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

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 genus Neisseria

The genus Neisseria comprises a number of closely related Gram-negative organisms isolated from humans and animals. Their interrelationships are poorly resolved by phenotypic approaches, and the classification of the species groups by molecular techniques has been confused by a combination of their genetic similarity and extensive shared sequence polymorphism as a consequence of shared ancestry, horizontal genetic exchange, or both. Whole genome sequence analysis, especially of large numbers of draft genome sequences, has enabled the comparison of core genes across the genus, and this has proved to be an effective means of defining species groups within the genus. This redefinition is largely consistent with previous species designations with relatively few adjustments necessary. Most members of the genus are not, or are very rarely, pathogenic, but the genus contains the globally significant pathogens Neisseria meningitidis, the meningococcus, and Neisseria gonorrhoeae, the gonococcus. The meningococcus is an ‘‘accidental pathogen’’: predominantly existing as a harmless commensal, with very few infections resulting in pathology. Pathology does not appear to play a role in the transmission of this organism, although some genotypes have a greater propensity to cause disease than others. The majority of work on the genus concentrates on the two pathogenic species, with attempts to develop a comprehensive vaccine against the meningococcus a major driver for research. The gonococcus is antigenically highly diverse but genetically quite uniform, and probably emerged from a single clone that changed its niche. Emerging antibiotic resistance of the gonococcus currently represents the most significant global health challenge presented by this genus

The genus Neisseria

The genus Neisseria comprises a number of closely related Gram-negative organisms isolated from humans and animals. Their interrelationships are poorly resolved by phenotypic approaches, and the classification of the species groups by molecular techniques has been confused by a combination of their genetic similarity and extensive shared sequence polymorphism as a consequence of shared ancestry, horizontal genetic exchange, or both. Whole genome sequence analysis, especially of large numbers of draft genome sequences, has enabled the comparison of core genes across the genus, and this has proved to be an effective means of defining species groups within the genus. This redefinition is largely consistent with previous species designations with relatively few adjustments necessary. Most members of the genus are not, or are very rarely, pathogenic, but the genus contains the globally significant pathogens Neisseria meningitidis, the meningococcus, and Neisseria gonorrhoeae, the gonococcus. The meningococcus is an ‘‘accidental pathogen’’: predominantly existing as a harmless commensal, with very few infections resulting in pathology. Pathology does not appear to play a role in the transmission of this organism, although some genotypes have a greater propensity to cause disease than others. The majority of work on the genus concentrates on the two pathogenic species, with attempts to develop a comprehensive vaccine against the meningococcus a major driver for research. The gonococcus is antigenically highly diverse but genetically quite uniform, and probably emerged from a single clone that changed its niche. Emerging antibiotic resistance of the gonococcus currently represents the most significant global health challenge presented by this genus