Treatment and Outcome-The horse responded well to doxycycline treatment (10
mg/kg [4.5 mg/lb], PO, q 12 h for 60 days) and returned to normal exercise.
However, 60 days after treatment was discontinued, the horse again developed
a stiff neck and rapidly progressive neurologic deficits, including severe
ataxia and vestibular deficits. The horse’s condition deteriorated rapidly
despite IV oxytetracycline treatment, and the horse was euthanatized.
Postmortem examination revealed leptomeningitis, lymphohistiocytic
leptomeningeal vasculitis, cranial neuritis, and peripheral radiculoneuritis
with Wallerian degeneration; findings were consistent with a diagnosis of
Clinical Relevance-Nervous system infection with B burgdorferi should be
considered in horses with evidence of meningitis and high or equivocal serum
anti-B burgdorferi antibody titers. Evaluation of immune function is
recommended in adult horses evaluated because of primary bacterial