The causative agent of mad-cow diesase is a

Options

A. Virus
B. Bacterium
C. Prion
D. Worm

Answer

### Step-by-Step Solution:

1. **Understanding the Disease**: Mad cow disease, scientifically known as Bovine Spongiform Encephalopathy (BSE), primarily affects cattle and is characterized by a spongy degeneration of the brain.

2. **Identifying the Causative Agent**: The causative agent of mad cow disease is not a conventional pathogen like a virus or bacterium. Instead, it is a type of infectious agent known as a prion.

3. **Defining Prions**: Prions are misfolded proteins that can induce other normal proteins in the brain to also misfold, leading to brain damage and the characteristic symptoms of the disease.

4. **Differentiating from Other Pathogens**: Unlike viruses, bacteria, or worms, prions do not contain nucleic acids (DNA or RNA) and are resistant to conventional methods of sterilization, making them unique among infectious agents.

5. **Conclusion**: Based on the information, the causative agent of mad cow disease is confirmed to be prions.

### Final Answer:
The causative agent of mad cow disease is a **prion**.

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