Light and electron microscopical observations were carried out on biopsy material obtained from human orf. In hematoxylin-eosin-stained sections, there were severe keratinocyte degeneration and heavy dermal inflammatory infiltration. Viral particles in electron microscopical preparations were found only in the cytoplasm of degenerating keratinocytes. Neither inclusion bodies nor virions were found in the nuclei of affected keratinocytes. An intriguing observation, not, to our knowledge, previously reported in human orf, was the presence of elongated virions with central narrowing and bending of the elementary bodies in ultrathin sections.
Yeh H, Soltani K. Ultrastructural Studies in Human Orf. Arch Dermatol. 1974;109(3):390-392. doi:10.1001/archderm.1974.01630030048012