Abstract
BackgroundParasitological methods are widely used for the diagnosis of schistosomiasis. However, they are insensitive, particularly in areas of low endemicity, and labour-intensive. Immunoassays based on detection of anti-schistosome antibodies have the merit of high sensitivity and recently a rapid diagnostic test (RDT), incorporating Schistosoma mansoni cercarial transformation fluid (SmCTF) for detection of anti-schistosome antibodies in blood has been developed. Here, we assessed the diagnostic performance of the SmCTF-RDT for S. mansoni and S. haematobium infections by comparing it with microscopy for egg detection.MethodsA cross-sectional survey was carried out in Azaguié, south Côte d’Ivoire. 118 pre-school-aged children submitted two stool and two urine samples, which were subjected to the Kato-Katz and urine filtration methods for the detection of S. mansoni and S. haematobium eggs, respectively. Urine was also subjected to a commercially available cassette test for S. mansoni, which detects circulating cathodic antigen. A finger-prick blood sample was used for the SmCTF-RDT for detection of anti-S. mansoni and anti-S. haematobium antibodies.ResultsThe prevalence of both anti-S. mansoni and anti-S. haematobium antibodies was more than three times higher than the prevalence of infection estimated by egg detection under a microscope. Using quadruplicate Kato-Katz as the reference standard for the diagnosis of S. mansoni infection, the sensitivity, negative predictive value (NPV), and positive predictive value (PPV) of the SmCTF-RDT was 75.0%, 84.2% and 22.5%, respectively. When two urine filtrations were considered as the reference standard for the diagnosis of S. haematobium infection, the sensitivity, NPV and PPV of SmCTF-RDT was 66.7%, 94.9% and 5.1%, respectively. The specificity of SmCTF-RDT, when using egg-detection as the reference standard, was estimated to be 34.4%. This low specificity may be a reflection of the relative insensitivity of the direct diagnostic approaches using microscopy.ConclusionsThe SmCTF-RDT is at least as sensitive as duplicate Kato-Katz and a single urine filtration for detection of S. mansoni and S. haematobium, respectively. Further investigations into the specificity of the test for anti-schistosome antibodies are necessary, but our results suggest that it may be a useful tool for mapping the prevalence of anti-schistosome antibodies in a given population pending intervention.
Highlights
Parasitological methods are widely used for the diagnosis of schistosomiasis
No association was observed between SmCTFRDT results and the socio-demographic factors listed in Table 1
This study was designed to evaluate the diagnostic potential of a rapid diagnostic test (RDT) (SmCTF-RDT) which is capable of detecting antibodies with specificity for the two main Schistosoma species occurring in Africa, S. mansoni and S. haematobium
Summary
Parasitological methods are widely used for the diagnosis of schistosomiasis. they are insensitive, in areas of low endemicity, and labour-intensive. The diagnosis of schistosomiasis is traditionally achieved through the use of parasitological methods (urine filtration for Schistosoma haematobium and Kato-Katz thick smears for S. mansoni and S. japonicum infections). They are the most direct and specific way of detecting active infection, but often miss light-intensity infections [1,2,3,4,5], since only small amounts of excreta are examined. Circulating antigen detection assays are considered desirable since they are predicted most likely to reflect active infection They have generally been shown to be no more sensitive than parasitological methods, in situations where egg counts are low [10,11]. Validations of various formulations of a point-of-care (POC) assay to detect circulating cathodic antigen (CCA) in urine, including a commercially available POC-CCA cassette test in different African settings, have revealed that a single POC-CCA is at least as sensitive as a single KatoKatz thick smear for the diagnosis of S. mansoni, but it is not useful for the diagnosis of S. haematobium [12,13,14,15,16]
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