Conditions · Infectious and tropical diseases
Schistosomiasis !
Schistosomiasis is a blood-fluke infection caught in fresh water; its eggs scar the liver, gut or bladder and can cause portal hypertension.
Updated 2026-11-01
Structures involved
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- Liver
- Portal vein
- Urinary bladder
- Spleen
- Mesenteric veins
- Splenic vein
- Esophagus
- Descending colon
- Sigmoid colon
- Rectum
- Ureters
- Kidneys
- Trigone of bladder
- Cervix
- Vagina
Microorganisms that cause it
Why it happens
- Granulomatous inflammation: caseating vs non-caseating, the causes to know
- Fibrosis in organs: TGF-β and the myofibroblast
- Metaplasia
- Oncogenic viruses and H. pylori: the table to know
- Splanchnic and portal circulation
- Liver: lobule, acinus, hepatocytes, sinusoids, Kupffer cells
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What it is
A chronic parasitic disease caused by Schistosoma blood flukes, whose larvae penetrate the skin in fresh water. Adult worms live in venous plexuses and their eggs, trapped in tissues, cause granulomas and fibrosis in the liver and intestine (S. mansoni) or the bladder and urinary tract (S. haematobium).
Who gets it
Over 200 million people are infected worldwide, mostly in sub-Saharan Africa. In the Americas only S. mansoni is transmitted, with foci in Brazil, Venezuela, Suriname and some Caribbean islands; Colombia has no established transmission, so cases there are imported (travellers and migrants). It is a classic exam topic as a cause of non-cirrhotic portal hypertension and of bladder squamous cell carcinoma.
Causes
- S. mansoni (Africa, Middle East, Brazil, Venezuela, Suriname, Caribbean): intestinal and hepatosplenic disease
- S. haematobium (Africa, Middle East): urogenital disease
- S. japonicum and S. mekongi (Asia): intestinal and hepatosplenic disease
- Infection through skin contact with fresh water containing cercariae released by snails
Risk factors
- Bathing, swimming, fishing, washing or farming in untreated fresh water in endemic areas
- Lack of safe water and sanitation
- Children and young people in endemic communities (highest worm burden)
- Travel or migration from Brazil, Venezuela or Africa
Pathophysiology
Cercariae penetrate the skin, become schistosomula and mature in the portal system, then pair and migrate to mesenteric or vesical venules. Disease comes mostly from eggs, not worms: eggs lodged in tissue trigger a Th2 granulomatous reaction that heals with fibrosis. In the liver this gives periportal (pipe-stem, Symmers) fibrosis with presinusoidal portal hypertension and preserved liver function; in the bladder, granulomas, calcification and chronic inflammation predispose to obstruction and squamous cell carcinoma.
Classification
- Cercarial dermatitis (swimmer's itch) at the entry site
- Acute schistosomiasis (Katayama syndrome): fever, urticaria, cough and eosinophilia weeks after first exposure
- Chronic intestinal and hepatosplenic schistosomiasis (S. mansoni, S. japonicum)
- Chronic urogenital schistosomiasis (S. haematobium), including female genital schistosomiasis
- Ectopic forms: neuroschistosomiasis (spinal cord) and pulmonary hypertension
Symptoms and signs
- Itchy papular rash after freshwater exposure
- Fever, urticaria, cough and myalgia weeks later in non-immune travellers
- Abdominal pain, diarrhoea and blood in the stool
- Hepatosplenomegaly, mainly an enlarged left lobe and a large spleen
- Terminal haematuria and dysuria (urogenital form)
- Anaemia and growth or learning problems in children
Diagnosis
- Clinical
- Suspected in anyone with fever and eosinophilia, haematuria, hepatosplenomegaly or variceal bleeding who has had freshwater exposure in an endemic area.
- Tests
- Microscopy for eggs in stool (Kato-Katz; lateral spine for S. mansoni) or in filtered urine collected around midday (terminal spine for S. haematobium). Serology and antigen tests (circulating cathodic antigen) help in travellers and low-intensity infection. Eosinophilia, anaemia; liver tests usually near normal. Rectal or bladder biopsy may show eggs.
- Imaging
- Ultrasound shows periportal fibrosis, splenomegaly and portal vein dilation, or bladder wall thickening, calcification and hydronephrosis. Endoscopy for varices; cystoscopy for bladder lesions; MRI of the spine for neuroschistosomiasis.
Differential diagnosis
- Cirrhosis from viral hepatitis or alcohol
- Other causes of eosinophilia: strongyloidiasis, fascioliasis, toxocariasis
- Urinary tract infection, urolithiasis or bladder cancer as causes of haematuria
- Amoebic or bacterial colitis
- Portal vein thrombosis
Goal of treatment
Kill the adult worms, reduce egg burden and fibrosis, manage portal hypertension and urinary complications, and cut transmission in endemic communities.
Treatment
- Medical
- Praziquantel, an anthelmintic active against adult worms of all species; it is repeated later because it does not kill immature stages. It is also the drug of mass preventive chemotherapy.
- Medical
- Corticosteroids added for severe Katayama syndrome and for neuroschistosomiasis, to limit the inflammatory reaction to dying worms and eggs.
- Procedure
- Endoscopic band ligation or sclerotherapy for oesophageal varices, with non-selective beta-blockers for prevention of rebleeding.
- Surgical
- Shunt or devascularisation surgery for refractory variceal bleeding; urological procedures for ureteric strictures or bladder cancer.
- Follow-up
- Follow-up stool or urine testing after treatment; ultrasound to follow fibrosis and screening for varices; travellers are asked about freshwater exposure.
Drugs for this condition
Complications
- Presinusoidal portal hypertension with variceal bleeding and splenomegaly
- Hydronephrosis, chronic kidney disease and recurrent urinary infections
- Squamous cell carcinoma of the bladder
- Female genital schistosomiasis, infertility and higher HIV acquisition risk
- Transverse myelitis and other neuroschistosomiasis
- Pulmonary hypertension and cor pulmonale
- Chronic anaemia and stunted growth in children
Prognosis
Early infection responds well to treatment and lesions can regress. Established periportal fibrosis and bladder damage improve only partly; variceal bleeding is the main cause of death, but because liver function is preserved it is better tolerated than in cirrhosis.
Prevention
- Safe water supply, sanitation and hygiene
- Avoiding contact with untreated fresh water in endemic areas
- Periodic mass treatment of school-age children and high-risk adults
- Snail control and health education
Test yourself
Think of the answer, then tap the question to see it.
How do humans acquire schistosomiasis?
Cercariae released by freshwater snails penetrate intact skin during contact with contaminated fresh water.
Which Schistosoma species is transmitted in the Americas, and what organ does it mainly damage?
S. mansoni, which causes intestinal and hepatosplenic disease with periportal fibrosis.
What type of portal hypertension does hepatosplenic schistosomiasis cause?
Presinusoidal portal hypertension (pipe-stem fibrosis) with relatively preserved liver function.
Which bladder cancer is linked to S. haematobium?
Squamous cell carcinoma of the bladder.
What is the drug of choice for all forms of schistosomiasis?
Praziquantel.
Related conditions
- Portal hypertension
- Cirrhosis
- Bladder cancer
- Hydronephrosis and obstructive uropathy
- Pulmonary hypertension and cor pulmonale
- Transverse myelitis
- Iron deficiency anaemia
- Strongyloidiasis
- Viral hepatitis
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Schistosomiasis (World Health Organization, 2025); About Schistosomiasis | Schistosomiasis | CDC (Centers for Disease Control and Prevention, 2024).
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