NOAA Fisheries advises caution on Leptospirosis

November 2017

A cyclic bacterial disease outbreak on the West Coast has affected about 50 California sea lions in Washington, Oregon and California since late summer. NOAA Fisheries advises beachgoers to exercise caution around any stranded California sea lion, since the bacteria involved can also infect humans and pets.

brown sea lion sitting on a mud flat with waves in the background

State wildlife officials suspected this sea lion at Oyhut Wildlife Recreation Area in Washington might have contracted leptosporosis, a bacterial disease that affects California sea lions on the West Coast in cycles of about every four to five years. Photo: Courtesy Washington Department of Fish and Wildlife

The bacteria is Leptospira interrogans Pomona, one of the few bacteria known to contribute to morbidity and mortality in pinniped populations. Starting in late September the West Coast Marine Mammal Stranding Network started getting reports of stranded California sea lions that exhibited signs of leptospirosis in Oregon. Since that time, eight cases of leptospirosis have been confirmed and results are pending in an additional 13 cases in Oregon. Several cases are suspected in Washington but have not been confirmed. Since late summer, The Marine Mammal Center in Sausalito, California, has diagnosed about 30 sea lions with leptospirosis after they became stranded on the central California coast. Most of the California cases occurred in October.

The disease appears in cyclic outbreaks every four to five years, presumably as herd immunity waxes and wanes. More intensive outbreaks may cause the stranding of adult and sub-adult males migrating from California to Washington. The West Coast Marine Mammal Stranding Network typically responds to cases between August and November. Leptospirosis has been confirmed in previous years in Steller sea lions and Northern fur seals in Washington. Another strain of Leptospirosis has also been previously confirmed in harbor seals and Northern elephant seals.

The California sea lion population on the West Coast is estimated at more than 250,000 animals and is considered healthy and flourishing. While California sea lions all breed on California’s Channel Islands, thousands of males regularly travel north to the Pacific Northwest and as far as Alaska during the winter before returning to the rookeries by late spring.

Further information

Signs of disease: Clinical signs include extreme thirst for fresh water, reluctance to use rear limbs, muscle tremors, vomiting, fever, profound weight loss, and depression. Animals affected are usually juvenile to sub-adult males in fair to poor body condition, may be dehydrated and show discomfort and are lethargic and weak.

Staying safe: Remember not to approach any stranded seal or sea lion, or touch or interact with the animal or carcass in any way. A number of potential zoonotic diseases can be transmitted from wildlife to humans and pets. Use common sense and follow good hygiene practices to protect yourself and reduce your chances of exposure. Keeping your dog on a leash and staying away from sea lions should avoid any risk to you or your pet.

Handling carcasses: Necropsies by biologists or veterinarians allow us to learn about wildlife but may not always be possible depending on the location. The Stranding Network is not responsible for removing dead marine mammals from the beach.

Reporting:  If you observe a sea lion exhibiting some of the clinical signs of leptospirosis, abnormal behavior or that is dead, please report it to NOAA’s West Coast Marine Mammal Stranding Network at 1-866-767-6114. The Network will monitor these animals and make decisions to intervene on a case-by-case basis.

Home Page photo: Courtesy Washington Department of Fish and Wildlife