CJD caused by prion proteins is seen in

Options

A. cattle
B. sheep
C. humans
D. all of these

Answer

To solve the question regarding Creutzfeldt-Jakob Disease (CJD) caused by prion proteins, let's break it down step by step:

### Step-by-Step Solution:

1. **Understanding CJD**:
- CJD stands for Creutzfeldt-Jakob Disease, which is a fatal neurodegenerative disorder.
- It is caused by prions, which are misfolded proteins that induce abnormal folding of normal cellular proteins in the brain.

2. **Identifying the Affected Organisms**:
- The question asks where CJD is seen. We need to analyze the options: cattle, sheep, humans, or all of these.
- CJD primarily affects humans.

3. **CJD in Other Animals**:
- In cattle, a similar prion disease is known as Bovine Spongiform Encephalopathy (BSE), commonly referred to as "mad cow disease."
- In sheep, the equivalent disease is called Scrapie.

4. **Conclusion**:
- While prion diseases do affect cattle and sheep, the specific disease known as CJD is primarily associated with humans. Therefore, the correct answer to the question is "humans."

### Final Answer:
CJD caused by prion proteins is seen in **humans**.