Brain Parasite Killing California Sea Otters

Veterinary pathologists from the California Department of Fish and Game’s Marine Wildlife Care and Research Center have examined otters discovered sick or dead in the Morro Bay/ Pismo Beach area last April and have determined that the majority were infected with a single-celled parasite called Sarcocystis neurona. Most had enlarged lymph nodes and microscopic evidence of brain inflammation. Infective ”eggs” of Sarcocystis neurona are shed in the feces of the opossum (a non-native species in California). This parasite causes damage to the brain and other tissues of sea otters and is commonly fatal. From the California Department of Fish and Game :Scientists Determine April Sea Otter Deaths Were Associated With Brain Parasite, Sarcocystis neurona

Veterinary pathologists from the California Department of Fish and Game’s (CDFG) Marine Wildlife Care and Research Center (MWVCRC) have examined otters discovered sick or dead in the Morro Bay/ Pismo Beach area last April and have determined that the majority were infected with a single-celled parasite called Sarcocystis neurona. Most had enlarged lymph nodes and microscopic evidence of brain inflammation.

Infective ”eggs” of Sarcocystis neurona are shed in the feces of the opossum (a non-native species in California). This parasite causes damage to the brain and other tissues of sea otters and is commonly fatal. It also is associated with neurological disease in horses.

In April, scientists were puzzled when 62 southern sea otters were found stranded alive or dead along the California coast. This was roughly three times the 10-year average, and far more than the 48 dead or stranded otters found in April 2003, a previous record high. The majority of the sick or dead otters were recovered near Morro Bay and Pismo Beach between April 4 and April 21.

Sea otter deaths due to Sarcocystis neurona have been reported in previous years. However, the number of otter deaths this year greatly exceeds those in previous years, and localized clustering of Sarocystis neurona-infected otters has not previously been documented. Possible contributing factors are under investigation.

To date, affected otters have tested negative for several pathogenic viruses, including West Nile virus. The harmful algal bloom (HAB) toxin, domoic acid, may have contributed to the deaths of a few sea otters, and a second protozoal parasite, Toxoplasma gondii, may have also have contributed to the sea otter mortality. Sea otter mortality levels have declined in May to more normal levels (11 strandings through May 17). Further investigation of this Sarcocystis neurona-associated mortality event is in progress.

Many otters stranded alive during this period had clinical signs suggesting brain damage. Two sea otters which were stranded alive and sick during this period are being treated at the Monterey Bay Aquarium (MBA) and are responding to therapy. Dead sea otters were recovered by the sea otter stranding network, which is comprised primarily of DFG, USGS-Biological Resources Division, MBA and Marine Mammal Center personnel. Diagnostic support was provided by several laboratories at the University of California, Davis, School of Veterinary Medicine.

Sea otters are listed as threatened under the U.S. Endangered Species Act and their population levels seem to be holding steady, DFG officials said. Sea otter counts in 2003 estimated the population at 2,505 otters, and 2004 surveys are currently underway. The recent otter deaths in April represent approximately 2 percent of the wild population of southern sea otters in California.

Persons finding beached sea otters are encouraged to contact the Marine Mammal Center at (415) 289-7325, the Monterey Bay Aquarium at (831) 648-4840, or CDFG at (805) 772-1135.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.