Tachyzoites are seen in –
**Core Concept**
The question is testing the student's knowledge of the life cycle of Toxoplasma gondii, a protozoan parasite that causes toxoplasmosis. Tachyzoites are a specific stage of the parasite's life cycle, characterized by rapid division and growth in the host's tissues.
**Why the Correct Answer is Right**
Tachyzoites are the rapidly dividing forms of T. gondii that are seen in the tissues of infected hosts, particularly in immunocompromised individuals or during the acute phase of infection. They are responsible for the clinical manifestations of toxoplasmosis, including fever, lymphadenopathy, and organ dysfunction. Tachyzoites are highly infectious and can be transmitted to other hosts through fecal-oral contamination or vertical transmission.
**Why Each Wrong Option is Incorrect**
* **Option B:** This option is incorrect because bradyzoites are a different stage of T. gondii's life cycle, characterized by slow growth and dormancy in tissue cysts. They are not associated with the acute phase of infection.
* **Option C:** This option is incorrect because oocysts are the environmental stage of T. gondii that is shed in the feces of infected cats. They are not seen in the tissues of infected hosts.
* **Option D:** This option is incorrect because sporozoites are the infective stage of T. gondii that is transmitted to hosts through the bite of an infected cat. They are not seen in the tissues of infected hosts.
**Clinical Pearl / High-Yield Fact**
Toxoplasmosis is a significant concern in immunocompromised individuals, including HIV/AIDS patients and organ transplant recipients, who are at risk of developing severe and life-threatening infections.
**Correct Answer: A. Tachyzoites are seen in the tissues of infected hosts, particularly in immunocompromised individuals or during the acute phase of infection.**