Schistosoma mansoni in schoolchildren in a Madagascan highland school assessed by PCR and sedimentation microscopy and Bayesian estimation of sensitivities and specificities

Prevalence and risk distribution of schistosomiasis among adults in Madagascar: a cross-sectional study

BACKGROUND

The goal to eliminate the parasitic disease of poverty schistosomiasis as a public health problem is aligned with the 2030 United Nations agenda for sustainable development goals, including universal health coverage (UHC). Current control strategies focus on school-aged children, systematically neglecting adults. We aimed at providing evidence for the need of shifting the paradigm of schistosomiasis control programs from targeted to generalized approaches as key element for both the elimination of schistosomiasis as a public health problem and the promotion of UHC.

METHODS

In a cross-sectional study performed between March 2020 and January 2021 at three primary health care centers in Andina, Tsiroanomandidy and Ankazomborona in Madagascar, we determined prevalence and risk factors for schistosomiasis by a semi-quantitative PCR assay from specimens collected from 1482 adult participants. Univariable and multivariable logistic regression were performed to evaluate odd ratios.

RESULTS

The highest prevalence of S. mansoni, S. haematobium and co-infection of both species was 59.5%, 61.3% and 3.3%, in Andina and Ankazomborona respectively. Higher prevalence was observed among males (52.4%) and main contributors to the family income (68.1%). Not working as a farmer and higher age were found to be protective factors for infection.

CONCLUSIONS

Our findings provide evidence that adults are a high-risk group for schistosomiasis. Our data suggests that, for ensuring basic health as a human right, current public health strategies for schistosomiasis prevention and control need to be re-addressed towards more context specific, holistic and integrated approaches.

Performance of a rapid immuno-chromatographic test (Schistosoma ICT IgG-IgM) for detecting Schistosoma-specific antibodies in sera of endemic and non-endemic populations

Background

Schistosomiasis, an acute and chronic parasitic disease caused by human pathogenic Schistosoma species, is a neglected tropical disease affecting more than 220 million people worldwide.

For diagnosis of schistosomiasis, stool and urine microscopy for egg detection is still the recommended method, however sensitivity of these methods is limited. Therefore, other methods like molecular detection of DNA in stool, detection of circulating cathodic antigen in urine or circulating anodic antigen in urine and serum, as well as serological tests have gained more attention. This study examines the sensitivity and specificity of a rapid diagnostic test based on immunochromatography (Schistosoma ICT IgG-IgM, LD Bio, Lyon, France) for simultaneous detection of specific IgG and IgM antibodies in serum, against Schistosoma spp. in endemic and non-endemic populations.

Methodology/Principal findings

Frozen banked serum samples from patients with confirmed schistosomiasis, patients with other helminth infections, patients with seropositive rheumatoid arthritis and healthy blood donors were used to assess the sensitivity and the specificity of the Schistosoma ICT IgG-IgM rapid diagnostic test.

The test showed a sensitivity of 100% in patients with parasitologically confirmed schistosomiasis, irrespective of the species (S. mansoni, S. haematobium, S. japonicum, S. mekongi). In healthy blood donors and patients with rheumatoid factor positive rheumatoid arthritis from Europe, specificity was 100%. However, in serum samples of patients with other tissue invasive helminth infections, the test showed some cross-reactivity, resulting in a specificity of 85%.

Conclusion/Significance

With its high sensitivity, the Schistosoma ICT IgG-IgM rapid diagnostic test is a suitable screening test for detection of Schistosoma specific antibodies, including S. mekongi. However, in populations with a high prevalence of co-infection with other tissue invasive helminths, positive results should be confirmed with other diagnostic assays due to the test’s imperfect specificity.

Serology- and Blood-PCR-Based Screening for Schistosomiasis in Pregnant Women in Madagascar-A Cross-Sectional Study and Test Comparison Approach

This work was conducted as a cross sectional study to define the disease burden of schistosomiasis in pregnant Madagascan women and to evaluate serological and molecular diagnostic assays. A total of 1154 residual EDTA blood samples from pregnant Madagascan women were assessed. The nucleic acid extractions were subjected to in-house real-time PCRs specifically targeting S. mansoni complex, S. haematobium complex, and African Schistosoma spp. on genus level, while the EDTA plasma samples were analyzed using Schistosoma-specific IgG and IgM commercial ELISA and immunofluorescence assays. The analyses indicated an overall prevalence of schistosomiasis in Madagascan pregnant women of 40.4%, with only minor regional differences and differences between serology- and blood PCR-based surveillance. The S. mansoni specific real-time PCR showed superior sensitivity of 74% (specificity 80%) compared with the genus-specific real-time PCR (sensitivity 13%, specificity 100%) in blood. The laborious immunofluorescence (sensitivity IgM 49%, IgG 87%, specificity IgM 85%, IgG 96%) scored only slightly better than the automatable ELISA (sensitivity IgM 38%, IgG 88%, specificity IgM 78%, IgG 91%). Infections with S. mansoni were detected only. The high prevalence of schistosomiasis recorded here among pregnant women in Madagascar calls for actions in order to reduce the disease burden.

