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Lyme disease may not get as much press as Hendra virus or the return of whooping cough in humans, but horse owners should still watch their horses for signs of disease. This illness is a threat wherever ticks are found, and early treatment gives the best chance for recovery. If you have pushed Lyme disease to the back of your mind, here’s a quick refresher course.

What is Lyme disease? Lyme disease is an illness that can affect horses, dogs, cats, humans, and other mammals. It is spread by ticks that infect animals with Borrelia burgdorferi bacteria. First identified in New England, cases of Lyme disease have spread throughout the equine population in the Northeast, Atlantic, and Great Lakes regions. Lyme disease has been diagnosed in humans in many states including California, Texas, Florida, and Maine.

What signs does an infected horse show? Horses with Lyme disease can show joint and muscle stiffness, lameness, fever, poor performance, lethargy, weight loss, eye inflammation, laminitis, hypersensitivity to touch, and behavioral changes including nervous or aggressive actions.

How is Lyme disease diagnosed and treated? Diagnosis based only on physical signs is not straightforward because horses might show all or only a few signs, and severity and frequency are variable. A veterinarian will try to rule out other possible causes of the horse’s disease signs and will also consider geographic location and probability of exposure. Standard blood tests can detect antibodies to Borrelia burgorferi bacteria but can’t differentiate between simple exposure and active infection. The Lyme Multiplex assay recently developed at Cornell University is able to differentiate among antibodies associated with new or older exposure or infection. Antibiotics in the tetracycline group are the preferred treatment, with intravenous administration more effective than oral or intramuscular methods.

How can owners protect their horses from Lyme disease? Avoiding contact with ticks is the most important step. Use insect repellent sprays or wipes on horses, restrict grazing in brushy or wooded areas, and keep pastures and fence rows cleared of brush and weeds. Check horses and remove any ticks several times a day because transmission of the bacteria apparently takes place only after a tick has been feeding for 24 to 48 hours. Ticks are especially fond of darker and warmer places, so check around and within the mane and tail hairs, between the hind legs, and in the area of the sheath or udder.

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