Abstract
During ultrahistological investigations of naturally occurring cases of stomatitis papulosa in cattle and Orf in sheep, nuclear changes consisting of aggregations of double membrane-containing tubular structures (outer diam. 100 to 130 nm, inner diam. 50 to 65 nm) and filamentous material were observed. These changes could be reproduced in vitro after infection of bovine (BEL) and ovine (OEL) embryonic lung cell cultures with stomatitis papulosa virus and Orf virus isolates. Nuclear tubules were mostly associated with stomatitis papulosa, whereas filaments were regularly detected in Orf virus infections in vivo. Stomatitis papulosa virus also induced nuclear tubules in vitro in the two cell culture types employed, whereas tubular structures after Orf virus infection only developed in ovine embryonic lung cell cultures in addition to filamentous structures. Orf virus infection of BEL cell cultures induced the formation of filaments. Fluorescent antibody staining revealed parapoxvirus-specific antigens only in the cytoplasm of infected cells.