Lyme Disease in Horses
Lyme disease is a tick-borne disease that affects humans and animals, including horses. It is caused by a bacterial spirochete, Borrelia burgdorferi. The disease is most prevalent in the northeast, upper Midwest, and California. The deer tick and the western black-legged tick are the thought to be the only ticks that carry the disease in the U.S.
Ticks are most often found living in the following conditions:
- In the tall grass
- In and around leaves and brush piles
- In yards or pastures boarded by brush thickets or forests
To reduce the risk of tick bites, the following are recommended:
- Reduce exposure to the tick-rich environments listed above.
- Keep yards, pastures, and barn areas mowed.
- Don’t use pastures that are boarded by thickets or dense woods.
- Apply insect repellents that contain permethrin or pyrethrin on a regular basis.
Horses, pets, and humans should be checked for ticks daily. Pay special attention to the mane and tail area on your horse. It takes 24 hours for an infected tick to pass the disease on to their host. Remove any ticks you find within 24 hours.
Symptoms in the horse:
The symptoms of Lyme disease are often vague and can be similar to other disorders. They include:
- Changes in behavior
- Low-grade fever
- Neck/back pain
- Neurologic signs
- Sporadic lameness
- Shifting leg lameness
- Swollen joints
- Weight loss
Because of a horse’s dense hair coat, owners are less likely to see the characteristic bull’s-eye pattern on the skin, but it can occur where hair is sparse so keep an eye out for any skin abnormalities.
Understanding the life cycle of the deer tick and black-legged tick can reduce the risk of exposure.
The deer tick and black-legged tick have a two-year life cycle that is split into three stages: larva, nymph, and adult.
- Eggs are laid on the ground by the adult female tick in the spring.
- Larvae hatch later in the summer and they are about the size of a period.
- The larvae reside on the ground and attach to small mammals or birds that rub up against them. They bite the host and feed on the blood of the host for several days before dropping off.
- If the host is infected with Lyme disease, it will pass the disease on to the larva. Infected hosts are considered Lyme reservoirs.
- During this stage the larvae will only feed from one host so they do not pose a threat to humans or animals.
- Larvae transform into nymphs in the fall
- Nymphs are inactive during the winter and early spring, but come May the action begins.
- Nymphs are about the size of a poppy seed. They wait on vegetation near the ground for a passing small mammal or bird. They latch onto this host and feed on its blood for 4 to 5 days.
- If the nymph was infected with Lyme disease during the larva stage then it continues to carry the disease and will transmit it to the host. If the nymph is disease-free but the host carries the disease, then the nymph will become infected at this time.
- The nymph prefers birds and small mammals but it will bite humans and other animals. Nymphs are responsible for most of the Lyme disease cases in humans.
- Once engorged, the nymph drops off the host and molts into an adult. Leaf litter is a common place to find molting nymphs.
- Peak activity for the adult is late October to early November.
- The adults lie in wait in tall grass and weeds for deer or other larger animals, including humans, to pass by. Deer are their preferred hosts. The tick takes in a blood meal and mates either on or off the host. The ticks overwinter in leaf litter, lay their eggs in early spring, and then die.
- Those ticks that are unsuccessful in getting a blood meal in the fall will overwinter in the leaf litter or other vegetation and try again in the spring. Generally they are inactive while the temperatures are less than 45 degrees. The second period of peak activity is March to early April. Once they succeed in feeding, they bred, lay eggs, and die.
- Each female tick lays around 3,000 eggs, which hatch later in the summer.
- Up to 50% of the adult ticks in highly endemic areas will carry Lyme disease and pass it on to their hosts.
Avoiding tick-infested environments, taking steps to protect your horse, and checking them daily for ticks can help reduce the risk of infection. If you suspect your horse has been exposed to, or is suffering from Lyme disease, contact your veterinarian immediately. Early diagnosis and treatment can mitigate the long-term, debilitating effects of the disease.