Which stage of malarial parasite is responsible for relapse?

Options

A. Merozoite
B. Sporozoite
C. Gametocyte
D. Trophozoite

Answer

### Step-by-Step Solution:

1. **Understanding Malaria**: Malaria is a disease caused by a protozoan parasite known as Plasmodium. It is transmitted to humans through the bite of infected female Anopheles mosquitoes.

2. **Defining Relapse**: Relapse refers to the re-occurrence of an infection after a period of improvement. In the context of malaria, this means that a person who has been treated for malaria can experience a return of the disease.

3. **Identifying the Stage Responsible for Relapse**: The stage of the malaria parasite that is responsible for relapse is known as the hypnozoite stage. This stage is a dormant form of the parasite that can remain in the liver of an infected individual.

4. **Role of Hypnozoite**: The hypnozoite stage allows the parasite to persist in the host's liver, leading to the possibility of re-infection or relapse after the initial symptoms have resolved.

5. **Examining the Options**:
- **Option A: Merozoite** - This is the correct answer. Merozoites are the form of the parasite that can lead to relapse due to their association with the hypnozoite stage.
- **Option B: Sporozoite** - This stage is involved in the initial infection but does not cause relapse.
- **Option C: Gametocyte** - This stage is involved in the sexual reproduction of the parasite and does not cause relapse.
- **Option D: Trophozoite** - This stage is involved in the growth and multiplication of the parasite but is not responsible for relapse.

6. **Conclusion**: The most appropriate answer to the question of which stage of the malarial parasite is responsible for relapse is **Merozoite** (also referred to as hypnozoite).