Parasitology-6: Toxoplasma gondii and Pathogenic Free-Living Amoebae

Flashcards covering the causative agents, life cycles, clinical manifestations, and treatments for Toxoplasma gondii and pathogenic free-living amoebae like Acanthamoeba and Naegleria fowleri.

Toxoplasma gondii

An intracellular parasite (except in RBCs) that causes toxoplasmosis, affecting the brain and eyes, with cats as the only definitive hosts.

Definitive Host (T. gondii)

Members of the Felidae family (cats), which are the only hosts where the parasite can reach maturity and undergo sexual reproduction.

Intermediate Host (T. gondii)

Mammals (including humans, sheep, and goats) and birds that can harbor the parasite in tissue cysts or tachyzoite forms.

Tachyzoites

The rapidly growing, crescent-shaped asexual form of T. gondii during the early stage of infection that multiplies by endodyogeny.

Bradyzoite

The slow-growing stage of T. gondii found inside tissue cysts during the chronic phase of infection; resistant to low pH and digestive enzymes.

Tissue Cysts

Structures measuring $50-70 ext{ mm}$ that contain $1-2000$ bradyzoites and remain in the body for life, usually in an inactive form.

Oocyst

A form shed in cat feces that is noninfectious before sporulation; each sporulated oocyst contains 2 sporocysts, each with 4 sporozoites.

Endodyogeny

The internal budding process of asexual multiplication used by Toxoplasma gondii.

Spiramycin

A medication specifically used for the treatment of toxoplasmosis during pregnancy.

Pyrimethamine

A folate antagonist used for treating toxoplasmosis but not used for pregnant women.

Acanthamoeba

Ubiquitous free-living amoebae that cause granulomatous amebic encephalitis (GAE), disseminated disease, and amebic keratitis.

Amebic keratitis

A sight-threatening corneal infection caused by Acanthamoeba, with $90\%$ of cases occurring in contact lens wearers.

Granulomatous amebic encephalitis (GAE)

A serious central nervous system infection caused by Acanthamoeba or Balamuthia mandrillaris, typically in severely immunocompromised hosts.

Naegleria fowleri

A thermophilic free-living amoeba found in fresh thermal water ($28\,^{\circ}\text{C} - 45\,^{\circ}\text{C}$) that causes Primary Amoebic Meningoencephalitis (PAM).

Primary Amoebic Meningoencephalitis (PAM)

An acute and usually fatal infection caused by Naegleria fowleri entering through the nose during swimming in thermal water.

Amoeboid Trophozoite

The active, feeding, and dividing stage of free-living amoebae like Naegleria fowleri and Acanthamoeba.

Flagellate form

A bi-flagellated stage of Naegleria fowleri that occurs in certain environmental conditions.

Amoeba Cyst

The double-walled, dormant, and resistant stage of free-living amoebae that forms in response to adverse conditions like desiccation or low nutrients.

Balamuthia mandrillaris

A causative agent of chronic granulomatous amebic encephalitis and granulomatous skin and lung lesions.

Biguanides and Diamidines

The classes of medication used for the treatment of pathogenic free-living amoebae infections.