Occurrence of pox in a northern fur seal on the Pribilof Islands in 1951.

The presence of pox in a northern fur seal pup, Callorhinus ursinus, examined at necropsy on the Pribilof Islands, Alaska, 13 September 1951 was confirmed by re-examination of formalin-fixed tissues collected at that time. The disease was characterized by multiple 3 to 8 mm modules in the skin of the nose and flippers. Unlike pox lesions in other pinnipeds studied so far, the nodules were discrete dermal epitheliomas free of any direct connections with the overlying atrophic epidermis. They most likely arose from outer sheath cells of hair follicles. The tightly packed epithelial cells forming the nodules contained large, round, eosinophilic, intracytoplasmic inclusion bodies. As demonstrated by electron microscopy nearly 27 years after the tissues were fixed in formalin, poxvirus virions also were present in these cells. These findings indicate pox was present in a northern fur seal, hitherto undescribed in that species, 18 years before the disease was first reported in pinnipeds.