Lyme’s disease is caused by the organism Borrelia Burgdorferri. This disease is most commonly transmitted by the deer tick during a blood meal. Small rodents serve as the reservoir for these bacteria. The tick feeds on the rodent and then transmits it to the horse (or human) the next time it feeds. It is felt that this disease is becoming more prevalent. The months of June and July seem to have the highest number of reported new cases.
Since a horse has a coat, the classic skin lesions seen in humans are often not present or not detected. The symptoms can be vague making diagnosis difficult. These symptoms include fever, depression, chronic weight loss, shifting leg lameness, laminitis, swollen joints, muscle tenderness and anterior uveitis. Chronic infections can exhibit neurologic signs such as depression, trouble eating, head tilt and encephalitis. A blood titer test for Lyme’s disease is available but not always reliable. Diagnosis is often made by excluding other potential diseases. Several antibiotics are available to treat Lyme’s disease, but an extended course of 21 days or more is often required.
The tick needs to feed to engorgement for transmission to occur. This makes the nymph stage the most dangerous. They are smaller and harder to detect and can feed to engorgement much more quickly. Therefore, it is important to check your horse daily as part of your grooming routine. You should pay special attention to the area just behind the shoulders, between back legs and at the base of the tail. These areas have less hair thus being easier locations for ticks to latch on. The inside of ears is another area ticks seem to like. Tick bites in the ears appear to be very painful and can cause a horse to become head shy.
Since small rodents are the natural harbor for Lyme’s disease, prevention is aimed at reducing the areas they live. Barns should be kept clean and feed properly stored. Pastures should be kept free of debris and other areas that would provide suitable habitat for small rodents. Pastures should be mowed to make it more difficult for ticks to transition to horses. Ticks like to hang out at the edges of wood lines. Keeping these areas open will also help reduce the tick population.
While there is a vaccine for available for dogs, it efficacy and safety has not been determined for horses and its use cannot be recommended.