KY Equine Research: Lyme Disease

Expanding Tick Range Causes Concern

By Kentucky Equine Research Staff | https://ker.com/ Black-legged ticks (Ixodes scapularis) rank high among problematic external parasites of horses for a single reason: they are vectors for Borrelia burgdorferi, the bacterium that causes Lyme disease. An escalating population of black-legged ticks in North America, including greater spread into Canada, led researchers to wonder about potentially for more cases of Lyme disease in horses. Though horses may become infected with Borrelia burgdorferi following a tick bite, the percentage of them that develop Lyme disease remains unknown. To determine the seroprevalence of Borrelia burgdorferi in horses in Ontario, Canada, and to evaluate risk factors associated with seropositivity, researchers at the University of Guelph reached out to over 300 veterinary clinics around Ontario and invited them to participate in an equine Lyme disease surveillance study. The study involved both questionnaires and serum samples. Questionnaires provided data for risk factor analysis. Researchers excluded horses that had travelled outside of Ontario and thus may have been exposed to the bacterium elsewhere, and horses younger than three years old and thus less likely to have been exposed. In the end, seventy-six clinics agreed to participate. Researchers asked clinics to submit serum samples from 10 clinically healthy horses, all from different farms. Serum samples from 551 horses were used in the final data analysis, and two tests were used to determine seropositivity of each sample. (1)

While all causes of subtle gait changes or stiffness should be ruled out with a comprehensive lameness examination, horses suspected of having Lyme disease may benefit from research-proven joint support, as discomfort may settle into joints, as has been described in humans.

In this study, fifteen horses tested positive for antibodies to Borrelia burgdorferi using both tests, accounting for about 16% of the 91 horses that had tested positive on at least one test. Of significance, the odds of being seropositive were increased when oak trees grew near pastures. Acorns represent an important food source for several woodland species, including certain mice and chipmunks, as well as white-tailed deer, and can be a draw for these animals. Rodents and deer serve as reservoirs and hosts of Borrelia burgdorferi and black-legged ticks, respectively. Female ticks often choose oak trees on which to lay eggs due to the hospitable habitat of creviced bark, lichen, and moss, and tick larvae prefer to mature at the base of oaks. (2) Diagnosing Lyme disease in horses is difficult because no definitive symptoms have been identified, thus making treatment similarly challenging. If a horse is diagnosed with Lyme disease, medications will be prescribed by the attending veterinarian. In addition to those, nutritional supplements might be helpful so long as the horse consumes a completely balanced diet with a full complement of vitamins and minerals, according to Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research. “Support of the immune system is the logical jumping-off point, and this can be achieved with a high-quality omega-3 supplement, preferably from a marine-derived source, and an effective antioxidant supplement,” she said. Second-level defense: Regular use of tick repellants. These may contain a single active ingredient or a combination of ingredients. Efficacy and duration of action depends on the ingredients. Some are sprays, others are spot-on or pour-on products. Various factors will limit effectiveness of these products – sweat, precipitation, grime – so frequent re-application may be necessary for optimal effectiveness.

If you live in an area known to have ticks, there are ways to keep your horses healthy.

A three-pronged approach is most effective:

First-level defense: Thorough grooming with regular tick checks over the entire body but with special attention to the forelock, chest, mane, and tail. Transmission of bacteria from the tick to the horse occurs 24-48 hours after attachment, so performing daily or near-daily checks and properly removing ticks could decrease the risk of infection.

Third-level defense: Careful management of vegetation in areas accessible to horses, including removing leaves and fallen limbs or trees; mowing pasture frequently to avoid tall grasses; limiting access to oak trees; and discouraging deer from entering paddocks and pastures. Environmental control may have negligible effect on reduction of risk, according to some research. Kentucky Equine Research is an international equine nutrition, research, and consultation company serving horse owners and the feed industry. The company ’ s goals are to advance the industry’s knowledge of equine nutrition and exercise physiology, and support the nutritional care of all horses throughout their life. Sources: (1) M. Neely, L.G. Arroyo, C. Jardine, A. Moore, M. Hazlett, K. Clow, H. Archer, and J.S. Weese. 2020. Seroprevalence and evaluation of risk factors associated with seropositivity for Borrelia burgdorferi in Ontario horses. Equine Veterinary Journal 53:331-338. (2) Ostfeld, R.S., C.D. Canham, K. Oggenfuss, R.J. Winchcombe, and F. Kessing. 2006. Climate, deer, rodents, and acorns as determinants of variation in Lyme-disease risk. PLos Biology 4:1058-1068.

https://ker.com/

Other references: American Association of Equine Practitioners. 2020. Borrelia burgdorferi infection and Lyme disease. (Accessed 3/24/2021). Divers, T.J., R.B. Gardner, J.E. Madigan, S.G. Witonsky, J.J. Bertone, E.L. Swinebroad, S.E. Schutzer, and A.L. Johnson. 2018. Borrelia burgdorferi infection and Lyme disease in North American horses: A consensus statement. Journal of Veterinary Internal Medicine 32:617-632.