Evaluation of purified 27.5 kDa protoscolex antigen-based ELISA for the detection of circulating antigens and antibodies in sheep and human hydatidosis.

Hydatidosis is a zoonotic disease caused by the larval stage of Echinococcus granulosus, and the diagnosis of hydatidosis to date remains unresolved despite the development of many serological techniques. The present study aimed to develop an antigen-based enzyme-linked immunosorbent assay (ELISA) using IgG anti-27.5 kDa protoscolex antigen (27.5 PA) for measuring circulating protoscolex antigen (CPA), for comparison with an antibody detection assay, in sera of naturally infected sheep and humans in highly endemic areas in Egypt. In sheep, the sensitivity of ELISA in detecting anti-27.5 PA IgG and CPA was 75.0 and 60.0%, respectively, and the recorded specificity was 80.0 and 88.0%, respectively. In humans, the sensitivity of ELISA in detecting anti-27.5 PA IgG and CPA was 62.5 and 52.5%, respectively, while the specificity of the assay was 66.7 and 75.0%, respectively. In conclusion, an antibody detection assay is still superior and is more sensitive than an antigen detection assay, especially in diagnosing an active infection in which hydatid cysts are predominant. An antigen detection assay may be a useful approach to assessment of the efficacy of treatment, especially after removal of the cyst. Further studies are recommended to improve the diagnostic efficacy of an antigen-based ELISA method by using a highly purified recombinant antigen.