Evaluation of the Razi Ornithobacterium rhinotracheale Vaccine by Experimental Challenge System Using LaSota Strain

BACKGROUND Ornithobacterium rhinotracheale (ORT) is a remarkable pathogen in the world poultry industry. The vaccine against this agent is used in poultry farms to prevent infection and reduce the incidence of disease. OBJECTIVES: In the present study, the efficacy of the first Iranian inactivated ORT vaccine produced by the Razi Vac-cine and Serum Research Institute was evaluated using the experimental challenge system . METHODS: Ninety day-old specific-pathogen-free White leghorn chickens were divided randomly into five groups of 18 chickens. The birds were housed in separate specific cages in isolation rooms. At the age of 14 days, the birds of two groups were vaccinated. Afterwards, at the age of 42 days, two groups of unvaccinated chickens and all of the vaccinated subjects were challenged with the LaSota strain of Newcastle Disease Virus (NDV) and ORT. One group of unvaccinated birds was maintained as the negative control. Blood samples were taken from chickens on days 14 (before vaccination) and 42 (before challenge) of the experiment. In addition, blood samples were collected on days 2, 4, 6, 8, 10, and 12 after the challenge (AC). On days 2, 4, 6, 8, 10, and 12 after challenging with ORT, the isolation and molecular detection of the bacteria were performed on samples from the trachea, lungs, air sacs, liver, and spleen. RESULTS: Following vaccination with the Razi ORT vaccine, the titers of antibody in vaccinated chickens were shown to be significantly higher than those of unvaccinated birds. In vaccinated groups, the ORT was not recovered in cultures from lungs, trachea, and air sacs. In the unvaccinated birds challenged with ORT, bacteria were isolated from lungs, tra-chea, and air sacs. Using the polymerase chain reaction method, ORT was only detected from samples of lungs, trachea, and air sacs 2 days after challenge (DAC) in vaccinated groups. Meanwhile, ORT was detected in lungs, trachea, and air sacs until 4 days after challenge in unvaccinated birds. CONCLUSIONS: We concluded that the Razi ORT vaccine was effective in protecting layer chickens against infection with serotype A of the ORT.