September 20, 2019 – About a decade ago, researchers noticed that infectious diseases were responsible for more than 40% of all sea otter deaths. One of the diseases noted was caused by a parasite, Toxoplasma gondii. The parasite caused brain infections and deaths and was contributing to further population declines in already threatened California sea otters.
The odd thing was that the organism has only one definitive animal host – cats. So how did the parasite get from land-bound cats to ocean-loving sea otters? In 2003, Morris Animal Foundation-funded researchers at the University of California, Davis, the California Department of Fish and Game, and the University of British Columbia School of Medicine were about to find out.
With a grant from Morris Animal Foundation, this collaborative team identified a unique strain of T. gondii in sea otters along the central California coast. This strain could be found in 70% of the T. gondii cases studied throughout the sea otters’ range.
The next question was were there any wild or domestic cats with the same unusual strain residing along the central coast of California? If so, could T. gondii reach threatened sea otters through contaminated freshwater runoff into the ocean – the suspected route of contamination? For the answer, the team tracked telltale signs and the trail of oocysts, the infectious form of the parasite shed in cat feces.
The group found evidence of the T. gondii strain in a few domestic cats. However, more definitive data was collected in two mountain lions, a bobcat and a red fox. These animals lived immediately upstream of nearshore watersheds and in the center of the southern sea otter range. They also identified the T. gondii strain in a wild mussel collected along the shoreline, located downstream of the Salinas river. The Salinas river is the largest watershed in central California and an area with heavy freshwater runoff and a large population of domestic and wild cats living nearby.
These findings supported the theory that sea otters were most likely infected with T. gondii via fecal-polluted terrestrial-to-marine runoff. Early data suggested the most efficient route for infection was sea otters eating some of their favorite foods, filter-feeding invertebrates. Mussels infected with T. gondii oocysts became concentrated sources of sea otter infection.
Thanks to this boots-on-the-ground research, findings from the study were critical in guiding management policies for sea otters and helped lead to public awareness campaigns on the importance of keeping cats indoors and properly disposing of their waste. Study findings also influenced the passage of California legislation that increased legal protection of the species as well as a law banning the use of flushable kitty litter. Flushable kitty litter is another route for the parasite to enter watersheds through treatment facility wastewater.
Other Threats to Otters
Another disease threat to sea otters is phocine distemper virus. With Morris Animal Foundation-funding, University of California, Davis, researchers identified, for the first time, the virus as the cause of sea otter deaths in Alaska. This was the first confirmation of phocine distemper in marine mammals in the Pacific Ocean. The movement of the virus was likely due to changes in migration patterns resulting from decreases in the ice pack caused by climate change. This allowed seals usually residing in the Atlantic Ocean to carry the virus to a new region and help spread the disease to new species. The virus is now considered to be an emerging health threat to sea otters and other marine mammals in the Pacific Ocean.
Cardiomyopathy, a disease of the heart muscle, is a newly recognized and also an important cause of death in Southern California sea otters. Risk factors for cardiomyopathy in sea otters include exposures to the parasite S. neurona as well as domoic acid, a toxin produced by marine algae blooms. Current Foundation- funded cardiomyopathy research is assessing the impact of algae bloom exposure on California sea otter health.
Because otters are highly dependent on their niche aquatic ecosystems, they are susceptible to environmental disruptions. Since 1998, Morris Animal Foundation has funded nearly two dozen otter studies, many of which are associated with changing marine environments that are exposing otters to new health threats.