Infective stage of Entamoeba histolytica is

Options

A. Trophozoite
B. Precystic form
C. Metacystic form
D. Quadrinucleate cyst

Answer

To determine the infective stage of Entamoeba histolytica, we will analyze the different stages mentioned in the question and their characteristics.

### Step-by-Step Solution:

1. **Understanding the Life Cycle**:
- Entamoeba histolytica has several stages in its life cycle, including trophozoite, precystic form, metacystic form, and quadranucleated cyst.

2. **Identifying the Stages**:
- **Trophozoite**: This is the active, feeding stage of the parasite. It is not the infective form as it is found in the intestinal lumen and is involved in causing disease.
- **Precystic Form**: This is an intermediate stage that occurs before the formation of cysts. It is also not the infective stage.
- **Metacystic Form**: This stage is characterized by being uni-nucleated and is formed after the cysts have been ingested. It is not the infective stage either.
- **Quadranucleated Cyst**: This is the mature cyst stage, which is tetranucleated and is known to be the infective form of Entamoeba histolytica.

3. **Conclusion**:
- The infective stage of Entamoeba histolytica is the **quadranucleated cyst** (option D). This cyst is resistant to environmental conditions and can survive outside the host, making it capable of causing infection when ingested through contaminated food or water.

### Final Answer:
The infective stage of Entamoeba histolytica is **D. Quadranucleated cyst**.

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