An Experimental Study of Histopathological Lesions Caused by H9N2 Subtype of Avian Influenza Virus and Ornithobacterium Rhinotracheale Co-Infection

Avian influenza virus H9N2 subtype and Ornithobacterium rhinotracheale (ORT) causes histopathological lesions in birds. Yet, there is not any study on tissue lesions caused by these pathogens co-infection in specific pathogen free (SPF) chicks. The aim of this study was to evaluate the type, severity and extent of histopathological lesions induced by co-infection of H9N2 subtype avian influenza virus and Ornithobacterium rhinotracheale in SPF chickens. Sixty, one-day-old SPF chicks were divided randomly into three groups of twenty. At 21 days, the chicks in the first group were infected with H9N2 subtype AI virus and the second group was inoculated with H9N2 subtype AI virus and ORT simultaneously. The third group was inoculated with PBS as control. Then, three birds from each group were randomly selected and euthanized and autopsied at 2 till 16 days post-inoculation (DPI). The tissue samples were collected from trachea, lungs, liver, spleen, thymus, kidneys, cecal tonsil and bursa of fabricius. They were cut into 5 to 6 μm thickness sections using paraffin embedding method and were stained by Hematoxylin and Eosin (H&E). The severity of histopathological lesions in the second group was higher than first group. Tissue changes were not observed in control group. The results of this study showed that infected chickens with H9N2 subtype AI virus and ORT simultaneously cause exacerbated histopathological lesions compared to H9N2 subtype of AI virus