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Tick-Borne Diseases on the Rise: Learn How to Protect Your Horse

If a film maker wanted to find a suitable villain for a horror movie, ticks would perfectly fit that description. Well-camouflaged and opportunistic, many ticks like to lurk in dark, wooded areas and climb up tall grass to find their victims. Although tiny in size, these highly adaptable creatures are capable of transmitting bacteria, viruses, and blood parasites, some of which can be life-threatening, even deadly.
horses grazing in pasture

There are nearly 900 tick species in the world, and unfortunately, tick-borne disease is becoming more common and at least three of those diseases can affect horses. But before you lock your horse in the barn and swear off riding in the woods forever, take heart in the fact that you can take practical steps to protect your horse—and yourself—from ticks.

“Tick-borne disease is on the rise for multiple reasons, including climate change and increased movement of both people and animals. We are also much more aware of new diseases ticks can carry, so based on increased tick movement and population, there are more diseases we can look for now,” notes Jennifer Thomas, DVM, a veterinarian at the Center for Veterinary Health Sciences at Oklahoma State University and an affiliate of the National Center for Veterinary Parasitology. Her research primarily focuses on parasites and tick-borne diseases.

Diseases of Concern to Horses

The three main tick-borne diseases that can affect horses are:

  • Lyme disease
  • Equine piroplasmosis
  • Anaplasmosis

“As far as we, know, those are the three big ones. In the past year, we’ve discovered other tick-borne viruses, but we don’t have enough research to know if these can also be transmitted to horses,” says Thomas. “Our pets—whether our horses, dogs or cats—also increase our contact with ticks. So you need to be concerned about more than just the diseases ticks can cause your animals.”

Diagnosis can be challenging because tick-borne diseases don’t have just one symptom.

“The hardest thing is that there’s no one sign that’s going to tell you it’s the disease just by looking at the horse,” says Thomas. “Some horses may show no signs at all and with some diseases, a horse will die quickly; it completely runs the gamut. When they do see signs, owners often think that it can’t be a tick disease because they don’t find a tick on the horse. It varies with each disease, but the tick may be long gone before symptoms appear. For example, with equine piroplasmosis, it can take seven days to a month after the tick has fed on the horse for signs of disease to appear.”

Let’s take a closer look at the three tick-borne diseases known to affect horses. It can be confusing because there have been multiple name changes of the various blood parasites.

Lyme disease is transmitted by ticks carrying the infective organism Borrelia burgdorferi. It is transmitted by Ixodes scapularis, found in the north and eastern U.S. and Ixodes pacificus, found in the western U.S. Both are colloquially known as “deer ticks” and “eastern or western black-legged ticks,” respectively. Lyme disease can affect humans as well as horses, dogs and cats.

Lyme disease has highly variable symptoms and, as in humans, can be tricky to diagnose because of how those symptoms may or may not appear. These can include stiffness, lameness in more than one leg, muscle tenderness, muscle wasting (atrophy), lethargy, behavioral changes, general dullness, sensitivity of skin making it painful to the touch, and weight loss. Severe presentations can cause neuroborreliosis (neurologic disease caused by Lyme disease) and uveitis (inflammation within the eye itself). Ironically, joint swelling, which is common in dogs and humans affected with Lyme, is rare in horses.

“Lyme disease is the wild card. Signs may not appear for years, or can appear shortly after the tick has fed on the horse,” says Thomas. “Some horses can get exposed to Lyme disease and never have symptoms; others can develop signs as severe as neurologic disease. After treatment with antibiotics, the horse may never show symptoms again or it can relapse later, even years later.”

Equine piroplasmosis is a general term given to infection with either Babesia caballi or Theileria equi (formerly called Babesia equi). Both of these blood parasites can be transmitted by several species of ticks. Infected animals may have few or no clinical signs. These can include mild to general weakness, depression, rapid shallow breathing, lack of appetite, weight loss, jaundice, dark-colored urine, and abortion in pregnant mares. In more acute phases, the animal will tend to have a high fever (over 104F), pale or yellow mucous membranes and lower limb swelling. The disease can affect horses, mules, donkeys and zebras.

