Assays which enable the detection of schistosome gut-associated circulating anodic (CAA) and cathodic (CCA) antigen in serum or urine are increasingly used as a diagnostic tool for schistosome infection. However, little is known about the production and clearance of these circulating antigens in relation to the sex and reproductive maturity of the parasite. Here we describe CAA and CCA excretion patterns by exploring a mouse model after exposure to 36 male-only, female-only and mixed (male/female) Schistosoma mansoni cercariae. We found that serum and urine CAA levels, analysed at 3 weeks intervals, peaked at 6 weeks post-infection. Worms recovered after perfusion at 14 weeks were cultured ex vivo. Male parasites excreted more circulating antigens than females, in the mouse model as well as ex vivo. In mixed infections (supporting egg production), serum CAA levels correlated to the number of recovered worms, whereas faecal egg counts or Schistosoma DNA in stool did not. No viable eggs and no inflammation were seen in the livers from mice infected with female worms only. Ex vivo, CAA levels were higher than CCA levels. Our study confirms that CAA levels reflect worm burden and allows detection of low-level single-sex infections.

We evaluated the quantitation of two schistosome circulating antigens in serum and urine as a tool for the assessment of the efficacy of praziquantel dosage regimens (40 versus 60 mg/kgbw). In addition we compared the efficacy of two different brands of praziquantel (Biltricide® and Distocide®), given at the same dosage (40 mg/kgbw). Thirty five Egyptian hospitalized schistosomiasis mansoni patients participated in this study. Thirteen patients (Group 1) received 60 mg/kgbw Biltricide®, administered in 3 oral doses of 20 mg in one day; 22 individuals (Group 2) were treated with 40 mg/kgbw (12 Biltricide®, 10 Distocide®), given in one oral dose. Circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were quantitated by monoclonal antibody-based ELISA's before, and 1, 3 and 6 weeks after chemotherapy. Before treatment, all patients were positive for at least one of the circulating antigen assays. Three to six weeks after treatment significantly more patients were found to be negative in Group 1 compared to Group 2 (X2 = 7·13, P = 0·008, n = 35). Also the levels of CCA and CAA in serum and of CCA in urine were found to be significantly higher in Group 2 (Mann- Whitney U < 85, P < 0·05, n = 35). These results were confirmed by parasitological data. No differences were found between treatment with Biltricide® or Distocide®. Our results indicate that praziquantel treatment of schistosomiasis with 60 mg/kgbw divided in 3 doses results in a higher cure rate compared to 40 mg/kgbw as a single dose, and provide further evidence for the use of the CAA and CCA assays as a sensitive method to monitor the efficacy of chemotherapy, particularly when circulating antigen assays are combined by parallel testing.