In recent years, wildlife veterinarians have become concerned about the increasing number of southern sea otters dying in California. The current otter population is 10 percent lower than it was in 1995. Disease has been identified as one reason. Two species of protozoa, Toxoplasma gondii and Sarcocystis neurona, have been identified as important causes of fatal brain infections in these otters.
To understand the rise in sea otter deaths, scientists from the Wildlife Health Center in the UC Davis School of Veterinary Medicine joined colleagues from other agencies to investigate potential sources of Toxoplasma contamination.
In a study published in the July issue of the International Journal for Parasitology, the scientists compiled environmental, demographic, spatial and serological data for 223 live and dead California sea otters tested between 1997 and 2001. Using a new diagnostic test developed by UC Davis scientists, the authors found that 42 percent of live otters and 62 percent of dead otters were infected with Toxoplasma. Their study suggests that land-based freshwater runoff is a source of Toxoplasma infection for sea otters.
Cats are the only animals known to shed oocysts, which are the tough, environmentally resistant eggs of Toxoplasma parasites, in their feces. However, the connection between land-loving felines and sea otters puzzles researchers.
Before analyzing their data, lead author Melissa Miller and her co-authors at UC Davis, the California Department of Fish and Game, the Central Coast Regional Water Quality Control Board and the Bay Foundation of Morro Bay theorized that sea otters might be exposed to Toxoplasma through both freshwater runoff and municipal waste (sewage), from cat feces flushed down toilets. Primary and secondary sewage treatment may
Contact: Pam Kan-Rice
University of California - Division of Agriculture & Natural Resources