238.1 🎓 醫學生版

238.1.0.1 📌 一頁重點

238.1.0.1.1 4 Main Soil-Transmitted Helminths (STH)

Pathogen	Source	Migration	Disease	Treatment
Ascaris lumbricoides	Egg ingestion (soil-contaminated produce)	Lung migration → coughed up + swallowed → intestine	Loeffler syndrome (lung); intestinal obstruction (heavy burden)	Albendazole 400 mg single dose
Hookworm (Necator americanus, Ancylostoma duodenale)	Larvae penetrate skin (walking barefoot)	Lung migration → intestine	Iron deficiency anemia (chronic blood loss); cutaneous larva migrans	Albendazole single dose; iron repletion
Strongyloides stercoralis	Larvae penetrate skin	Autoinfection → chronic + hyperinfection in immunocompromise	Chronic abdominal + skin (larva currens); Hyperinfection fatal	Ivermectin 200 µg/kg × 1-2 doses
Trichuris trichiura (Whipworm)	Egg ingestion	NO lung migration	Often asymptomatic; heavy: bloody diarrhea, rectal prolapse (pediatric)	Albendazole × 3 days (less responsive)

238.1.0.1.2 Other STH (Lesser Burden)

• Enterobius vermicularis (Pinworm) — perianal itching, pediatric
• Toxocara canis / cati (visceral / ocular larva migrans)

238.1.0.1.3 Burden (WHO 2024)

• 1.5 billion+ STH infections globally (mostly children)
• Africa + Asia + Latin America endemic
• WHO MDA: 800+ million pediatric doses annually
• Major public health priority

238.1.0.1.4 Diagnosis

• Stool O+P × 3 — visualize eggs
• Concentration techniques (Kato-Katz, Baermann for larvae)
• Strongyloides: Baermann concentration for larvae (egg laying intracorporeal — larvae mostly seen, not eggs); serology IgG high sensitivity; PCR emerging
• Eosinophilia common (especially tissue migration / chronic Strongyloides)

238.1.0.1.5 Mass Drug Administration (MDA)

• Albendazole 400 mg or Mebendazole 500 mg single dose for school-age children annually / biannually
• Reduces morbidity (mostly Ascaris, hookworm, Trichuris)
• WHO + partner-funded global programs

238.1.0.1.6 Strongyloides Hyperinfection (Critical)

• In immunocompromise (corticosteroids, organ transplant, HTLV-1)
• Autoinfection cycle amplifies → massive worm load + gram-negative bacteremia + multi-organ
• Mortality 60-85%
• Pre-immunosuppression screening + treatment in patients from endemic regions

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238.1.0.2 1️⃣ Ascaris lumbricoides (Giant Roundworm)

238.1.0.2.1 Microbiology

• Largest nematode parasite of humans (15-35 cm)
• Pinkish, smooth
• Female lays 200,000+ eggs daily

238.1.0.2.2 Life Cycle

1. Eggs in soil + ingested (contaminated produce, soil contact)
2. Hatch in small intestine
3. Larvae penetrate intestinal wall → portal blood → liver → lungs
4. Migrate through alveoli → coughed up → swallowed
5. Mature to adult worms in small intestine
6. Live 1-2 years
7. Eggs shed in feces → contaminate soil

238.1.0.2.3 Epidemiology

• ~ 800 million infections globally (#1 STH by burden)
• Africa + Asia + Latin America
• Children primarily
• Egg highly resistant (years viable in soil)

238.1.0.2.4 Clinical

238.1.0.2.4.1 Pulmonary Phase (Loeffler Syndrome)

• During larval migration through lungs (2-3 wk post-ingestion)
• Cough + wheeze + transient pulmonary infiltrates + eosinophilia
• Self-limited 1-2 weeks
• Atopic individuals more symptomatic

238.1.0.2.4.2 Intestinal Phase

• Mostly asymptomatic
• Heavy burden: intestinal obstruction (especially pediatric, malnourished)
• Worms can migrate into biliary tract → cholangitis, pancreatitis
• Worm migration to other sites: appendix, hernia sac

