Abstract

Alaska has two genetically distinct populations of Steller sea lions (Eumetopias jubatus): the eastern and western stocks that are listed under the Endangered Species Act as threatened and endangered, respectively. During the course of multidisciplinary studies on free-ranging, live-captured and released pups and juveniles, two animals were found to have skin lesions consistent with active poxvirus infection. Both animals were from Prince William Sound, and part of the western stock. Both were females in poor body condition at two and five months of age. Hematologic indices were within normal limits. In the two-month-old animal, raised, umbilicated and occasionally ulcerated nodules were present primarily on the foreflippers. In the second animal, similar lesions were present over extensive areas of the body. These lesions were biopsied, one half placed in 10 percent buffered formalin, the other half frozen on dry ice, then stored at -70°C. Histologically, the lesions were very similar and consistent with poxviral infection, including epithelial cell proliferation with nodule formation in the dermis and presence of intracytoplasmic inclusion bodies within these epithelial cells. Viral cultures were unsuccessful. Skin biopsies were analyzed by polymerase chain reaction for poxvirus DNA using two sets of consensus primers that target highly conserved regions within the DNA polymerase and the DNA topoisomerase genes of capripoxvirus and swinepox virus. These yielded fragments of 543-bp and 344-bp, respectively. Both fragments were sequenced, and their deduced amino acid sequences were aligned and compared to homologous sequences of other chordopoxvirinae available in the GenBank database. The homologous nucleotide sequences derived from the skin lesions of both animals were identical. The deduced amino acid sequence of the Steller sea lion poxvirus DNA polymerase gene fragment was aligned and compared with homologous sequences of camelpox, capripox, smallpox, swinepox and vaccinia viruses, and their identity varied between 71.7 and 77.2 percent. When the DNA topoisomerase amino acid sequence was aligned and compared to the homologous sequence of the same viruses, the identities varied between 75.4 and 79.8 percent. These results indicate that the Steller sea lion poxvirus involved in these clinical cases is a member of the chordopoxvirinae subfamily of poxviruses.

Acknowledgements

The authors would like to thank Tom Gelatt, Lorrie Rea and the capture crews of the Alaska Department of Fish and Game for making collection of these samples possible. We would also like to thank Chris Terzi of University of Alaska, Fairbanks for her assistance with collecting samples and photography. These samples were collected under the Alaska Department of Fish and Game National Marine Fisheries Service (NMFS) Scientific Research Permit Number 358-1564-00.