Development of a SAG1-based colloidal gold immunochromatographic strip for rapid serological detection of swine Toxoplasma gondii

BACKGROUND: Toxoplasmosis is a globally prevalent zoonosis caused by Toxoplasma gondii (T. gondii), a parasite that infects nearly all warm-blooded animals, including humans, cats, and pigs. Beyond incurring substantial economic losses to the swine industry, T. gondii infection poses a severe threat to public health, as pigs, which are key intermediate hosts for T. gondii transmission, serve as a major source of human infection via the food chain. Thus, developing specific, sensitive, rapid, and easy-to-perform detection methods for porcine T. gondii is of paramount importance for the prevention, control, and eventual eradication of this pathogen in swine populations. METHODS: To address this need, a novel colloidal gold immunochromatographic strip (CGIS) was developed for the rapid serological detection of T. gondii infection in swine. The strip was constructed using recombinant surface antigen 1 (SAG1) expressed in a baculovirus-insect cell system, which ensures that the protein retains native antigenic epitopes. The purified SAG1 protein was conjugated to colloidal gold nanoparticles and loaded onto a conjugate pad, while staphylococcal protein A and a polyclonal anti-SAG1 antibody were immobilized on a nitrocellulose membrane to form the test line (T line) and control line (C line), respectively. RESULTS: Clinical validation demonstrated that the developed CGIS exhibits high specificity, with no cross-reactivity to sera positive for 13 common porcine pathogens. The strip achieved a visual limit of detection of 1:25,600 dilution of positive serum. In parallel, a commercial enzyme-linked immunosorbent assay kit yielded positive results up to a 1:800 dilution according to the manufacturer's diagnostic cutoff. Importantly, evaluation of 300 clinical porcine serum samples demonstrated a 98.3% concordance rate with the reference microscopic agglutination test. CONCLUSIONS: This SAG1-based CGIS provides a practical, user-friendly tool for large-scale surveillance and on-farm screening of porcine toxoplasmosis, thereby offering potential support for the prevention and control of T. gondii infection in pigs.