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!