Development and comparison of challenge models for three serovars of Avibacterium paragallinarum.

Infectious coryza (IC), caused by Avibacterium paragallinarum (Av. paragallinarum), imposes a substantial economic burden on global poultry production. This study established and standardized comparative challenge models employing infraorbital sinus injection and intranasal inoculation to evaluate the pathogenicity of Av. paragallinarum serovars A, B, and C in SPF chickens. Infraorbital sinus injection leads to rapid onset, stable incidence, and more severe disease progression. The clinical symptom scores at 1 days post-infection (dpi) were higher in the infraorbital sinus injection group compared to the intranasal inoculation group. Additionally, the clinical symptoms in the 2019/JS31 (serovar B) and 2020/JS80 (serovar C) groups were more severe than those in the 2019/HB64 (serovar A) group. The disease progression in the intranasal inoculation group was more prolonged, with slightly higher clinical symptom scores at 7 dpi compared to the infraorbital sinus injection group. The trends in gross lesions and histopathological lesions were consistent with the clinical symptoms. Bacterial shedding results indicated that the infraorbital sinus injection group exhibited higher bacterial shedding than the intranasal inoculation group, demonstrating a dose-dependent relationship. The 2020/JS80 (serovar C) group had slightly higher bacterial shedding than the 2019/HB64 (serovar A) and 2019/JS31 (serovar B) groups. In all groups, bacterial shedding peaked at 5 dpi. This study provides a basis for investigating the mechanisms of pathogenesis in IC and the disease mechanisms associated with different serovars.