New Developments in PCR-Based Diagnostics for Bacterial Pathogens Causing Gastrointestinal Infections-A Narrative Mini-Review on Challenges in the Tropics

The application of modern PCR approaches for the diagnosis of bacterial gastrointestinal pathogens is on the rise due to their rapidly available results combined with high sensitivity. While multiple studies describe the ongoing implementation of this technique for routine diagnostic purposes in laboratories in Western industrialized countries, reports on successful and also sustainable respective approaches in resource-poor tropical settings are still scarce. In order to shed light on potential reasons for this marked discrepancy, this narrative review summarizes identified challenges for the application of diagnostic PCR targeting bacterial gastrointestinal pathogens from stool samples in the tropics. The identified and discussed issues comprise the lack of generally accepted definitions for (1) minimum standards regarding sample acquisition, storage and transport time for diagnostic PCR analyses in the tropics, (2) nucleic acid extraction standards allowing an optimum detection of all types of pathogens which may be responsible for gastroenteritis in the tropics, (3) validation standards to ensure comparable quality of applied diagnostic assays, and (4) cut-offs for a reliable discrimination of infection and mere colonization in areas where semi-immunity due to repeated exposition associated with poor hygiene conditions has to be expected. Further implementation research is needed to solve those issues.

Evaluation of a duplex real-time PCR in human serum for simultaneous detection and differentiation of Schistosoma mansoni and Schistosoma haematobium infections - cross-sectional study

BACKGROUND

We evaluated a one-tube multiplex real-time PCR targeting DNA of Schistosoma haematobium complex and S. mansoni complex in serum samples obtained at different German diagnostic centers.

METHODS

Simplex real-time PCR protocols for the detection of the multi-copy DNA-repeats Dra1 of S. haematobium complex and Sm1-7 of S. mansoni complex in serum were combined to a new one-tube multiplex format. The new PCR was subjected to full validation including evaluation in a diagnostic real-life setting with travelers and migrants. PCR results were compared with those of stool and urine microscopy, serology, and circulating cathodic antigen (CCA) rapid diagnostic tests in urine. Sensitivity and specificity of the diagnostic approaches were analyzed using latent class analysis (LCA).

RESULTS

LCA assessment indicated sensitivity and specificity of 94.9% and 98.4%, respectively, for serum PCR if serology was included in the calculation, and 100% and 95.6%, respectively, if serology was not included as a parameter not necessarily associated with active infection. Agreement between the compared diagnostic procedures at genus level was fair (kappa 0.273) if serology was included and moderate (kappa 0.420) if serology was not included.

DISCUSSION

The PCR assay proved to be highly reliable for the diagnosis of schistosomiasis in travelers and migrants.

Performance of an Ultra-Sensitive Assay Targeting the Circulating Anodic Antigen (CAA) for Detection of Schistosoma mansoni Infection in a Low Endemic Area in Brazil

Techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings, where the conventional parasitological methods are insensitive. We determined the accuracy of an up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay in urine and serum for Schistosoma mansoni diagnosis in low-prevalence settings in Ceará, Brazil, before and after praziquantel treatment. Clinical samples of a total of 258 individuals were investigated by UCP-LF CAA, point-of-care—circulating cathodic antigen (POC-CCA), soluble worm antigen preparation (SWAP)-ELISA and Kato-Katz (KK); a selection of 128 stools by real-time PCR technique. Three and 6-weeks after treatment, samples were collected and evaluated by detection Schistosoma circulating antigens (CAA and CCA). The UCP-LF CAA assays detected 80 positives (31%) with urine and 82 positives (31.8%) with serum. The urine POC-CCA and serum SWAP-ELISA assays detected 30 (11.6%) and 107 (40.7%) positives, respectively. The Kato-Katz technique revealed only 4 positive stool samples (1.6%). Among the 128 individuals with complete data records, 19 cases were identified by PCR (14.8%); Sensitivities and specificities of the UCP-LF CAA assays, determined versus a combined reference standard based on CCA/KK/PCR positivity, ranged from 60–68% to 68–77%, respectively. In addition only for comparative purposes, sensitivities of the different assays were determined vs. a comparative reference based on CAA/KK/PCR positivity, showing the highest sensitivity for the urine CAA assay (80%), followed by the serum CAA (70.9%), SWAP-ELISA (43.6%), PCR (34.5%), POC-CCA (29.1%), whilst triplicate Kato-Katz thick smears had a very low sensitivity (3.6%). CAA concentrations were higher in serum than in urine and were significantly correlated. There was a significant decrease in urine and serum CAA levels 3 and 6-weeks after treatment. The UCP-LF CAA assays revealed 33 and 28 S. mansoni-infected patients at the 3- and 6-week post-treatment follow-up, respectively. The UCP-LF CAA assays show high sensitivity for the diagnosis of S. mansoni in low-endemicity settings. It detects a considerably higher number of infections than microscopy, POC-CCA or PCR. Also it shows to be very useful for evaluating cure rates after treatment. Hence, the UCP-LF CAA assay is a robust and promising diagnostic approach in low-transmission settings.

