Diagnosis of Schistosomiasis without a Microscope: Evaluating Circulating Antigen (CCA, CAA) and DNA Detection Methods on Banked Samples of a Community-Based Survey from DR Congo

Abstract

Detection of Schistosoma eggs in stool or urine is known for its low sensitivity in diagnosing light infections. Alternative diagnostics with better sensitivity while remaining highly specific, such as real-time PCR and circulating antigen detection, are progressively used as complementary diagnostic procedures but have not yet replaced microscopy. This study evaluates these alternative methods for the detection of Schistosoma infections in the absence of microscopy. Schistosomiasis presence was determined retrospectively in 314 banked stool and urine samples, available from a previous survey on the prevalence of taeniasis in a community in the Democratic Republic of the Congo, using real-time PCR, the point-of-care circulating cathodic antigen (POC-CCA) test, as well as the up-converting particle lateral flow circulating anodic antigen (UCP-LF CAA) test. Schistosoma DNA was present in urine (3%) and stool (28%) samples, while CCA (28%) and CAA (69%) were detected in urine. Further analysis of the generated data indicated stool-based PCR and the POC-CCA test to be suitable diagnostics for screening of S. mansoni infections, even in the absence of microscopy. A substantial proportion (60%) of the 215 CAA-positive cases showed low antigen concentrations, suggesting that even PCR and POC-CCA underestimated the “true” number of schistosome positives.

Schistosoma mansoni coinfection is associated with high Plasmodium falciparum infection intensity among 10 -15 year old children living along the Albert Nile in Uganda

“…Our ndings add to previous studies that indicated PCR as a better indicator for S. mansoni infection intensity than the Kato Katz assay and can be used without microscopic examination of stools for parasite eggs [26,27] although less sensitive than CAA [27]. PCR is a more sensitive method of P. falciparum detection compared to microscopy especially at low intensity [28,29].…”

Insights into the epidemiology, pathogenesis, and differential diagnosis of schistosomiasis

“…Real-time PCR based on amplification of the genus-specific ITS-2 sequence of Schistosoma spp. is the molecular assay that has found greater use and standardisation in routine diagnostic practice for schistosomiasis [ 63 ]. Another molecular technique that can be used for diagnosis is the search for cell-free DNA, which can be actively released by the parasite or can be derived from dead or decaying worms [ 64 ].…”

Reproducibility matters: intra- and inter-sample variation of the point-of-care circulating cathodic antigen test in two Schistosoma mansoni endemic areas in Uganda

“…The point-of-care-circulating cathodic antigen test (POC-CCA) (Rapid Medical Diagnostics, Pretoria, RSA; currently distributed by ICT International on behalf of Rapid Medical Diagnostics) is a urine-based lateral flow assay that requires no equipment, is easy to read by the naked eye, enables higher throughput and less processing than microscopy, uses the more popular sample of urine rather than stool, and is recommended for the detection of S. mansoni infections [12][13][14], and endorsed by WHO since 2017 [15]. The POC-CCA is more sensitive than Kato-Katz, especially for low-intensity infections [16][17][18][19], but issues exist with batch variation [20], low specificity including in samples from non-endemic areas [21][22][23] and cross-reactivity with other helminths [22], interreader variability especially with trace results, and interpretation of these [24,25], all of which can affect individual diagnoses and prevalence estimates [26]. Improved standardization and quality control is required for the POC-CCA to be more reliable [27], which becomes more important as regions and countries move towards the WHO goal of elimination as a public health problem [28].…”