The major objectives of this thesis were to identify the tick species parasitizing companion dogs in southeastern Ontario, determine demographic and management factors associated with the carriage of I. scapularis and B. burgdorferi-positive ticks, and identify clustering of the carriage of these organisms in space, time, and space-time. Seven species of ticks from 543 companion dogs were collected from 20 participating veterinary hospitals. Ixodes scapularis were detected on 85.6% of parasitized dogs, and 7.5% of these dogs were carrying at least one B. burgdorferi-positive tick. The odds of I. scapularis parasitism was significantly greater in fall and spring compared to summer, with closer proximity to Lake Ontario, in female compared to male dogs, in dogs weighing over 30 kg, and in dogs that had not visited a farm. Significant spatial, temporal and space-time clusters were identified that were frequently consistent with surveillance data acquired from active tick surveillance.