Question of the Week: Lyme Disease Outbreak

Q: There has been an outbreak of Lyme disease in my area. What can I do to reduce the risk of my horse getting it? Is there a vaccination for horses? If my horse does get it, is there anything I can do to treat it?

A: Cases of Lyme disease, in humans, canines and equines, have been increasing rapidly over the past decade. A majority of this clinical rise has to do with encroachment of urban/suburban housing and development into wooded land which in turn causes an increase in human and domestic animal exposure to deer and other wildlife. White-tailed deer are the primary host of the deer tick, the ectoparasite responsible for transmitting Borrelia burgdorferi, the spiral-shaped bacteria called spirochetes that cause Lyme disease.

Historically, equine Lyme disease has been somewhat difficult to diagnose, as the clinical signs can wax and wane and be somewhat indistinguishable from other musculoskeletal disorders. Lyme disease has been labeled “the great imitator” by many a frustrated veterinarian and physician, as clinical signs can sometimes be a challenge to pin down. Clinical signs of horses suffering an active infection of Lyme disease can present with signs similar to canine Lyme disease: shifting leg lameness, a low-grade fever, stiffness, and muscle soreness. Measuring Lyme disease antibodies in equine serum via a test called an ELISA (enzyme-linked immunosorbent assay) test or a Western blot can also be indicative of active infection. However, test results can become complicated by the fact that horses can have antibodies to the disease and not have an active infection.

If your horse exhibits lethargy, fever, or muscle soreness (which may be in the legs, neck, back, or a shifting leg lameness), have your vet out for a complete physical exam and blood work to rule out other cases of this group of clinical signs. Lyme disease is present predominantly in the Northeast, (in fact Lyme disease was first discovered in Old Lyme, CT, hence its name), but is gradually moving across the US and is seen frequently now down as far south as Florida and is spreading across the Midwest.

If Lyme disease if diagnosed in your horse, your vet will likely prescribe a three to six week course of a daily oral antibiotic called doxycycline and maybe even an NSAID (non-steroidal anti-inflammatory) such as flunixin meglumine (Banamine) to make your horse more comfortable. Intravenous injections of the antibiotic tetracycline can also be used to cure this disease. Cases of equine Lyme disease tend to respond fairly quickly to either antibiotic therapy – sometimes owners may see clinical improvement within a few days. However, it is imperative to continue treatment for the fully prescribed period to ensure proper clearance of the bacteria from within the body.

Due to a horse’s coat, the classic bull’s eye skin lesion seen in humans with Lyme disease is not evident in horses (or dogs for the same reason). Additionally, one of the more serious complications sometimes seen in dogs and humans called Lyme nephritis, or kidney inflammation, luckily hasn’t really been demonstrated in the equine world so far.

As with most diseases, an ounce of prevention is worth a pound of cure. Make it part of your daily grooming routine to check your horse for ticks, keeping in mind that deer ticks are very small and like to attach in hidden crevices on the body, so be sure to check behind your horse’s elbows, along the cinch, groin, behind the ears, under the jaw, and between his hind legs. If you see an attached tick, remove it with tweezers by steady pressure at the head. It can be a bit distressing (and disgusting!) to see a huge, engorged tick attached to your beloved companion but take heart – the transmission of Lyme disease requires tick attachment for 12 to 24 hours – so as long as you are removing ticks on a once to twice daily basis, chances for transmission of this disease are greatly minimized.

There is currently no USDA approved equine vaccine for Lyme disease. Anecdotally some individuals have used the canine vaccine on their horses but this is highly discouraged as there is no scientific data to prove this helps in equine prevention against Lyme disease. Furthermore, administering a canine vaccine to a horse may increase the risk of causing an adverse reaction in your horse. Proper tick control is currently the best way to help prevent this disease.

— Anna O’Brien, DVM

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