Immunodiagnostic differentiation of alveolar and cystic echinococcosis using ELISA test with 18-kDa antigen extracted from Echinococcus protoscoleces.

Immunoblotting analysis was carried out using crude extracts of Echinococccus multilocularis and E. granulosus. A total of 214 serum samples were examined for the detection of antibody responses against 18-kDa polypeptides (Eg18 and Em18). Of 44 sera from patients with alveolar echinococcosis (AE) 91% were positive against both Eg18 and Em18, compared with 10% and 13%, respectively, of 70 cystic echinococcosis (CE) samples and 13% and 17% of 29 cysticercosis samples. A relatively purified 18-kDa antigen was extracted from E. granulosus protoscoleces and an 18-kDa-ELISA test which is simple, fast and highly sensitive and specific has been established. A comparative ELISA analysis, using the purified 18-kDa antigen and pooled AE and CE serum, indicated that there are significant differences in antibody levels between AE and CE sera. The maximum ratio for the evaluation of AE to CE was 2.26. The 18-kDa-ELISA was positive for 91% (40/44) and 11% (8/70) of AE and CE sera, respectively, and there was no cross-reactivity with cysticercosis sera or healthy controls. The overall diagnostic values of 18-kDa-ELISA for AE sera were sensitivity 91%, specificity 94%, positive predictive value 83% and negative predictive value 97%. We conclude that (i) the 18-kDa antigenic component may not be species specific but (ii) levels of antibody to the 18-kDa antigen are significantly different between AE and CE sera. Therefore, the 18-kDa antigen can be a reliable serological marker for differentiation of AE from CE.