The Immunogenic Potential of an Inactivated Vaccine Candidate against Ornithobacterium Rhinotracheale in SPF Chicken

Ornithobacterium rhinotracheale (ORT) is a gram-negative bacterium causing respiratory infection in chickens and turkeys. Co-infection of ORT with other viral or bacterial pathogens leads to severe clinical symptoms and great economic losses. The percentages of ORT strains resistant to the current antibiotics used in flocks have increased in successive years depending on the source of the isolate. Administration of the inactivated whole-cell vaccine (bacterin) is recommended against multi-drug resistant strains of ORT circulating in poultry farms. In the present study, a formalin-inactivated bacterin formulated with an oil adjuvant was developed based on a local ORT isolate. A prime-boost regimen was applied for the immunization of specific pathogen-free chicken (SPF) groups. Then the immunogenic potency of the vaccine candidate was evaluated by ELISA and compared with a commercial inactivated ORT vaccine. Vaccine safety was studied following inoculation twice the recommended dose of the prepared bacterin. The commercial inactivated ORT vaccine as well as the prepared bacterin induced specific antibodies after three weeks of primary vaccination that were continued to ۱۶ weeks post-vaccination. Immunization of chickens with the commercial vaccine induced a higher level of antibody compared to the experimental vaccine, however, no significant difference (P<۰.۰۵) was overall observed between the treated groups. In the safety test, no adverse local or systemic reactions were found in chickens throughout the post-vaccination period. Based on the data, the prepared ORT-inactivated vaccine is safe and can induce adequate and long-lasting immune responses in experimental SPF chickens. Results of field trials are necessary to ensure the effectiveness of this vaccine candidate against ORT infection.

Keywords:

Ornithobacterium rhinotracheale , ۱۶S rRNA , Inactivated vaccine , Immune response , ELISA