Abstract

Southern sea otters (Enhydra lutris nereis) are a threatened subspecies in California, and are sympatric with pacific harbor seals (Phoca vitulina richardsi). Since 1992, complete sea otter necropsies have been performed by Nancy Thomas and colleagues at the National Wildlife Health Center, who determined that protozoal encephalitis was present in 8.5% of all sea otters received for necropsy¹. These intracellular protozoal parasites had never before been recognized as a significant cause of mortality in sea otters. During this same period protozoal brain infections were also recognized as an important cause of mortality in adult harbor seals at The Marine Mammal Center in Marin, California². Starting in May of 1998, a collaborative project was initiated to study protozoal encephalitis in sea otters and harbor seals. Complete necropsy and histopathologic examination of otters and seals was coupled with immunohistochemistry for the protozoal parasites Toxoplasma gondii, Sarcocystis neurona and Neospora caninum. We inoculated homogenates of brain tissue into cell culture in an attempt to isolate parasites associated with encephalitis. Resulting isolates were maintained in continuous cell culture. Parasite isolation was attempted using brain tissue from 19 different otters, and 9 isolates were obtained. Only one harbor seal was submitted for necropsy in 1998. However, protozoal parasites were successfully isolated from brain tissue from this animal. Current efforts are focused on the genetic, serologic and ultrastructural characterization of these isolates, and investigating the relationship between protozoal infection and protozoal disease. Additional goals will be to identify risk factors for infection and disease and to develop tests for serodiagnosis and epidemiologic investigation.

Acknowledgments

Partial funding for this project was obtained from the California Department of Fish and Game and the Genetic Resource Conservation Program at U.C. Davis. Dr. Chechowitz's travel costs were covered in part by a scholarship from the Wildlife Disease Association.

References

1.  Thomas NJ, RA Cole. 1996. The risk of disease and threats to the wild population. Endangered Species UPDATE 13(12) 23-27.

2.  Lapointe JM, Padraig J, Marsh AE, Gulland FM, Barr BC, Naydan DK, King DP, Farman CA, Burek Huntingdon KA, Lowenstine LJ. 1998. Meningoencephalitis due to Sarcocystis neurona-like protozoan in Pacific harbor seals (Phoca vitulina richardsi). J. Parasitol. 84(6) 1184-1189.