A study led by Dr. Luis Arroyo at the Ontario Veterinary College, set out to determine the prevalence of Lyme Disease and Anaplasmosis in the Ontario horse population, and to identify geographic risk factors for the tick-borne infections. Blood serum samples were submitted from 564 horses and tested for Borrelia burgdorferi and Anaplasma phagocytophilum bacteria, which cause Lyme Disease and Anaplasmosis respectively, and are transmitted in Ontario by the blacklegged or deer tick, Ixodes scapularis.

According to the team’s report, the overall prevalence of B. burgdorferi exposure for all of Ontario was 14% (80/564), with pronounced regional variability. The prevalence appears to be highest in eastern Ontario, where 27 of
115 (24%) samples tested positive. The prevalence in southern Ontario was 15% (40/269); central Ontario was 10% (14/146), and in northern Ontario the prevalence was found to be 6% (2/33).

Researchers noted that Anaplasmosis is a new and emerging disease in Ontario, with only one case officially diagnosed, and that the distribution of the causative bacterium, A. phagocytophilum, is assumed to be predominantly in the eastern counties. Further, as the climate continues to change, the distribution of the deer tick is estimated to cover a large proportion of the province.

From data collected in the questionnaires, researchers learned that the majority of the horses (47%) lived outside 24/7 on pasture, particularly during tick season, in the summer months. In addition, half of the horse owners surveyed said they regularly check their horses for ticks, and only 15% reported that they had found a tick on their horse.