TREMATODES – FASCIOLA HEPATICA

TREMATODES – FASCIOLA HEPATICA

Definition – Fasciola hepatica is a trematode (liver fluke) that infects the liver and bile ducts of humans and herbivorous mammals

Cause – ingestion of metacercariae on contaminated aquatic vegetation or water

Types – Fasciola hepatica (common) and Fasciola gigantica (giant) – both cause fascioliasis

Morphology – adult flat leaf‑shaped, 2–3 cm long, 1 cm wide, oral sucker anterior, ventral sucker (acetabulum) mid‑body, hermaphroditic; eggs operculated, 150‑200 µm × 80‑100 µm; miracidia ciliated; cercariae tadpole‑like; metacercariae encysted on plants

Life cycle –

1. Adult flukes live in bile ducts → lay eggs → eggs passed in feces
2. Eggs reach fresh water → embryonate → hatch into miracidia
3. Miracidia penetrate suitable freshwater snail (Lymnaea spp.) – first intermediate host
4. Within snail → develop into sporocyst → redia → produce cercariae
5. Cercariae leave snail, swim → encyst on aquatic plants → become metacercariae
6. Human or animal eats raw/undercooked watercress, lettuce etc. → metacercariae excyst in duodenum
7. Juvenile flukes penetrate intestinal wall → migrate through peritoneal cavity → reach liver capsule → enter hepatic parenchyma → finally settle in bile ducts → mature adult (≈8‑12 weeks)

Pathogenesis – Ingestion of metacercariae → excystation in duodenum → penetration of intestinal wall → migration through peritoneum → hepatic tissue invasion → mechanical damage & inflammatory response → bile duct obstruction → fibrosis & cholangitis

Clinical features –

• Acute phase: fever, right upper quadrant pain, hepatomegaly, nausea, vomiting, diarrhea, eosinophilia, anemia, weight loss, sub‑capsular hemorrhages on US/CT
• Chronic (biliary) phase: persistent right upper quadrant pain, jaundice, cholestasis, biliary colic, cholangitis, fatigue, malabsorption

Complications – bile duct obstruction → cholangitis, cholecystitis; hepatic fibrosis → cirrhosis; secondary bacterial infection; portal hypertension (rare)

Diagnosis – stool examination for operculated eggs (best after 8‑12 weeks); serology (ELISA IgG) for early detection; imaging (US/CT shows hypoechoic lesions, “tunnel” tracks, dilated ducts); fecal antigen ELISA (rapid)

Management – first‑line drug Triclabendazole 10 mg/kg single dose (or two doses 10 mg/kg 12 h apart) effective against immature and adult stages; alternative Nitazoxanide if triclabendazole unavailable; supportive care (analgesics, antipyretics, iron for anemia); surgical drainage only for obstructive complications

Prevention – avoid raw aquatic plants from endemic areas; wash and cook vegetables thoroughly; ensure safe drinking water (filter/boil); control snail intermediate host by molluscicides and drainage

Memory trick – “Eggs Miracidia Snail, Cercariae Ride, Plant‑Metacercariae Hide, Gut‑Fluke Glide.” (E‑M‑S‑C‑P‑G) helps recall: Eggs → Miracidia → Snail → Cercariae → Plant (metacercariae) → Gut (excyst & glide)