Question

The infective stage of Plasmodium is

• A. Trophozoite
• B. Cryptozoite
• C. Sporozoite
• D. Merozoite

Hint:

Think about which parasite form the mosquito actually injects into the bloodstream.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which stage of the Plasmodium life cycle is responsible for transmitting infection to humans.

Step 2: Key Concept or Approach:
The Plasmodium life cycle alternates between a mosquito vector and a human host. Inside the female Anopheles mosquito, sporozoites develop in the salivary glands and are injected into human blood during a bite. This sporozoite is the stage that actually establishes new infection in a human, making it the infective stage for humans.

Step 3: Working Through the Options:
Trophozoite is the feeding, growing stage found inside human red blood cells during the erythrocytic cycle, not the stage that starts infection. Cryptozoite refers to the tissue (exoerythrocytic) stage that develops in the liver after sporozoites enter, not the entry stage itself. Sporozoite is the motile form injected by the mosquito bite and is the true infective stage for humans. Merozoite is released from liver cells or infected red cells to invade fresh red blood cells, but it is not the stage that transmits infection from mosquito to human.

Step 4: Conclusion:
The correct answer is sporozoite, the stage injected by the mosquito that infects humans.