Koch's postulates are not applicable to

Options

A. cholera
B. leprosy
C. TB
D. diphtheria

Explanation

**Step-by-Step Solution:**

1. **Understanding Koch's Postulates**: Koch's postulates are a set of criteria established by Robert Koch to identify the causative agents of infectious diseases. They include:
- The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

2. **Identifying the Options**: The question asks which disease does not follow Koch's postulates. The options typically include diseases like cholera, tuberculosis (TB), diphtheria, and leprosy.

3. **Analyzing Each Disease**:
- **Cholera**: Caused by Vibrio cholerae, this bacterium can be cultured in the laboratory and meets all Koch’s postulates.
- **Tuberculosis (TB)**: Caused by Mycobacterium tuberculosis, this bacterium can also be cultured and fulfills Koch's postulates.
- **Diphtheria**: Caused by Corynebacterium diphtheriae, it is culturable and meets the postulates.
- **Leprosy**: Caused by Mycobacterium leprae, this bacterium is unique as it cannot be cultured in the laboratory, making it unable to fulfill Koch's postulates.

4. **Conclusion**: Since leprosy (Mycobacterium leprae) cannot be cultured, it does not meet Koch's postulates. Therefore, the answer to the question is that Koch's postulates are not applicable to leprosy.

5. **Final Answer**: Leprosy (Mycobacterium leprae) is the disease to which Koch's postulates do not apply.

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