrants (2.0% [0.0-7.7]). Restricting the analysis to sub-Saharan Africa migrants arriving to the host country within the previous year, the PCR-based prevalence was 11.6% (6.9-17.4).

CONCLUSION

We provide estimates on the malaria parasite prevalence in migrants in non-endemic setting. Despite heterogeneity between settings, these findings can contribute to inform screening strategies and guidelines targeting malaria in migrants.

Malaria parasite prevalence in Sub-Saharan African migrants screened in Sweden: a cross-sectional study

Background

Asymptomatic infections with malaria parasites are common in populations in endemic areas. These infections may persist in migrants after arrival in a non-endemic area. Screening to find and clear these infections is generally not implemented in non-endemic countries, despite a potential negative health impact. We performed a study to evaluate the Plasmodium parasite prevalence in migrants living in Sweden.

Methods

Adults and children born in Sub-Saharan Africa (SSA) were invited in the study between April 2019 and June 2022 at 10 different sites, mainly as part of the national Migrant Health Assessment Program in Stockholm and Västerås, Sweden. Rapid diagnostic tests (RDT) and real-time PCR were used to detect malaria parasites. Prevalence and test sensitivity were calculated with 95% confidence intervals (CI). Univariate and multivariable logistic regression were used to evaluate associations with PCR positivity.

Findings

In total, 789 individuals were screened for Plasmodium spp. of which 71 (9.0%) were positive by PCR and 18 (2.3%) also by RDT. When performed during the national screening program, 10.4% was PCR positive. A high prevalence was detected in migrants with Uganda as the country of last residence, 53/187 (28.3%), and in this group the prevalence was highest in children, 29/81 (35.8%). Among the PCR positive, 47/71 (66.2%) belonged to families with at least one other member testing positive (odds ratio [OR] 43.4 (95% CI 19.0-98.9), and the time lived in Sweden ranged between 6 and 386 days.

Interpretation

A high malaria parasite prevalence was found in migrants from SSA, particularly in children offered screening in Stockholm, Sweden during the study period. Awareness of asymptomatic malaria infection is needed and screening for malaria in migrants arriving from high endemic countries should be considered.

Funding

The Swedish Research Council, Stockholm County Council and Centre for Clinical Research, Västmanland, Sweden.

Screening of imported malaria infection in asymptomatic migrants from Sub-Saharan Africa: A retrospective analysis of a 2010-2019 cohort

BACKGROUND

Up to 40% of cases of imported malaria in Europe are diagnosed in recently arrived migrants, who generally exhibit asymptomatic or mild symptoms and show low parasitaemia (submicroscopic). The study describes the prevalence of malaria infection among asymptomatic Sub-Saharan African migrants (ASSAM) and compares asymptomatic malaria-infected (AMI) vs non-malaria infected patients.

METHODS

An observational, comparative, retrospective study was carried out in ASSAM who underwent a medical examination, between 2010 and 2019 at the National Reference Unit for Tropical Diseases (NRU-Trop) in Madrid, Spain. Medical examination and systematic screening protocol for infectious diseases, including screening for malaria infection by Polymerase Chain Reaction (PCR) was performed.

RESULTS

During the study period, 632 out of 1061 ASSAM were screened for malaria, median age: 24 years (IQR:1-5); median time from arrival to diagnosis: 2 months (IQR:1-5). P. falciparum was the most frequent species: 61 patients (67.8%). Compared to non-malaria infected, AMI subjects had: higher rate of co-infection with S. stercoralis (41.1%VS 22.9%;p < 0.001) and filariae (8.9% VS 2.4%;p = 0.006), lower erythrocyte corpuscular volume (83.6 VS 84.4;p = 0.008) and lower levels of cholesterol (151.0 VS 167.3;p < 0.001).

CONCLUSIONS

We observed a high prevalence of AMI among ASSAM. This highlights the need to consider routing screening of migrants from endemic areas and to study if such screening could avoid the potential morbidities associated with chronic infection, reduce morbi-mortality of acute malaria and the risk of transmission in host communities.

Fast detection and quantification of Plasmodium species infected erythrocytes in a non-endemic region by using the Sysmex XN-31 analyzer

Background

Due to increased travel from endemic countries, malaria occurs more frequently in non-endemic regions. It is a challenge for diagnostic laboratories in non-endemic countries to provide reliable results, as experience of staff is often limited to only a few cases per year. This study evaluated the diagnostic accuracy of the fully automated Sysmex XN-31 malaria analyzer in a routine diagnostic setting in a non-endemic region was evaluated.

