A 55-year-old man is brought to his physician's office with a 3-month history of progressive mental deterioration in the form of memory loss, mood changes, and errors in judgment. His gait is unsteady, and he requires assistance to prevent falling. He has no history of seizures, head trauma, or incontinence. Computed tomography (CT) scan and lumbar puncture are unremarkable. Physical examination reveals hypeonicity of all extremities, bilateral equivocal plantar response, ataxic gait, and myoclonic jerks in the lower extremities. What is the mechanism by which this infectious agent causes its pathology?