Bacterial Disease Outbreak Affecting Hundreds Of California Sea Lions

The Marine Mammal Center in Sausalito says it's responding to the second-largest outbreak on record of a potentially fatal bacterial disease in California sea lions.

So far this year 220 sea lions have tested positive for leptospirosis, an infection that can cause the animals to go into kidney failure. During the last outbreak in 2011, around 200 were diagnosed. Dr. Shawn Johnson, the center's director of veterinary science, said two-thirds of the sea lions diagnosed with the disease this year have died.

"[It] is really difficult to treat and very severe, and unfortunately it causes a high level of mortality in these sea lions," Johnson said.

He said it's a cyclical outbreak that happens every three to five years, but the magnitude of cases this year was unexpected. Almost half of all of the sea lions the center has rescued have been diagnosed with the disease.

Researchers believe the outbreak could be caused by changes in sea surface temperatures, herd immunity and migration patterns. 

"But there are some unknowns, too, as to why some years we see huge numbers of animals and other years we don't see hardly any or none,” Johnson said. “In the last couple of years we had no cases of leptospirosis."

The Marine Mammal Center's rescue range extends along 600 miles of coastline from San Luis Obispo through Mendocino.