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Unprecedented Early Sea Lion Leptospirosis Surge Hits Bay Area

More than 100 early-season admissions at Sausalito’s Marine Mammal Center signal an escalating Bay Area outbreak with rising health risks.

Sea lions rest on floating platforms adjacent to Pier 39 in San Francisco in 2024. A disease is sweeping through sea lions on the Central Coast, and has also reached the Bay Area.
Image
FILE: As the sun sets, a sea lion looks out at the waves.
Tightly tucked flippers on a sea lion are a sign of the malaise.

Overview

  • The outbreak has continued into early August with no indication of decline following July’s unprecedented admission surge.
  • Sea lions suffering from acute leptospirosis have been documented across Marin, Sonoma, San Mateo and San Francisco counties, reflecting their wide-ranging movements.
  • Intensive treatments leave about two-thirds of infected sea lions succumbing to irreversible kidney failure despite aggressive care.
  • Long-term warming events, notably the 2013–2015 Pacific “Blob,” are believed to have disrupted normal migration and immune patterns, leading to off-schedule outbreaks.
  • The Marine Mammal Center cautions that leptospirosis can infect humans and dogs, advising beach users to leash pets, keep distance from wildlife and seek vaccinations.