Canine surveillance system for Lyme borreliosis in Wisconsin and northern Illinois: geographic distribution and risk factor analysis.

A seroprevalence survey for Borrelia burgdorferi was conducted among the healthy canine pet population in selected counties of Wisconsin and northern Illinois to determine the distribution of Lyme disease and associated risk factors. Information obtained for each dog included place of residence, Lyme disease vaccination status, history of travel and tick exposure, signalment, and medical history. Serum samples were screened by enzyme-linked immunosorbent assay and confirmed by an immunoblot procedure. Seroprevalence by county ranged 0-40%, with the highest estimates from west-central Wisconsin. The spatial pattern was significantly correlated with human incidence of Lyme disease and with abundance of the tick vector, Ixodes scapularis. A geographic information system (GIS) was used to integrate environmental data with the location of the residences of the dogs to determine environmental risk factors. Seropositivity among dogs was positively associated with increased tick exposure and time spent outdoors and negatively associated with vaccination against Lyme disease. Seropositivity was also associated with living in forested and urban areas, and on sandy, fertile soils. A canine surveillance system is a useful method for assessing the geographic distribution of Lyme disease, and in combination with a GIS, it can be effective in determining environmental factors associated with I. scapularis endemicity.