Methods

Samples from 112 patients suspected for malaria were examined by the Sysmex XN-31 analyzer to determine the absolute count of malaria-infected red blood cells count (MI-RBC/µL). Microscopic examination of both Quantitative Buffy Coat capillary tubes and thick and thin blood films were used as reference methods. Limits of blank (LoB), detection (LoD) and quantification (LoQ) were investigated using an in vitro Plasmodium falciparum culture. Nine hundred twenty samples of patients with RBC abnormalities were included to determine which RBC abnormalities trigger indeterminate or false positive results.

Results

No false positive nor false negative results were obtained for the examined patient samples suspected for malaria. For 3% of samples an indeterminate result by the XN-31 was obtained. The Passing-Bablok regression line for diagnostic accuracy of the parasitaemia was y = 39.75 + 0.7892 × showing a positive bias of about 21% when comparing the MI-RBC results to microscopy. The LoB, LoD and LoQ were calculated to be 4.7, 5.9, and 19.0 infected RBC/μL, respectively. From the 920 abnormal RBC samples collected, 4.6% resulted in a false positive MI-RBC result and almost half of the samples produced indeterminate results. These results were related to increases in nucleated red blood cells, reticulocytes and other abnormal RBC morphologies such as sickle cells.

Conclusions

Based on the results, the XN-31 is a fast and reliable screening method in the detection and quantification of Plasmodium species in patients However, if an abnormal red blood cell morphology is present, the results of the XN-31 should be interpreted with caution as false positive results can be caused by interfering abnormal erythrocytes.

Migration-associated malaria from Africa in southern Spain

Background

The western area of the province of Almeria, sited in southern Spain, has one of the highest immigrant population rates in Spain, mainly dedicated to agricultural work. In recent years, there has been a significant increase in the number of cases of imported malaria associated with migrants from countries belonging to sub-Saharan Africa. The objective of our study is to describe the epidemiological, clinical and analytical characteristics of malaria patients treated in a specialized tropical unit, paying special attention to the differences between VFR and non-VFR migrants and also to the peculiarities of microscopic malaria cases compared to submicroscopic ones.

Methods

Retrospective observational study of migrants over 14 years of age with imported malaria treated from October 2004 to May 2019. Characteristics of VFR and non-VFR migrants were compared. Malaria cases were divided into microscopic malaria (MM) and submicroscopic malaria (SMM). SMM was defined as the presence of a positive malaria PCR test together with a negative direct microscopic examination and a negative rapid diagnostic test (RDT). Microscopic malaria was defined as the presence of a positive RDT and/or a positive smear examination.

Results

Three hundred thirty-six cases of malaria were diagnosed, 329 in sub-Saharan immigrants. Of these, 78.1% were VFR migrants, in whom MM predominated (85.2% of cases). In non-VFR migrants, SMM represented 72.2% of the cases. Overall, 239 (72.6%) patients presented MM and 90 (27.4%) SMM. Fever was the most frequent clinical manifestation (64.4%), mainly in the MM group (MM: 81.1% vs SMM: 20.0%; p < 0.01). The most frequent species was P. falciparum. Patients with SMM presented fewer cytopenias and a greater number of coinfections due to soil-transmitted helminths, filarial and intestinal protozoa compared to patients with MM.

Conclusions

Imported malaria in our area is closely related to sub-Saharan migration. VFR migrants are the main risk group, highlighting the need for actions aimed at improving disease prevention measures. On the other hand, almost a third of the cases are due to SMM. This fact could justify its systematic screening, at least for those travelers at greater risk.

Graphic Abstract

The role of ultra-sensitive molecular methods for detecting malaria - the broader perspective

Ultra-sensitive molecular diagnostics are lowering the limit of detection for malaria parasites in the blood and providing insights not captured by conventional tool such as microscopy and rapid antigen tests. Low-level malaria infections identified by molecular tools may influence clinical outcomes, transmission events, and elimination efforts. While many ultra-sensitive molecular methods require well-equipped laboratories, technologies such as loop-mediated isothermal amplification (LAMP) or recombinase polymerase amplification (RPA) provide more portable and analytically sensitive solutions. These tools may benefit asymptomatic patient screening, antenatal care, and elimination campaigns. We review the recent evidence, offer our perspective on the impact of these new tests and identify future research priorities.