High burden of Schistosoma mansoni infection in school-aged children in Marolambo District, Madagascar

Background

A school-based survey was undertaken to assess prevalence and infection intensity of schistosomiasis in school-aged children in the Marolambo District of Madagascar.

Methods

School-aged children from six purposively selected schools were tested for Schistosoma haematobium by urine filtration and Schistosoma mansoni using circulating cathodic antigen (CCA) and Kato-Katz stool analysis. The investigators did not address soil-transmitted helminths (STH) in this study.

Results

Of 399 school-aged children screened, 93.7% were infected with S. mansoni based on CCA analysis. Kato-Katz analysis of stool revealed S. mansoni infection in 73.6% (215/ 292). Heavy infections (> 400 eggs per gram) were common (32.1%; 69/ 215), with a mean of 482 eggs per gram of stool. Moderate infection intensities were detected in 31.2% (67/ 215) and light infection intensities in 36.7% (79/ 215) of infected participants. No infection with S. haematobium was detected by urine filtration.

Conclusions

Intestinal schistosomiasis appears a considerable public health issue in this remote area of Madagascar where there is a pressing need for mass drug administration.

Microbiological screenings for infection control in unaccompanied minor refugees: the German Armed Forces Medical Service's experience

BACKGROUND

The German Military Medical Service contributed to the medical screening of unaccompanied minor refugees (UMRs) coming to Germany in 2014 and 2015. In this study, a broad range of diagnostic procedures was applied to identify microorganisms with clinical or public health significance. Previously, those tests had only been used to screen soldiers returning from tropical deployments. This instance is the first time the approach has been studied in a humanitarian context.

METHODS

The offered screenings included blood cell counts, hepatitis B serology and microscopy of the stool to look for protozoa and worm eggs as well as PCR from stool samples targeting pathogenic bacteria, protozoa and helminths. If individuals refused certain assessments, their decision to do so was accepted. A total of 219 apparently healthy male UMRs coming from Afghanistan, Egypt, Somalia, Eritrea, Syria, Ghana, Guinea, Iran, Algeria, Iraq, Benin, Gambia, Libya, Morocco, Pakistan, and Palestine were assessed. All UMRs who were examined at the study department were included in the assessment.

RESULTS

We detected decreasing frequencies of pathogens that included diarrhoea-associated bacteria [Campylobacter (C.) jejuni, enteropathogenic Escherichia (E.) coli (EPEC), enterotoxic E. coli (ETEC), enteroaggregative E. coli (EAEC), enteroinvasive E. coli (EIEC)/Shigella spp.), Giardia (G.) duodenalis, helminths (comprising Schistosoma spp., Hymenolepis (H.) nana, Strongyloides (S.) stercoralis] as well as hepatitis B virus. Pathogenic microorganisms dominated the samples by far. While G. duodenalis was detected in 11.4% of the assessed UMRs, the incidence of newly identified cases in the German population was 4.5 cases per 100,000 inhabitants.

CONCLUSIONS

We conclude that the applied in-house PCR screening systems, which have proven to be useful for screening military returnees from tropical deployments, can also be used for health assessment of immigrants from the respective sites. Apparently healthy UMRs may be enterically colonized with a broad variety of pathogenic and apathogenic microorganisms. Increased colonization rates, as shown for G. duodenalis, can pose a hygiene problem in centralized homes for asylum seekers.

