In the Great Lakes region and eastern United States, which are the areas known to have the highest tick-borne-disease incidence in both human and animals, one suspect for fevers without accompanying respiratory signs is tick-borne disease. | Photo: iStock

To find out how prevalent tick-related fevers are in horses, Linda Mittel, MSPH, DVM, senior extension associate at Cornell University’s College of Veterinary Medicine, in Ithaca, New York, studied causes of fever of unknown origin (FUO). She presented her results at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

In her case-control study Mittel surveyed clientele from 15 equine practices in nine eastern states and Wisconsin, which are known to have high tick populations. From the responses, she included 52 horses that had experienced a fever of unknown origin (FUO) and 52 healthy horses from the same farm as matched controls in the study. She also included an additional 23 FUO cases without matched controls. Ticks were collected from each farm environment and identified and tested for agents they were carrying.

Mittel obtained blood samples from each horse and tested for DNA of two of the most common causes of equine fever without respiratory signs—the bacteria Anaplasma phagocytophilum, which causes the tick-borne disease anaplasmosis, and Neorickettsia risticii, which causes Potomac horse fever—plus other bacteria and parasites. She also analyzed other genetic material in each sample