Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Lyme Disease, Borreliosis

Synonyms: Lymes Disease, Lyme Arthritis or Borreliosis, Erythema Migrans with Polyarthritis


Lyme disease is a tick borne bacterial disease that can cause chronic illness in horses. The disease is very regional, and is far more common in the Northeastern United States. It has also been reported in Europe and Australia. Humans, horses and many other species can get the disease, but it is not transmissible from horse to human or vice-versa. In humans, the disease causes chronic pain, malaise, and joint swelling.

The most common signs of this disease in horses is low grade joint swelling, stiffness, lameness, and hypersensitivity to touch. However, there are a variety of other signs that have been associated with Lyme disease, including eye inflammation (uveitis) and skin inflammation (dermatitis).

Since the signs of Lyme disease are similar to those of several other diseases, it is often mistaken for other illnesses. This disease is also difficult to diagnose, and requires laboratory confirmation through blood titer. Even this is not always clear, as some horses that have no signs of disease test positive and some with compatible signs test negative.

Treatment is long-term tetracycline class antibiotics. In many cases, if we think that a horse likely has Lyme, we treat presumptively. If the horse improves, that suggests that we were correct!

my vet's role



Other conditions or ailments that might also need to be ruled out by a vet.

Very Common
Less Common
more diagnoses

Diagnostics Used

These are tests that might be helpful to make this diagnosis or further characterize the condition.

Very Common
Less Common
more diagnostics


The prognosis is fair to good with treatment. Generally, however, chronically infected horses have a poorer prognosis. Success of treatment is based on improved signs of disease, and lowering of antibody titer.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • Does every horse that tests positive for this disease require treatment?
  • How long should we treat & how do we know it is effective?

Good facilities management to decrease the population of ticks is recommended, including the use of tick insecticide sprays, regular mowing of tall grassy areas and management to reduce exposure. Frequent examination of horses and other animals for ticks, and their prompt removal may help prevent infection. Flea and tick shampoos may also be of value.

Look carefully along the neck, around the ears, under the throat, on the belly and at the base of the mane and the rectal region.

You can also reduce the tick population on your property by keeping pastures mowed and reduce the rodent population. Good facilities management to decrease the population of rodents is recommended, including the use of traps and bait. Remove brush piles where rodents like to live. Keep your tack room clean and keep all grain and treats in sturdy trash cans or plastic bins with lids.

The Lyme vaccine for dogs is considered by some vets to have protective value in horses. Talk to your vet about whether they recommend this vaccine for your horses.

Author: Doug Thal DVM Dipl. ABVP