Development of a colloidal gold immunochromatographic strip based on recombinant mixed antigens SAP-2 and CatL1 for rapid detection of Fasciola gigantica infection in buffaloes.

Fasciolosis is a zoonotic parasitic disease caused by liver flukes Fasciola hepatica and Fasciola gigantica, which is distributed worldwide, causes significant losses to livestock farming. The development of a rapid detection method will aid in disease prevention and control. Although there are many studies on rapid diagnostics, most are based on natural antigens. A colloidal gold detection method based on recombinant antigens for diagnosing F. gigantica infection is lacking. Given the potential of mixed recombinant antigens for enhanced diagnostic efficacy, a colloidal gold method based on recombinant mixed antigens is established in this study. An indirect ELISA based on mixed recombinant FgSAP-2 (rFgSAP-2) and FgCatL1 (rFgCatL1) was developed and assessed. Then a colloidal gold immunochromatographic test strip against F. gigantica infection (FgICS) based on mixed rFgSAP-2 and rFgCatL1 was further developed, and the sensitivity, cross-reactivity and accuracy of the established FgICS was assessed by serum samples. When testing 300 field serum samples, the mixed-antigen ELISA yielded a positive rate of 75.00%, which was higher than ELISAs coated with antigens rFgSAP-2 (60.67%), rFgCatL1 (63.00%) and F. gigantica excretory and secretory protein (FgESP) (65.33%). Subsequently, a colloidal gold test strip labeled with Staphylococcus aureus protein A (SPA) based on mixed antigens was also developed, remained positive at a serum dilution of 1:1280, with no cross-reactivity. Testing of 100 serum samples yielded an overall accuracy of 89% for FgICS when referenced against the 4-ELISA consensus standard. An ELISA based on mixed antigens FgSAP-2 and FgCatL1 showed better sensitivity and stability. The newly developed mixed antigens colloidal gold strip also retained high sensitivity and accuracy, which can be used for development of point‑of‑care test kits and provides a theoretical basis for the diagnosis and control of F. gigantica infection.