The point-of-care strip assay for the detection of the schistosome Circulating Cathodic Antigen (POC-CCA) in urine has shown to be a user-friendly and sensitive alternative to stool microscopy for the diagnosis of Schistosoma mansoni infections. However, visual scoring of the test is by definition observer dependent and leads to discussion about the qualitative interpretation, in particular in low intensity infections when test lines tend to be weak. In order to standardise visual scoring, an innovative approach for semi-quantitative interpretation of the POC-CCA cassettes, called G-scores, was developed and evaluated. Urines (n = 110) from a S. mansoni endemic area were used to evaluate this new approach. Test lines of the POC-CCA were visually compared against the G-scores, i.e. a series of artificial cassettes containing inkjet-printed strips of different intensities in order to grade the POC-CCA test line on a scale of 1 to 10. A significant positive correlation (Spearman 0.660, p < 0.001) was observed between G-scores and eggs per gram of faeces. This proof-of-concept study demonstrates the usefulness of the G-scores for standardising the visual scoring of the POC-CCA urine strip assay. Several research groups have already indicated an interest in the G-scores for their field work. Further distribution of the cassettes, in particular when provided in combination with reference standards, will assist the wider schistosomiasis community in dealing with issues like batch-to-batch differences and interpretation of trace readings.

Schistosomiasis is a parasitic disease caused by trematode blood flukes of the genusSchistosoma, affecting over 250 million people mainly in the tropics. Clinically, the disease can present itself with acute symptoms, a stage which is relatively more common in naive travellers originating from non-endemic regions. It can also develop into chronic disease, with the outcome depending on theSchistosomaspecies involved, the duration and intensity of infection and several host-related factors. A range of diagnostic tests is available to determineSchistosomainfection, including microscopy, antibody detection, antigen detection using the Point-Of-Care Circulating Cathodic Antigen (POC-CCA) test and the Up-Converting Particle Lateral Flow Circulating Anodic Antigen (UCP-LF CAA) test, as well as Nucleic Acid Amplification Tests (NAATs) such as real-time PCR. In this mini review, we discuss these different diagnostic procedures and explore their most appropriate use in context-specific settings. With regard to endemic settings, diagnostic approaches are described based on their suitability for individual diagnosis, monitoring control programs, determining elimination as a public health problem and eventual interruption of transmission. For non-endemic settings, we summarize the most suitable diagnostic approaches for imported cases, either acute or chronic. Additionally, diagnostic options for disease-specific clinical presentations such as genital schistosomiasis and neuro-schistosomiasis are included. Finally, the specific role of diagnostic tests within research settings is described, including a controlled human schistosomiasis infection model and several clinical studies. In conclusion, context-specific settings have different requirements for a diagnostic test, stressing the importance of a well-considered decision of the most suitable diagnostic procedure.

Background: Traditional microscopic examination of urine or stool for schistosome eggs lacks sensitivity compared to measurement of schistosome worm-derived circulating antigens in serum or urine. The ease and non-invasiveness of urine collection makes urine an ideal sample for schistosome antigen detection. In this study several user-friendly, lateral-flow (LF) based urine assays were evaluated against a composite reference that defined infection as detection of either eggs in urine or anodic antigen in serum. Method: In a Tanzanian population with a S. haematobium prevalence of 40–50% (S. mansoni prevalence <2%), clinical samples from 44 women aged 18 to 35 years were analyzed for Schistosoma infection. Urine and stool samples were examined microscopically for eggs, and serum samples were analyzed for the presence of the anodic antigen. Urines were further subjected to a set of LF assays detecting (circulating) anodic (CAA) and cathodic antigen (CCA) as well as antibodies against soluble egg antigens (SEA) and crude cercarial antigen preparation (SCAP). Results: The urine LF anodic antigen assay utilizing luminescent upconverting reporter particles (UCP) confirmed its increased sensitivity when performed with larger sample volume. Qualitatively, the anodic antigen assay performed on 250 μL urine matched the performance of the standard anodic antigen assay performed on 20 μL serum. However, the ratio of anodic antigen levels in urine vs. serum of individual patients varied with absolute levels always higher in serum. The 10 μL urine UCP-LF cathodic antigen assay correlated with the commercially available urine POC-CCA (40 μL) test, while conferring better sensitivity with a quantitative result. Urinary antibodies against SEA and SCAP overlap and correlate with the presence of urinary egg and serum anodic antigen levels. Conclusions: The UCP-LF anodic antigen assay using 250 μL of urine is an expedient user-friendly assay and a suitable non-invasive alternative to serum-based antigen testing and urinary egg detection. Individual biological differences in the clearance process of the circulating antigens are thought to explain the observed high variation in the type and level of antigen (anodic or cathodic) measured in urine or serum. Simultaneous detection of anodic and cathodic antigen may be considered to further increase accuracy.

