240.1 🎓 醫學生版

240.1.0.1 📌 一頁重點

240.1.0.1.1 Major Tissue Nematodes

Pathogen	Source	Migration	Disease
Trichinella spp.	Undercooked pork, wild game (bear, boar)	Encysts in muscle	Fever + myalgia + periorbital edema + eosinophilia
Anisakis	Raw / undercooked saltwater fish (sushi)	Gastric / intestinal	Acute gastric / intestinal pain + eosinophilia
Gnathostoma spinigerum	Raw / undercooked freshwater fish (Asia, Latin America)	Migratory swellings + CNS	Migratory subcutaneous + neurologic + eye
Angiostrongylus cantonensis	Slug / snail / undercooked seafood	CNS migration	Eosinophilic meningitis (Hawaii, Caribbean, Asia)
Toxocara canis / cati	Dog / cat parasite eggs	Visceral + ocular larva migrans	Pediatric VLM + OLM
Capillaria philippinensis	Raw freshwater fish	Intestinal autoinfection	Severe diarrhea + malabsorption

240.1.0.1.2 Trichinella spiralis (Trichinellosis)

240.1.0.1.2.1 Source

• Undercooked pork (less common with regulation in developed countries)
• Wild game: bear, wild boar, walrus, fox, cougar, etc.
• USA outbreaks linked to wild boar + bear hunting + small-pork producers

240.1.0.1.2.2 Life Cycle

1. Human eats meat containing encysted Trichinella larvae
2. Stomach acid + small intestine: larvae released
3. Larvae mature to adult worms in small intestine mucosa
4. Adult worms produce newborn larvae (viviparous — unique among helminths)
5. Newborn larvae enter bloodstream → migrate to skeletal muscle
6. Encyst in muscle (lifelong calcified cysts eventually)
7. Cycle continues if another animal eats infected muscle

240.1.0.1.2.3 Clinical (3 Phases)

240.1.0.1.2.4 Phase 1: Intestinal Phase (Days 1-7)

• Adult worms in gut
• Nausea, vomiting, diarrhea, abdominal pain
• Often mild / overlooked

240.1.0.1.2.5 Phase 2: Muscle Invasion Phase (Weeks 1-4)

• Fever (often high, sustained)
• Severe myalgia (especially extraocular, masseter, intercostal, diaphragm)
• Periorbital edema (pathognomonic in classic case)
• Marked eosinophilia (often > 50%)
• Elevated CK (muscle damage)
• Rash, urticaria, splinter hemorrhages
• Conjunctival hemorrhages
• Headache + photophobia

240.1.0.1.2.6 Phase 3: Convalescent Phase (Months)

• Encysted larvae in muscle
• Persistent myalgia weeks-months
• Eosinophilia normalizes over months

240.1.0.1.2.7 Severe Complications

• Myocarditis (cardiac muscle invasion) — most common cause of death; arrhythmia, heart failure
• Encephalitis (CNS larvae)
• Pneumonitis (lung larvae)
• Death rare with treatment but reported

240.1.0.1.2.8 Diagnosis

• Clinical (classic triad: fever + myalgia + eosinophilia in patient with appropriate food history)
• Eosinophilia + elevated CK + LDH
• Anti-Trichinella IgG (ELISA) — positive 2-3 weeks post-infection
• Muscle biopsy (rarely needed) — encysted larvae in muscle

240.1.0.1.2.9 Treatment

• Albendazole 400 mg PO bid × 8-14 days (preferred)
• Mebendazole 200-400 mg PO tid × 3-14 days (alternative)
• Prednisolone for severe (myocarditis, encephalitis, severe systemic) — reduces inflammation
• Supportive: rest, analgesia, hospitalization for severe

240.1.0.1.2.10 Prevention

• Cook pork to internal 145°F (63°C) or freeze at -15°C (5°F) × 20+ days
• Wild game especially bear: cook thoroughly (freezing less effective)
• WHO ban on garbage-feeding pigs (vector)
• Public education

240.1.0.1.3 Anisakis (Anisakidosis)

240.1.0.1.3.1 Source

• Raw / undercooked saltwater fish (sushi, ceviche, lightly pickled, smoked)
• Common in Japan + Korea + Spain + Italy (sushi culture)
• USA cases increasing with sushi popularity
• Larvae visible in fish flesh (small white)

240.1.0.1.3.2 Clinical

• Acute gastric phase (within hours):
  • Severe epigastric pain
  • Nausea, vomiting
  • Sometimes hematemesis
• Intestinal phase (1-3 days):
  • Abdominal pain (often RLQ)
  • Diarrhea
  • Eosinophilia
• Allergic phase:
  • IgE-mediated hypersensitivity
  • Urticaria, angioedema, anaphylaxis
  • Can persist even after worm dies

240.1.0.1.3.3 Diagnosis

• Gastroscopy in acute gastric phase: visible worm + edema + erosion → removal (definitive Tx)
• Imaging (CT) for intestinal involvement
• Serology + PCR (limited)
• Eosinophilia common

240.1.0.1.3.4 Treatment

• Endoscopic removal of visible worm (definitive)
• Albendazole 400 mg PO bid × 14 days for residual / intestinal
• Antihistamine / steroid for allergic
• Surgery rare for severe intestinal

240.1.0.1.3.5 Prevention

• Cook fish thoroughly
• FDA: Freeze fish at -20°C × 7 days (or -35°C × 15 hr) for raw consumption (sushi)
• Avoid raw fish if uncertain handling

