Establishment of an Indirect Competitive ELISA for Detection of Antibodies against Goose Astrovirus Genotype 1 Based on ORF2 Protein.

Goose astrovirus genotype 1 (GAstV-1) is a major causative agent of visceral gout in goslings, leading to substantial economic losses across Chinese poultry farms. Currently, no commercial vaccine is available, rendering early serological surveillance essential for disease control. In this study, a sensitive and specific indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed using a monoclonal antibody (mAb) targeting the ORF2 capsid protein of GAstV-1. Following optimization of antigen coating concentration, serum dilution, mAb concentration, and incubation time, the assay demonstrated a detection limit at a serum dilution of 1:160 and showed no cross-reactivity with antisera against other avian pathogens, including H9N2 avian influenza virus (H9N2-AIV), avian reovirus (ARV), goose parvovirus (GPV), goose astrovirus genotype 2 (GAstV-2), and Tembusu virus (TMUV). The cutoff percent inhibition (PI) value was established at 25%, based on 40 GAstV-negative sera. Intra- and inter-assay coefficients of variation (CV) ranged from 0.41-0.88% and 3.12-6.95%, respectively, confirming excellent reproducibility. Evaluation of 35 clinical serum samples revealed an 88.6% (31/35) concordance with virus neutralization tests (VNT), with a kappa value of 0.77. These findings indicate that the ORF2-based ic-ELISA is a reliable, cost-effective, and high-throughput tool for seroepidemiological investigation and post-vaccination monitoring of GAstV-1 in geese.