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Dr. Sarah L. Timm, D.V.M.: Horses and Tick-borne Diseases

Keeping you and your horse safe is critical to prevention of tick-borne diseases. Nancy Whyte-Olay interviews veterinarian Dr. Sarah L. Timm, who explains some of the signs and symptoms of tick-borne disease in horses. Dr. Timm, who grew up in Ridgefield, can be reached at the Roxbury Animal Clinic in Roxbury, CT.

What are the most common tick-borne diseases that affect horses in this region? Have you observed a change in incidence? Have you observed any emerging tick-borne diseases?

Lyme disease and anaplasmosis are the most common tick-borne diseases in this area. I cannot comment as to specific changes in incidence, but anecdotally, I have observed more Lyme disease in Fairfield County and more anaplasmosis in Litchfield County. Currently, there are no emerging tick-borne diseases that we know of in horses. We commonly see co-infections with both Lyme and Anaplasma bacteria. As both infections generally respond to the same treatment, we often do not specifically diagnose one over another. Horses do get neuroborreliosis, but it is usually only definitively diagnosed on post-mortem examination. Post-mortem examinations are not commonly done on horses unless they are at a university hospital, so it’s hard to say how prevalent neuroborreliosis really is. Horses with severe neurological deficits can quickly become a danger to the people around them, so regardless of the cause, they are often euthanized.

How reliable are the diagnostic tests? The UCONN Connecticut Veterinary Medical Diagnostic Laboratory offers Elisa, Western Blot, PCR and serologic testing. Are these the tests used as standards of practice? Is the Multiplex procedure test only available at Cornell?

All of the diagnostic tests available have varying degrees of reliability and usefulness. The 4DX snap test designed for dogs tests for Lyme, Anaplasma, Ehrlichia and heartworm in dogs, but the Lyme portion of the test can be used to screen for exposure in horses. It is a simple, handheld ELISA test and can be run on the farm, so we sometimes use it to screen for Lyme infection. But more commonly I send out the Lyme Multiplex test to Cornell, as it gives us more information about the duration of infection by evaluating the types of antibodies produced. The Lyme Multiplex tells us if the immune response is acute or chronic and helps us build a larger clinical picture of the individual case, as there are often multiple potential problems with the horse, only one of which may be Lyme. There is the tendency for owners of high-performing horses with intermittent lameness or other musculoskeletal problems to presume Lyme is a component and want to treat for it. It is such a grey area, I cannot say it is the wrong or right thing to do. At the same time, horses that show acute symptoms of Lyme or Anaplasma infection (e.g., lethargy, fever, lameness) are often treated presumptively without testing, and a positive response to treatment generally confirms the diagnosis of a tick-borne disease. Horses (and dogs) will frequently test positive for Lyme disease and be completely asymptomatic.

Is oral doxycycline the standard treatment for Lyme disease? How effective is it and how long should the treatment last?

Oral doxycycline for 30 days is the current standard treatment for Lyme disease in horses. However, this may be changing. Some veterinarians are starting to use minocycline to treat horses, as it has higher bioavailability and it also reaches higher concentrations in cerebrospinal fluid. Therefore, it may be more effective in cases of neuroborreliosis. Intravenous oxytetracycline has also been used successfully, and historically was the treatment of choice prior to the use of oral doxycycline. Doxycycline does seem to be very effective. There are some cases where I question if they are truly clinically symptomatic of Lyme disease, or rather they are asymptomatic of Lyme but have another concurrent orthopedic problem. In these cases we often treat with doxycycline regardless, as we cannot say for sure if Lyme is a component or not.

Is there an equine vaccine in the future? Do veterinarians use the canine vaccine for horses?

To my knowledge, there is no equine vaccine in the pipeline. Some veterinarians will use the canine vaccine off-label for horses. Currently there is no evidence to show it is effective. I personally do not use it in horses.

I’ve read recommendations to use permethrin based insect repellents on horses. Is that a safe product to use on horses?

Yes, it is safe to use permethrin based insect repellents on horses. You just have to make sure that you follow directions carefully, as dilution may be required if the product is concentrated, and as to frequency of application. Dr. Timm adds that the best resource for horse owners and riders is their equine veterinarian.

Sarah L. Timm, is a Bachelor of Veterinary Medicine and Surgery (BVMS) and a member of the Royal College of Veterinary Surgeons (MRCVS).

Some Key Points
∙ Do daily tick checks on both yourself and your horse, especially after trail riding. Don’t forget to check the horse’s mane, belly, tail and dock
∙If you find a tick, carefully remove it with tweezers, grasping the tick by its mouth parts, close to the horse’s skin
∙Horses do not show a skin rash
∙Signs of Lyme disease include weight loss, low-grade fever, sporadic or shifting leg lameness, muscle tenderness, arthritis, behavioral changes, poor performance, and skin hypersensitivity
∙Some signs of the tick-borne bacterial infection Anaplasma include lethargy/depression, limb swelling, small red/purple spots on the mucous membranes (nostrils, lips, mouth), yellow mucous membranes, and poor appetite
∙Cranial nerve deficits and uveitis (inflammation of the uveia, part of the eye) may be frequent features among horses with Lyme neuroborreliosis
∙Topically treat horses with a permethrin repellent, especially when they’ll be turned out to pasture or when riding on trails
∙Minimize habitat for mice, chipmunks, and other small creatures that carry ticks. Keep pasture free of brush and woodpiles
∙Keep deer out of pastures

For more information:
The UCONN Department of Animal Science

Lyme disease testing:
The Connecticut Veterinary Medical Diagnostic Laboratory (CVMDL) at the University of Connecticut, describes the diagnostic testing offered, including the ELISA, Western Blot, and PCR.

The Connecticut Agricultural Experimentation Station (CAES) provides information on how to reduce tick habitats.

Also, follow the BLAST steps and enjoy time outdoors this autumn.