Vet. Res. 38 (2007) 37-50
DOI: 10.1051/vetres:2006043

Use of a case-control study and geographic information systems to determine environmental and demographic risk factors for canine leptospirosis

George S. Ghneim^{a, b}, Joshua H. Viers^c, Bruno B. Chomel^d, Philip H. Kass^d, Daphne A. Descollonges^a and Michael L. Johnson<sup>e

a</sup>  Center for Companion Animal Health, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
^b  RTI International, 3040 Cornwallis Rd, PO Box 12194, Research Triangle Park, NC, 27709-2194, USA
^c  Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA
^d  Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
^e  John Muir Institute of the Environment, University of California, Davis, CA 95616, USA

(Received 1 April 2006; accepted 19 July 2006; published online 1 November 2006)

Abstract - 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.

Key words: leptospirosis / dogs / GIS / California / disease geography

Corresponding author: gsghneim@rti.org

© INRA, EDP Sciences 2007