Determining Pathogenicity of Infectious Bronchitis Virus Isolated in Korea 2018

Infectious bronchitis virus (IBV) is an acute respiratory disease, causing economic losses in poultry production. IBV commonly manifests respiratory disease symptoms and poor egg quality in poultry, affecting overall performance of both broilers and layers. IBV infection further predisposes poultry to secondary opportunistic bacterial infections. IBV undergoes rapid genetic evolution resulting in various new strains. There is no cross protection among IBV serotypes which makes full protection against wild-type IBV virtually impossible. In this study, recently isolated IBVs (K24/18, K29/18, K183/18) from Korean broiler farms were genetically analyzed based on S1 gene. According to the results, IBV isolates showed highest homology with QX-IBV. However, phylogenetic tree analysis revealed that isolates were divided into distinct sub-clusters within QX-IBV. To determine pathogenicity of IBV, day-old chicks were challenged with IBV through ocular route. After challenging the chicks, we executed microscopic examination, virus detection in their organs, and observation of clinical signs and mortality. We found that the K24/18, K29/18, K183/18 challenge groups showed 28%, 57%, and 42% mortality, respectively, with high microscopic trachea lesion scores, indicating that these QX-IBV-like strains are pathogenic to chicks and can therefore be a threat to poultry production.