238.1.0.2.5 Diagnosis

• Stool O+P: brown corticated eggs (very distinctive)
• Adult worms occasionally passed (long pinkish worms)
• Larvae in sputum during Loeffler phase
• Eosinophilia during migration

238.1.0.2.6 Treatment

• Albendazole 400 mg PO single dose
• Mebendazole 100 mg PO bid × 3 days or 500 mg single dose
• Ivermectin alternative
• Pyrantel pamoate OTC option
• Mass deworming programs

238.1.0.2.7 Complications

• Intestinal obstruction — surgical
• Biliary ascariasis — endoscopic extraction
• Pancreatitis

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238.1.0.3 2️⃣ Hookworm (Necator americanus + Ancylostoma duodenale)

238.1.0.3.1 Species

• Necator americanus (worldwide, USA SE)
• Ancylostoma duodenale (Asia, Mediterranean, Africa)

238.1.0.3.2 Life Cycle

1. Eggs in feces → soil → hatch → larvae (rhabditiform → filariform)
2. Filariform larvae penetrate intact skin (walking barefoot)
3. Migrate via blood → lung → coughed up → swallowed
4. Mature in small intestine
5. Adult worms attach to mucosa → suck blood (chronic blood loss)
6. Eggs in feces

238.1.0.3.3 Epidemiology

• ~ 470 million infections globally
• Tropical + subtropical
• Africa + Asia + Latin America
• USA SE historically (now rare with sanitation)
• Walking barefoot major risk

238.1.0.3.4 Clinical

238.1.0.3.4.1 Ground Itch (Skin Penetration)

• Pruritic papular rash at penetration site
• Hours after exposure
• Self-limited days

238.1.0.3.4.2 Pulmonary Phase

• Mild Loeffler-like
• Cough, wheeze, eosinophilia
• 1-2 weeks post-penetration

238.1.0.3.4.3 Intestinal + Anemia

• Chronic blood loss from adult worms attached to mucosa
• Iron deficiency anemia (chronic + significant in heavy burden)
• Protein-losing enteropathy + hypoalbuminemia + edema (severe)
• Growth retardation in children
• Mental impairment in pediatric from anemia

238.1.0.3.4.4 Cutaneous Larva Migrans (Animal Hookworm)

• Ancylostoma braziliense / caninum (dog/cat hookworm; humans accidental)
• Serpiginous pruritic skin tract (linear / S-shaped)
• Beach + soil exposure (sand fleas)
• Self-limited eventually but severe pruritus
• Treatment: ivermectin single dose or albendazole 400 × 3 days

238.1.0.3.5 Diagnosis

• Stool O+P: thin-shelled oval eggs
• Adult hookworms rarely seen (small, ~ 1 cm)
• Eosinophilia + iron deficiency anemia + hypoalbuminemia
• Tests for occult blood

238.1.0.3.6 Treatment

• Albendazole 400 mg PO single dose (cure 80%+)
• Mebendazole 100 mg bid × 3 days
• Iron supplementation for anemia (oral + sometimes IV)
• Protein supplementation if hypoalbuminemia
• Mass deworming reduces morbidity

238.1.0.3.7 Severe Complications

• Severe anemia → cardiac failure
• Growth retardation
• Cognitive impairment in children

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238.1.0.4 3️⃣ Strongyloides stercoralis

238.1.0.4.1 Microbiology

• Soil-dwelling nematode
• Unique among STH for autoinfection capability
• Filariform + rhabditiform larvae

238.1.0.4.2 Life Cycle

238.1.0.4.2.1 Initial Infection

1. Filariform larvae in soil → penetrate intact skin
2. Migrate via blood → lung → coughed up → swallowed
3. Mature in small intestine
4. Female lays eggs intramurally
5. Eggs hatch to rhabditiform larvae in gut
6. Most rhabditiform larvae shed in feces
7. Some rhabditiform larvae transform to filariform larvae IN HOST (autoinfection)