Emerging Infectious Diseases in Pregnant Women in a Non-Endemic Area: Almost One Out of Four Is at Risk

We report the results of a targeted testing strategy for five emerging infectious diseases (Chagas disease, human T-lymphotropic virus 1 infection, malaria, schistosomiasis, and Zika virus infection) in pregnant women accessing an Italian referral centre for infectious diseases in pregnancy for unrelated reasons. The strategy is based on a quick five-question questionnaire which allows the identification of pregnant women at risk who should be tested for a specific disease. One hundred and three (24%) out of 429 pregnant women evaluated in a 20 month period were at risk for at least one emerging infectious disease. Three (2.9%, all from sub-Saharan Africa) out of 103 at-risk women resulted in being affected (one case of Plasmodium falciparum malaria, two cases of schistosomiasis) and were appropriately managed. Prevalence of emerging infectious disease was particularly high in pregnant women from Africa (three out of 25 pregnant women tested, 12%). The proposed strategy could be used by health care professionals managing pregnant women in non-endemic setting, to identify those at risk for one of the five infection which could benefit for a targeted test and treatment.

Should obstetricians working in non-endemic countries care about emerging tropical diseases?

Due to migration and international travels, obstetricians are increasingly faced with a globalized obstetric setting and should adapt their daily clinical and diagnostic approach to the modifications of tropical and subtropical infections epidemiology. This paper is focused on five emerging infectious diseases, namely Chagas disease, HTLV-1 infection, malaria, schistosomiasis and Zika virus infection, having a high prevalence in migrant populations and which can affect international travelers. These diseases frequently pass unrecognized since they are characterized by few or no symptoms during pregnancy, however they may cause a relevant maternal, fetal and neonatal impact. Specific and reliable diagnostic and treatment options are available but are rarely used during routine obstetrical practice.

Overcoming challenges in the diagnosis and treatment of parasitic infectious diseases in migrants

Introduction: Recent increases in population movements have created novel health challenges in many areas of the World, and health policies have been adapted accordingly in several countries. However, screening guidelines for infectious diseases are not standardized and generally do not include comprehensive screening for parasitic infections.Areas covered: Malaria, Chagas disease, leishmaniasis, amebiasis, filariases, strongyloidiasis, and schistosomiasis are reviewed, focusing on the challenges posed for their diagnosis and management in vulnerable populations such as migrants. The methodology included literature searches in public databases such as PubMed.gov and Google Scholar and search of the US National Library of Medicine online database of privately and publicly funded clinical studies (ClinicalTrials.gov) until November 2019.Expert opinion: Parasitic infections which may remain asymptomatic for prolonged periods, leading to chronic infection and complications, and/or may be transmitted in non-endemic areas are ideal candidates for screening. Proposed strategies to improve diagnosis in vulnerable groups such as migrants include facilitating access to healthcare in a multi-dimensional manner considering location, individual characteristics, and timing. Limitations and availability of specific diagnostic techniques should be addressed and focus on drug and vaccine development for these neglected infections should be prioritized through collaborative initiatives with public disclosure of results.

Prevalence of submicroscopic malaria infection in immigrants living in Spain

BACKGROUND

The importance of submicroscopic malaria infections in high-transmission areas could contribute to maintain the parasite cycle. Regarding non-endemic areas, its importance remains barely understood because parasitaemia in these afebrile patients is usually below the detection limits for microscopy, hence molecular techniques are often needed for its diagnosis. In addition to this, the lack of standardized protocols for the screening of submicroscopic malaria in immigrants from endemic areas may underestimate the infection with Plasmodium spp. The aim of this study was to assess the prevalence of submicroscopic malaria in afebrile immigrants living in a non-endemic area.

METHODS

A prospective, observational, multicentre study was conducted. Afebrile immigrants were included, microscopic observation of Giemsa-stained thin and thick blood smears, and two different molecular techniques detecting Plasmodium spp. were performed. Patients with submicroscopic malaria were defined as patients with negative blood smears and detection of DNA of Plasmodium spp. with one or both molecular techniques. Demographic, clinical, analytical and microbiological features were recorded and univariate analysis by subgroups was carried out with STATA v15.

RESULTS

A total of 244 afebrile immigrants were included in the study. Of them, 14 had a submicroscopic malaria infection, yielding a prevalence of 5.7% (95% confidence interval 3.45-9.40). In 71.4% of the positive PCR/negative microscopy cases, Plasmodium falciparum alone was the main detected species (10 out of the 14 patients) and in 4 cases (28.6%) Plasmodium vivax or Plasmodium ovale were detected. One patient had a mixed infection including three different species.

CONCLUSIONS

The prevalence of submicroscopic malaria in afebrile immigrants was similar to that previously described in Spain. Plasmodium vivax and P. ovale were detected in almost a third of the submicroscopic infections. Screening protocols for afebrile immigrants with molecular techniques could be useful for a proper management of these patients.