Schistosomiasis Japonica

Schistosomiasis japonica is caused by S. japonicum in the portal venous system; skin contact with cercariae-infested water. Main lesions: egg granulomas in liver/colon. Acute: fever, tender hepatomegaly, bloody diarrhea, eosinophilia. Chronic: hepatosplenomegaly. Late: periportal fibrosis → portal hypertension, megalosplenia, ascites.

Common Symptoms

Bleeding tendency; diarrhea; ascites; abdominal distension; abdominal pain; constipation; convulsion; low fever; remittent fever; hypoproteinemia

Causes and Pathogenesis

(1) Etiology: dioecious worms in copula; inferior mesenteric vein; survival 4-5 years (up to 10). Female lays ~1000 eggs/day in submucosal venules. Eggs hatch miracidia at 25-30°C → infect Oncomelania snails → mother/sporocyst → cercariae exit 7-8 weeks later. Cercariae fork-tailed, penetrate skin in 10 s; schistosomulae migrate via lungs to liver; mature ~1 month; migrate retrograde to mesenteric veins to oviposit. Human = definitive host; Oncomelania = obligate intermediate; 40+ reservoir hosts (cattle/pig/sheep/dog/cat/rodents). (2) Pathogenesis: egg granuloma = delayed T-cell mediated hypersensitivity (soluble egg antigen). Japanese = larger clustered granulomas with monocyte/neutrophil infiltrate; Hoeplli phenomenon (eosinophilic rays); mixed humoral+cellular in acute; chronic/late = cytokine network dysregulation; hepatic fibrosis on granuloma basis, types I/III collagen, periportal pipestem fibrosis. Concomitant immunity; antigen disguise; antibody-dependent eosinophil cytotoxicity. Pathology: (a) colon (rectum/sigmoid/descending; acute hyperemia/egg nodules/ulcers; chronic thickening/polyps/stricture); (b) liver (early miliary yellow nodules; late periportal fibrosis/pipestem cirrhosis → pre-sinusoidal portal HTN → congestive splenomegaly/hypersplenism/collaterals/variceal bleeding); (c) ectopic (lung/brain granulomas).

Treatment

Drug therapy, supportive therapy

Preventive Measures

Mollusciding + mass treatment + fecal/water management + personal protection. (1) Source control: praziquantel mass chemo; amoscanate 1.5-2 mg/kg IV for cattle. (2) Transmission: snail survey/mapping; environmental control (earth burial, damming, planting); niclosamide molluscicide; fecal 1:5 urine sealing fermentation (3-5 d summer, 7-10 d winter); biogas pits; water protection/chlorination. (3) Personal: education; avoid infested water; fatty acid + 2% niclosamide + turpentine repellent; chemoprophylaxis: artemether 6 mg/kg q15d starting day 15 post-exposure (4-10 doses); artesunate 6 mg/kg weekly starting day 7 (8-15 doses); protective rate 88.2-100%.

Department to Visit

It is recommended to visit the Infectious Diseases department; an appointment can be booked on this platform before the visit.

Warm reminder: The above information is for health science reference only and cannot replace professional medical diagnosis. If you have related symptoms, please seek medical attention at a regular hospital promptly.