Synergistic Pathogenic Effects of Riemerella anatipestifer and Infectious Bronchitis Virus in Layer Chicks

In recent years, Riemerella anatipestifer (RA) has been detected with increasing frequency in layer chick flocks. RA infection can lead to reproductive tract lesions, including salpingitis. Epidemiological surveillance further indicates that RA infection often occurs as a co-infection with other respiratory pathogens, among which infectious bronchitis virus (IBV) is the most common. To elucidate the pathogenicity of chicken-derived RA and its synergistic effects with IBV, a serotype 10 RA strain and a GI-19 lineage IBV strain co-isolated from a layer chick with oviductal obstruction were used in animal experiments to compare disease outcomes following single infection and co-infection in layer chicks. The results demonstrated that IBV single infection caused typical clinical signs and pathological lesions characteristic of infectious bronchitis, but did not induce pericarditis, airsacculitis, or oviductal obstruction. By contrast, aerosol challenge with chicken-derived RA resulted in pronounced pericarditis, airsacculitis, and caseous salpingitis. Further co-infection experiments showed that IBV combined with chicken-derived RA exacerbated clinical signs and pathological lesions, suggesting a synergistic interaction between the two pathogens. This study confirms chicken-derived RA as a major primary pathogen in caseous oviductal obstruction of layer chicks, and demonstrates its synergistic pathogenic effects during IBV co-infection. These findings support the etiological diagnosis and targeted prevention and control of oviductal obstruction in layer chicks.