Given the restricted distribution of Schistosoma mekongi in one province in Lao People’s Democratic Republic (Lao PDR) and two provinces in Cambodia, together with progress of the national control programmes aimed at reducing morbidity and infection prevalence, the elimination of schistosomiasis mekongi seems feasible. However, sensitive diagnostic tools will be required to determine whether elimination has been achieved. We compared several standard and novel diagnostic tools in S. mekongi-endemic areas. The prevalence and infection intensity of S. mekongi were evaluated in 377 study participants from four villages in the endemic areas in Lao PDR and Cambodia using Kato-Katz stool examination, antibody detection based on an enzyme-linked immunosorbent assay (ELISA) and schistosome circulating antigen detection by lateral-flow tests. Two highly sensitive test systems for the detection of cathodic and anodic circulating antigens (CCA, CAA) in urine and serum were utilized. Stool microscopy revealed an overall prevalence of S. mekongi of 6.4% (one case in Cambodia and 23 cases in Lao PDR), while that of Opisthorchis viverrini, hookworm, Trichuris trichiura, Ascaris lumbricoides and Taenia spp. were 50.4%, 28.1%, 3.5%, 0.3% and 1.9%, respectively. In the urine samples, the tests for CCA and CAA detected S. mekongi infections in 21.0% and 38.7% of the study participants, respectively. In the serum samples, the CAA assay revealed a prevalence of 32.4%, while a combination of the CAA assay in serum and in urine revealed a prevalence of 43.2%. There was a difference between the two study locations with a higher prevalence reached in the samples from Lao PDR. The CCA, CAA and ELISA results showed substantially higher prevalence estimates for S. mekongi compared to Kato-Katz thick smears. Active schistosomiasis mekongi in Lao PDR and Cambodia might thus have been considerably underestimated previously. Hence, sustained control efforts are still needed to break transmission of S. mekongi. The pivotal role of highly sensitive diagnostic assays in areas targeting elimination cannot be overemphasised.

Methodological applications of the high sensitivity genus-specific Schistosoma CAA strip test, allowing detection of single worm active infections (ultimate sensitivity), are discussed for efficient utilization in sample pooling strategies. Besides relevant cost reduction, pooling of samples rather than individual testing can provide valuable data for large scale mapping, surveillance, and monitoring. The laboratory-based CAA strip test utilizes luminescent quantitative up-converting phosphor (UCP) reporter particles and a rapid user-friendly lateral flow (LF) assay format. The test includes a sample preparation step that permits virtually unlimited sample concentration with urine, reaching ultimate sensitivity (single worm detection) at 100% specificity. This facilitates testing large urine pools from many individuals with minimal loss of sensitivity and specificity. The test determines the average CAA level of the individuals in the pool thus indicating overall worm burden and prevalence. When requiring test results at the individual level, smaller pools need to be analysed with the pool-size based on expected prevalence or when unknown, on the average CAA level of a larger group; CAA negative pools do not require individual test results and thus reduce the number of tests. Straightforward pooling strategies indicate that at sub-population level the CAA strip test is an efficient assay for general mapping, identification of hotspots, determination of stratified infection levels, and accurate monitoring of mass drug administrations (MDA). At the individual level, the number of tests can be reduced i.e. in low endemic settings as the pool size can be increased as opposed to prevalence decrease. At the sub-population level, average CAA concentrations determined in urine pools can be an appropriate measure indicating worm burden. Pooling strategies allowing this type of large scale testing are feasible with the various CAA strip test formats and do not affect sensitivity and specificity. It allows cost efficient stratified testing and monitoring of worm burden at the sub-population level, ideally for large-scale surveillance generating hard data for performance of MDA programs and strategic planning when moving towards transmission-stop and elimination.