Final answer:
Creutzfeldt-Jakob disease (CJD) is the disease thought to be caused by prions, which are infectious protein agents resulting in fatal neurodegenerative conditions.
Step-by-step explanation:
The disease state that is thought to be caused by infectious protein agents known as prions is Creutzfeldt-Jakob disease (CJD). Prions are misfolded proteins which can trigger normal proteins in the brain to also misfold, resulting in a group of fatal neurodegenerative disorders called transmissible spongiform encephalopathies (TSEs). CJD is one such disease, characterized by rapid neurodegeneration and spongiform changes in the brain, leading to dementia and ultimately death. Disorders like Lewy body disease, Pick's disease, Parkinson's disease, and Progressive supranuclear palsy are linked to other pathologies involving proteins misbehaving, but not specifically to prions.