Which of the following stage of life cycle of Plasmodium is seen in humans?
**Core Concept**
The life cycle of Plasmodium involves several stages, including sporozoites, trophozoites, schizonts, and gametocytes. However, not all stages occur within humans, as the parasite requires a mosquito vector for part of its life cycle. The stage of Plasmodium seen in humans is crucial for understanding the pathogenesis of malaria.
**Why the Correct Answer is Right**
The stage of Plasmodium seen in humans is the **trophozoite**. This stage occurs within the erythrocytes (red blood cells) of the human host, where the parasite undergoes asexual reproduction, leading to the production of more trophozoites and ultimately schizonts. The trophozoite stage is responsible for the clinical manifestations of malaria, such as fever, anemia, and organ dysfunction.
**Why Each Wrong Option is Incorrect**
* **Option A:** Sporozoites are the stage of Plasmodium that is injected into the human host by the mosquito vector and initially infect liver cells, but they do not occur within erythrocytes.
* **Option B:** Schizonts are the stage of Plasmodium that occurs within erythrocytes, but they are a later stage than trophozoites and are responsible for the rupture of erythrocytes, leading to anemia.
* **Option D:** Gametocytes are the stage of Plasmodium that occurs within erythrocytes and are responsible for the transmission of the parasite to the mosquito vector, but they are not the primary stage seen in humans.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the trophozoite stage of Plasmodium is responsible for the clinical manifestations of malaria, and its identification is crucial for diagnosing the disease. A mnemonic to remember the stages of Plasmodium is "Sporozoites-Schizonts-Trophozoites-Gametocytes," which can help in recalling the correct sequence of stages.
**Correct Answer:** B.