Experimental study on tissue tropism of Iranian isolate of infectious bronchitis serotype 793/B in SPF chickens

Avian infectious bronchitis virus (IBV) is an important pathogen in poultry flocks, that primarily induces respiratory diseases, but different IBV strains may also affect the other tissues. The aim of this study was to investigate the tissue tropism of avian infectious bronchitis virus strain 793/B in experimentally infected SPF chickens by RT-PCR and Nested-PCR assays. In this study, tissue dissemination of Iranian isolate IR/773/2001(793/B) of IBV in different organs of SPF chickens was studied. Forty two one-day-old SPF chicks were divided randomly into two groups (21chicks per group). At the age of 12 days old the chicks in group1 were inoculated intra-ocularly with 103EID50 of the 793/B isolate, and group2 was control group. The samples from various tissues were collected at 2, 4, 6, 8, 10 and 12 days post-inoculation (PI). The chicks of infected group exhibited depression at 2 to 4 days PI. The IBV virus was detected in the cecal tonsils and cloaca from days 2-12 PI. Also virus detected in kidneys from days 4-10 PI, and in Bursa of fabricius from 4-12 days PI. In the trachea virus was detected on days 2 and 4 PI and in thymus samples virus was detected on days 6 and 8 PI. The positive sample from the lungs only was at day 4 PI. The results of this study indicated that the 793/B serotype of IBV cannot cause mortality, sever clinical signs or gross lesions in infected chickens, but its replication in some tissues could expose birds to other micro-organisms.