236.1 🎓 醫孞生版

236.1.0.1 📌 䞀頁重點

236.1.0.1.1 Schistosoma Species
Species Geography Disease Eggs
S. mansoni Africa + S America (Brazil) + Caribbean Hepatic + intestinal Lateral spine
S. japonicum E Asia (China, Philippines, Indonesia) Hepatic + intestinal Round, small spine
S. mekongi Cambodia, Laos Hepatic + intestinal Similar to japonicum
S. haematobium Africa + Mid East Urinary + bladder CA Terminal spine
S. intercalatum W + C Africa Intestinal Terminal spine
236.1.0.1.2 Life Cycle
  • Eggs in stool / urine → freshwater → hatch → miracidium → enters snail intermediate host → multiplies → cercariae released from snail → swim in water + penetrate skin of human → schistosomulae enter bloodstream → mature to adult worms (paired in venous system) → eggs deposited in vasculature
  • Liver granulomas (S. mansoni, japonicum, mekongi)
  • Bladder + ureter (S. haematobium)
  • 240 million chronic globally; 600 million at risk
236.1.0.1.3 Clinical Stages
236.1.0.1.3.1 Stage 1: Swimmer’s Itch (Cercarial Dermatitis)
  • Hours after exposure
  • Pruritic papular rash at penetration site
  • Self-limited 24-48 hr
  • More common with non-human schistosomes (bird, animal cercariae) → “swimmer’s itch”
236.1.0.1.3.2 Stage 2: Acute Schistosomiasis (Katayama Fever)
  • 4-8 weeks post-exposure (response to maturing worms + egg release)
  • Fever, malaise, myalgia, urticaria, hepatosplenomegaly, eosinophilia, cough
  • S. japonicum + S. mansoni in non-immune travelers especially
  • Self-limited weeks but can be severe
236.1.0.1.3.3 Stage 3: Chronic Schistosomiasis
236.1.0.1.3.4 Intestinal + Hepatic (S. mansoni, japonicum, mekongi)
  • Colonic schistosomiasis: chronic bloody diarrhea, abdominal pain, weight loss
  • Hepatic schistosomiasis (years):
    • Periportal fibrosis (“Symmers’ pipe-stem fibrosis”)
    • Hepatosplenomegaly + portal hypertension
    • Variceal bleeding
    • Ascites
    • LFTs often near normal
    • Liver function preserved early (unlike cirrhosis)
  • Pulmonary hypertension from emboli + lung granulomas
236.1.0.1.3.5 Urinary (S. haematobium)
  • Hematuria + dysuria (terminal hematuria classic)
  • Bladder fibrosis + calcification
  • Bladder cancer (squamous cell carcinoma!) — chronic egg-induced inflammation
  • Hydronephrosis from ureteral fibrosis
  • Renal failure
236.1.0.1.3.6 Genital Schistosomiasis (S. haematobium)
  • Female: cervical / vaginal lesions, infertility, increased HIV transmission
  • Male: hematospermia, semen abnormalities
236.1.0.1.3.7 Neuroschistosomiasis (Rare but Important)
  • S. japonicum / S. mansoni / S. haematobium
  • Cerebral or spinal cord
  • Mass effect, transverse myelitis
  • Aberrant egg deposition
236.1.0.1.4 Diagnosis
  • Stool O+P for S. mansoni / japonicum / mekongi (look for eggs with characteristic spines)
  • Urine O+P for S. haematobium (concentrate urine, terminal hematuria sample)
  • Serology (anti-schistosome Ab)
  • PCR (research / specialty)
  • Eosinophilia + IgE elevation
  • Imaging: US (hepatic fibrosis, bladder thickening), CT, MRI
  • Bladder cystoscopy for chronic S. haematobium
236.1.0.1.5 Treatment
  • Praziquantel 40 mg/kg PO single dose (S. mansoni, S. haematobium)
  • 60 mg/kg PO single dose (S. japonicum, S. mekongi) — divided over 1 day
  • 85-95% cure rate
  • Mass drug administration in endemic regions
236.1.0.1.6 Other Trematodes
  • Fasciola hepatica: liver fluke, sheep + cattle; watercress + waterborne; biliary disease + eosinophilia → triclabendazole single dose
  • Clonorchis sinensis + Opisthorchis viverrini: liver flukes, undercooked freshwater fish (Asia); biliary + cholangiocarcinoma association → praziquantel
  • Paragonimus westermani: lung fluke, freshwater crab/crayfish; chronic cough + hemoptysis → praziquantel
  • Heterophyes / Metagonimus: intestinal flukes, undercooked fish (Asia); diarrhea → praziquantel
236.1.0.1.7 Prevention
  • Avoid freshwater swimming in endemic areas (Africa, Brazil, China, SE Asia)
  • Treat water (chlorination, boiling, filtering)
  • Snail control programs (molluscicides)
  • WHO MDA programs in endemic
  • Sanitation (proper waste disposal)

