Objective: To develop and preliminarily evaluate two immunodiagnostic methods for clonorchiasis using Clonorchis sinensis PPMP I antigen Cs2 recombinant protein (rCs2).
Methods: Using the soluble rCs2, an indirect ELISA and a colloidal-gold immuno-chromatography assay (GICA) dynamic flow strip was developed for detecting specific antibodies in serum. Serum samples from 35 egg-positive clonorchiasis patients, 33 healthy individuals, 15 schistosomiasis patients, 15 paragonimiasis westermani patients and 13 cysticercosis patients were examined by ELISA and GICA strip test. To further evaluate the diagnostic value of these two methods, eight New Zealand rabbits were randomly divided into infected group and treatment group. Each rabbit was infected with 600 C. sinensis metacercaria. Rabbits in treatment group were treated with praziquantel [150 mg/(kg x d) x 2d] individually at day 56 post-infection. ELISA and GICA strip test were used to observe the dynamic changes of specific antibodies against rCs2 in the two parallel groups during the period of 0-44 weeks.
Results: The sensitivity, specificity and total coincidence rate determined by the ELISA method were 71.4% (25/35), 93.4% (71/76), and 86.5% (96/111), respectively, and the cross reaction with schistosomiasis, paragonimiasis and cysticercosis patients were 1/15, 1/15, and 1/13, respectively. The sensitivity, specificity and coincidence rate in the GICA strip test were 85.7% (30/35), 92.1% (70/76), and 90.1%(100/111), respectively. In C sinensis infected rabbits, antibodies level began to increase at 4 weeks after infection, peaked at the 6th week, and declined rapidly to a lower level in the 20th week, while the changing pattern of antibodies level in the treatment group was similar with that of infected group (P > 0.05). In the GICA strip test, antibodies in two groups could be detected in 4-16 weeks.
Conclusion: Indirect ELISA and the GICA dynamic flow strip developed in this study may be of value in the immunodiagnosis of clonorchiasis.