Lyme disease and EPM research

Lyme disease (infection with Borrelia bugdoferi) can confound EPM research because the diseases may have similar presentations. Clinically, there is no clear distinction that indicates a horse with Lyme disease from a horse with EPM.  Researchers are making an effort to describe the typical Lyme case.  Signs consistent with Lyme disease include ataxia, peripheral neuropathies, cranial nerve inflammation, muscle wasting, skin sensitivity, stiff neck, and possibly uveitis.  Changes may be observed in CSF fluid prompting collection of fluid by a spinal tap to look for organisms or antibodies against B bugdorferi.

There is no good diagnostic test to define the actively infected horse with neuroborelliosis (organisms in the central nervous system).  Detecting the organism in the central nervous system isn’t easy and requires molecular analysis and reasonable certainty that there is antibody production in the CSF, not antibody contamination from the periphery.  Similar to a supportive diagnosis of EPM, some clinicians use the serum/CSF ratio—generally a referral facility.  A test-positive interpretation may necessitate detection of antibodies against several Borrelia antigens as well as paying close attention to dilution factors used in the laboratory.

 

CDC Map of Lyme Disease in the US

Where the horse lives is an important consideration when including Lyme as the cause of neurologic disease because Borreliosis is a regional disease.  Check out the CDC’s map, shown above. Serum testing for Borrelia antibodies by ELISA is helpful to support a diagnosis, most Borrelia infected horses have serum antibodies.  This is another disease in which ruling out other causes of the signs is key.  And a negative serum test supports another cause of neurologic dysfunction and maybe helpful to rule in other diseases on the differential diagnosis list.

Several treatment protocols for Lyme are published, however, the ability to eliminate the organism by antibiotic therapy (in some infections) may not be possible.  Chronic disease is suspected in horses just like the syndrome in people.  Lyme disease does cause inflammation increasing the expectation that inflammatory markers like C-reactive protein will be elevated. Likewise, treating the inflammation can alleviate some signs of the disease and is useful.

Because horses can have antibodies against S. neurona, horses with and without EPM can have Lyme.  Lyme and EPM are a serious combination and can be lethal.  In our research it is important to include horses that have disease exclusively due to EPM.  It helps our final FDA submission that we are conducting laboratory studies because we know the horses don’t have Lyme disease.  But we’d like to avoid the  issues that would complicate our analysis of field cases.  That is why we ask you if Lyme disease is a consideration, you’ll find it on our submission form.  Being aware of Lyme, the regional nature of the disease, and ruling it in or out in a horse with ataxia is important to us.

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