An experimental study of histopathological lesions of secondary infection with H9N2 avian influenza virus following inoculation by Ornithobacterium rhinotracheale in SPF chickens

The purpose of this study was to evaluate the type, severity and extent of tissue lesions induced by secondary infection with avian influenza virus following inoculation by ORT in SPF chickens. Sixty, one-day-old SPF chicks were provided and divided randomly into three groups. At the age of 21 days, the chicks in the first group were inoculated only with ORT and second group inoculated first with ORT and three days later with H9N2 virus. Each bird in third group was received only with PBS as control. Tissue samples were taken from trachea, lungs, liver, kidneys, bursa of fabricius, thymus, spleen and cecal tonsils for histopathological studies and after preparation and tissue sections were stained by Hematoxylin and Eosin (H&E) method. In chickens of the first group, ORT bacteria in addition to cause tissue lesions in organs of the respiratory system (loss of cilia with infiltration of mononuclear cells under the mucosa in the trachea, hyperemia and pneumonia in the lung), liver (congestion of sinusoids and central veins) and the kidneys (Hemorrhage and necrosis of urinary tubes) in  immune system organs also cause tissue lesions such as lymphocyte depletion in the bursa of fabricius, congestion and heterophil infiltration in thymus and increase in the of lymphoid follicles in the spleen and cecal tonsils. The histopathological lesions in chickens of the second group was more severe and longer than that of the first group. Tissue changes were not observed in control group. The results of this study showed that in chickens inoculated by ORT and under secondary infection with avian influenza virus cause exacerbate and lunge histopathological lesions induced by ORT.