Parasitic diseases affecting the nervous system and special senses

🧠 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

1. Enumerate parasites affecting the CNS (Trematoda, Cestoda, Nematoda, Protozoa, Arthropods).
2. What are the three mechanisms of CNS damage (ectopic, inflammatory, cystic).
3. Classify Coenurosis cerebralis correctly → a Cestode disease.
4. Differentiate hosts of Taenia multiceps → Dog (definitive), Sheep (intermediate).
5. Explain arthropod effect → usually indirect; direct example is Tick Paralysis Syndrome (temporary).