238.1.0.4.2.2 Autoinfection (Critical)

• Filariform larvae penetrate gut wall or perianal skin
• Re-infect same host
• Allows chronic infection for decades
• Amplifies in immunosuppression → hyperinfection

238.1.0.4.3 Epidemiology

• ~ 30-100 million infected globally (likely underestimate)
• Tropical + subtropical
• Sub-Saharan Africa, Latin America, SE Asia, Appalachian USA, parts of Eastern Europe
• Increasing recognition in HTLV-1 endemic regions (Caribbean, Japan, S America) — synergistic immunosuppression

238.1.0.4.4 Clinical

238.1.0.4.4.1 Acute Cutaneous

• Larva penetration: pruritic papular rash
• “Larva currens” (running larva) — serpiginous pruritic rash typically on lower trunk + thighs (from autoinfection, perianal larva migration)

238.1.0.4.4.2 Pulmonary

• Loeffler-like during migration
• Cough, wheeze, eosinophilia

238.1.0.4.4.3 Chronic (Months-Years-Decades)

• Often asymptomatic
• Chronic abdominal pain, diarrhea, bloating, weight loss
• Recurrent larva currens (intermittent itchy rash on trunk/buttocks)
• Eosinophilia (intermittent or chronic)
• Long-standing infection without symptoms common

238.1.0.4.4.4 Hyperinfection Syndrome (Critical!)

• Immunosuppression triggers:
  • Corticosteroids (most common; dose-dependent)
  • Organ transplant
  • HTLV-1
  • Hematologic malignancy
  • Chemotherapy
• Autoinfection accelerates → massive worm load
• Multi-organ disease:
  • Severe abdominal pain + ileus
  • Acute respiratory distress (worms in alveoli)
  • Bacterial sepsis (Gram-negative from gut translocation)
  • Meningitis (Gram-negative)
  • Hepatic involvement
• Mortality 60-85%

238.1.0.4.4.5 Disseminated Strongyloidiasis

• Larvae throughout body
• CNS, kidney, heart, liver, muscle
• Severe systemic illness

238.1.0.4.5 Diagnosis

• Stool O+P × 3 (sensitivity low — 30-50%; larvae mostly seen, not eggs)
• Baermann concentration (warm water method to concentrate motile larvae)
• Agar plate method
• Strongyloides serology IgG — highly sensitive (90%+)
• PCR of stool (emerging, sensitive)
• Eosinophilia common in chronic (intermittent)
• Sputum / BAL larvae in hyperinfection

238.1.0.4.6 Treatment

238.1.0.4.6.1 Standard

• Ivermectin 200 µg/kg PO × 1 dose (preferred)
• Repeat in 2 weeks (kills surviving worms + larvae)
• 90%+ cure for uncomplicated

238.1.0.4.6.2 Alternative

• Albendazole 400 mg PO bid × 7 days
• Less effective than ivermectin

238.1.0.4.6.3 Hyperinfection / Disseminated

• Ivermectin 200 µg/kg PO daily × 2 weeks (extended)
• Add albendazole 400 mg PO bid × 2 weeks (combination)
• Reduce immunosuppression if possible
• Supportive care (ICU, ventilator, dialysis, IV antibiotic for gram-negative sepsis)
• Subcutaneous ivermectin for severe / inability to take orally

238.1.0.4.6.4 Pre-Treatment Screening

• All patients from endemic regions starting corticosteroids / immunosuppression:
  • Stool O+P × 3
  • Serology
  • Treat empirically if positive or high suspicion
• Critical to prevent hyperinfection

238.1.0.4.7 Prevention

• Footwear in endemic regions
• Sanitation
• Surveillance + treatment programs
• Pre-immunosuppression screening + empirical treatment for high-risk

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238.1.0.5 4️⃣ Trichuris trichiura (Whipworm)

238.1.0.5.1 Microbiology

• Adult worm: 3-5 cm; “whip handle” thin anterior + thicker posterior
• Lives in cecum + colon, anterior end embedded in mucosa

