Prevalence of and risk factors for canine tick infestation in the United States, 2002-2004

Knowledge of the geographic range and seasonal activity of vector ticks is important for determining which people or animals are at risk of acquiring tick-borne infections. Several time-consuming methods requiring large-scale organization are used to map geographic and seasonal variations in tick distribution. A cost-effective, complementary approach to study tick distribution using a large nation-wide veterinary database is described in this paper. Prevalence of canine tick infestation in 40 states was estimated by analyzing electronic medical records of more than 8 million dog visits to Banfield veterinary hospitals in 2002-2004. Prevalence was defined as the proportion of dog visits in which tick infestation was recorded, and was expressed per 10,000 dog visits with 95% confidence intervals (CI). The overall prevalence (CI) of tick infestation was 52 (51, 53) dogs per 10,000 dog visits. Among states, Oklahoma (249 [229, 271] dogs with ticks per 10,000 dog-visits), Arkansas (242 [213, 274]), Connecticut (136 [119, 155]), West Virginia (130 [105, 161]), and Rhode Island (122 [97, 154]) ranked highest in prevalence of canine tick infestation. Overall prevalence peaked from May through July, although monthly prevalence varied by geographic region. In multiple logistic regression, younger dogs, male dogs, and sexually intact dogs, were at increased risk of tick infestation. Toy breeds were least likely to be infested, but no linear pattern of risk was evident with body weight. Identified risk factors should enable veterinarians to prevent tick infestation in pet dogs although differences in risk of tick infestation may be related to outdoor activity of dogs. Feasibility of collecting information for surveillance of vectors ticks on a national level using this large, electronic veterinary database is discussed.