An Indirect ELISA for Diagnosing Duck Short Beak and Dwarfism Syndrome

Objective A rapid serological method was developed for detecting antibodies against the Short Beak and Dwarf Syndrome Virus (SBDSV) in ducks.

Methods The epidemic strain M15 of SBDSV was purified by sucrose density gradient centrifugation and inactivated to be used as the solid-phase coating antigen. After optimization of reaction conditions, a highly specific indirect enzyme-linked immunosorbent assay (ELISA) was developed and verified by testing for assay specificity, repeatability, and accuracy on clinic specimens for detecting the specific antibody in ducks.

Results The optimal ELISA analytical conditions included the uses of antigen at the concentration of 0.1 mg·mL⁻¹, coating the antigen at 37 ℃ for 2 h followed by incubation overnight at 4 ℃ and blocked with 1% BSA at 37 ℃ for 2 h, serum dilution at the rate of 1∶200, and 0.3214 as the positive/negative cutoff point. The newly developed assay exhibited high specificity with no cross-reactivity on other common waterfowl viruses. It was highly sensitive as shown by remaining positive on hyperimmune serum (with an LPAI titer of 2⁸) up to 1∶204 800 dilution. The repeatability on the intra- and inter-assays was high with coefficients of variation below 6%. On 70 serum specimens of ducks suspected of SBDSV infection, the assay delivered 90% of the results agreed with those obtained by LPAI. On the 648 serum samples of 1-day-old ducklings submitted for testing in Fujian, an antibody positivity rate of approximately 48.30% was detected by the new assay indicating some degrees of SBDSV infection on the birds at duck farms in the province.

Conclusion The indirect ELISA for detecting SBDSV serum antibodies newly developed in this study could facilitate a rapid and effective monitoring means on epidemic SBDSV in the country and, in general, provide a technic support for the detection of the viral infection in ducklings.