Don't Get Ticked Off:  Learn the Facts About Tick-borne Disease

Emily Steele, DVM

 Living in Minnesota, most of us and our horses have had an encounter with that irritating pest – the tick.  Besides causing pain and having a disgusting appearance, ticks  carry diseases that make us and our horses sick. 

One tick borne disease that commonly affects horses in our area is known as Anaplasmosis.  Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum.  Studies done on the disease show that it can be spread by the western black-legged tick,  a close relative of the deer tick.  Reasearchers believe that all ticks in this particular family are able to spread the disease, making the deer tick the likely culprit in our area.  Horses infected with Anaplasma phagocytophilum usually become depressed, have a high fever, and their lower limbs and abdomen may even become swollen.  In our practice, we have found that horses may develop one or all of these signs when infected.  In naturally infected horses, signs can take as long as 18 to 25 days after the tick bite to develop.  So, a tick can bite your horse, have a meal and fall off long before your horse ever gets sick.  Luckily, Anaplasma phagocytophilum can be found through blood testing and can be effectively treated with an antibiotic. 

Another disease our horses catch from ticks is Lyme's disease.  Just like humans, Lymes disease in horses is transmitted by the deer tick and is caused by the bacterium Borrelia burgdorferi.  Lymes disease is very difficult to diagnose in horses.  One reason for this is that the clinical signs of the disese are nonspecific and often occur in many body systems.  Signs include chronic weight loss, sporadic lameness, laminitis, low-grade fever, swollen joints, muscle tenderness, and anterior uveitis.  All of the clinical signs associated with Lymes disease can be caused by other diseases and may be mild.  A blood test is available to test for Lymes disease, however; horses can be exposed to Lymes disease and not develop any illness.  Therefore, although a horse may test positive, Lymes disease may not be the source of its illness.  Often, a positive diagnosis of Lymes disease is made if a horses responds well to treatment.           

No vaccine exists for either tick disease in horses.  There are vaccines available to prevent Lymes disease in other species, however; none of the available vaccines are approved for horses.  Our best defense against tick borne diseases is daily grooming, tick removal and using tick repellents that contain permethrin. Continue to use repellent into the late fall as ticks are plentiful long after other insects have died off.  Keeping pastures mowed and removing brush and woodpiles can also decrease the number of ticks in your horse's environment. 

If you notice any signs of Erlichiosis or Lymes disease in your horse, contact you veterinarian as soon as possible.