**Core Concept**
Prion-associated diseases are a group of neurodegenerative disorders caused by misfolded proteins called prions, which can induce normal proteins to also misfold, leading to cell death and tissue damage. These diseases are unique in that they can be transmitted through infectious prions, rather than through a traditional infectious agent like a virus or bacteria.

**Why the Correct Answer is Right**
Alzheimer's disease is the most common cause of dementia, but it is not classified as a prion-associated disease. Unlike prion diseases, Alzheimer's disease is characterized by the accumulation of amyloid-beta plaques and tau tangles in the brain, which lead to neuronal loss and cognitive decline. The pathophysiology of Alzheimer's disease is distinct from prion diseases, and it is not transmitted through infectious prions. The main prion protein associated with Alzheimer's disease is not a prion but a normal cellular protein that is involved in the disease process.

**Why Each Wrong Option is Incorrect**
**Option A:** Scrapie is a prion-associated disease that affects sheep and goats, causing neurodegeneration and death. It is a classic example of a prion disease and is transmitted through infectious prions.
**Option B:** Kuru is another prion-associated disease that was transmitted through cannibalism in Papua New Guinea. It is characterized by progressive neurological degeneration and is caused by infectious prions.
**Option C:** Creutzfeldt-Jakob's disease is a human prion disease that is caused by infectious prions and is characterized by rapid neurodegeneration and death.

**Clinical Pearl / High-Yield Fact**
Prion diseases are unique in that they can be transmitted through infectious prions, which can be present in contaminated tissue or medical equipment. This highlights the importance of proper handling and disposal of tissue and equipment to prevent transmission of prion diseases.

**✓ Correct Answer: D. Alzheimer's disease**