Development of a rapid, sensitive, dye immunoassay for schistosomiasis diagnosis: a colloidal dye immunofiltration assay.

The colloidal dye immunofiltration assay (CDIFA) combines the concepts of the double-antigen sandwich assay, the Dot immunofiltration assay, and colloidal dye-linked antigen technique to produce a new dye immunoassay for antibody detection in schistosomiasis. The CDIFA consisted of soluble egg antigen (SEA) of Schistosoma japonicum coated onto nitrocellulose membrane, mounted on a flow-through test device to provide the assay capture matrix. SEA absorbed to a red colloidal dye, R-3, produced in China, served as the antigen-antibody complex detecting reagents. The results showed that the sensitivity of the CDIFA was 100% in 35 cases of acute schistosomiasis (35/35), 98% in 50 cases of chronic schistosomiasis (49/50). The specificity of the assay was 99.4% in 180 healthy individuals (179/180). The cross-reaction was 13.3% in 30 cases of paragonimiasis, 2.6% in 38 cases of clonorchiasis sinensis and 0% in 20 cases of hookworm infection, 20 cases of fasciolopsiasis and 16 cases of ascariasis. The results were similar to those detected by routine enzyme-linked immunosorbent assay (ELISA). In a field evaluation of the CDIFA kit, the positivity rate of the CDIFA was 97.5% in 157 cases of schistosomiasis, compared with 91.1% with the circumoval precipitin test (COPT). The dye-labeled SEA conjugate was stable at room temperature for at least 6 months. The results indicated that the CDIFA provided an economic, simple, rapid, robust test for the detection of schistosome infection, suitable for a wide variety of field applications without any instrumentation.