Trematodes (flukes): clinical diagnosis and management
Trematodes are leaf-shaped flatworms whose complex life cycles usually involve freshwater snails and, for some species, fish, crustaceans or aquatic plants. Human disease is determined by the adult habitat: intestinal flukes cause enteritis and malabsorption; liver flukes cause biliary inflammation and obstruction; and blood flukes (Schistosoma) cause intestinal, hepatosplenic, urinary or genital disease. Chronic inflammation and fibrosis can produce portal hypertension, renal disease, infertility and cancer.
Ask specifically about freshwater contact, swimming, fishing, raw/undercooked fish or crab, water plants, sanitation and residence in endemic districts.
Learning objectives
- Classify trematodes by habitat and route of human infection.
- Explain snail and intermediate-host stages and relate them to prevention.
- Recognise acute schistosomiasis, hepatobiliary disease, portal hypertension, urinary disease and ectopic complications.
- Interpret stool/urine microscopy, concentration, serology, antigen tests and imaging.
- Use praziquantel safely, manage complications and prevent reinfection.
Classification
| Group | Examples | Acquisition and main disease |
|---|---|---|
| Blood flukes | S. mansoni, S. haematobium, S. japonicum | Cercariae penetrate skin in freshwater; intestinal/hepatosplenic or urinary disease |
| Liver flukes | Clonorchis, Opisthorchis, Fasciola | Raw fish for clonorchiasis/opisthorchiasis; water plants for fascioliasis; biliary disease |
| Intestinal flukes | Fasciolopsis, Heterophyes | Raw aquatic plants or fish; enteritis and protein loss |
| Lung flukes | Paragonimus | Raw/undercooked crab or crayfish; chronic haemoptysis and ectopic CNS disease |
Life cycle and pathogenesis
Eggs leave the definitive host in stool or urine. In water they hatch, infect a snail, multiply asexually and emerge as cercariae. Schistosome cercariae directly penetrate human skin; other trematodes encyst as metacercariae on plants or in fish/crustaceans and are swallowed. Adult worms mature in target organs. Most tissue injury comes from host granulomatous and fibrotic responses to eggs rather than adult worms themselves.
Schistosomiasis
Adult pairs live in mesenteric or vesical venous plexuses. Eggs traverse bowel or bladder walls and cause granulomas, polyps, bleeding and fibrosis. Eggs that embolise to liver, lungs, spinal cord or brain cause ectopic disease. S. mansoni and S. japonicum mainly cause intestinal/hepatosplenic disease; S. haematobium causes urinary and genital disease.
Fascioliasis
Metacercariae on watercress or other aquatic plants excyst in the duodenum, cross the intestinal wall and migrate through liver parenchyma before entering bile ducts. The hepatic migratory phase causes fever, right-upper-quadrant pain and eosinophilia; the chronic phase causes cholangitis and obstruction.
Clonorchis/Opisthorchis
Metacercariae in raw fish mature in intrahepatic ducts. Repeated inflammation, epithelial hyperplasia and pigment stones increase cholangitis and cholangiocarcinoma risk.
Clinical features
Acute schistosomiasis (Katayama syndrome)
Weeks after a new exposure: fever, urticaria, cough, malaise, headache, abdominal pain, diarrhoea, hepatosplenomegaly and marked eosinophilia. Stool or urine egg shedding may still be negative early.
Chronic intestinal/hepatosplenic disease
Abdominal pain, bloody diarrhoea, fatigue and hepatosplenomegaly progress to periportal fibrosis, portal hypertension, varices, hypersplenism and preserved liver function until late. Ascites or gastrointestinal bleeding requires urgent care.
Urinary and genital schistosomiasis
Terminal haematuria, dysuria, frequency, recurrent urinary infection, bladder wall calcification, hydronephrosis, renal impairment, genital lesions, infertility and increased bladder cancer risk may occur.
Fascioliasis
Fever, painful hepatomegaly, right-upper-quadrant pain, urticaria and high eosinophilia occur during migration. Chronic disease causes biliary colic, obstructive jaundice, cholangitis and gallbladder involvement.
Paragonimiasis and intestinal flukes
Paragonimus causes chronic cough, pleuritic pain, rusty or blood-stained sputum and pleural effusion; cerebral disease causes seizures or focal deficits. Intestinal flukes cause diarrhoea, abdominal pain, malabsorption and protein loss.
History and examination
- Map all freshwater exposure, including bathing, fishing, irrigation and childhood swimming.
