**Core Concept**
Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of rare, fatal neurodegenerative disorders caused by misfolded proteins called prions. These diseases are characterized by the deposition of amyloid plaques in the brain, leading to neuronal loss and brain damage.

**Why the Correct Answer is Right**
Prion diseases are unique in that they are caused by a protein, not a virus or bacteria. This protein, the prion, is misfolded and can induce normal proteins in the brain to also misfold, leading to the characteristic amyloid plaques. The prion protein (PrP) is primarily expressed on the surface of neurons and is responsible for the transmission of the disease. There is no cure or treatment available for prion diseases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because prion diseases are indeed transmissible to other animals, including humans, through contact with infected tissue or contaminated food products.
**Option B:** This option is incorrect because prion diseases are not caused by a viral or bacterial infection, but rather by the misfolded prion protein.
**Option C:** This option is incorrect because prion diseases are not caused by a genetic mutation, but rather by the misfolding of the prion protein.

**Clinical Pearl / High-Yield Fact**
Prion diseases are a classic example of a "protein-only" infectious agent, and their unique transmission properties make them a fascinating area of study in the field of microbiology and infectious diseases.

**Correct Answer:** None of the above.