- د. نهى مدبولي
🧠 Parasites Affecting the Central Nervous System (CNS)
🖇 I. Mechanisms of CNS Damage
Parasites can affect the CNS through three main mechanisms:
1️⃣ Ectopic Lesion / Embolus: The parasite or its stage migrates and lodges in the CNS.
2️⃣ Inflammatory Reaction: The parasite causes inflammation and tissue damage.
3️⃣ Cystic Lesions: Formation of cysts inside brain tissue, causing pressure and neurological signs.
🟠 II. Parasite Groups Affecting the CNS
1. Trematoda (Flukes):
- Paragonimus westermani → immature stage may reach the brain.
- Heterophyes heterophyes → eggs may cause embolic lesions.
🧩 Mechanism: Both produce ectopic lesions in the CNS.
2. Cestoda (Tapeworms):
- Diphyllobothrium mansoni → Sparganosis.
- Taenia solium → Cysticercosis (larval cysts in brain).
- Echinococcus → Hydatid cyst in brain.
- Taenia multiceps → Coenurosis cerebralis (larval cyst in brain).
🧩 Mechanism: All cause cystic lesions (tissue cestodes).
3. Nematoda (Roundworms):
- Toxocara species → Visceral larva migrans (larvae migrate to brain).
- Trichinella spiralis → Cyst formation in muscles and sometimes brain.
🧩 Mechanism: Both cause cystic or inflammatory lesions.
4. Protozoa:
- Entamoeba histolytica → Amoebic brain abscess.
- Naegleria & Acanthamoeba → Cause meningitis or encephalitis.
- Trypanosoma → Sleeping sickness (African trypanosomiasis).
- Plasmodium → Cerebral malaria.
- Toxoplasma gondii → CNS toxoplasmosis, especially in immunocompromised patients.
🧩 Mechanism: Inflammation, necrosis, or abscess formation.
5. Arthropods:
- Example: Tick Paralysis Syndrome → tick toxin causes temporary paralysis that disappears after tick removal.
🧩 Mechanism: Usually act indirectly by transmitting parasites (e.g., Trypanosoma), but tick paralysis is a direct effect.
🟣 III. Coenurosis Cerebralis (Detailed Focus)
🔹 Definition:
A parasitic disease affecting mainly the brain and CNS of animals, especially sheep.
Human infection is accidental.
🔹 Causative Agent:
Caused by the larval stage (Coenurus cerebralis) of Taenia multiceps (also called Multiceps multiceps).
🔹 Hosts:
- Definitive host: Dog or other canids (adult worm in intestine).
- Intermediate host: Sheep (larval cysts in brain).
- Accidental host: Human (infection through contaminated food).
🔹 Pathogenesis:
- Dog passes eggs in feces.
- Sheep or humans ingest contaminated food.
- Larvae migrate to the brain via circulation → form cystic lesions.
- Symptoms depend on cyst size and site due to pressure on brain tissue.
🔹 Symptoms:
- Neurological deficits (weakness, paralysis, incoordination).
- Behavioral changes (depression, aggression, anxiety).
- Seizures or convulsions.
🔹 Diagnosis:
- Imaging (MRI / CT): Detect cystic lesion.
- Serological tests + exposure history: Useful when imaging is unclear.
- Parasite stages (eggs or larvae) rarely found in stool or blood.
🔹 Treatment:
- Surgical removal of cyst = only effective option.
- No medical (drug) treatment available.
- Prognosis: Usually poor.
🔹 Prevention & Control:
1️⃣ Regular deworming of dogs.
2️⃣ Proper disposal of dog feces.
3️⃣ Avoid feeding dogs raw or undercooked meat/offal.
🚨 IV. Key Questions Emphasized by the Doctor
- Enumerate parasites affecting the CNS (Trematoda, Cestoda, Nematoda, Protozoa, Arthropods).
- What are the three mechanisms of CNS damage (ectopic, inflammatory, cystic).
- Classify Coenurosis cerebralis correctly → a Cestode disease.
- Differentiate hosts of Taenia multiceps → Dog (definitive), Sheep (intermediate).
- Explain arthropod effect → usually indirect; direct example is Tick Paralysis Syndrome (temporary).