Exploring the potential pathogenicity of Ornithobacterium rhinotracheale isolates, individually and in association with avian influenza virus infection

Ghodsian, Naser; Banani, Mansour; Shahsavandi, Shahla; Ebrahimi, Mohammad Majid

doi:10.22092/ari.2025.369907.3717

Exploring the potential pathogenicity of Ornithobacterium rhinotracheale isolates, individually and in association with avian influenza virus infection

Articles in Press

Document Type : Original Articles

Authors

¹ Razi Vaccine and Serum Research Institute, Agricultural Research Education and Extension Organization, Karaj, Iran.

² Razi Vaccine and Serum Research Institute, Agricultural Research Education and Extension Organization, Karaj, Iran

10.22092/ari.2025.369907.3717

Abstract

Ten field isolates of Ornithobacterium rhinotracheale (ORT) were studied for their pathogenicity in specific pathogen-free (SPF) embryonated chicken eggs and 71-day-old chickens. The lethal dose 50 (LD50) of each ORT isolate was determined by intraperitoneal injection of chickens with serial CFU dilutions from the bacterial samples. SPF embryonated eggs were inoculated through the allantoic sac at 11 days of age and monitored daily for 14 days. The ORT isolates appeared to be non-pathogenic, with only one strain showing low pathogenicity, resulting in a 10% mortality rate within 8 days post-infection. In another experiment, 71-day-old chickens were grouped based on the ORT isolates (Groups 1 to 10) and inoculated intratracheally with 1×1010 LD50 of each bacterial suspension. No obvious clinical signs were observed in live or necropsied chickens. At 3 days post-inoculation, birds from each group were divided into two equal subgroups. Subgroups (1A-10A) were inoculated with 106EID50 of H9N2 avian influenza virus (AIV) via eye drop and compared with the other subgroup (1B-10B). Within two weeks after inoculation, chickens given ORT+AIV exhibited slight depression, sneezing, and coughing. Histological examination revealed mild to severe hemorrhagic tracheitis, heterophil infiltration in the trachea, pneumonia with necrosis and mononuclear infiltration in the lung, and necrotic sinusitis with mononuclear cell infiltration. The average HI titer of the ORT+AIV subgroups was associated with early viral replication in the chicken respiratory tract. There were no mortalities in the ORT+AIV-infected chickens. Since chickens are less susceptible to ORT infection than embryonated chicken eggs, it is recommended to inoculate embryonated eggs as an alternative method to obtain more accurate pathological data.

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