-Leptospirosis is increasingly diagnosed as a re-emerging canine disease in the USA. Our objectives were to describe potential risk factors for canine leptospirosis infections in northern California, through the use of a case-control study, and to perform a spatial analysis to investigate which aspects of the landscape and land use patterns are important in the transmission of leptospirosis. Forty-three cases and 59 controls were enrolled into the study. Serological results showed that 17 (39.5%) of the 43 dog cases were infected with serovar pomona. Cases were 7.86 times more likely to have been walked in a rural environment rather than an urban environment. Cases also had eight times higher odds of swimming in outdoor water, and approximately 12 times higher odds of drinking from outdoor water in the two weeks preceding illness. At smaller distances from the dogs' homes (radius ≤ 0.5 km) hydrographic density was positively correlated with cases, while at larger distances (radius ≥ 5 km) there was a positive relationship between leptospirosis cases and percent of wetlands or public open space. Intervention measures for the prevention of canine leptospirosis should include reducing access to potentially infectious bodies of water that are close to canine homes, and to large areas of wetlands and public open space in the general vicinity. We have shown that a spatial analysis in conjunction with traditional epidemiological analysis is a powerful combination in identifying risk factors for infectious diseases.leptospirosis / dogs / GIS / California / disease geography

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.

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Current plans for control of pandemic influenza vary, and many do not include nonpharmaceutical interventions.