This study was designed to investigate clinical and pathologic characteristics of acute and subacute lumpy skin disease (LSD) among naturally infected cattle and to study the localization of LSDV capsid antigen within the different cells of the skin and regional lymph nodes using immunohistochemistry. Herein, we describe the gross, histologic, and immunohistochemical findings in 13 dairy cattle, 11 beef calves and 2 newly born calves that were naturally infected with LSDV.  Prominent gross changes in all cases included numerous 1-6 cm well circumscribed, round cutaneous nodules with severe enlargement of superficial lymph nodes. Histologic changes in all acute cases consisted of severe ballooning degeneration of the epidermis, lymphoplasmacytic dermatitis, folliculitis, furunculosis, with severe vasculitis affecting the dermal capillaries, venules, and arterioles.  Rare intracytoplasmic inclusions were present in degenerated epidermal cells. Subacute cases showed multifocal areas of pannicular infarction with severe vasculitis affecting the neighboring arterioles and venules.  Strong positive immunoreactivity for LSDV was identified primarily within macrophages and in degenerated epidermal cells. However, no viral antigen was present in endothelial cells. It can be concluded that vasculitis is a constant lesion in acute and subacute LSD and is most likely of an immune-mediated mechanism rather than a true tropism of the LSDV to endothelial cells.

Key words: Capripoxvirus, Egypt, Immunohistochemistry, Lumpy skin disease, Pathology, Vasculitis