An experimental study on early pathogenesis of a very virulent isolate of infectious bursal disease virus, employing immunohistochemistry

In this study, immunohistochemistry was used to clarify the early stages of viral kinetics and cyclic course of IBDV, IR499, which has been described earlier as a very virulent strain (vvIBDV). Fifteen, 4-week-old SPF chickens were inoculated with 10³ EID50 of vvIBDV, IR499, via oculo/nasal route. Five birds served as controls, and inoculated with phosphate buffered saline (PBS). The birds were then bled, and tissue samples from bursa of Fabricius, cecal tonsils, liver, spleen, thymus and thigh muscle were harvested at 3, 6, 12, 24 and 48 h post-inoculation (p.i.). Typical positive signals were first observed as early as 3 h p.i. in lymphoid cells of cecal tonsils (the organ of primary affinity) and Kupfer cells of liver. Viral antigens in bursa were first found at 6 h p.i. which represents the occurrence of primary viraemia. After secondary viraemia, the virus appeared in spleen and thymus at 12 h p.i. These findings at early stages of viral infection, represented IBDV, IR499, as a very virulent strain with a rapid and generalized course, at in vivo level.