Which of the following is the infective stage of Plasmodium in the secondary host?

Options

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

Answer

To determine the infective stage of Plasmodium in the secondary host, we need to analyze the stages of Plasmodium and identify which one is responsible for infecting the host. Here’s a step-by-step breakdown:

### Step 1: Understand the lifecycle of Plasmodium
Plasmodium is a protozoan parasite that causes malaria. It has a complex lifecycle involving two hosts: the primary host (the mosquito) and the secondary host (humans).

### Step 2: Identify the stages of Plasmodium
The key stages of Plasmodium include:
- **Trophozoite stage**: This is the active feeding stage that occurs inside the human host. It is not the infective stage.
- **Sporozoite stage**: This stage is formed in the salivary glands of the mosquito. When the mosquito bites a human, it injects these sporozoites into the bloodstream, making this the infective stage for humans.
- **Microgametocyte**: This stage refers to the male gametes formed in the mosquito. It is not directly infective to humans.
- **Merozoite stage**: This stage occurs after the sporozoites invade liver cells and multiply. Merozoites are released into the bloodstream and can infect red blood cells, but they are not the initial infective stage.

### Step 3: Determine the infective stage for the secondary host
From the analysis, the sporozoite stage is the one that is injected into the human body by the mosquito and is responsible for initiating the infection in the secondary host.

### Conclusion
The infective stage of Plasmodium in the secondary host (humans) is the **Sporozoite stage**.

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