Abstract

Cutaneous pox-like lesions are a common complication in the rehabilitation of pinnipeds. However, the identity and taxonomy of pinniped poxviruses remain largely unknown. During a recent poxvirus outbreak in California sea lions (Zalophus californianus) at The Marine Mammal Center in California, multiple nodules from the head, neck and thorax of one deceased animal were collected. All biopsies were processed for routine histology, polymerase chain reaction (PCR) and virus isolation. Histologically, the nodules were characterized by epithelial hyperplasia, acanthosis, ballooning degeneration of the stratum spinosum and s. granulosum, and eosinophilic cytoplasmic inclusions in the s. granulosum. A poxvirus belonging to the genus Parapoxvirus was isolated from a tissue homogenate of a skin nodule following inoculation of early passage California sea lion kidney cells. The assignment of the sea lion poxvirus to the genus Parapoxvirus was confirmed via electron microscopy and molecular characterization, consisting of partial sequencing of the genomic region encoding the putative major virion envelope antigen p42K. Analogue sequences were also obtained from pox-like lesions of other California sea lions and other pinniped species of the east and west coast of North America. Thus far, two independent virus strains have been detected in California sea lions. A third strain was identified in harbor seals (Phoca vitulina) from the northeastern United States. All detected pinniped poxviruses belong to the genus Parapoxvirus. Comparative partial sequence analysis revealed that the pinniped poxviruses are significantly different from all other parapoxviruses.