ABSTRACT
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 10[3] EID[50] 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