Assessment of the diagnostic efficacy of enolase as an indication of active infection of Schistosoma japonicum

Schistosomiasis is a common zoonoses affecting humans. The atypical clinical symptoms, low morbidity, and low degree of infection impede diagnosis and assessment of epidemics. Detecting circulating antigens from adult worms in patients' body fluids should be diagnostically superior to examining eggs in feces. Herein, the excretory-secretory proteins of adult worms were analyzed by using 2-D protein electrophoresis and mass spectrometry. The Schistosoma japonicum enolase (Sj enolase) was identified as the most abundant excretory-secretory antigen. Purified recombinant Sj enolase was prepared, and specific monoclonal and polyclonal antibodies were raised against it. A sandwich enzyme-linked immunoassay (sandwich ELISA) was established that used the monoclonal antibody as a capture antibody and the polyclonal antibody as a detection antibody. The linear detection range was 0.7-1000 ng/ml (minimum 700 pg/ml). Sj enolase could be detected in the sera of infected rabbits and disappeared rapidly postpraziquantel treatment. The sensitivity and specificity of this sandwich ELISA to detect field serum samples of schistosomiasis were 84.61 and 95.83 %, respectively. The cross-reaction rates for clonorchiasis and paragonimiasis were 3.33 and 5 %, respectively. This ELISA assay was used to test 45 matching sera of schistosomiasis patients before treatment and at 3, 6, 9, and 12 months posttreatment. Among the sera, 88.89 % were positive before treatment. At 3, 6, 9, and 12 months postpraziquantel treatment, 93.33, 97.78, 100, and 100 % tested negative, respectively. Therefore, Sj enolase can be used to indicate active Schistosoma infection, and detecting serum Sj enolase is important for diagnosis and evaluating treatment effect.