Lyme disease is caused by a bacterial spirochete called Borrelia burgdorferi. it's spread to horses via the bite of the deer tick, also called black legged tick and officially known as Ixodes scapularis. The disease is most often diagnosed in the Northeast, the mid Atlantic states, the Great Lakes and areas of northern California.
SYMPTOMS. In horses, Lyme disease is a multi-system disease, so it can cause a wide range of symptoms. Your horse might show ?shifting leg? lameness, meaning lame on his right fore on Monday, his left hind on Tuesday. He may indicate muscle pain or have swollen joints. The most commonly reported symptoms are increased skin sensitivity and behavior changes. The behavior changes may show up as reluctance to work or irritability toward horses they were formerly best paddock buddies with.
Inflammation of the eyes is also seen quite frequently. Weight loss may be noted in chronic cases.
TRANSMISSION. So how does your horse get Lyme' Tick larval stages get a blood meal from infected rodents. White-footed deer mice are a favorite host for that stage. The nymph has many hosts, but the adult likes the white-tailed deer. Still, horses are an acceptable substitute for a blood meal.
it's believed that a tick must attach and feed for 24 to 48 hours in order to transmit the disease causing organism. Adult ticks can live up to two years. That includes over winter, even in the colder climates.
Adult ticks are the ones usually found on horses. Their numbers tend to be highest in the fall and early spring. Ticks can be picked up all year round, however.
PREVENTION. You can't prevent it, but you can minimize the chances of your horse getting Lyme disease. Mow pastures (which is good pasture management anyway). Trim back brushy areas. Discourage wildlife.
Use insect repellants with a pyrethrin, especially permethrin, as the main active ingredient. Keep any woodpiles well away from your horse's areas. Consider the use of aromatherapy oils or essential oils around your horse's ears, face and tail to deter the ticks.
We knew Buzz Guard, from EarthHeart (www.earthheartinc.com, 847-551-1806), works well on dogs, so we sent it to a reader with a horse plagued by ticks in her ears. She said that this ?tick magnet? horse doesn't like her ears handled and required two people to do the treatments, which meant it was applied less frequently than she?d like. Still, the product worked well, but the owner felt more frequent applications would help even more. The product worked very well on her other horses. Cost is $11.98 for two ounces. If you have serious tick problems, we think it's worth a try.
Get some chickens or guinea hens. These birds are known for their tick-eating appetites. If your tick population is thriving despite all of this, you may want to investigate the use of a pesticide that will kill or repel the ticks.
Check your horse daily for ticks, especially head, throatlatch, belly and under the tail. Remember that ticks need to be attached for one to two days to transmit the disease-causing organism. A quick daily check could save your horse from this illness and you from some expensive veterinary care.
DIAGNOSIS. This can be tricky.? Over 60 to 70 % of horses in some areas will be seropositive (have antibodies indicating exposure), but that doesn't mean they?ll ever get ill and show clinical signs. Less than 10% get ill. Still, with the disease clearly mimicking many illnesses with its wide range of possible symptoms, blood work is the fall-back method for diagnosis.
The antibodies stimulated by this illness are long-lasting. They remain detectable in the blood sample long after the tick and the organisms are gone. it's difficult to separate out horses that are truly ill, horses that have simply been exposed and horses that may have been given the canine vaccine simply by blood work.
The new multiplex test from Cornell?s AHDC (Animal Health Diagnostic Center) should simplify things a bit. This test has improved accuracy, specificity and sensitivity over previous blood tests. (See HJ August 2011, New Lyme Disease Test, at www.horse-journal.com.)
One small blood sample looks at three different antibodies. These antibodies reflect different stages of infection, so this test can distinguish between infection versus vaccination response and early versus chronic infections.
The other method of diagnosis is to response to therapy. Fortunately, most horses with Lyme disease do respond to antibiotics fairly quickly, so this can work.
TREATMENT. Treatment generally centers around the tetracycline family of antibiotics. These medications are usually given for weeks to truly be effective even though most horses will show some improvement in two to five days.
A few horses may actually look worse for a day or two as the toxins from the organisms are released as the organisms die. Watch your horse carefully for any signs of laminitis caused by this toxin release at this time.
Common versions of the antibiotic therapy include giving oral doxycycline (or doxy) for 30 to 45 days, giving IV (intravenous) oxytetracycline for 30 days or using a combination of the two methods. That might mean IV antibiotic for two weeks, then switching to oral.
Tetracycline antibiotics may cause soft stool, so be prepared with some pre- and pro-biotics, like Ration Plus. Your veterinarian may have a protocol he or she prefers.
BOTTOM LINE. If you catch this disease early most horses have a good recovery. You might want to recheck their antibody levels six to eight weeks later to be sure the disease is responding fully. For chronic cases, where diagnosis was delayed, you should wait at least three months to see if the antibody levels go down.
Article by Deb Eldredge, DVM, Contributing Veterinary Editor.