Development and Evaluation of an Indirect ELISA for Detection of Infection with Teladorsagia Circumcincta in Sheep

Abstract

Background The gastrointestinal helminth, Teladorsagia circumcincta, is one of the major health risk and production-limiting disease in small ruminant populations, particularly in temperate regions. With the increasing importance of the disease management and recruited anthelminic resistant types, accurate approaches are needed for diagnosis of the infection in the host. Because of uncertain results using faecal examinations, the ELISA method was indicated for detection of the nematode antigenic materials. Despite some promising results, problems were described in terms of the test specificity and the cross-reactions. The aim of this study was therefore to evaluate worm somatic and excretory/secretory (ES) products using western blot analysis and an indirect ELISA for detecting T. circumcincta infection in sheep. Results Based on the immuno-reactivity analysis, immunogenic fractions with molecular weights of approximately 60, 75 and 100 kDa were detected in somatic content and two antigens of about 63 and 75 kDa in ES material. Accordingly, a specific product at 75 kDa had the strongest reaction and appeared as the most common antigenic protein. In ELISA, all sera from the infected sheep revealed the OD rates above the calculated cut-off value with about two-fold greater in average. Negative control samples were also specifically recognized with the mean OD rate of about 1/3 of the estimated cut-off value. The cross-reaction test, using rabbit hyperimmune sera, did not show reactivity with ES antigens of other prevalent nematodes include Haemonchus contortus, Protostrongylus rufescens and Marshallagia marshalli. In contrast, a strong positive reaction was found with the somatic antigens of M. marshalli. Conclusions The results obtained here indicates the indirect ELISA method using the ES content enables distinguishing the T. circumcincta infected sheep with high specificity. Those antigenic ES peptides with 63 and particularly 75 kDa molecular weights should be more investigated due to the potential for serological diagnostic methods and immunoprotective targets in the host.