Abstract
Northern elephant seals (Mirounga angustirostris) can be found on the offshore islands and along the coast of central California during their breeding and molting seasons.1 These phocids were hunted almost to extinction by the early 20th century, and the population has since rebounded and now includes approximately 150,000 individuals. The population may be increasing at a rate of 6% annually.2
The Marine Mammal Center, a rehabilitation facility in central California, admits approximately 100 elephant seals pups each year for treatment. Ten weaned pups died between 1998 and 2002 with ulcerative lesions on the tongue or palatine mucosa and inflamed tonsils. The causes of death identified included verminous pneumonia and arteritis due to Otostrongylus circumlitus infection, as well as endotoxemia secondary to acute enterocolitis. Histologic examination of the oral ulcerative lesions revealed eosinophilic to amphophilic intranuclear inclusions bodies suggestive of a herpesviral infection. Electron microscopic examination supported the presence of a herpesviral infection characterized by nonenveloped intranuclear 90–110 nm diameter icosahedral nucleocapsids that occasionally contained central dense core, and enveloped extracellular virions were detected. Polymerase chain reaction, using previously published degenerate primers on samples collected from three of these animals, detected the presence of herpesviral DNA in these tissues.3 An elephant seal herpes-specific primer pair was then developed to further analyze samples collected from elephant seals. This molecular analysis showed that the new herpesviral isolate was most similar to three viruses: an unidentified herpesvirus from a black rhinoceros, Chlorocebus rhadinovirus-1 from African green monkeys, and Alcelaphine herpesvirus-1 (malignant catarrhal fever virus from wildebeest). This places the elephant seal herpesvirus in the gamma-herpesvirus subgroup.
Identical herpesviral DNA was also detected in blood and mucosal swabs collected from five healthy pups that were released. These data suggest that this gamma-herpesvirus can be found in the secretions and tissues from healthy elephant seals as well as in ulcerative lesions. Therefore, further work needs to be done to understand the epidemiology and pathogenicity of this infection in northern elephant seals.
Acknowledgments
We would like to thank the staff, volunteers and interns from The Marine Mammal Center for help collecting samples, especially Denise Greig, Marty Haulena and Christy McKnight. We are also grateful to the residents and pathologists at UC Davis and AFIP for assisting in the histopathologic examination of tissues, especially Katie Colegrove. Thanks to Brian Aldridge and Ken Jackson for help with the phylogenetic analysis. Samples were collected under the authority of Marine Mammal Protection Act permit number 932-1489-00.
Literature Cited
1. Stewart, B. S., and H. R. Huber. 1993. Mirounga angustirostris. Mam. Spec. 449:1–10.
2. Stewart, B. S., Yochem, P. K., Huber, H. R., DeLong, R. L., Jameson, R. J., Sydeman, W. J., Allen, S. G. and LeBoeuf, B. J. 1994. History and present status of the northern elephant seal population. In: LeBoeuf, B. J. and Laws, R. M. (eds.): Elephant Seals: Population Ecology, Behavior and Physiology. University of California Press, Berkeley, pp. 29–48.
3. VanDevanter, D. R., P. Warrener, L. Bennett, E. R. Schultz, S. Coulter, R. L. Garber and T. M. Rose. 1996. Detection and analysis of diverse herpesviral species by consensus primer PCR. J. Clin. Micro. 34: 666–1671.