238.1.0.5.2 Life Cycle

1. Eggs in feces → soil → embryonate (weeks-months)
2. Eggs ingested with soil-contaminated produce
3. Hatch in small intestine → migrate to cecum
4. Mature in cecum + colon
5. NO lung migration (unlike Ascaris, hookworm)
6. Eggs shed in feces

238.1.0.5.3 Epidemiology

• ~ 460 million globally
• Children + tropics
• Co-infection with Ascaris + hookworm common

238.1.0.5.4 Clinical

• Most asymptomatic (light infections)
• Heavy infection:
  • Bloody diarrhea + abdominal pain
  • Rectal prolapse (pediatric)
  • Trichuriasis dysentery syndrome
  • Growth retardation
  • Cognitive impairment in children

238.1.0.5.5 Diagnosis

• Stool O+P: barrel-shaped (football) eggs with polar plugs

238.1.0.5.6 Treatment

• Albendazole 400 mg PO daily × 3 days (single dose less effective than for Ascaris/hookworm)
• Mebendazole 100 mg bid × 3 days
• Ivermectin combination for refractory
• Less responsive to single-dose deworming than other STH

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238.1.0.6 5️⃣ Enterobius vermicularis (Pinworm)

238.1.0.6.1 Microbiology

• Small white worms (1-13 mm)
• Adult females migrate to perianal area at night to lay eggs

238.1.0.6.2 Epidemiology

• Pediatric most common
• Cool climates more common
• Worldwide, including USA
• Daycare, schools, family

238.1.0.6.3 Life Cycle

• Egg ingestion (fecal-oral, contaminated fingers, food)
• Larvae hatch in small intestine
• Mature in cecum + colon
• Females migrate to perianal area at night → lay eggs
• Eggs viable on perianal skin, underwear, bedding

238.1.0.6.4 Clinical

• Perianal itching (nocturnal)
• Sleep disturbance
• Vaginitis (rare)
• Mostly asymptomatic in many

238.1.0.6.5 Diagnosis

• “Scotch tape test” — apply tape to perianal area in morning → microscopic exam → eggs
• Sometimes visible worms perianally at night
• Stool O+P low sensitivity

238.1.0.6.6 Treatment

• Pyrantel pamoate 11 mg/kg PO single dose, repeat in 2 weeks
• Mebendazole 100 mg PO single dose
• Albendazole 400 mg PO single dose
• Treat all household contacts simultaneously
• Wash bedding + clothing + hot water
• Recurrence common (cycle in family/daycare)

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238.1.0.7 6️⃣ Toxocara canis / Toxocara cati (Visceral + Ocular Larva Migrans)

238.1.0.7.1 Source

• Dog (T. canis) or cat (T. cati) intestinal nematodes
• Humans accidental hosts
• Children playing in contaminated soil

238.1.0.7.2 Clinical

238.1.0.7.2.1 Visceral Larva Migrans

• Eosinophilia + fever + hepatosplenomegaly + pneumonitis
• Pediatric primarily
• Long-distance migration of larvae through tissue

238.1.0.7.2.2 Ocular Larva Migrans

• Visual loss in pediatric (often unilateral)
• Granuloma at retina + vitreous
• Mimics retinoblastoma

238.1.0.7.3 Diagnosis

• Serology (anti-Toxocara IgG)
• Eosinophilia
• Imaging
• Ophthalmology consultation for ocular form

238.1.0.7.4 Treatment

• Albendazole 400 mg bid × 5 days
• Steroid if severe inflammation
• Ophthalmologist for ocular form

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238.1.0.8 7️⃣ Diagnostic Considerations

238.1.0.8.1 Eosinophilia in Returning Traveler / Immigrant

• Strongyloides serology essential (most missed)
• Stool O+P × 3
• Schistosoma serology if freshwater exposure
• Filariae serology if tropical regions
• Trichinella, others as indicated
• Imaging (US abdomen, CT chest)

238.1.0.8.2 Stool Studies

• × 3 samples on different days
• Concentration techniques (Kato-Katz, formalin-ethyl acetate, Baermann for Strongyloides)
• PCR multiplex panels emerging

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