Risk factors associated with the carriage of Ixodes scapularis relative to other tick species in a population of pet dogs from southeastern Ontario, Canada

Abstract

In eastern North America, the blacklegged tick, Ixodes scapularis, is the vector for Borrelia burgdorferi sensu stricto and Anaplasma phagocytophilum, the causal agents for human and canine Lyme disease and anaplasmosis, respectively. The extensive range expansion of I. scapularis in Ontario is a growing veterinary and public health concern. However, there is limited information on the risk factors associated with I. scapularis carriage on dogs. Within an emerging area for Lyme disease risk in southeastern Ontario, we identified the tick species carried by dogs; determined the prevalence of B. burgdorferi and A. phagocytophilum in I. scapularis; and examined associations between pet demographics, travel history, and geographical location and the odds of: a dog carrying I. scapularis relative to other tick species (i.e., case-case design), and a removed I. scapularis being infected with B. burgdorferi. Seven species of ticks were collected from 543 companion dogs at 20 participating veterinary hospitals from April to December 2015. 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. Based on a multivariable logistic regression model, the odds of I. scapularis infestation relative to other tick species was significantly higher 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 compared to lighter dogs, and in dogs that had not visited a farm in the 7 days prior to tick removal. Based on univariable exact logistic regression models, the odds of B. burgdorferi-positive I. scapularis carriage relative to B. burgdorferi-negative I. scapularis were significantly higher for dogs that traveled in the 14 days prior to tick removal, for those dogs under 1 year of age, and for those weighing less than 10 kg. This case-case study provides information for veterinarians and public health practitioners to help protect dogs and their owners from Lyme disease in southeastern Ontario.

Keywords: Anaplasma phagocytophilum; Borrelia burgdorferi sensu stricto; Canine; Epidemiology; Logistic regression; Lyme disease.