Serological approaches for the diagnosis of schistosomiasis - A review

Schistosomiasis is a common disease in endemic areas of Sub-Saharan Africa, South America and Asia. It is rare in Europe, mainly imported from endemic countries due to travelling or human migration. Available methods for the diagnosis of schistosomiasis comprise microscopic, molecular and serological approaches, with the latter detecting antigens or antibodies associated with Schistosoma spp. infection. The serological approach is a valuable screening tool in low-endemicity settings and for travel medicine, though the interpretation of any diagnostic results requires knowledge of test characteristics and a patient's history. Specific antibody detection by most currently used assays is only possible in a relatively late stage of infection and does not allow for the differentiation of acute from previous infections for therapeutic control or the discrimination between persisting infection and re-infection. Throughout the last decades, new target antigens have been identified, and assays with improved performance and suitability for use in the field have been developed. For numerous assays, large-scale studies are still required to reliably characterise assay characteristics alone and in association with other available methods for the diagnosis of schistosomiasis. Apart from S. mansoni, S. haematobium and S. japonicum, for which most available tests were developed, other species of Schistosoma that occur less frequently need to be taken into account. This narrative review describes and critically discusses the results of published studies on the evaluation of serological assays that detect antibodies against different Schistosoma species of humans. It provides insights into the diagnostic performance and an overview of available assays and their suitability for large-scale use or individual diagnosis, and thus sets the scene for serological diagnosis of schistosomiasis and the interpretation of results.

Baseline prevalence and intensity of schistosomiasis at sentinel sites in Madagascar: Informing a national control strategy

BACKGROUND

Schistosomiasis affects more than 800 million people, mostly in sub-Saharan Africa. A baseline sentinel site study was conducted in the Western half of Madagascar to determine the prevalence and intensity of schistosomiasis and soil-transmitted helminth (STH) infections prior to mass drug administration, and to explore the associations between infection and school attendance, and access to water, sanitation and hygiene (WASH) facilities.

METHODS

A three-stage, cluster-randomised cross-sectional study was conducted in 29 sentinel sites in October 2015. Twenty school attending and 4 non-attending children in each of the age groups from 7 to 10 years old were randomly selected at each site for detection of Schistosoma haematobium eggs in a single urine slide by filtration, and of S. mansoni, Ascaris lumbricoides, Trichuris trichiura and hookworm eggs in duplicate Kato-Katz slides from a single stool sample. School attendance was registered individually, and school-level access to WASH facilities was scored through pre-defined observed and reported factors. Logistic regression analysis was performed, adjusting for gender, age and study site. School-level WASH status was analysed using Spearman's rank correlation coefficient.

RESULTS

A total of 1,958 children were included. The prevalence of S. haematobium infection and heavy-intensity infection was 30.5% and 15.1%, respectively. The prevalence of S. mansoni infection and heavy-intensity infection was 5.0% and 0.9%, respectively. The prevalence of any STH infection was 4.7%. There was no significant difference in prevalence of infection or heavy-intensity infection of either schistosome species between attending and non-attending children, apart from heavy-intensity S. mansoni infection that was significantly more common in children who did not attend school regularly (aOR = 7.5 (95% CI = 1.1-49.5); p = 0.037). Only a minority of schools had adequate access to WASH facilities, and in this study, we found no significant association between school-level WASH status and schistosomiasis.

CONCLUSIONS

This study found an alarmingly high prevalence and intensity of schistosomiasis, and the results warrant urgent scale-up of the national NTD control programme that will need to include both non-attending and attending school-age children in order to reach WHO roadmap targets for the control of schistosomiasis by 2020.

Is PCR the Next Reference Standard for the Diagnosis of Schistosoma in Stool? A Comparison with Microscopy in Senegal and Kenya

BACKGROUND

The current reference test for the detection of S. mansoni in endemic areas is stool microscopy based on one or more Kato-Katz stool smears. However, stool microscopy has several shortcomings that greatly affect the efficacy of current schistosomiasis control programs. A highly specific multiplex real-time polymerase chain reaction (PCR) targeting the Schistosoma internal transcriber-spacer-2 sequence (ITS2) was developed by our group a few years ago, but so far this PCR has been applied mostly on urine samples. Here, we performed more in-depth evaluation of the ITS2 PCR as an alternative method to standard microscopy for the detection and quantification of Schistosoma spp. in stool samples.

METHODOLOGY/PRINCIPAL FINDINGS

Microscopy and PCR were performed in a Senegalese community (n = 197) in an area with high S. mansoni transmission and co-occurrence of S. haematobium, and in Kenyan schoolchildren (n = 760) from an area with comparatively low S. mansoni transmission. Despite the differences in Schistosoma endemicity the PCR performed very similarly in both areas; 13-15% more infections were detected by PCR when comparing to microscopy of a single stool sample. Even when 2-3 stool samples were used for microscopy, PCR on one stool sample detected more infections, especially in people with light-intensity infections and in children from low-risk schools. The low prevalence of soil-transmitted helminthiasis in both populations was confirmed by an additional multiplex PCR.

