EQUUS ‘Farm Calls’ episode 16: Tick-borne diseases

Learn more about diseases that ticks can spread to horses in this discussion with Dr. Toby Pinn-Woodcock.

The three major tick-borne diseases diagnosed in the United States are Lyme disease, piroplasmosis and anaplasmosis (a bacterial disease).

In this episode of EQUUS “Farm Calls,” we talk to Toby Pinn-Woodcock, DVM, DACVIM (Large Animal). She is an assistant clinical professor in the Department of Population Medical and Diagnostic Sciences at Cornell University’s College of Veterinary Medicine. She received her DVM from the University of Wisconsin and did her internal medicine residency at Cornell.

Pinn-Woodcock reminded the audience that ticks can vary in size from tiny nymphs to large ticks. The key is to try and prevent ticks from attaching to horses, no matter their size.

Unfortunately, horse owners “might not realize a horse has been bitten,” said Pinn-Woodcock.


Horses that develop anaplasmosis usually develop a fever, are lethargic, “stock up” and show edema in their lower limbs. Pinn-Woodcock said these horses also show sheath swelling or will have edema just behind the girth area. She said the swelling is usually cool to the touch and not painful. “It indents when you push it (the swelling) with your finger,” she described.

She said anaplasmosis horses can become jaundiced, showing a yellowish tint in the eyes and gums.

Anaplasmosis also can cause neurologic signs in horses, Pinn-Woodcock said. That means the horses might appear unbalanced, ataxic or have tremors.

Lyme Disease

Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi. There are at least three species of ticks that can spread the bacterium.

Lyme disease can cause a variety of clinical signs, including shifting limb lameness, back pain, muscle atrophy, skin sensitivity and fever.

Lyme disease is most commonly found in the northeastern and mid-Atlantic states, the upper Midwest, and on the Pacific Coast.

She said there is an antibody “multiplex” test that is only run at Cornell University that shows if horses were exposed recently or a long time ago. “That along with clinical signs may encourage the veterinarian to treat with antibiotics,” she added.

While there isn’t a vaccine against Lyme disease for horses, some veterinarians will use a canine Lyme vaccine “off-label” for horses in areas with high Lyme disease problems. Some horses will have a good response to this vaccine, and others don’t make antibodies. “That is up to the vet and owner to decide,” said Pinn-Woodcock.


While piroplasmosis is not considered endemic (naturally occurring) in the United States, Mexico, other South American countries and European countries have many horses with piroplasmosis. If a horse is imported legally, it is tested for piroplasmosis and either has to be free of the disease or undergo a long treatment protocol to clear the bacterium.

Unfortunately, some horses from these countries are illegally imported into the United States, so it is possible to have horses with this disease in the population. USDA officials have said that the rise of illegally imported horses and “bush track” Quarter Horse racing in this country will continue to cause more cases of equine infectious anemia (EIA) and piroplasmosis. (To learn more about this problem check out the article and podcast on our sister publication EquiManagement.com.) https://equimanagement.com/disease-du-jour-podcast/disease-du-jour-eia-and-piroplasmosis/


While there are no vaccines licensed for horses against any of these diseases, there are things horse owners can do to help prevent ticks from attaching to horses.

Use products labeled to prevent ticks on horses. Keep horses away from “bushy” areas where ticks like to live. That might mean mowing those areas or fencing them off so horses can go there.

Owners should groom horses daily and remove ticks. Those ticks should be killed and disposed of so they can’t attach to other animals or horses.

This episode of EQUUS “Farm Calls” podcast is brought to you by Farnam—Your Partner in Horse Care. Farnam’s Equi-Spot Spot-On Protection is ideal for pastured horses because it keeps your horse protected through rain, sweat and the outdoors. Applied once every two weeks, it provides long-lasting control against dangerous ticks that can spread Lyme disease and mosquitoes that may transmit West Nile virus and equine encephalitis, as well as biting flies and gnats! 




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