It can affect any age, breed or gender. Cases may follow a previous outbreak of the abortion or respiratory forms. Has also occurred where no additions to the farm and no previous outbreaks of any form. Most commonly the clinical signs are ataxia and weakness in the limbs, sometimes with urinary incontinence and fecal retention. Often signs start in the rear limbs and progress to the fore limbs.
Many horses progress to recumbency.
Lesions in the CNS of horses resembles an Arthus reaction or type III hypersensitivity. They may be the result of an immune-complex vasculitis. Vasculitis, congestion and degeneration of nervous tissue may be mutifocal and widespread. Historical findings and ruleouts of other neurologic diseases. CSF is often xanthochromic with few to no cells present.