It’s not just an Eastern problem.
It’s rare — but we do have Lyme disease in Oregon.
Here’s what you need to know.
What is Lyme disease?
Lyme disease is caused by a bacterium called Borrelia burgdorferi and is spread through tick bites. The causative type of tick in our area is called the western blacklegged tick (Ixodes pacificus, see illustration below). Ticks must be attached for 36-48 hours in order to transmit the bacterium that causes the disease. It is important to note that immature ticks (also called nymphs) can also spread the disease and are very small, about the size of a flea, which can be difficult to spot unless looking closely. Lyme disease has been rarely reported in Oregon as we have a low incidence of infected ticks – annually there are roughly 40-50 human cases.
Lyme disease can be found all over Oregon. The Southwestern corner has the highest incidence, which includes our neighboring Douglas County.
Symptoms
The symptoms of Lyme disease are nonspecific, which means that many other more common diseases present the same way. When considering asking for a Lyme test, know that there are many other diagnostics that may also be recommended to rule out causes of your horse’s symptoms. Symptoms include chronic weight loss, sporadic, shifting leg lameness, low grade fever, muscle tenderness, swollen joints, change in behavior, increased skin sensitivity, depression, and head tilt.
Testing
The current test of choice is a Lyme multiplex assay which is a blood test that measures the antibody response to several proteins present (OspA, OspC, and OspF). This test can diagnose Lyme disease as early as 3-5 weeks after infection and is sensitive for both acute and chronic infections.
If neurologic symptoms are observed, a cerebrospinal fluid (CSF) sample must be taken and compared to the blood test. Neurologic symptoms due to Lyme are extremely rare.
Prevention
There is no approved vaccination for Lyme disease in horses. Use of the dog vaccine has been studied in horses, however it has not been shown to provide significant protection and is very short lived in horses (it lasts for a maximum of 4 months and horses have gotten infected with Lyme even when the vaccine should have been considered protective).
Western Blacklegged Tick (click to enlarge)
Environmental management and topical treatments are paramount. Mow pastures with tall grass and brush to eliminate the tick’s natural environment. Use topical insecticides that contain pyrethrins, such as Equi-Spot or Ultra-Boss. Commercial pyrethroids are also available to apply to pastures and paddocks, make sure to follow label directions when applying.
Deworming with ivermectin and moxidectin are also effective, however the tick must have a blood meal to be affected so this does not prevent bites but will aid in infestations.
Check horses daily – the most common areas for ticks are on the chest, underbelly, mane, tailhead, or flanks. Remove ticks with tweezers – do not crush or twist the tick, do not apply baby oil or other topicals to smother the tick or use a match to get the tick to detach. Just grasp the tick as near the skin as possible with the tweezers and slowly but firmly pull it out of the horse. Drop the tick into a small jar of rubbing alcohol to kill it. Wash the site with a mild antiseptic such as Betadine or Chlorhexidine.
If you have any questions, please do not hesitate to contact the clinic at 541-689-0205 or email [email protected]
