Evaluation of circulating cathodic antigen (CCA) urine-cassette assay as a survey tool for Schistosoma mansoni in different transmission settings within Bugiri District, Uganda
Graphical abstract
We present an evaluation of two urine circulating cathodic antigen (CCA) cassette assays, one commercially available (CCA1 upper) and the other in experimental production (CCA2 lower) shown in the photograph below. The assays were evaluated against Kato-Katz test as a gold standard. Overall, the performance of the commercially available CCA1 test was more informative than by faecal smear microscopy, and is recommended as a satisfactory method for Schistosoma mansoni mapping and surveillance.
Introduction
Intestinal schistosomiasis, also called Bilharzia, is one of the leading causes of morbidity and disability in many fishing communities lying along large water bodies in Uganda, such as Lakes Albert, Victoria, Kyoga and along the Albert Nile (Nelson, 1958), as well as in rice paddy fields in Eastern Uganda (Bukenya et al., 1994). It is estimated that over 60% of the people in these communities have the disease (Kabatereine et al., 2004); with Schistosoma mansoni infections recorded in 64 out of 112 districts of Uganda. By contrast, urinary schistosomiasis, caused by S. haematobium, exists in only a few districts near Lake Kyoga and is much rarer (Schwetz, 1951, Rosanelli, 1960). Nation-wide, it is estimated that up to 4 million people are affected and 16.7 million are at risk of schistosomiasis (Kabatereine et al., 2006a). The disease affects both children and adults, with the peak infection and intensity levels being in the age group 10–20 years (Kabatereine et al., 2006b).
Nation-wide schistosomiasis control in Uganda was initiated in 2003 under the auspices of the Schistosomiasis Control Initiative (SCI) with funding from the Bill & Melinda Gates Foundation (Kabatereine et al., 2006a, Kabatereine et al., 2006b). The objective was to control morbidity through regular chemotherapy of at-risk communities as identified based on the WHO mapping protocol which uses the single Kato-Katz thick smear method for diagnosis (WHO, 2006). Although this test has several advantages such as low cost, high specificity, simplicity to perform and concurrent detection of other helminth species, the counting of excreted parasite eggs in just 41.7 mg of stool is unreliable and inaccurate (Booth et al., 2004, Gryseels, 1996). Consequently, the method has low sensitivity especially in low transmission settings which can become more common after many years of control, at which time excreted egg-outputs fall within infected children (Colley et al., 2013). Although the sensitivity of the Kato-Katz method can be improved through increasing the number of examined smears (de Vlas et al., 1993), such an approach is time consuming and limited by operational challenges and costs. The single Kato-Katz method is also prone to error in estimating the true prevalence of infection as it is affected by day to day variability in egg excretion (de Vlas et al., 1993, Teesdale et al., 1985) especially in ‘light’ infection intensities when egg-output is sporadic, hence the method cannot adequately guide interventions to meet the current WHO target of disease elimination (WHO, 2012, Standley et al., 2010b).
Consequently, a more sensitive tool such as the “Point-of-Care Circulating Cathodic Antigens” test (POC-CCA, Rapid Medical Diagnostics, Pretoria, South Africa) which is based on direct detection of parasite CCA in host urine and gives results within few minutes has been developed to augment and perhaps replace the Kato-Katz method (Stothard et al., 2009, Standley et al., 2009, Standley et al., 2010a, Standley et al., 2010b). This rapid diagnostic test (RDT) became commercially available in 2003 (Stothard et al., 2006, Standley et al., 2010a) and it is the only rapid assay for diagnosis of S. mansoni currently commercially available retailing for approximately 1.75 USD per test (Colley et al., 2013). The POC-CCA cassettes are portable, easy to use; require minimal staff training, data interpretation is simple and has characteristics observed in other Rapid Diagnostic Tests (RDTs) such as those applied in Malaria diagnosis (Colley et al., 2013, Stothard et al., 2006, Coulibaly et al., 2011, Shane et al., 2011, Tchuem Tchuente et al., 2012). This implies that CCA tests can be easily incorporated in the existing health systems for rapid diagnosis and treatment of cases in health facilities (Colley et al., 2013). The POC-CCA test uses a drop of urine on a lateral flow strip to detect the presence of adult worm infection, and has been successfully tested for disease mapping around Lake Victoria in school age children (Standley et al., 2010b) and in Ugandan preschool age children (Sousa-Figueiredo et al., 2013). However, a more comprehensive evaluation of the test was arranged recently by Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) and conducted under a multi-country study involving Cote d’Ivoire (Coulibaly et al., 2011) Kenya (Shane et al., 2011) and Cameroon (Tchuem Tchuente et al., 2012). The combined results of the multi-country study were recently published (Colley et al., 2013) and our current study is part of that multi-country investigations whose objective was to evaluate the CCA diagnostic accuracy for rapid S. mansoni mapping in an area in Uganda where the original high prevalence and intensity of infection was significantly reduced through many rounds of MDA with praziquantel (Kabatereine et al., 2007).
Earlier reports had observed high sensitivity results of the POC-CCA assay when compared to the WHO recommended Kato-Katz method prompting a suggestion that the test might be producing many false positives (Stothard et al., 2006, Standley et al., 2010a). As a consequence, the manufacturer produced another CCA version here designated as CCA2 believed to be less sensitive than the original CCA1 assay (Colley et al., 2013). Under the current study, the performance of CCA1 and its alternative version CCA2 were both evaluated against the Kato-Katz thick smear method (Katz et al., 1972) as a reference test.
Section snippets
Study area
The study was conducted in five primary schools in Bugiri district which lie along the shoreline of Lake Victoria in south-eastern Uganda (longitude 33°10′ E, 34 E and latitude 6°1′ N, 12′ E, Fig. 1). Annual mass treatment with praziquantel had been administered in the area for five years before the study begun and the campaign had reduced the endemicity of the disease from high to medium levels.
Selection of study population and data collection
Following the pre-screening SCORE guidelines using the Lot Quality Assurance Sampling (LQAS, where a
Study adherence
Overall, a total of 500 pupils with mean age of 10.4 years were included in the study. There were slightly more females included than males (259 vs. 241). The number of children surveyed in epidemiological setting A was 100 and 200 children were included for each of settings B and C. Altogether, 500 children provided both stool and urine samples on the first day while just 496 and 469 children submitted their stool samples for day two and day three, respectively. Of the 469 pupils who provided
Discussion
Earlier studies had indicated that reagent strip/dipstick based assays are highly sensitive and specific in detecting CCA in urine in active S. mansoni-infected individuals (Legesse and Erko, 2008). Indeed, in all endemic settings, results from this study showed higher S. mansoni prevalence scores by CCA1 assay than those obtained when double, quadruple or sextuple Kato-Katz thick smears were applied. Our results were consistent with recently published data collected elsewhere as part of this
Conflict of interest
None of the authors have a conflict of interest.
Acknowledgements
The authors would like to thank in particular the VCD technicians who were involved in the collection of the samples, making the Kato-Katz slides and reading of samples in the field. We are also grateful for the contribution of DVCO, Kadama for his effort in mobilising the schools for the study. This research would not have been possible without funding from the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE; http://score.uga.edu/) through SCI. Approval for the
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