Experimental study on histopathological changes and tissue tropism of Iranian infectious bronchitis serotype 793/B-like virus in SPF chickens.

Avian infectious bronchitis virus (IBV) is prevalent in all countries with intensive poultry flocks. This disease is characterised primarily by respiratory signs, but some IBV strains may also infect other organs such as the intestinal and urogenital tracts. The aim of this study was to characterise the histopathological lesions and tissue tropism of Iranian isolate IR/773/2001(793/B) of avian infectious bronchitis virus in different organs of experimentally infected SPF chickens. Forty-two one-day-old, specific pathogen-free (SPF) chicks were divided randomly into two groups (21 chicks to each group). At the age of 12 days, one group was inoculated intra-ocularly with 10(3) EID 50 of the 793/B isolate, and the other was kept as the control group. Tissue samples were collected at 2, 4, 6, 8, 10 and 12 days post-inoculation (PI). The IBV virus was detected in the caecal tonsils and cloaca from the 2nd to the 12th day PI. The virus was also detected in the kidneys from days 4-10 PI and in the bursa of Fabricius from days 4-12 PI. The virus was detected in the trachea, lungs and thymus. The most obvious histopathological lesions were found in the trachea, kidney, lungs and bursa of Fabricius. Amongst the lymphoid tissues, histopathological changes were found most frequently in the bursa of Fabricius. The results of this study indicated that the 793/B serotype of IBV is unlikely to cause mortality, severe clinical signs or gross lesions in infected chickens, but its replication in some tissues including the bursa of Fabricius could render birds susceptible to other micro-organisms.