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.
Highlights
Accurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools
In the current study we demonstrate further improvement of the sensitivity of the Upconverting phosphor (UCP)-lateral flow (LF) circulating anodic antigen (CAA) assay by including a concentration step in the sample pretreatment protocol as proposed previously [26]
CAA levels are determined with the UCAA2000 assay and arbitrarily expressed by UCP-LF assay values (T/flow control signals (FC) ratio)
Summary
Accurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools. A highly sensitive and increasingly applied method to detect pathogen infections is by means of PCR, detecting nucleic acids This has been demonstrated using urine and stool samples for the major human Schistosoma infections [21,22,23,24,25] and has excellent multiplex capability (simultaneous screening for and detection of multiple infections/pathogens). This technology is very expensive and not readily available for resource limited setting and remote areas. Nucleic acid based assays mostly detect egg DNA and similar to egg counts have some limitation in testing effects of drugs shortly after administration
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