Lyme Disease (a Timely Tick Topic)

What is Lyme Disease?
     Lyme disease is a bacterial infection caused by Borrelia burgdorferi, a spirochete transmitted by Ixodes ticks.  Deer and mice are the normal mammals in the Lyme disease cycle, and other species such as horses and humans are "aberrant" or unintentional hosts of the disease.
How does a horse contract Lyme Disease?
     An adult tick that is infected with Borrelia burgdorferi must attach and feed for longer than 24hrs to infect a horse with Lyme disease.  The bacteria lives in the "gut" of the tick and is transferred to the animal as the tick feeds.
What are the Clinical Signs of Lyme Disease?
     Fever, diffuse muscle soreness and generalized joint stiffness are the most commonly seen clinical signs.  The presenting signs can be vague, and many clinical signs can be caused by a combinations of other factors such as age, level of work, orthopedic problems, or other infections.  
How is Lyme Disease Diagnosed?
     Diagnosing lyme disease is complicated by the fact that many horses have been exposed to Lyme disease and will have detectable antibodies to Borrelia burgdorferi but may not actually be infected.  Immunofluorescent Antibody (IFA) testing is the optimal testing method, but only diagnoses exposure as many healthy horses may have antibody titers.  
A new "multi-plex" test available through Cornell Animal Health Diagnostic Lab, identifies antibody titers to three seperate Borrelia antigens, and can be used to distinguish between acute (new infections), chronic (or exposure), and vaccine related titers.
     Response to treatment is often used to diagnose Lyme disease, but is also complicated as the antibiotics used to treat (tetracylcines) also have anti-inflammatory properties which may reduce muscle and joint pain, even without an infection to treat.  
     For a definitive diagnosis of Lyme disease, an IFA test should be performed before and after starting treatment, and a notable decrease in the level of antibodies should be seen.
Is there Treatment for Lyme Disease?
     As mentioned above, Lyme disease can be treated with tetracycline antibiotics (oxytetracycline or doxycycline).  Oxytetracycline is used most commonly in horses and is administered intravenously (IV).  Treatment is typically continued for 3 weeks and titers should be retested to document a decrease below "normal" exposure levels before treatment is stopped.
How can I Prevent Lyme Disease?
     Tick control is key to preventing lyme disease.  Regular grooming and checking under mane/forelock and around the base of tail during tick season (mid spring through late fall), with quick removal of any ticks is the most important form of prevention.  In some areas a topical tick preventative may need to be used, and your veterinarian may be able to recommend what has worked best in that area.
     Although a vaccine is available for Lyme disease, it is not commonly used in horses, and vaccination will create elevated antibody levels, which can create difficulties in diagnosing infection.  This is less of a concern with the new "multi-plex" test through Cornell.