⭐ THE 20% THAT GIVES 80% MARKS (SUPER HIGH-YIELD)

1. Organism: Toxoplasma gondii — intracellular protozoan parasite.
2. Transmission:
• Oocysts from cat feces
• Tissue cysts in undercooked meat
• Transplacental (primary maternal infection → fetal infection)
3. Forms:
• Tachyzoite → acute infection
• Bradyzoite → chronic latent tissue cyst
• Oocyst → shed in cat feces
4. Immunocompetent adults: asymptomatic OR mild flu-like disease + lymphadenopathy.
5. AIDS patients: ring-enhancing brain lesions, seizures, encephalitis.
6. Congenital triad:
• Chorioretinitis
• Hydrocephalus
• Intracranial calcifications

(± blueberry muffin rash, hepatosplenomegaly)

7. Diagnosis:
• Serology (IgM = acute; IgG = past infection)
• PCR of amniotic fluid for fetus
• CT/MRI in AIDS → multiple ring-enhancing lesions
8. Treatment:
• Pyrimethamine + sulfadiazine + folinic acid
• Pregnancy prophylaxis with spiramycin
9. Prevention: no cat litter exposure in pregnancy; avoid raw meat.

If you remember these → you can answer almost all exam questions.

🔬 FULL HIGH-YIELD MICROBIOLOGY (CLEAR & SIMPLE)

1️⃣ The Organism

Toxoplasma gondii is a protozoan parasite (Apicomplexa).

Forms:

1. Tachyzoites
• Rapidly dividing
• Responsible for acute infection
2. Bradyzoites
• Slow-growing, form tissue cysts
• Persist in muscles, brain, retina (latent infection)
3. Oocysts
• Found in cat feces
• Become infective after 1–5 days in environment

Cats = definitive hosts

Humans = intermediate hosts

2️⃣ Life Cycle (Very Exam Important)

1. Cats shed oocysts in feces.
2. Humans get infected by:
• Contaminated soil/food/water
• Handling cat litter
• Eating undercooked meat containing tissue cysts
• Transplacental infection from mother to fetus
3. In humans:
• Oocysts → tachyzoites (acute phase)
• Later turn into bradyzoites (latent cysts in brain/muscle/eye)

3️⃣ Transmission Routes (Key Exam Area)

A. Cat feces

• Oocysts
• Gardening, cleaning litter boxes

B. Undercooked meat

• Tissue cysts in pork, lamb, venison

C. Congenital

Occurs if mother gets primary infection during pregnancy.

D. Blood transfusion / organ transplantation

Rare.

4️⃣ Clinical Features

A. Immunocompetent Adults

Usually asymptomatic.

If symptoms:

• Mild flu-like illness
• Fatigue
• Fever
• Tender cervical lymphadenopathy
• Myalgia

Reactivation (if immunosuppressed later)

→ encephalitis.

B. Immunocompromised (AIDS, transplant)

Toxoplasma encephalitis:

• Fever
• Headache
• Confusion
• Seizures
• Focal neurological deficits
• MRI/CT: multiple ring-enhancing lesions

Eye involvement:

• Chorioretinitis
• Vision loss
• Floaters, photophobia

C. Congenital Toxoplasmosis

Highest risk: maternal primary infection in 1st or 2nd trimester.

Classic congenital triad:

1. Chorioretinitis
2. Hydrocephalus
3. Intracranial calcifications

Other findings:

• Developmental delay
• Seizures
• “Blueberry muffin” rash (extramedullary hematopoiesis)
• Hepatosplenomegaly
• Prematurity

5️⃣ Diagnosis

A. Serology

• IgM positive → acute infection
• IgG positive only → past infection (protective)
• IgG avidity testing helps identify recent vs old infection

B. In fetus

• PCR of amniotic fluid
• Ultrasound may show hydrocephalus, calcifications

C. CNS toxoplasmosis (AIDS)

• CT/MRI: multiple ring-enhancing lesions
• Serology + imaging usually enough
• Brain biopsy only if diagnosis unclear

6️⃣ Treatment

Acute or CNS Toxoplasmosis

Pyrimethamine + sulfadiazine + folinic acid (leucovorin)

— prevents bone marrow toxicity from pyrimethamine.

Alternative

• Clindamycin + pyrimethamine
• Atovaquone (if sulfa allergy)

Congenital infection

• Treat mother + neonate with same combination.

Pregnancy

• If mother infected but fetus unaffected → spiramycin

(reduces transplacental transmission)

• If fetal infection proven → pyrimethamine + sulfadiazine (2nd/3rd tri)

7️⃣ Prevention

Pregnancy advice

• Avoid changing cat litter
• Wear gloves when gardening
• Avoid raw/undercooked meat
• Wash vegetables thoroughly
• Avoid drinking untreated water

HIV patients

• Prophylaxis when CD4 < 100 AND IgG positive
• TMP-SMX once daily

⭐ MUST-MEMORISE SUPER SUMMARY (20% → 80%) ⭐

1. Toxoplasma gondii = intracellular protozoa.
2. Transmission: cats, raw meat, transplacental.
3. Acute infection: mild flu-like illness.
4. AIDS: multiple ring-enhancing brain lesions → encephalitis.
5. Congenital triad: chorioretinitis + hydrocephalus + intracranial calcifications.
6. Diagnosis: IgM, PCR, MRI.
7. Treatment: pyrimethamine + sulfadiazine + folinic acid.
8. Prevention: avoid cat feces + raw meat, spiramycin in pregnancy.
9. Lives in bradyzoite tissue cysts for life.
10. Reactivates when immunity drops.

🧠 TOXOPLASMA GONDII — COMPLETE HIGH-YIELD MASTER TABLE (ZERO-OMISSION)

🎯 ULTIMATE EXAM LOCK (ONE-LOOK MEMORY)

• Cats + raw meat + pregnancy
• AIDS → ring-enhancing brain lesions
• Congenital triad = eye + brain + CSF obstruction
• Treatment = pyrimethamine + sulfadiazine + folinic acid
• Spiramycin = pregnancy prophylaxis