Field assessment in Cameroon of a reader of POC-CCA lateral flow strips for the quantification of Schistosoma mansoni circulating cathodic antigen in urine

Abstract

Background Determining Schistosoma mansoni infection rate and intensity is challenging due to the low sensitivity of the Kato-Katz (KK) test that underestimates the true disease prevalence. Circulating cathodic antigen (CCA) excreted in urine is constantly produced by adult worms and has been used as the basis of a simple, non-invasive point of care test (POC-CCA) for Schistosoma mansoni infections. Although the abundance of CCA in urine is proportional to worm burden, the POC-CCA test is marketed as a qualitative test, making it difficult to investigate the wide range of infection intensities. This study was designed to compare the prevalence and intensity of S. mansoni by KK and POC-CCA and quantify, on fresh and frozen (<-20°C) urine samples, CCA using the visual scores and the ESEquant LR3 reader. Methodology Stool and urine samples were collected from 759 school-aged children. The prevalence and intensity of S. mansoni were determined using KK and POC-CCA. The degree of the positivity of POC-CCA was estimated by quantifying CCA on fresh and frozen urine samples using visual scores and strip reader. The prevalence, the infection intensity as well the relative amounts of CCA were compared. Results The S. mansoni infection rates inferred from POC-CCA and KK were 40.7% and 9.4% respectively. Good correlations were observed between infection intensities recorded by; i) the reader and visual scoring system on fresh (Rho = 0.89) and frozen samples (Rho = 0.97), ii) the reader on fresh urine samples and KK (epg) (Rho = 0.44). Nevertheless, 238 POC-CCA positive children were negative for KK, and sixteen of them had high levels of CCA. The correlation between results from the reader on fresh and frozen samples was good (Rho = 0.85). On frozen samples, CCA was not detected in 55 samples that were positive in fresh urine samples. Conclusion This study confirmed the low sensitivity of KK and the high capacity of POC-CCA to provide reliable data on the prevalence and intensity of S. mansoni infections. The lateral flow reader enabled accurate quantification of CCA under field conditions on fresh and frozen urine samples with less time and effort than KK.

Candidate gene family-based and case-control studies of susceptibility to high Schistosoma mansoni worm burden in African children: a protocol

“…In our analysis we will compare the two readings, where we expect to see a concordance between the qualitative readings by eye with those from the reader. We have observed this already in one site, Cameroon (Mewamba et al 2021).…”

“…We have recently extended this method by using the ESEQuant LR3reader to read the intensity of the positive band. In field trials ESEQuant readings correlated well with estimates of band intensity using the reference cassettes developed by Casacuberta-Partal et al ( 2019) with a Spearman rank correlation coefficient = 0.89 (Mewamba et al, 2021). We will therefore use the ESEQuant LR3 reader to objectively quantify band intensity on POC-CCA cassettes in a standardized way at all sites in Study 1 except the samples from Lake Victoria.…”

“…This is what is practical in the field for us. The CAA test is a true quantitative measure (van Dam et al, 2013), while the reflection from the CCA test has been modified for use as a quantitative test (Mewamba et al, 2021). Whilst we accept that multiple KK readings on consecutive days gives a more reproducible results than duplicate readings on a single day, we are planning to use the CCA as it is more reproducible from a single reading than the KK.…”

Reliability of point-of-care circulating cathodic antigen assay for diagnosing schistosomiasis mansoni in urine samples from an endemic area of Brazil after one year of storage at -20 degrees Celsius

“…A recently published study 36 using the same batch of POC-CCA both in fresh and frozen urine (-20°C) after one year found a significant decrease in the positive rate, from 100% (95%CI: 98.0%-100.0%) to 74.4% (95%CI: 66.9%-80.7%), considering trace as positive (t+). This was ascribed to the degradation of CCA, which might have occurred because the study area was susceptible to recurrent power failure, leading to undue thawing of the urine samples.…”

Fine-scale mapping of Schistosoma mansoni infections and infection intensities in sub-districts of Makenene in the Centre region of Cameroon

“…The amount of CCA in each urine sample was determined by reading each POC-CCA cassette with a lateral flow strip reader (ESEQuant LR3 reader) and the visual scoring system as described by Mewamba et al [ 21 ] and Casacuberta et al [ 22 ] respectively.…”