A Rapid and Sensitive Lanthanide-Based Fluorescent Microsphere Immunochromatographic Test for Quantitative Detection of infectious bursal disease virus (IBDV) in Poultry

Infectious bursal disease virus (IBDV) is a major immunosuppressive pathogen threatening global poultry production. The emergence of very virulent (vvIBDV) and novel variant strains (nVarIBDV) has increased immune escape and reduced vaccine efficacy, underscoring the need for rapid and reliable diagnostic tools. This study developed a simple, rapid, and sensitive fluorescent microsphere immunochromatographic test strip (FM-ICTS) for quantitative detection of IBDV antigen. The FM-ICTS was constructed using lanthanide fluorescent microspheres conjugated to an anti-VP2 monoclonal antibody within a double-antibody sandwich lateral flow format. Reaction conditions were optimized, and a quantitative standard curve was established using serial dilutions of inactivated IBDV (B87 strain). The assay generated stable fluorescence signals within 15 minutes and showed high analytical sensitivity, detecting IBDV antigen at dilutions up to 1:5120. No cross-reactivity with CAV, ALV, AIV, or MDV was observed, confirming excellent specificity. Repeatability tests demonstrated low coefficients of variation (< 10%). When evaluated using 50 clinical samples, FM-ICTS exhibited 97.5% concordance with the national standard RT-PCR method and accurately identified vvIBDV, clIBDV, and nVarIBDV strains. Overall, the developed FM-ICTS provides a rapid, sensitive, specific, and quantitative method suitable for field diagnostics and vaccine quality monitoring, supporting timely prevention and control of IBD.