Assessing mechanisms of persistence of Leptospira spp in California sea lions

Leptospirosis is a bacterial infection routinely observed in California sea lions, but characterized by outbreaks (every four to five years) when large numbers of affected sea lions come ashore along the coast of California. Among those that are admitted to rehabilitation for this disease, mortality is quite high (~70%), suggesting that this disease may affect population numbers. A missing piece of information needed to understand the disease cycles in California sea lions is whether individuals can act as maintenance hosts for Leptospira, i.e. whether individual sea lions can become chronic carriers of the pathogen while exhibiting few or no signs of disease. Testing clinically healthy, wild-caught sea lions for this pathogen will help us determine prevalence of exposure as well as the prevalence of sea lions that are shedding the pathogen and potentially capable of infecting other sea lions. We propose to sample apparently healthy sea lions on Ano Nuevo Island and test their blood and urine for Leptospira. Maintenance hosts will be identified by the combination of an absence of clinical illness (normal serum chemistry), little to no antibody titer against Leptospira spp. (serology), and the concurrent shedding of viable leptospires in the urine (positive PCR or culture). These data will provide an important piece of information to aid in efforts to model the disease dynamics of Leptospira within the sea lion population and to understand the affect of this pathogen on the California sea lion population.