A chronic parasitic disease caused by trematode blood flukes of the genus Schistosoma
Aetiology
Causative Organisms
Species | Main Geographic Area | Target Organ | Major Disease Pattern |
Schistosoma haematobium | Africa, Middle East | Urinary bladder | Urinary schistosomiasis |
Schistosoma mansoni | Africa, South America, Middle East | Intestine, liver | Intestinal/hepatic disease |
Schistosoma japonicum | China, Philippines, Indonesia | Intestine, liver | Severe hepatosplenic disease |
Schistosoma mekongi | Mekong River region | Intestine | Hepatosplenic disease |
Schistosoma intercalatum | Central Africa | Intestine | Intestinal disease |
Pathophysiology
Infection occurs via contact with freshwater contaminated with cercariae released from infected freshwater snails.
Life Cycle Stages
- Eggs excreted in urine or stool
- Eggs hatch in water → miracidium
- Miracidium infects freshwater snail (intermediate host)
- Cercariae released from snail
- Cercariae penetrate human skin
- Develop into schistosomula → adult worms in venous plexus
Adult worm locations:
Species | Adult Location |
S. haematobium | Vesical venous plexus |
S. mansoni | Inferior mesenteric vein |
S. japonicum | Superior mesenteric vein |
Clinical Presentation
Clinical Stages
Stage | Time After Infection | Clinical Features |
Cercarial dermatitis | Hours–days | Itchy papular rash (“swimmer’s itch”) |
Acute schistosomiasis (Katayama fever) | 3–8 weeks | Fever, cough, eosinophilia, hepatosplenomegaly |
Chronic schistosomiasis | Months–years | Organ-specific damage |
Clinical Manifestations by Species
Feature | Urinary Schistosomiasis | Intestinal Schistosomiasis |
Species | S. haematobium | S. mansoni, S. japonicum |
Main symptom | Terminal hematuria | Bloody diarrhea |
Urinary symptoms | Dysuria, frequency | Rare |
GI symptoms | Rare | Abdominal pain, diarrhea |
Hepatomegaly | Mild | Common |
Portal hypertension | Rare | Common |
Cancer risk | Squamous cell carcinoma of bladder | Rare |
Investigations
Test | Findings |
Stool microscopy | Eggs of S. mansoni / S. japonicum |
Urine microscopy | Eggs of S. haematobium |
Eosinophil count | Eosinophilia |
Serology (ELISA) | Detects antibodies |
Ultrasound | Hepatosplenic disease |
Cystoscopy | Bladder lesions |
Egg Morphology
Species | Egg Shape | Spine Location |
S. haematobium | Oval | Terminal spine |
S. mansoni | Oval | Large lateral spine |
S. japonicum | Round | Small lateral spine |
Management
First-Line Therapy
Drug | Dose | Indication |
Praziquantel | 40 mg/kg single day (2 divided doses) | S. haematobium & S. mansoni |
Praziquantel | 60 mg/kg single day (3 divided doses) | S. japonicum |
Alternative Therapy
Drug | Dose | Indication |
Oxamniquine | 15 mg/kg single dose | S. mansoni |
Metrifonate | 7.5–10 mg/kg × 3 doses | S. haematobium |
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