The causative agent of mad-cow diesase is a

Options

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

Answer

**Step-by-Step Solution:**

1. **Identify the Disease**: The question refers to "mad cow disease," which is scientifically known as Bovine Spongiform Encephalopathy (BSE).

2. **Understand the Nature of the Disease**: Mad cow disease is a fatal neurodegenerative disease that affects cattle, leading to spongy degeneration of the brain and spinal cord.

3. **Identify the Causative Agent**: The causative agent of mad cow disease is not a bacterium, worm, or virus. Instead, it is a specific type of infectious agent.

4. **Define the Causative Agent**: The infectious agent responsible for mad cow disease is a misfolded protein known as a prion.

5. **Conclude the Answer**: Therefore, the correct answer to the question is that the causative agent of mad cow disease is a prion.

**Final Answer**: Prion

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