A Clonorchis sinensis-specific antigen that detects active human clonorchiasis

A Clonorchis sinensis-specific antigen in excretory-secretory product of C. sinensis (CsE) was assessed in human clonorchiasis by immunoblot. Thirty and 7 kDa antigens of CsE2, one of four different batches of CsEs reacted strongly with infection sera from clonorchiasis patients; however, the antigens reacted weakly with 6-month post-treatment sera from praziquantel-cured cases, but were still highly detected by the sera from praziquantel-failed patients, indicating that the 30 and 7 kDa antigens can detect antibodies during an active infection. The 30 kDa antigen showed some cross reactions with sera from patients with Paragonimus westermani and Metagonimus yokogawai, while the 7 kDa antigen did not, suggesting that the 7 kDa antigen has high specificity. The 30 kDa antigen reacted with some past clonorchiasis sera, whereas the 7 kDa antigen did not, supporting that antibodies to the 7 kDa antigen are not present in sera from past clonorchiasis patients. In an endemic area, 92% (23/25) of active clonorchiasis patients and 91% (10/11) of mixed infection patients with C. sinensis and M. yokogawai had IgG antibodies to the 7 kDa antigen, while 40% (6/15) of past clonorchiasis individuals and 43% (3/7) of metagonimiasis patients cross-reacted to the antigen. These data suggest that the 7 kDa antigen in an excretory-secretory antigen may serve as a marker of an active clonorchiasis with reliable specificities in past clonorchiasis, paragonimiasis and metagonimiasis.