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Laboratory diagnosis of sheep fasciolosis is commonly performed by coprological examinations; however, this method may lead to false negative results during the acute phase of the infection. Furthermore, the poor sensitivity of coprological methods is considered to be a paradox in the chronic phase of the infection. In this study, we compared the immunoreactivity of native and recombinant forms of Fasciola hepatica excretory/secretory antigens and determined their capabilities for the development of F. hepatica-specific immunoassays. Immunoreactivity and specificity of recombinant and native forms of F. hepatica antigens, including fatty acid binding protein (FABP), glutathione-S-transferase (GST), and cathepsin L-1 (CL1), in parallel with native forms of FABP and GST, were studied for serodiagnosis of the chronic form of sheep fasciolosis, individually or in combination with each other by enzyme-linked immunosorbent assays (ELISA). The correlation of the findings was assessed by receiver-operator characteristic (ROC); furthermore, the specificity and sensitivity were assessed by Youden's J. Serologic cross-reactivity was evaluated using samples from healthy sheep (n = 40), Fasciola-infected sheep (n = 30), and sheep with other parasitic infections (n = 43). The FABPs were determined to be greater than 95% sensitive for F. hepatica serodiagnosis. The most desirable diagnostic recombinant antigen was rCL1, which showed 100% sensitivity and 97% specificity in ELISA and was capable of discriminating the positive and negative samples by maximum Youden's J results. We conclude that rCL1 can be used for routine serodiagnosis of chronic fasciolosis. Thus, it could be advantageous in development of immunoassays for screening of ovine herds in fasciolosis-endemic areas and as a reliable agent for detection of fasciolosis in non-endemic regions.

Background: Coprological examinations are commonly used for diagnosis of fasciolosis. However, these methods are not useful during the acute phase of the infection and also show poor sensitivity during its chronic phase. In this study we compared the immunoreactivity of the native and recombinant forms of Fasciola hepatica excretory/secretory antigens and determined the most appropriate one for development of F. hepatica-specific immunoassays., Methods: The coding sequences of previously-determined immunogenic proteins including cathepsin L1 (CL1), fatty acid binding protein (FABP) and glutathione-S-transferase (GST) were cloned and expressed in E. coli BL-21 cells. Native forms of FABP and GST were also purified. We evaluated the immunoreactivity of the native and recombinant proteins by ELISA using sera from 40 healthy individuals, 15 fasciolosis patients, and 57 patients with other infectious diseases., Results: All of the studied proteins showed high sensitivity and specificity for F. hepatica serodiagnosis. However, CL1 was more sensitive and specific (100%) than the others for the detection of F. hepatica-specific antibodies. Notably, both FABP and GST showed significant cross-reactivity with hydatidosis patients' sera while CL1 did not., Conclusions: Cathepsin L1 has acceptable sensitivity and specificity for serodiagnosis of F. hepatica and its application could be advantageous in immunoassay development., (© The Author 2016. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)