Rapid serological detection of smooth Brucella strain antibodies in bovine and sheep using a dynamic flow immunochromatographic test.

Brucellosis, a severe zoonotic disease with over 2,000,000 annual human cases, poses a major threat to the livestock industry and public health. Early and accurate diagnosis in animals is crucial for control, but current methods are often time-consuming, equipment-dependent, or prone to cross-reactivity. This study developed a cost-efficient dynamic flow immunochromatography (DFICT) technique for the accurate diagnosis of bovine and sheep Smooth brucellosis. The assay utilizes a test strip with Smooth lipopolysaccharide and Streptococcus protein G (SPG) immobilized as the Test (T) and Control (C) lines, employing gold nanoparticle-SPG conjugates as the tracer. To perform the DFICT, 100 μL of the liquid conjugate is applied to the reagent well, followed by 5 μL of serum to the sample well. The results were observable within 10 min by the naked eye. The DFICT demonstrated high sensitivity, detecting antibodies in sera diluted up to 1:64, and exceptional specificity with no cross-reactivity to other common pathogens. The DFICT can be stored for 12 months at 4 °C with no loss of sensitivity or specificity. Clinical validation with 80 bovine and 161 sheep field sera showed strong agreement with standard methods (ELISA, RBT), achieving sensitivities of 94.6% (bovine) and 98.2% (sheep), and specificities of 100% and 84.0%, respectively. It's simple, equipment-free operation and reliability make the established DFICT a vital and necessary tool for large-scale, on-site screening, significantly enhancing Smooth brucellosis surveillance and control capabilities.