Improved sensitivity of the urine CAA lateral-flow assay for diagnosing active Schistosoma infections by using larger sample volumes

Abstract

BackgroundAccurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools. An existing lateral flow (LF) based test demonstrating ongoing infections through detection of worm circulating anodic antigen (CAA), was improved for sensitivity through implementation of a protocol allowing increased sample input. Urine is the preferred sample as collection is non-invasive and sample volume is generally not a restriction.MethodsCentrifugal filtration devices provided a method to concentrate supernatant of urine samples extracted with trichloroacetic acid (TCA). For field trials a practical sample volume of 2 mL urine allowed detection of CAA down to 0.3 pg/mL. The method was evaluated on a set of urine samples (n = 113) from an S. mansoni endemic region (Kisumu, Kenya) and compared to stool microscopy (Kato Katz, KK). In this analysis true positivity was defined as a sample with either a positive KK or UCAA test.ResultsImplementation of the concentration method increased clinical sensitivity (Sn) from 44 to 98% when moving from the standard 10 μL (UCAA10 assay) to 2000 μL (UCAA2000 assay) urine sample input. Sn for KK varied between 23 and 35% for a duplicate KK (single stool, two slides) to 52% for a six-fold KK (three consecutive day stools, two slides). The UCAA2000 assay indicated 47 positive samples with CAA concentration above 0.3 pg/mL. The six-fold KK detected 25 egg positives; 1 sample with 2 eggs detected in the 6-fold KK was not identified with the UCAA2000 assay.ConclusionsLarger sample input increased Sn of the UCAA assay to a level indicating ‘true’ infection. Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy. The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions. Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.

Schistosomiasis and Human Immunodeficiency Virus in Men in Tanzania

“…Several population-based studies in Tanzania and Uganda, which included both men and women, did not find an increased prevalence of HIV among those with S. mansoni infection. 5,6 Neither of these studies stratified data by gender, and both relied on schistosome egg excretion as the primary endpoint, which is less sensitive than schistosome antigen testing 7 and may be diminished in the setting of HIV infection. 8,9 Of note, in a subset of the Ugandan individuals who underwent urine schistosome antigen testing, the odds ratio (OR) for HIV infection was 1.5 with a P value of 0.19, suggesting that the study may have lacked sufficient power to detect a smaller increased risk.…”

Sm‐p80‐based vaccine trial in baboons: efficacy when mimicking natural conditions of chronic disease, praziquantel therapy, immunization, and Schistosoma mansoni re‐encounter

“…Urine samples were tested with the UCAA50 assay as described elsewhere . For the standard CAA50 assay, urine samples were extracted with an equal volume of 4% w/v trichloroacetic acid (TCA).…”

“…To evaluate efficacy, we measured active schistosome infections by identifying schistosome eggs in feces of infected baboons by the standard Kato‐Katz method of microscopy . We also assessed the efficacy of both PZQ and the Sm‐p80 vaccine through detection of circulating anodic antigen (CAA) in host urine; quantification of CAA antigens levels has been shown to be highly specific and reliable at determining the effects of drug treatment, worm burden, and egg production . We further analyzed the transcriptomic profiles and molecular mechanisms associated with trickle infection, chronic schistosomiasis, PZQ‐mediated parasite killing, and Sm‐p80 vaccine effect following re‐encounter with the parasite .…”

Selecting accurate post-elimination monitoring tools to prevent reemergence of urogenital schistosomiasis in Morocco: a pilot study

“…Enhanced sensitivity of this UCP-LF CAA strip testis achieved utilizing centrifugal filtration devices which permit larger sample input. The analysis of a sample volume of 0.5 ml serum or 2 ml urine is believed to allow detection of single worm infections [15]; these two assays are referred to respectively as the SCAA500 and UCAA2000 test, with ‘S’ indicting serum, ‘U’ urine and the number the amount of sample (in μl) concentrated and analyzed on the strip. The amount of sample input is flexible, but relates directly to the achieved analytical sensitivity.…”