Schistosomiasis is a chronic parasitic disease caused by blood flukes of the genus Schistosoma, acquired when freshwater contaminated with the larval form (cercariae) penetrates intact human skin during bathing, wading, or fishing. The World Health Organization estimates roughly 251 million people require preventive treatment each year, with more than 90% of cases concentrated in sub-Saharan Africa and over 200,000 deaths annually from late complications.
Schistosomiasis (ICD-10: B65), also called bilharzia or snail fever, is a chronic infection by trematode flatworms of the genus Schistosoma. Five species infect humans: Schistosoma mansoni and Schistosoma japonicum cause intestinal and hepatosplenic disease through eggs lodged in mesenteric venules; Schistosoma haematobium causes urogenital disease through eggs trapped in vesical venules and the bladder wall; Schistosoma mekongi affects the lower Mekong basin; and Schistosoma intercalatum and Schistosoma guineensis cause focal intestinal disease in central and west Africa. The life cycle requires a specific freshwater snail intermediate host — Biomphalaria for S. mansoni, Bulinus for S.
The key symptoms of Schistosomiasis are: Painless visible blood at the end of urination (terminal hematuria), the hallmark of urogenital schistosomiasis, often appearing in school-age boys 2-6 months after first exposure., Frequency, urgency, dysuria, and suprapubic pain from bladder-wall inflammation and granulomas in chronic S. haematobium infection., Intermittent bloody or mucoid diarrhea with crampy abdominal pain in intestinal schistosomiasis caused by S. mansoni, S. japonicum, or S. mekongi., Itchy maculopapular rash at the site of cercarial penetration within hours of freshwater exposure (cercarial dermatitis or swimmer's itch)., Fever, urticaria, generalized myalgia, fatigue, marked eosinophilia (often >20%), hepatosplenomegaly, and cough 4-8 weeks after first exposure in non-immune travelers — the Katayama syndrome., Progressive abdominal distension with a firm enlarged spleen and prominent abdominal collateral veins in late hepatosplenic disease., Hematemesis, melena, or syncope from ruptured esophageal varices secondary to schistosomal portal hypertension..
Diagnosis begins with travel and exposure history — every freshwater contact in an endemic region within the past five years matters. In the acute phase, marked peripheral eosinophilia (often above 1,500/µL) combined with fever and recent exposure is highly suggestive of Katayama syndrome, but egg-shedding is usually negative for 6-8 weeks after infection. The reference standard for chronic infection is microscopic detection of characteristic eggs: a terminal-spined egg in urine for S. haematobium and a lateral-spined egg in stool for S. mansoni; S. japonicum eggs are small and round with a lateral knob. The Kato-Katz thick-smear technique on stool and filtration of 10 mL of midday urine for S. haematobium remain the WHO-recommended quantitative methods. Sensitivity falls in light infections; in returning travelers and chronic cases serology (ELISA or immunoblot for soluble worm antigens) is more sensitive but cannot distinguish active from past infection. The circulating cathodic antigen (CCA) urine cassette is a point-of-care test that detects active worm infection within 20 minutes and is now widely used in field surveys. Cystoscopy with bladder biopsy is reserved for hematuria with negative urinalysis or to assess fibrosis, and ultrasound of liver, spleen, kidneys, ureters, and bladder grades organ damage. In suspected neuroschistosomiasis, MRI with gadolinium and CSF eosinophilia support the diagnosis.
Outlook depends on the stage at diagnosis. Recently acquired light infections treated with praziquantel have an excellent prognosis: more than 80% achieve parasitological cure, eosinophilia normalizes within 3-6 months, and structural sequelae are uncommon. Chronic urogenital disease shows substantial regression of bladder-wall thickening and hydronephrosis on ultrasound within 12 months of treatment in roughly 60% of patients, especially in children. Established hepatic periportal fibrosis does not reverse fully, but progression usually halts, and portal pressure may fall enough to reduce variceal bleeding rates. Untreated heavy chronic infection over 10-20 years carries a mortality risk dominated by variceal hemorrhage, end-stage renal disease from bilateral hydronephrosis, and squamous-cell bladder cancer; the latter develops in roughly 2-14 per 100,000 person-years in heavily infected populations. Female genital schistosomiasis recognized early responds to praziquantel with improvement in lesions and fertility outcomes, but advanced cervicovaginal damage may be permanent.
Tropical medicine and infectious disease specialists confirm species, exclude co-infections (malaria, strongyloides, HIV), and decide on repeat dosing or steroid cover, especially in Katayama syndrome and neuroschistosomiasis. Hepatology, urology, or gynecology referral is needed once portal hypertension, bladder fibrosis, or female genital schistosomiasis is diagnosed.
Find specialists →Acute symptoms resolve within 1-2 weeks of praziquantel. Eosinophilia, hematuria, and stool egg counts typically normalize within 3 months. Ultrasound evidence of bladder-wall thickening and hydronephrosis regresses over 6-12 months. Hepatic periportal fibrosis does not regress fully but stabilizes after parasitological cure. Female genital schistosomiasis lesions improve over 6-24 months in 60-80% of women treated early.
Light to moderate aerobic activity is safe during and after treatment. Patients with hepatosplenic disease and significant splenomegaly should avoid contact sports because of splenic rupture risk; once portal hypertension is controlled, walking, cycling, and swimming in chlorinated pools are encouraged.
Look for a clinician with documented work in tropical infectious disease, ideally affiliated with a WHO-collaborating centre, a travel-medicine clinic, or a national reference laboratory that performs schistosome serology and CCA testing. For complications, choose a hepatologist or urologist who manages portal hypertension or bladder reconstruction at high volume.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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