Lyme disease in horses: more likely than expected

A 2016 research study by the Ontario Animal Health Network (OAHN), equine network yielded some surprising results about the prevalence and distribution of infection by Borrelia burgdorferi, which causes Lyme disease in horses and humans, and Anaplasma phagocytophilum, another tick-transmitted zoonotic pathogen in Ontario horses. The research was requested by equine vets as Lyme disease is difficult to diagnose in horses (as it is in humans) and can be hard to treat. Lyme disease is a public health concern, given the increasing incidence of confirmed human infections in Ontario.

Equine veterinarians from clinics across the province provided more than 500 blood samples from horses that met the study criteria: more than two years of age, living outdoors more than six hours per day and remaining within the province.

Results showed that 14 per cent of the horses sampled had exposure to Borrelia burgdorferi. Six horses tested positive for Anaplasma phagocytophilum, a notable observation given that no cases had been confirmed in horses before 2015. Three were infected with both organisms. The greatest percentage of horses infected with Borrelia (24 per cent) were in eastern Ontario. Most of the horses (47 per cent) lived outside 24/7 on pasture, especially in summer (tick season).

Equine practitioners were kept informed of the study through quarterly OAHN equine reports and the Animal Health Laboratory (AHL) newsletter, and the findings were presented at the 2017 Ontario Association of Equine Practitioners annual meeting. This study was useful to identify the presence of infected horses and the geographical areas of greatest risk.

The AHL receives funding from the Ontario Agri-Food Innovation Alliance.

This article originally appeared in the 2018 Agri-Food Yearbook edition of Research magazine.