CONCLUSIONS/SIGNIFICANCE

The ITS2-based PCR was more sensitive than standard microscopy in detecting Schistosoma spp. This would be particularly useful for S. mansoni detection in low transmission areas, and post-control settings, and as such improve schistosomiasis control programs, epidemiological research, and quality control of microscopy. Moreover, it can be complemented with other (multiplex real-time) PCRs to detect a wider range of helminths and thus enhance effectiveness of current integrated control and elimination strategies for neglected tropical diseases.

New diagnostic tools in schistosomiasis

Schistosomiasis is a water-based parasitic disease that affects over 250 million people. Control efforts have long been in vain, which is one reason why schistosomiasis is considered a neglected tropical disease. However, since the new millennium, interventions against schistosomiasis are escalating. The initial impetus stems from a 2001 World Health Assembly resolution, urging member states to scale-up deworming of school-aged children with the anthelminthic drug praziquantel. Because praziquantel is safe, efficacious and inexpensive when delivered through the school platform, diagnosis before drug intervention was deemed unnecessary and not cost-effective. Hence, there was little interest in research and development of novel diagnostic tools. With the recent publication of the World Health Organization (WHO) Roadmap to overcome the impact of neglected tropical diseases in 2020, we have entered a new era. Elimination of schistosomiasis has become the buzzword and this has important ramifications for diagnostic tools. Indeed, measuring progress towards the WHO Roadmap and whether local elimination has been achieved requires highly accurate diagnostic assays. Here, we introduce target product profiles for diagnostic tools that are required for different stages of a schistosomiasis control programme. We provide an update of the latest developments in schistosomiasis diagnosis, including microscopic techniques, rapid diagnostic tests for antigen detection, polymerase chain reaction (PCR) assays and proxy markers for morbidity assessments. Particular emphasis is placed on challenges and solutions for new technologies to enter clinical practice.

PCR for enteric pathogens in high-prevalence settings. What does a positive signal tell us?

BACKGROUND

Molecular methods, in particular PCR, are increasingly used for the diagnosis of enteric pathogens in stool samples. In high-endemicity settings, however, asymptomatic carriage or residual DNA from previous infections will hamper the interpretation of positive test results. We assessed the quantitative dimension of this problem in schoolchildren in the rural highlands of Madagascar.

METHODS

Stool samples were collected from 410 apparently healthy Madagascan schoolchildren and analysed by multiplex real-time PCR for enteroinvasive bacteria (Salmonella spp., Shigella spp./enteroinvasive Escherichia coli (EIEC), Campylobacter jejuni, Yersinia spp.), enteric protozoa (Entamoebea histolytica, Giardia duodenalis, Cryptosporidium spp., Cyclospora spp.), and helminths (Ascaris lumbricoides, Ancylostoma spp., Necator americanus, Strongyloides stercoralis). Symptoms of gastrointestinal disease were assessed.

RESULTS

Among the 410 samples, we detected Giardia duodenalis in 195, Campylobacter jejuni in 91, Ascaris lumbricoides in 72, Cyclospora cayetanenesis in 68, Shigella spp./EIEC in 56, and Strongyloides stercoralis and Cryptosporum spp. in 1 case each. Salmonella spp., Yersinia spp. and hookworms were not observed. Relative risk assessment suggested few and incoherent associations with pathogen detections, indicating asymptomatic carriage or DNA residuals. Only 26.1% of the schoolchildren were tested negative for all analysed pathogens.

CONCLUSIONS

The very high risk of detecting traces of asymptomatic carriage or residual DNA from previous infections limits the value of highly sensitive PCR for the causal attribution of detected enteric pathogens from stool samples to an infectious gastrointestinal disease in the high-endemicity setting. Evaluated standards for the interpretation of such results are needed both for the diagnostic routine and for epidemiological assessments.

Cyclovirus CyCV-VN species distribution is not limited to Vietnam and extends to Africa

Cycloviruses, small ssDNA viruses of the Circoviridae family, have been identified in the cerebrospinal fluid from symptomatic human patients. One of these species, cyclovirus-Vietnam (CyCV-VN), was shown to be restricted to central and southern Vietnam. Here we report the detection of CyCV-VN species in stool samples from pigs and humans from Africa, far beyond their supposed limited geographic distribution.