Orf virus is a zoonotic, epitheliotropic DNA parapox virus that principally infects sheep and goats. The fact that the virus can repeatedly reinfect sheep has provoked an interest in the underlying cellular, virological and molecular mechanisms for its apparent escape from the host protective immune response. The local immune and inflammatory response in skin and the cell phenotype and cytokine response in lymph analysed around a single lymph node are characteristic of an anti-viral response. An unusual feature is the dense accumulation of MHC Class II+ dendritic cells in the skin lesion. The function of these cells is not known. Orf virus virulence genes and activities have been identified that may interfere with the development of the host protective immune and inflammatory response.