The problems started with stiffness in your horse's right hock. Now the hock seems better, but he's off in front. And he's definitely not his normal, perky self--he mopes around in his paddock, and he pins his ears and tries to move away when you groom him.
On-again, off-again lameness, low energy levels, a cranky attitude--those signs could point to something as simple as overwork. But Lyme disease could produce all those problems, and it may be a growing problem for horses in parts of the United States. Lyme disease can have long-term complications that include damage to your horse's joints, skin, nervous system and even vision.
Who's at Risk?
Disease-carrying blacklegged ticks (deer ticks) have three life stages (larva, nymph and adult) and need a blood meal before they can molt into the next stage. They pick up the bacteria as larvae and nymphs by feeding on the blood of infected mice, and they transmit the infection to their next hosts--human, horse, dog, deer or any passing mammal or bird. They seem most likely to feed on horses as adults. In cold-winter regions, adults typically appear in early fall, spend the winter dormant in brush and leaf litter and come out again in early spring. This makes early spring and fall prime times for infection. But horses can get Lyme disease whenever infected ticks are active.
Several factors likely contribute to the spread:
- Wildlife populations: Deer and other wildlife hosts, including migratory birds, can carry the ticks and move them to new areas.
- Changing landscapes: In many areas abandoned farmland is reverting to forest, and the ticks prefer forest habitat to fields. They're often found in the brush of the forest understory and forest edge and suburban yards, which mimic that habitat.
- Warming climate: Warmer winters allow ticks to expand their range northward and to spread the disease for most of the year, as they are active whenever the temperature is above 40 F.
Reports of Lyme disease have also increased as people have become more aware of it. If your horse is in a region where blacklegged ticks live, he's at risk. But even if he's bitten, he may not get sick. Even if a tick is packing the bacteria, it generally must attach and feed for more than 24 hours before it transmits the infection to its new host. And even when a horse is infected, he may not develop any signs of the disease. It's difficult to prove Lyme disease. You may never see the tick that bit your horse; the ticks generally drop off after feeding. Signs of the disease often don't emerge for five to six weeks after the bite, and the signs vary widely and are notoriously vague.
Common symptoms are:
- Stiffness in large working joints (fetlock, knee, elbow, hock or stifle, for example).
- Lameness that's sporadic, affects multiple sites or shifts from limb to limb is characteristic.
- Generalized tenderness or sensitivity your horse flinches, perhaps, when you curry him or seems to overreact to other sensory stimuli. This condition, called hyperesthesia, results from inflammation in the skin and nearby nerves.
- Behavioral changes, such as an unwillingness to work and a depressed or irritable attitude.
You may see other signs low energy levels, low-grade fever, joint swelling, a sore back. Often early signs fade, and they may never return. But persistent Lyme disease has been linked to weight loss, chronically stiff and swollen joints, neurological problems and inflammation of the eye. Some of the damage may stem from the immune response the horse mounts against the infection, rather than from the bacteria themselves.
Where the disease is common, worry about it sometimes leads horse owners to think "Lyme" at the first sign of trouble. It's essential to rule out other possible causes overwork, injuries, other diseases that can produce similar signs. For this, your veterinarian will start with a thorough exam and a review of your horse's history. If the results suggest Lyme disease, the next step is to confirm, through blood tests, that your horse has been infected with Bb bacteria.
When Lyme disease is recognized and treated early, the outlook for recovery is good. Most cases respond to antibiotics. Tetracycline and doxycycline are the most recommended treatments. Your vet may also suggest an anti-inflammatory such as flunixin meglumine (Banamine) or phenylbutazone to ease discomfort. Most horses show improvement within days of starting antibiotics, but that doesn't mean the bacteria are gone. Treatment generally continues for 30 days. The longer it goes untreated, the greater the risk that its effects will linger. Tissue damage in joints and other areas, whether caused by the bacteria or the inflammation that results from the disease, can be lasting.
There is no approved vaccine against Lyme disease for horses. For now, the best way to protect your horse is to limit his exposure to the ticks that carry the Bb bacteria. If you live where Lyme disease is prevalent:
- Apply fly repellents that contain permethrins- These insecticides are effective against ticks as well as flies, so the repellents will help discourage ticks from attaching to your horse. Be sure to use the repellents in fall and early spring, times when adult ticks are active even though flies may not be a major problem.
- Give your horse a thorough daily grooming - Pay special attention to the base of his mane and tail and around his ears, throatlatch and belly. Blacklegged ticks are so small that they're really hard to find, but rigorous grooming may help keep them from hiding out in these areas. If you find a tick, use tweezers to grasp it right at the skin, where its mouthparts are embedded, and pull gently up.
- Make your horse's turnout space unfriendly to ticks - Tall grass, brush and overhanging branches make great tick habitats; the little pests can crawl to the tips of leaves and branches and latch onto your horse as he brushes past. If you mow the grass, cut the brush and trim the branches, you'll have fewer ticks to worry about.