- Ask about raw fish, crab, crayfish, watercress and other uncooked aquatic foods.
- Document haematuria, dysuria, genital symptoms, diarrhoea, blood in stool, cough, haemoptysis, jaundice and weight loss.
- Examine pallor, fever, urticaria, hepatosplenomegaly, ascites, oedema, abdominal tenderness, neurological signs and respiratory findings.
- Look for chronic liver disease and portal-hypertension complications, while remembering that schistosomal portal hypertension may occur with relatively preserved hepatocyte function.
Investigations
- Full blood count with eosinophils, liver profile, renal function, urinalysis and urine microscopy.
- Stool microscopy with concentration and Kato-Katz where available; collect multiple samples because egg output varies.
- Urine filtration or sediment microscopy for S. haematobium, ideally midday urine after activity; inspect for haematuria.
- Serology or circulating antigen tests assist when egg shedding is low, especially early or light infection, but may not distinguish past infection.
- Ultrasound assesses periportal fibrosis, splenomegaly, portal vein, bladder lesions and hydronephrosis; CT/MRI evaluates ectopic disease.
- Endoscopy for varices; ERCP or MRCP for biliary obstruction; chest imaging and sputum microscopy for paragonimiasis.
- Biopsy is occasionally required when eggs are suspected in tissue and non-invasive tests are inconclusive.
Differential diagnosis
Malaria, typhoid, viral hepatitis, bacterial cholangitis, gallstones, liver abscess, inflammatory bowel disease, tuberculosis, urinary stones, glomerulonephritis, urological malignancy, eosinophilic disease and other helminths.
Management
Schistosomiasis
Praziquantel is the standard treatment; dose and number of administrations depend on species and national guideline. In heavy infection or early treatment, repeat dosing after maturation of immature worms may be required. Treat anaemia and complications, and reassess egg clearance.
Fascioliasis
Triclabendazole is preferred because Fasciola is not reliably cured by praziquantel. Treat biliary infection and obstruction, and involve specialists for cholangitis or persistent duct disease.
Clonorchis/Opisthorchis and intestinal flukes
Use praziquantel or another locally recommended regimen, treat cholangitis, and counsel about avoiding raw fish or aquatic plants. Evaluate persistent biliary symptoms and malignancy risk.
Paragonimus
Use praziquantel or an alternative guideline-recommended agent; drain significant pleural collections and assess the brain urgently when seizures or focal signs occur.
Complications and emergencies
- Variceal haemorrhage, severe anaemia, portal-hypertension ascites and hypersplenism.
- Obstructive uropathy, recurrent pyelonephritis and renal failure from urinary schistosomiasis.
- Acute cholangitis, obstructive jaundice, pancreatitis or liver abscess-like lesions.
- Neurological schistosomiasis or paragonimiasis with seizures, myelopathy or raised intracranial pressure.
- Secondary bacterial infection of damaged urinary or biliary tracts.
- Cholangiocarcinoma and bladder squamous-cell carcinoma risk in chronic endemic infection.
Prevention and public health
- Safe water, sanitation and elimination of open defecation reduce egg contamination.
- Avoid swimming or wading in potentially infested freshwater; provide safe bathing and occupational alternatives.
- Cook freshwater fish, crab, crayfish and aquatic plants thoroughly; do not rely on marination or alcohol.
- Community praziquantel programmes and surveillance reduce morbidity; reinfection remains possible.
- Snail-control and environmental measures require coordinated public-health programmes.
- Screen and treat migrants or travellers with compatible exposure, especially before chronic organ complications develop.
Follow-up and exam pearls
- Praziquantel kills mature worms but not all immature stages; timing of repeat testing and treatment matters.
- High eosinophilia with liver pain after water-plant exposure suggests acute fascioliasis, not routine schistosomiasis.
- Periportal fibrosis can cause portal hypertension with relatively preserved transaminases.
- Terminal haematuria is a classic clue to urinary schistosomiasis.
- Fasciola requires triclabendazole; empiric praziquantel may fail.
- Persistent haemoptysis after raw-crab exposure suggests paragonimiasis.
References
- SlideShare: Trematodes.
- WHO schistosomiasis and foodborne trematode guidance.
- Current Uganda Clinical Guidelines and local neglected-tropical-disease protocols.
Safety note: Confirm species, pregnancy considerations, paediatric dosing, drug interactions and local treatment schedules before prescribing.
