Winter has finally loosened its grip on Western NY and we are all just itching to get outside and ride our horses.  But there is a very small bug to look out for that can cause a very big problem for your horse.

Lyme Disease and Horses

Lyme disease is the most common tick-borne disease in humans and animals in the United States.   It is caused by the bacteria Borrelia burgdorferi.  This bacteria is carried by Ixodes scapularis, the black-legged deer tick, and Ixodes pacificus, the western black-legged tick.  Transmission occurs when an infected tick bites an animal or person.  It must be attached for 24-36 hours for transmission to occur.  Although we most often find adult ticks on horses, the greatest transmission occurs at the nymphal stage.   Peak nymphal stages are from May to August, which is also when the highest transmission of Lyme disease occurs.  Lyme disease is most heavily reported in the northeast, upper mid-west and California.


Life Cycle of Deer Ticks

The tick has a two year life cycle.  Eggs are laid on the ground.  The adult female may lay up to 3000 eggs.  After laying the eggs, the female will die.  In order for the tick to develop, it requires a blood meal.  In the spring, eggs hatch into larva.  The larva feed on small animals, especially mice which in turn may become infected with the bacteria causing Lyme disease.  The larva is dormant in the fall and winter.  The following spring the larva becomes a nymph which is the most aggressive stage.  The nymph is the size of a poppy seed.  The nymph may transmit the disease to its mammalian host.  The nymph develops into an adult tick in the fall.  Adults are most active in the fall and winter when temperatures are greater than 40 degrees.  They tend to feed on larger mammals, especially white-tailed deer.



Diagnosis of Lyme disease can be difficult, as clinical signs are not specific to the disease.  In humans, clinical signs include fever, muscle soreness, fatigue and joint pain.  One of the early signs of the disease in humans is a red, circular patch called erythema migrans (EM) at the site of the bite.  Multiple spots may occur.  In horses, clinical signs include muscle soreness, hypersensitivity to touch, shifting-leg lameness, muscle soreness, low-grade fever, behavioral changes and poor performance.    There have also been reports of neuroborreliosis, an infection of the central nervous system.  These horses have shown neurologic symptoms such as ataxia, depression, inability to eat and/or head tilt, for example.  Diagnosis was made via cerebrospinal fluid analysis.  Borrelia-associated uveitis, inflammation in the eye, has also been diagnosed via sampling of the ocular fluid.

The most reliable diagnostic test available for Lyme disease is the Lyme Multiplex test performed at the Animal Health Diagnostic Center at Cornell University.  Blood is tested for the presence of antibodies to B. burgdorferi in the blood.  Results from this test can indicate whether the infection is recent or is chronic.  



Horses with Lyme disease are usually treated with a course of antibiotics, most commonly oxytetracycline, doxycycline, or minocycline.  The course of treatment may range from 30-60 days.  The most common side effect of the antibiotic is soft manure.  Evaluation of treatment is based on response to treatment.  A decline in antibodies also supports that treatment has been successful.  Testing may be done 6 weeks following treatment for early infection and 3 months after treatment of chronic infections.



Horses should be examined twice daily for the presence of ticks.  Adults and nymphs should be removed by closely grasping the tick close to the skin with fine tweezers or a tick key.  

Tick Key

The nymphs are the size of a poppy seed so can be difficult to see.  The neck, ears, under the mane and between the hind legs should be examined closely.  After removing the tick, place it in a container with a sealed top and dispose of it in the garbage.  Do not leave the tick on your barn floor or pasture, ready to re-attach to another animal!  Topical permethrin or pyrethrin-containing fly sprays or topical fly products such as Equi-spot´┐Ż may also be used.  At this time there are no FDA-approved vaccines for horses. 

The area around pastures should be maintained to deter tick infestation.  Remove brush and leaf piles.  Grass should be mowed to minimize mouse habitat and keep vegetation low.  Wood chips or gravel can be used between wooded areas and pasture to deter tick migration to grassy areas. 



Tick season is here, so be on the lookout.   Please call Genesee Valley Equine Clinic at 585-889-1170 if you have any questions.






Genesee Valley Equine Clinic continues its
 "How To" Video Series with Dr. Ann Dwyer.  
Anyone who has ever had to treat a horse's eye will tell you it is no easy task. Dr. Dwyer teaches you her technique to help you get the ointment medication in your horse's eye.
Genesee Valley Equine Clinic's How To: Medicate A Horses Eye
Genesee Valley Equine Clinic's How To: Medicate A Horse's Eye

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