Trematodes (flukes)

Trematodes - General Fluke Facts

• Leaf-shaped, bilaterally symmetric flatworms.
• Most are hermaphroditic (monoecious).
• Possess two suckers: oral (feeding) and ventral (attachment).
• Life cycle requires snails as the first intermediate host.
• Eggs are typically operculated (lidded), aiding in identification.
• Transmission involves ingestion of metacercariae or skin penetration by cercariae.

⭐ High-Yield Exception: Schistosoma species are not hermaphroditic (dioecious) and lay non-operculated eggs.

Schistosoma - Blood Fluke Blues

• Transmission: Free-swimming cercariae in freshwater (from snail hosts) penetrate human skin.
• Pathogenesis: It's the eggs, not the adult worms, that trigger a Th2-mediated granulomatous response, leading to fibrosis and organ damage.
• Clinical Syndromes:
  • Intestinal: S. mansoni, S. japonicum → portal hypertension, hepatosplenomegaly, varices.
  • Urogenital: S. haematobium → hematuria, dysuria, hydronephrosis.
  • Acute: Katayama fever (systemic hypersensitivity reaction).
• Diagnosis: Eggs in stool (mansoni/japonicum) or urine (haematobium).
• Treatment: Praziquantel.

⭐ Exam Favorite: Schistosoma haematobium is strongly associated with Squamous Cell Carcinoma of the bladder.

Clonorchis & Fasciola - Liver Invaders

• Clonorchis sinensis (Chinese Liver Fluke)

  • Transmission: Undercooked freshwater fish.
  • Pathology: Lives in biliary ducts, causing inflammation, fibrosis, and pigmented gallstones.
  • Major risk for cholangiocarcinoma.
  • Diagnosis: Operculated eggs in stool.
  • Treatment: Praziquantel.

• Fasciola hepatica (Sheep Liver Fluke)

  • Transmission: Ingesting aquatic plants like watercress.
  • Pathology: Migrates through liver parenchyma, causing RUQ pain, fever, and hepatomegaly.
  • Diagnosis: Large, operculated eggs in stool.
  • Treatment: Triclabendazole (Praziquantel-resistant).

⭐ Marked eosinophilia during the acute migratory phase is characteristic of Fasciola infection.

Paragonimus - Lung Fluke Woes

• Organism: Paragonimus westermani (Lung Fluke).
• Transmission: Ingesting undercooked freshwater crabs or crayfish containing metacercariae.
• Clinical: Chronic cough with bloody sputum (hemoptysis), mimicking tuberculosis; pleuritic chest pain.
• Diagnosis: Oval, operculated eggs in sputum or feces; eosinophilia; chest X-ray shows infiltrates/cavities.
• Treatment: Praziquantel.

⭐ Ectopic migration to the brain can cause seizures and neurological deficits, a key differential for cysticercosis in endemic areas.

Fluke Dx & Rx - The Praziquantel Plan

• Diagnosis (Dx): Stool/urine microscopy for eggs (O&P).
  • S. haematobium: Urine (look for terminal spine).
  • S. mansoni: Stool (look for lateral spine).
  • S. japonicum: Stool (look for small, round egg).
  • Paragonimus westermani: Sputum O&P.
• Treatment (Rx): Praziquantel is the drug of choice for most flukes.

⭐ Praziquantel works by increasing calcium permeability in the fluke, causing paralysis, contraction, and detachment from the host vessel wall.

High‑Yield Points - ⚡ Biggest Takeaways

• Schistosoma are blood flukes with separate sexes, unlike other trematodes; transmission involves snails and skin penetration.
• Paragonimus westermani (lung fluke), from undercooked crab, causes hemoptysis, mimicking TB.
• Clonorchis sinensis (liver fluke), from undercooked fish, is a major risk factor for cholangiocarcinoma.
• Fasciola hepatica (sheep liver fluke) is acquired from contaminated watercress.
• Diagnosis relies on identifying characteristic eggs in stool, urine, or sputum.
• Praziquantel is the drug of choice for nearly all fluke infections.