Diphtheria is caused by

Options

A. poisons released by living bacterial cells into the host tissue
B. poisons released from dead bacterial cells into the host tissue
C. poisons released by virus into the host tissues
D. excessive immune response by the host's body

Explanation

**Step-by-Step Solution:**

1. **Identify the Cause of Diphtheria**: Diphtheria is an infectious disease that is primarily caused by a specific type of bacteria.

2. **Determine the Specific Bacteria**: The bacteria responsible for diphtheria is called *Corynebacterium diphtheriae*.

3. **Understand the Mechanism of Disease**: This bacterium releases a toxin (poison) that affects the host's tissues, leading to the symptoms of the disease.

4. **Evaluate the Options Given**:
- **Option 1**: Poison released by living bacterial cells into the host tissue. This is correct as the toxin is produced by living *Corynebacterium diphtheriae*.
- **Option 2**: Poison released from dead bacterial cells into the host tissue. This is incorrect because the toxin is produced by living bacteria.
- **Option 3**: Poison released by a virus into the host tissue. This is incorrect because diphtheria is caused by bacteria, not viruses.
- **Option 4**: Excessive immune response by the host body. This is incorrect as the disease is not caused by an immune response but by the toxin from the bacteria.

5. **Conclusion**: Based on the evaluation of the options, the correct answer is that diphtheria is caused by the poison released by living bacterial cells.

**Final Answer**: Diphtheria is caused by poison released by living bacterial cells into the host tissue.

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