Monitoring the treatment outcome of chemotherapy is an important component of the strategy to control schistosomiasis. Reliable laboratory tests are urgently needed to monitor the treatment status in infected patients. Most immunologically based diagnostic approaches currently used in endemic regions were developed to detect specific antibodies in patients' sera against crude parasite antigens that are not very effective in serving this purpose. 
Similarly, recent studies using monoclonal antibodies to detect circulating antigens could not demonstrate high specificity and sensitivity to determine the course of infection in chronic cases of schistosomiasis 
. The efficacy of such monoclonal antibody-based approaches was not better than the traditional antibody-based detection approaches in evaluating the effect of chemotherapy. In the current study, we attempted to develop a novel and more effective immunodiagnostic assay to address this need.
Our results showed that the FA-ELISA assay had high sensitivity and high specificity, with minimal cross reactivity with other parasite antigens. The positive rate for chronic schistosomiasis detection with the assay was more than 90%, which was not significantly different from the results obtained using the SEA-ELISA. However, results obtained using the S-ELISA assay (detecting circulating antigen) were lower than the other two assays. The specificity of the FA-ELISA was 100% as it does not score positive among healthy individuals and had no cross reactivity against paragonimiasis, fasciolopsiasis, or clonorchiasis. The old SEA-ELISA and S-ELISA showed different levels of cross reactivity, especially with paragonimiasis. The FA-DIGFA also had high sensitivity and specificity as the positive rate for chronic schistosomiasis detection was 94.4% and results were all negative for healthy individuals and in patients with clonorchiasis or paragonimiasis. However, with the SEA-DIGFA, the cross reaction rates with clonorchiasis and paragonimiasis were 10% (10/30) and 26.3% (5/19). Our result indicate that either the FA-ELISA or FA-DIGFA could be applied for diagnosis of schistosomiasis in endemic areas.
The animal experiment results showed that the antibodies to the 107–121 kDa fraction antigens of SEA disappeared earlier in the cured host compared to other fractions. Our assay, using fractions 107–121 KDa, is therefore, proven to be a good candidate for monitoring the efficacy of chemotherapy.
The nature of 107–121 kD fractions is still unknown but it is important in future studies to identify the amino acid sequences of these fractions so that the genes coding for these fractions can be cloned and recombinant proteins similar to these fractions can be produced in higher level and more standardized conditions.
The sensitivities of FA-ELISA and FA-DIGFA were somewhat lower than SEA-ELISA and SEA-DIGFA (, ); however, no significant difference was detected when the tests were repeated twice (p>0.05). Because we did not test sera at different levels of infection or at different times post infection, we do not know the results for early infection or low level infection.
At the same time, the reported test in the current study can be used for monitoring of therapeutic effects or for the detection of new infection. This novel test can potentially play a major role in following people who have been treated effectively, especially in China. Currently with the adoption of various strategies in prevention and control of schistosomiasis, among 453 endemic regions, 269 (59.38%) have met the criteria of transmission interruption and another 104 (22.96%) met the criteria of transmission control 
. In order to achieve full control in China, a comprehensive control strategy with emphasis on infectious source control has been proposed 
. With this strategy, it is necessary to quickly diagnose new cases or re-infections before effective treatment can be provided. However, due to low infection rates, the common diagnostic methods, such as the Kato-Katz method, have low sensitivity and may miss up to 40–60% of infected cases 
. At the same time, the existing immunodiagnostic approaches using conventional ELISA or IFA showed low antibody specificity as such antibodies can persist for 3–5 years or even longer after effective treatment 
and therefore, cannot be used to detect current infection. Using such methods to diagnose infection will lead to overuse of chemotherapy causing waste of resources and induction of drug resistance. Because our FA-ELISA can reliably detect current infection, and have very low cross-reactivity with other parasites, it is an effective approach to make a correct diagnosis and effectively control the source of infection. This will benefit the ultimate control of schistosomiasis throughout China.
It is possible that our technique can be adapted to other schistosome species but we have not yet conducted such study. It will be important to determine whether the antigen used in our study can also be applied to other schistosome species and whether the homologous antigen can be identified with the other schistosome species. These efforts will be facilitated by determining the protein sequence (or at least the partial sequence) of the antigen used in our assay, which may guide the search of homologous antigens for other schistosome species.