Development of a rapid, simple dipstick dye immunoassay for schistosomiasis diagnosis.

In order to develop a rapid, simple immunodiagnostic assay for schistosomiasis, soluble egg antigen (SEA) of Schistosoma japonicum was conjugated with a blue colloidal dye (D-1) produced in China and used to detect antibodies in the sera of schistosomiasis patients. The antigen-antibody complex was captured by anti-human IgG absorbed onto a nitrocellulose membrane dipstick by means of immunochromatography. The results showed that the sensitivity of the dipstick dye immunoassay (DDIA) was 96.7% in 30 cases of acute schistosomiasis (29/30) and 94.1% (79/84) in 84 cases of chronic schistosomiasis. The specificity of the assay was 96.7% in 60 healthy subjects. Cross-reactions were observed in 10.0% of 20 cases of clonorchiasis and in 70.0% of 20 cases of paragonimiasis. The results were similar to those detected by routine ELISA. In a field evaluation of the DDIA kit, the positive rate of the DDIA was 96.7% in 121 cases of schistosomiasis, compared with 90.1% with the circumoval precipitin test (COPT). The antigen conjugated with dye was stable at room temperature for at least 6 months. The results indicated that the dipstick dye immunoassay provided high sensitivity and good specificity for the detection of schistosomiasis and the assay was rapid, simple and cheap, and did not need any equipment. It was more useful for screening target populations for selective chemotherapy than other immunoassays.