Which disease is caused by virus?

Options

A. polio
B. leprosy
C. TB
D. malaria

Answer

To determine which disease is caused by a virus, we can analyze the options provided and identify the causative agents of each disease.

### Step-by-Step Solution:

1. **Identify the Diseases**: The question asks for a disease caused by a virus. We will consider the diseases mentioned: polio, leprosy, tuberculosis (TB), and malaria.

2. **Analyze Polio**:
- Polio is a disease that affects the nervous system and can lead to paralysis.
- The causative agent of polio is the poliovirus.
- Therefore, polio is a viral disease.

3. **Analyze Leprosy**:
- Leprosy is a chronic infectious disease that primarily affects the skin, nerves, and mucous membranes.
- It is caused by the bacterium Mycobacterium leprae.
- Thus, leprosy is not a viral disease.

4. **Analyze Tuberculosis (TB)**:
- Tuberculosis is a serious infectious disease that mainly affects the lungs but can also affect other parts of the body.
- It is caused by the bacterium Mycobacterium tuberculosis.
- Therefore, TB is also not a viral disease.

5. **Analyze Malaria**:
- Malaria is a disease caused by parasites that infect red blood cells.
- The specific parasites responsible for malaria are from the genus Plasmodium.
- Hence, malaria is not a viral disease.

6. **Conclusion**: After analyzing all the diseases, we find that the only disease caused by a virus among the options is polio.

### Final Answer:
The disease caused by a virus is **Polio**, which is caused by the **poliovirus**.