Performance of an Ultra-Sensitive Assay Targeting the Circulating Anodic Antigen (CAA) for Detection of Schistosoma mansoni Infection in a Low Endemic Area in Brazil.

Fernando Schemelzer Moraes Bezerra,Mariana Silva Sousa,Jose Mauro Peralta,Regina Helena Saramago Peralta,Elizabeth de Francesco Daher,Paul L. A. M. Corstjens,Claudia J. de Dood,Govert J. van Dam,Marta Cristhiany Cunha Pinheiro

doi:10.3389/fimmu.2019.00682

Abstract

Techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings, where the conventional parasitological methods are insensitive. We determined the accuracy of an up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay in urine and serum for Schistosoma mansoni diagnosis in low-prevalence settings in Ceará, Brazil, before and after praziquantel treatment. Clinical samples of a total of 258 individuals were investigated by UCP-LF CAA, point-of-care—circulating cathodic antigen (POC-CCA), soluble worm antigen preparation (SWAP)-ELISA and Kato-Katz (KK); a selection of 128 stools by real-time PCR technique. Three and 6-weeks after treatment, samples were collected and evaluated by detection Schistosoma circulating antigens (CAA and CCA). The UCP-LF CAA assays detected 80 positives (31%) with urine and 82 positives (31.8%) with serum. The urine POC-CCA and serum SWAP-ELISA assays detected 30 (11.6%) and 107 (40.7%) positives, respectively. The Kato-Katz technique revealed only 4 positive stool samples (1.6%). Among the 128 individuals with complete data records, 19 cases were identified by PCR (14.8%); Sensitivities and specificities of the UCP-LF CAA assays, determined versus a combined reference standard based on CCA/KK/PCR positivity, ranged from 60–68% to 68–77%, respectively. In addition only for comparative purposes, sensitivities of the different assays were determined vs. a comparative reference based on CAA/KK/PCR positivity, showing the highest sensitivity for the urine CAA assay (80%), followed by the serum CAA (70.9%), SWAP-ELISA (43.6%), PCR (34.5%), POC-CCA (29.1%), whilst triplicate Kato-Katz thick smears had a very low sensitivity (3.6%). CAA concentrations were higher in serum than in urine and were significantly correlated. There was a significant decrease in urine and serum CAA levels 3 and 6-weeks after treatment. The UCP-LF CAA assays revealed 33 and 28 S. mansoni-infected patients at the 3- and 6-week post-treatment follow-up, respectively. The UCP-LF CAA assays show high sensitivity for the diagnosis of S. mansoni in low-endemicity settings. It detects a considerably higher number of infections than microscopy, POC-CCA or PCR. Also it shows to be very useful for evaluating cure rates after treatment. Hence, the UCP-LF CAA assay is a robust and promising diagnostic approach in low-transmission settings.

Highlights

In a nation-wide study during a 12-year period, with 12, 491,280 deaths in Brazil, 76,847 deaths (0.62%) were caused by Neglected Tropical Diseases (NTDs)
Specificity and sensitivity were calculated and used for indication of the performances of the up-converting phosphor (UCP)-LF circulating anodic antigen (CAA) assays and of the SWAP-ELISA against a combined reference standard constructed by Kato-Katz and/or PCR and/or POCCCA results; On the other hand, specificity, sensitivity and positive and negative predictive values of the diagnostic tests were calculated following an approach described previously [47, 48], but only for comparative reasons
The current study highlights the potential of serum as well as urine samples for a CAA diagnostic approach to accurately determine the S. mansoni infections using the ultra-sensitive UCP-LF assay, as evaluated for the first time in a low endemic area in Brazil

Summary

Introduction

In a nation-wide study during a 12-year period, with 12, 491,280 deaths in Brazil, 76,847 deaths (0.62%) were caused by Neglected Tropical Diseases (NTDs). Mortality has greatly been reduced over the last years, schistosomiasis is still a neglected cause of death in Brazil, with considerable regional differences [2]. According to data obtained by the national prevalence survey (2010–2015), an estimated 1.5 million people are infected in Brazil (nearly 1% of the population) [3]. Another study with a spatiotemporal analysis identified high-risk clusters of deaths, mainly in highly schistosomiasisendemic areas along the coast of Brazil’s Northeast Region [5]. According to data from the Brazilian Ministry of Health, the municipality of Capistrano, from 2008 to 2012, was among the five municipalities with the highest prevalence in Ceará state [6]

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Results

Conclusion