Diagnosis can be challenging because tick-borne diseases don’t have just one symptom.

Equine granulocytic anaplasmosis is transmitted by deer ticks, but caused by a different bacteria than that causing Lyme disease. It tends to occur in young horses, often under four years old. Signs of illness don’t usually appear for eight to 14 days after the infected tick feeds on the horse. Symptoms can include high fever (over 104F), depression, decreased appetite, moderate limb edema, stumbling, and ataxia. As Thomas explains, the agent of equine granulocytic anaplasmosis, Anaplasma phagocytophilum, can cause clinical disease in humans, too, but then it is called human granulocytic anaplasmosis.

Diagnosis for these diseases is made by blood testing. Antibiotics are typically used to treat anaplasmosis and Lyme disease. With piroplasmosis, treatment is based on the species of parasite involved, however, the drugs used have adverse side effects and a definitive cure is unlikely.

“If a horse is diagnosed with piroplasmosis, state and federal veterinarians will be involved,” notes Thomas. “To treat equine piroplasmosis, vets may use an antibiotic, along with an anti-parasitic drug, which targets these types of parasites, but the general consensus is that the horse’s body will never clear those organisms totally. The horse will likely remain infected, although you may be able to get them through the clinical symptoms of the disease.”

It’s important to realize that even if a tick doesn’t transmit a disease, it can still cause inflammation, swelling and itching.

“I would never consider any tick on a horse to be a ‘safe’ tick,” cautions Thomas. “We keep discovering new viruses and bacteria that they can transmit, so I wouldn’t feel safe saying there’s any tick that doesn’t transmit a disease.”

It’s generally believed that a tick must be attached for 24 hours before disease can be transmitted, but this isn’t a risk you want to take. It’s always best to err on the side of caution and check your horse—and yourself—thoroughly immediately after your ride in the woods.

Develop a Strategy

At this time, there are no vaccines labeled for use in horses for tick-borne diseases. Protecting your horse from ticks is the best way to prevent infection. Thomas advises having a general discussion about ticks with your vet during your horse’s annual wellness exam.

Before you can protect your horse, you have to know the enemy.

One of the first things you should know is that ticks aren’t just a warm weather concern. These hardy creatures can even survive in winter, comfortably insulated in the vegetation beneath a blanket of snow. There is even one species, the “winter tick,” that is only on horses during the cool seasons—even during sub-zero winter weather—and spends the summer away from animals.

“We recommend year-round tick control and vigilance,” notes Thomas. “This means integrated management, which includes avoidance, treating the premises and treating the horse specifically.”

Ticks thrive in protective layers of vegetation and tall grasses, so one of the best ways to avoid tick exposure is to limit or prevent access to wooded areas, including the boundaries to such wooded areas. You should also keep pastures mowed to prevent excessively tall grass, and clear brush from around fence lines. In general, ticks avoid crossing hot, sunny areas with little vegetation.

“Some horse owners will hire a licensed pest control company to spray along the wooded areas to create a chemical barrier. It can also be nice to have a fresh set of eyes to help find problem areas on your property,” says Thomas.

“To protect the horses themselves, look for an approved product that specifically addresses ticks and is made for use on horses. Read the whole label, including the warning section, before applying. If you have a foal, make sure the product is approved for use on young animals,” she notes. “Spot-on (topical) products are most commonly used for pastured horses and these horses are ideal candidates for such a product when you can’t groom them daily and check for ticks.”

If you do find a tick on your horse, Thomas suggests using fine-tipped tweezers and the same method of removal recommended for humans by the Centers for Disease Control. Use tweezers to grasp the tick by its mouthparts as close to the horse’s skin as possible. Don’t twist or jerk; just pull it out with steady, even pressure and don’t squeeze the tick’s body.

By Cynthia McFarland
Stable Talk | Farnam