Molecular characterization of quail bronchitis virus isolated from bobwhite quail in Minnesota

Abstract

From 2008 to 2012, 4 separate cases of quail bronchitis virus infection were seen in bobwhite quail (Colinus virginianus) raised in Minnesota. The quail chicks ranged in age from 5 d to 8 wk and suffered from respiratory distress and elevated mortality. On necropsy, gross lesions consisted of mucus in trachea, congested lungs, caseous air sacculitis, accumulation of chalky white urates on internal organs, necrotic foci in liver, and enlarged spleen. Histologic examination revealed fibrinoheterophilic rhinitis, heterophilic bronchitis, heterophilic tracheitis, and interstitial pneumonia in addition to deciliation, desquamation, and necrosis of bronchial respiratory epithelium. Karyomegaly with basophilic intranuclear inclusions was also seen in affected epithelium. Severe epicarditis, pericarditis, myocarditis, multifocal necrotizing hepatitis, and splenitis were additional pathological findings. Quail bronchitis virus (QBV) was isolated from all four samples when inoculated in specific-pathogen-free (SPF) embryonated chicken eggs. The virus was confirmed by electron microscopy and polymerase chain reaction using fowl adenovirus (FAdV) hexon gene-specific primers. Nucleotide sequences of the four isolates showed 99.0% identity with CELO strain of fowl adenovirus A. Nine nucleotide substitutions were observed; 3 of these were nonsynonymous (A281G, C314T and G565C), leading to changes in deduced amino acid sequences (S94G, T105M and A189P, respectively). Based on partial sequence of the hexon gene, QBV isolates of this study clustered closely with fowl adenovirus A and were different from FAdV groups B through E and from adenoviruses of goose, duck, turkey, and pigeon. Further studies are indicated to determine the impact of nonsynonymous substitutions on host specific pathogenicity of these viruses.