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In this study we have used [he three pathogenic strains of IBV having respiratory and renal (M 41, Holte and Australian T strains). Although similar gross lesions, which are congestion and oedem, were observed in kidneys, significant differences were observed in the period of development, severity and the appearance of the histopathological findings in different strain groups. In our study, on the acut phase it was also observed that M41 strain caused severe lesions in the respiratory system and also diffuse lesions characterised with nephrosis in kidneys. While Holte and Australian T strains caused mild lesions in the respiratory system on the acut phase, in kidney it was observed that Australian T strains caused more severe tubuler and interstitial diffuse lesions characterised with nephritis-nephrosis than Holte strain.
On the acut phase it was observed microscopical kidney lesions started with vacuolisation in the tubular epithelium around glomeruli and in medulla and nephrosis characterized with granular degeneration and changes from the necrosis of the tubular epithelium until their desquamation, and than changes to interstitial nephritis in a short time. While interstitial nephritis characterised with edema in the intertubular area and dense inflammatory cell infiltrations were observed in only a few chicks of the M 41 strain group, it was observed milder in Holte strain group and severe in the Australian T strain group.
In the chronical phase, reticulum formations started around cell infiltrations and transformed lymphoid nodules as permanent focal areas and localised in medullar zone were observed to be active type of chronical interstitial nephritis in Australian T strain group. This lesions were observed similar to inactive form in only a few animals in Holte and M 41 strain groups.
Under the light of these lesions; it is thought to be also effective in differentiation of virus strains when microscopical lesions of respiratory and urinary tract of IB is considered together.