Pathogenesis of Ornithobacterium rhinotracheale in egg-laying hens with coexisting infectious bronchitis virus and Escherichia coli infections

Ornithobacterium rhinotracheale (ORT) is recognized as an important respiratory pathogen in turkeys and chickens. The severity of the disease is worsened when birds have coexisting infections with other respiratory pathogens. The objectives of this study were to investigate the pathogenesis of ORT infection with exposure to infectious bronchitis virus (IBV), Escherichia coli, or both in laying chickens. A total of 160 eight-week-old specific pathogen-free White Leghorn chickens were exposed experimentally to 1 of 7 treatments: ORT alone; E. coli alone; IBV alone; ORT + E. coli; ORT + IBV; IBV + E. coli; or ORT + IBV + E. coli. The clinical signs and pathological changes were evaluated in birds from all groups. Birds exposed to ORT or E. coli alone did not show any overt clinical signs. Birds exposed to IBV, ORT + IBV, IBV + E. coli, and ORT + IBV + E. coli exhibited clinical signs that varied from depression and nasal discharge to mortality. The ORT + IBV + E. coli-infected birds exhibited gross lesions, which included hemorrhagic tracheitis, fibrinous pneumonia, airsacculitis, pericarditis, and peritonitis. Histopathological studies of this group revealed distinct pathological changes. Immuno-histochemistry staining demonstrated the presence of ORT antigens in the tracheas and lungs of the ORT + IBV + E. coli-infected birds. Mortality after ORT infection was noticed only in the ORT + IBV + E. coli group. We conclude that IBV and E. coli infections exacerbate ORT pathogenesis in adult laying hens. We also conclude that ORT persists in tissues such as the infraorbital sinuses for longer periods without causing significant respiratory disease by itself. This presence of ORT may predispose birds to the development of peritonitis and death with subsequent IBV and E. coli coinfections.