In which of the following disease, the number of `T_H` cells in body considerably decreases over the period of time ?

Options

A. AIDS
B. Cancer
C. Malaria
D. Typhoid

Answer

To solve the question regarding which disease leads to a considerable decrease in the number of T_H cells in the body over time, we can follow these steps:

### Step-by-Step Solution:

1. **Understand T_H Cells**: T_H cells, or Helper T cells, are a type of T-lymphocyte that plays a crucial role in the immune system by helping to activate other immune cells.

2. **Identify the Diseases**: The diseases mentioned in the question are AIDS, Cancer, Malaria, and Typhoid.

3. **Analyze Each Disease**:
- **AIDS**: This disease is caused by the Human Immunodeficiency Virus (HIV), which specifically targets and destroys T_H cells. Over time, as the virus replicates, the number of T_H cells decreases significantly, leading to immunodeficiency.
- **Cancer**: While cancer can affect the immune system, it does not specifically target T_H cells. The immune response may be compromised, but T_H cells do not necessarily decrease in number due to cancer itself.
- **Malaria**: This disease is caused by the Plasmodium parasite, which primarily affects red blood cells. It does not directly target T_H cells.
- **Typhoid**: Caused by the Salmonella typhi bacteria, typhoid affects the digestive system and does not specifically reduce T_H cell numbers.

4. **Conclusion**: Among the options provided, AIDS is the only disease that leads to a significant decrease in the number of T_H cells over time due to the direct action of the HIV virus on these cells.

### Final Answer:
The disease in which the number of T_H cells in the body considerably decreases over time is **AIDS**.

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