Abstract
Nephritis in chickens caused by infectious bronchitis virus (IBV) was studied by virological, histological and electron microscopical methods. The T strain of the virus caused only mild respiratory signs in both Rhode Island Red (RIR) and White Leghorn (WL) breeds; the 50 per cent mortality induced was due to acute nephritis. All the infected birds developed high titres of antibody to IBV for up to 30 weeks. In spite of the persistence of antibody, about 35 per cent of the RIR developed chronic progressive nephritis. The histology showed varying degrees of pathological changes in the tubules, with relatively unaffected glomeruli. Foci of mononuclear cell infiltration were prominent in the cortex and medulla, particularly in chronic nephritis. Cytoplasmic IBV immunofluorescence was found in all segments of the tubules, but not in the glomeruli. There was no evidence of virus replication in the caecal tonsil and bursa of Fabricius. Evidence of extensive coronavirus replication was found in the cells of the tubules. A large number of viral inclusion bodies as seen containing dark smooth particles 120 nm in diameter within a single membrane. Virus was readily recovered from the kidneys as well as faeces of birds with acute and chronic nephritis. It is concluded that direct virus-induced cell lysis is the primary cause of IBV nephritis. In addition, about 50 per cent of the chronically infected birds also developed brush-border auto-antibody.