236.1.0.2 1⃣ Schistosoma Microbiology + Life Cycle

236.1.0.2.1 Adult Worms
  • Paired in venous plexuses (male + female)
  • Male carries female in gynecophoric canal
  • Live for years (5-10 yr typical, up to 30 yr)
  • Female produces eggs daily
  • Eggs migrate through vascular endothelium → tissue → into intestinal / urinary lumen → shed in stool / urine
236.1.0.2.2 Eggs (Key Diagnostic)
  • S. mansoni: lateral spine
  • S. japonicum: round with small lateral knob (smaller)
  • S. haematobium: terminal spine
  • S. intercalatum: terminal spine
236.1.0.2.3 Life Cycle
  1. Eggs shed in stool / urine to freshwater
  2. Egg hatches → miracidium (free-swimming)
  3. Miracidium penetrates snail intermediate host (specific snail per species)
  4. Asexual reproduction in snail
  5. Cercariae released from snail (free-swimming, fork-tailed)
  6. Cercariae penetrate human skin during freshwater contact
  7. Shed tail → become schistosomulae
  8. Migrate via venous system → heart → lung → liver
  9. Mature to adult worms in liver
  10. Migrate to specific final habitat:
    • Mesenteric veins (intestinal/hepatic forms): S. mansoni, japonicum, mekongi
    • Vesical venous plexus (urinary form): S. haematobium
  11. Lay eggs → cycle continues
236.1.0.2.4 Pathology
  • Granulomatous response to eggs (Th2-mediated)
  • Egg-induced inflammation → fibrosis
  • Tissue damage: liver, bladder, ureter, lung, CNS
236.1.0.2.5 Intermediate Snail Hosts
  • Biomphalaria (S. mansoni)
  • Oncomelania (S. japonicum)
  • Bulinus (S. haematobium)
  • Neotricula aperta (S. mekongi)

236.1.0.3 2⃣ Schistosomiasis Clinical Stages

236.1.0.3.1 Stage 1: Cercarial Dermatitis (Swimmer’s Itch)
  • Hours after exposure
  • Pruritic papular rash at skin penetration sites
  • Self-limited 24-48 hr
  • More common with avian schistosomes (non-human; do not develop into adult worms) → “swimmer’s itch” globally
  • Human schistosomes cause similar but less prominent rash
236.1.0.3.2 Stage 2: Katayama Fever (Acute Schistosomiasis)
  • 4-8 weeks post-exposure (corresponds to maturing worms + initial egg release)
  • Particularly in non-immune travelers / new exposure
  • Sx:
    • Fever (often high)
    • Malaise
    • Myalgia
    • Urticaria, angioedema, erythematous rash
    • Hepatosplenomegaly
    • Marked eosinophilia (often > 50%)
    • Cough, wheeze
    • Diarrhea
  • Self-limited weeks
  • Can be severe in heavy exposure
  • Misdiagnosed as flu, malaria
236.1.0.3.3 Stage 3: Chronic Schistosomiasis
236.1.0.3.3.1 Intestinal + Hepatic Forms (S. mansoni, japonicum, mekongi)
236.1.0.3.3.2 Colonic Schistosomiasis
  • Chronic intermittent bloody diarrhea
  • Abdominal pain
  • Weight loss
  • Polypoid lesions colon (severe)
  • Mimics IBD or colon CA on colonoscopy
  • Pancolitis or focal involvement
236.1.0.3.3.3 Hepatic Schistosomiasis
  • Years-decades after infection
  • Egg granulomas in liver → periportal fibrosis “Symmers’ pipe-stem fibrosis”
  • Hepatosplenomegaly
  • Portal hypertension:
    • Esophageal + gastric varices
    • Variceal bleeding
    • Splenomegaly + hypersplenism (cytopenia)
    • Ascites (late)
  • LFTs often near-normal initially (presinusoidal portal HTN, hepatocytes preserved)
  • Pulmonary hypertension from chronic emboli + lung granulomas (HOP — hepatopulmonary)
  • Renal disease (MPGN, IgA nephropathy)
236.1.0.3.3.4 Urinary Form (S. haematobium)
236.1.0.3.3.5 Acute / Subacute
  • Hematuria (especially terminal) + dysuria
  • Hematuria may be intermittent
  • Frequency, urgency
236.1.0.3.3.6 Chronic
  • Bladder fibrosis + calcification
  • Reduced bladder capacity
  • Recurrent UTI
  • Hydronephrosis from ureteral fibrosis (typically lower ureter)
  • Renal failure
  • Squamous cell carcinoma of bladder — chronic inflammation, fibrosis, calcified eggs
  • Africa: schistosomiasis is leading cause of bladder cancer
236.1.0.3.3.7 Genital Schistosomiasis
  • Female: cervical/vaginal lesions, infertility, hypertrophic granular changes, increased HIV transmission risk (mucosal disruption)
  • Male: hematospermia, semen abnormalities, prostatic involvement
236.1.0.3.3.8 Neuroschistosomiasis (Rare but Important)
  • S. japonicum (more common) > S. mansoni > S. haematobium
  • Cerebral: epilepsy, mass lesion, focal signs
  • Spinal: transverse myelitis, paraplegia
  • Aberrant egg deposition + granuloma
  • Treatment: praziquantel + steroid
236.1.0.3.3.9 Pulmonary
  • Chronic emboli + granulomas
  • Pulmonary arterial hypertension
  • Cor pulmonale
  • Late chronic schistosomiasis
236.1.0.3.3.10 Other Manifestations
  • Glomerulonephritis (MPGN, IgA nephropathy)
  • HIV transmission: enhanced by genital schistosomiasis
  • Hepatitis B + C co-infection increases hepatic disease severity

