On June 2005, a respiratory disease was observed in the chickens of a large broiler farm in Kermanshah
province, west of Iran. Relatively severe respiratory signs started with sneezing at 27 days of age. The
disease lasted up to the end of fattening period and accompanied by increased mortality (13.6%). At postmortem
examination, tracheitis, airsacculitis and pneumonia were obvious. Serologic examinations were
negative for Mycoplasma gallisepticum and Mycoplasma synoviae. On virologic examinations, virulent
infectious bronchitis virus (IBV), avian influenza virus (AIV) and virulent Newcastle disease virus (NDV)
could not be isolated. Histopathologic examinations showed no pathognomonic lesion typical for infectious
laryngotracheitis. On bacteriologic examinations, Ornithobacterium rhinotracheale (ORT) was isolated from
trachea, lungs and air sacs of the affected birds. Based on clinical, post-mortem and laboratory findings, ORT
could be probably the primary cause of respiratory disease on this farm