Cyclical changes in seroprevalence of leptospirosis in California sea lions: endemic and epidemic disease in one host species?

Abstract

BackgroundLeptospirosis is a zoonotic disease infecting a broad range of mammalian hosts, and is re-emerging globally. California sea lions (Zalophus californianus) have experienced recurrent outbreaks of leptospirosis since 1970, but it is unknown whether the pathogen persists in the sea lion population or is introduced repeatedly from external reservoirs.MethodsWe analyzed serum samples collected over an 11-year period from 1344 California sea lions that stranded alive on the California coast, using the microscopic agglutination test (MAT) for antibodies to Leptospira interrogans serovar Pomona. We evaluated seroprevalence among yearlings as a measure of incidence in the population, and characterized antibody persistence times based on temporal changes in the distribution of titer scores. We conducted multinomial logistic regression to determine individual risk factors for seropositivity with high and low titers.ResultsThe serosurvey revealed cyclical patterns in seroprevalence to L. interrogans serovar Pomona, with 4–5 year periodicity and peak seroprevalence above 50%. Seroprevalence in yearling sea lions was an accurate index of exposure among all age classses, and indicated on-going exposure to leptospires in non-outbreak years. Analysis of titer decay rates showed that some individuals probably maintain high titers for more than a year following exposure.ConclusionThis study presents results of an unprecedented long-term serosurveillance program in marine mammals. Our results suggest that leptospirosis is endemic in California sea lions, but also causes periodic epidemics of acute disease. The findings call into question the classical dichotomy between maintenance hosts of leptospirosis, which experience chronic but largely asymptomatic infections, and accidental hosts, which suffer acute illness or death as a result of disease spillover from reservoir species.

The Role of Domoic Acid in Abortion and Premature Parturition of California Sea Lions (Zalophus Californianus) on San Miguel Island, California

“…As in the 1970s, calicivirus was present in premature pups, and although anticipated histopathology associated with caliciviral-induced abortion was not present, its contribution to reproductive failure could not be excluded. In contrast to the earlier study, evidence of Leptospira infection was not detected in any of the pups examined, although leptospirosis is still endemic in sea lions (Lloyd-Smith et al, 2007). Organochlorine compounds have decreased in tissues from premature pups since the 1970s, and PAH metabolites were measured in a subset of animals, but it is unknown if these compounds contributed to reproductive failure.…”

Association of an Unusual Marine Mammal Mortality Event With Pseudo-Nitzschia Spp. Blooms Along the Southern California Coastline

“…Leptospirosis typically affects juvenile male sea lions in central and northern California during the fall (Gulland et al, 1996;Lloyd-Smith et al, 2007), and malnutrition associated with El Niñ o events typically affects yearlings . Speciesspecific ecologic and demographic factors may influence the distinct sex and age composition of stranded animals observed in association with DA toxicity.…”

Surveillance for zoonotic and selected pathogens in harbor seals Phoca vitulina from central California

“…Among stranded California sea lions, which experience periodic outbreaks of leptospirosis caused by L. interrogans serovar Pomona, 2004 was a peak year for cases of leptospirosis (Lloyd-Smith et al 2007). The Leptospira have recently been reclassified, and there is not agreement between serovar and genotype (Resch et al 2007); therefore, without an isolate from a harbor seal it cannot be determined if the strain infecting harbor seals is the same or different from the strain isolated from sea lions.…”

“…The Leptospira have recently been reclassified, and there is not agreement between serovar and genotype (Resch et al 2007); therefore, without an isolate from a harbor seal it cannot be determined if the strain infecting harbor seals is the same or different from the strain isolated from sea lions. However, harbor seal exposure to Leptospira may be modulated by some of the same environmental drivers that affect cycles of leptospirosis in sea lions, or reflect the cycles observed in the sea lion population (Lloyd-Smith et al 2007). …”