236.1.0.4 3⃣ Diagnosis

236.1.0.4.1 Stool Examination
  • S. mansoni: stool O+P, characteristic lateral spine egg
  • S. japonicum + mekongi: stool O+P, round eggs with small knob
  • Multiple stool samples increase sensitivity
  • Concentration techniques
  • Quantitative egg counts (intensity of infection)
236.1.0.4.2 Urine Examination
  • S. haematobium: urine concentration, terminal hematuria sample best
  • Eggs with terminal spine
  • 24-hour urine collection for low parasite burden
236.1.0.4.3 Serology
  • Anti-Schistosoma antibodies (ELISA, IFA)
  • Reasonable sensitivity but cross-reactivity
  • Useful in travelers with negative egg exam but exposure history
  • Remains positive after treatment (limits cure monitoring)
236.1.0.4.4 PCR
  • Sensitive, species-specific
  • Research / specialty labs
  • Useful in low-burden + travelers
236.1.0.4.5 Eosinophilia
  • Common in acute / Katayama
  • Less prominent in chronic
  • Workup for unexplained eosinophilia → schistosomiasis if travel hx
236.1.0.4.6 Imaging
236.1.0.4.6.1 Hepatic
  • US: Symmers’ pipe-stem fibrosis (echogenic periportal); splenomegaly; portal vein dilation
  • CT / MRI: similar findings
236.1.0.4.6.2 Urinary
  • US bladder: thickened wall, calcifications, polyps, hydronephrosis
  • CT / MRI: bladder changes, ureter
  • Cystoscopy: bladder mucosa changes, polyps, tumors (biopsy for SCC if suspicious)
236.1.0.4.7 Endoscopy
  • Colonoscopy for chronic intestinal Schistosomiasis
  • Mucosal changes + biopsies
236.1.0.4.8 Liver Biopsy
  • Rarely needed (US sufficient)
  • Egg granulomas + Symmers’ pipe-stem fibrosis

