Ans. D) Toxoplasma gondii

The given image shows the lifecycle of Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular parasite that causes toxoplasmosis.

Definitive hosts - Members of Felidae (domestic cats and their relatives). The enteric cycle occurs in definitive hosts.

Intermediate hosts in nature (including birds and rodents). Exoenteric cycle occurs in intermediate hosts such as humans, mice, rats, etc.

Life cycle of toxoplasma gondii

Unsporulated oocysts are shed in the cat’s feces. Although oocysts are usually only shed for 1–3 weeks, large numbers may be shed.
Oocysts take 1–5 days to sporulate in the environment and become infective. Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with oocysts.
Oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites.
Cats become infected after consuming intermediate hosts harboring tissue cysts. Cats may also become infected directly by ingestion of sporulated oocysts.
Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment.

Humans can become infected by any of several routes:

Eating undercooked meat of animals harboring tissue cysts
Consuming food or water contaminated with cat feces or by contaminated environmental samples (such as fecal-contaminated soil or changing the litter box of a pet cat).
Blood transfusion or organ transplantation.
Transplacentally from mother to fetus.
In the human host, the parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain, and eyes; these cysts may remain throughout the life of the host.

Diagnosis is usually achieved by serology, although tissue cysts may be observed in stained biopsy specimens.

Diagnosis of congenital infections can be achieved by detecting T. gondii DNA in amniotic fluid using molecular methods such as PCR

Other Options

Option A. Cystoisospora: Causes isosporiasis, primarily affecting the gastrointestinal tract. Its lifecycle involves humans as the definitive host.

Option B. Cryptosporidium: Causes cryptosporidiosis, an intestinal illness. The lifecycle involves direct fecal-oral transmission.

Option C. Plasmodium knowlesi: Causes malaria, with a lifecycle involving mosquitoes as vectors and humans as host.

Educational Objective

Toxoplasma gondii is an obligate intracellular parasite with a complex lifecycle involving cats as definitive hosts and various animals, including humans, as intermediate hosts. The lifecycle stages, including oocysts and tissue cysts, are crucial for transmission and infection.

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