Early stages of infectious bursal disease virus infection in chickens detected by in situ reverse transcriptase-polymerase chain reaction

Two infectious bursal disease virus (IBDV) strains were inoculated both intranasally and by eye drop into 5-week-old specific pathogen free chickens. The bursa, the liver, the kidney, the spleen, the thymus, the caecal tonsil and the thigh muscle were harvested at 4, 8, 16, 28, 40, 56, 72, 96 h post-inoculation (p.i.) for IBDV detection by in situ reverse transcriptase-polymerase chain reaction and, at the same time, the pathological changes in these tissues were investigated. A typical positive signal was detected in the liver, the kidney and the spleen of chickens inoculated with the very virulent IBDV H strain at 4 h p.i., but not in the thymus, the caecal tonsil or the thigh muscle until 8 h p.i. Virus was also found in the liver, the spleen, the kidney, the thymus, the caecal tonsils and the muscle of birds inoculated with the cell-adapted Ts strain at 4 h p.i. A positive signal was observed in the bursa later than in the other tissues. The signals increased markedly at 8 h p.i. A decrease in bursal lymphocytes was observed in haematoxylin and eosin stained sections at 28 h p.i. for the H strain and at 40 h p.i. for the Ts strain.