236.1.0.5 4⃣ Treatment

236.1.0.5.1 Praziquantel
236.1.0.5.1.1 S. mansoni + S. haematobium
  • 40 mg/kg PO single dose OR divided BID
  • 85-95% cure rate
  • Egg counts decrease 80-90% by 4-6 weeks
  • Test of cure 4-12 weeks post
236.1.0.5.1.2 S. japonicum + S. mekongi
  • 60 mg/kg PO divided over 1 day (split dose)
236.1.0.5.1.3 Treatment Failure / Heavy Infection
  • Repeat in 4-6 weeks if still positive
  • Consider longer regimen
  • Some areas: combination with other agents (rare)
236.1.0.5.1.4 Mechanism
  • Disrupts schistosome membrane Ca++ permeability
  • Adult worms susceptible (immature worms less so — may need retreatment)
236.1.0.5.2 Adjunctive
236.1.0.5.2.1 Acute Schistosomiasis (Katayama Fever)
  • Steroid for severe acute presentation
  • Praziquantel less effective on immature worms — may be ineffective during acute → delay 1-2 months or repeat course
236.1.0.5.2.2 Severe Chronic
  • Variceal bleeding management (banding, beta-blocker)
  • Portosystemic shunt for refractory variceal bleeding
  • Hepatosplenomegaly + cytopenia management
236.1.0.5.2.3 Bladder Cancer
  • Schistosomiasis-associated SCC
  • Cystectomy + chemotherapy
  • Continued schistosomicidal therapy
236.1.0.5.2.4 Neuroschistosomiasis
  • Praziquantel + steroid (high-dose)
  • Anticonvulsants
  • Surgical for mass effect rare
236.1.0.5.3 Mass Drug Administration (MDA)
  • WHO praziquantel MDA for endemic communities (annual)
  • School-age children + at-risk adults
  • 2024+: increasing access to praziquantel + new formulations (kid-friendly pediatric)
  • Reductions in chronic disease + transmission
236.1.0.5.4 Pregnancy
  • WHO + studies support praziquantel safety in pregnancy
  • Some guidelines: avoid 1st trimester unless severe
  • Generally safe + indicated in 2nd-3rd trimester for severe
236.1.0.5.5 Pediatric
  • Praziquantel 40 mg/kg single dose
  • Tablet difficult for young children (research on pediatric formulations)

236.1.0.6 5⃣ Other Trematodes

236.1.0.6.1 Fasciola hepatica (Liver Fluke)
236.1.0.6.1.1 Source
  • Sheep + cattle endemic
  • Watercress + freshwater plants (especially raw watercress)
  • Contaminated water
236.1.0.6.1.2 Clinical
  • Acute phase: fever + eosinophilia + RUQ pain + hepatosplenomegaly
  • Chronic biliary: biliary obstruction, cholangitis, gallstones
  • Migration through liver tissue → “tunneling” lesions on imaging
236.1.0.6.1.3 Diagnosis
  • Stool O+P (operculated eggs)
  • Serology
  • Imaging (US, CT — tracks in liver)
236.1.0.6.1.4 Treatment
  • Triclabendazole 10 mg/kg PO single dose (only effective drug)
  • Repeat in 12 hr if heavy infection
  • Praziquantel NOT effective for Fasciola
236.1.0.6.2 Clonorchis sinensis + Opisthorchis viverrini (Asian Liver Flukes)
236.1.0.6.2.1 Source
  • Undercooked freshwater fish (Asia — China, Korea, Vietnam, Thailand, Laos)
  • Pickled / salted fish vehicles
  • Endemic areas
236.1.0.6.2.2 Clinical
  • Chronic biliary tract infestation
  • Cholangitis, cholecystitis
  • Gallstone formation
  • Cholangiocarcinoma association (Opisthorchis: WHO Group 1 carcinogen for cholangiocarcinoma)
236.1.0.6.2.3 Diagnosis
  • Stool O+P (small operculated eggs)
  • Serology
  • Imaging (biliary dilation, fluke shadows)
236.1.0.6.2.4 Treatment
  • Praziquantel 25 mg/kg PO tid × 1-2 days
236.1.0.6.3 Paragonimus westermani (Lung Fluke)
236.1.0.6.3.1 Source
  • Undercooked freshwater crustaceans (crab, crayfish)
  • Asia, Africa, Latin America
236.1.0.6.3.2 Clinical
  • Chronic pulmonary disease
  • Cough + hemoptysis + chest pain (mimics TB!)
  • CXR: pulmonary cysts, infiltrates, effusion
  • Pleural disease
  • Ectopic disease: brain (seizures), abdomen
236.1.0.6.3.3 Diagnosis
  • Sputum / stool O+P (golden brown operculated eggs)
  • Serology
  • CT chest
236.1.0.6.3.4 Treatment
  • Praziquantel 25 mg/kg PO tid × 2 days
236.1.0.6.4 Heterophyes / Metagonimus (Intestinal Flukes)
  • Undercooked fish (Asia, Mediterranean)
  • Mild diarrhea
  • Praziquantel single dose
236.1.0.6.5 Fasciolopsis buski (Giant Intestinal Fluke)
  • Water plants (water chestnuts, water caltrops) in Asia
  • Watery diarrhea, abdominal pain
  • Praziquantel
236.1.0.6.6 Schistosoma sangini
  • Bird schistosome
  • “Swimmer’s itch” only (cercarial dermatitis)
  • Doesn’t develop in humans