240.1.0.1.4 Gnathostoma spinigerum

240.1.0.1.4.1 Source

• Raw / undercooked freshwater fish (especially Asia — Thailand classic; also Mexico, S America, Africa)
• Larvae in fish muscle
• Snake + frog less commonly

240.1.0.1.4.2 Clinical

• Migratory subcutaneous swellings (intermittent over years)
• Painful, pruritic
• CNS involvement: eosinophilic meningitis, transverse myelitis, encephalitis
• Eye: ocular gnathostomiasis (rare, severe)
• Eosinophilia
• Hepatitis, pulmonary lesions

240.1.0.1.4.3 Diagnosis

• Clinical + serology + biopsy (rare)
• Eosinophilia

240.1.0.1.4.4 Treatment

• Albendazole 400 mg PO bid × 21 days + Ivermectin 200 µg/kg × 1 dose
• Surgical removal of accessible worms
• Steroid for severe CNS

240.1.0.1.5 Angiostrongylus cantonensis (Rat Lungworm)

240.1.0.1.5.1 Source

• Slug / snail intermediate hosts (also paratenic: crab, shrimp, prawn, frog)
• Hawaii + Caribbean + SE Asia + Pacific
• Eaten raw or contaminated produce

240.1.0.1.5.2 Clinical

• Eosinophilic meningitis (severe, common manifestation)
• Headache + fever + neck stiffness + photophobia
• Cranial nerve palsies
• Sometimes encephalitis + radiculitis
• Self-limited (4-6 weeks)
• Some severe sequelae

240.1.0.1.5.3 Diagnosis

• CSF: lymphocytic + eosinophilic pleocytosis (eosinophils 10-30%)
• Travel + food history (Hawaii, Caribbean)
• Serology
• PCR of CSF

240.1.0.1.5.4 Treatment

• Supportive (most self-limited)
• Steroid (dexamethasone) for severe + headache control
• Albendazole controversial (may worsen by killing more worms in CNS) — generally not first-line
• Pain control + ICP management

240.1.0.1.6 Toxocara canis / cati (Visceral + Ocular Larva Migrans)

240.1.0.1.6.1 Source

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

240.1.0.1.6.2 Clinical

240.1.0.1.6.3 Visceral Larva Migrans (VLM)

• Pediatric primarily
• Eosinophilia + fever + hepatosplenomegaly + pneumonitis
• Wheeze + cough
• Larvae migrate through tissue

240.1.0.1.6.4 Ocular Larva Migrans (OLM)

• Pediatric visual loss (often unilateral)
• Granuloma at retina + vitreous
• Mimics retinoblastoma

240.1.0.1.6.5 Diagnosis

• Serology (anti-Toxocara IgG)
• Eosinophilia (VLM)
• Imaging (US for VLM, ophth exam for OLM)

240.1.0.1.6.6 Treatment

• Albendazole 400 mg PO bid × 5 days
• Steroid for severe inflammation
• Ophthalmology for ocular

240.1.0.1.7 Capillaria philippinensis (Intestinal Capillariasis)

240.1.0.1.7.1 Source

• Raw freshwater fish (Philippines, Thailand, parts of Asia)
• Autoinfection possible

240.1.0.1.7.2 Clinical

• Watery diarrhea
• Severe malabsorption + protein loss
• Untreated severe + fatal
• Eosinophilia

240.1.0.1.7.3 Diagnosis

• Stool O+P (eggs)
• PCR

240.1.0.1.7.4 Treatment

• Albendazole 400 mg PO bid × 10 days OR mebendazole

240.1.0.1.8 Capillaria hepatica

• Liver capillariasis from animal exposure
• Rare in humans (often misdiagnosed)
• Severe hepatic damage

240.1.0.1.9 Dirofilaria immitis (Heartworm of Dogs)

• Mosquito-borne
• Humans accidental
• Pulmonary nodules (“coin lesions”) on CXR
• Often discovered incidentally (mistaken for lung cancer)
• Surgical resection for diagnostic certainty
• Usually no specific treatment needed

240.1.0.1.10 Dracunculiasis (Guinea Worm)

240.1.0.1.10.1 Background

• Dracunculus medinensis
• Drinking water containing infected copepods
• Endemic to Africa historically (Sudan, Chad, Mali, Ethiopia)
• WHO global eradication near (< 30 cases/yr globally 2024+)
• 100,000+ cases/yr in 1980s

240.1.0.1.10.2 Clinical

• Adult female worm emerges through skin (typically lower extremity)
• Painful blister + ulcer
• Worm released over days-weeks
• Painful + secondary infection
• Disability + agricultural impact

240.1.0.1.10.3 Treatment

• No specific drug (anti-nematode ineffective once worm emerges)
• Slow extraction over days-weeks (winding worm on stick)
• Wound care + antibiotic for bacterial superinfection
• Education: filter drinking water

240.1.0.1.11 Loa loa, Onchocerca, Wuchereria

• See Ch 239 (filariases)

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240.1.0.2 1️⃣ Trichinella spp.

240.1.0.2.1 Species

• T. spiralis (worldwide; pigs primary)
• T. nativa (Arctic; bear, walrus; freeze-resistant — important!)
• T. britovi (Europe + W Asia)
• T. murrelli (USA; wild game)
• T. pseudospiralis (no encapsulation; birds + mammals)
• T. nelsoni (Africa)
• T. papuae, T. zimbabwensis, etc.

240.1.0.2.2 Life Cycle

1. Human eats undercooked meat with encysted larvae
2. Larvae released in stomach
3. Mature to adults in small intestine (5-7 days)
4. Adult female releases newborn larvae directly (viviparous)
5. Newborn larvae migrate via bloodstream + lymph to skeletal muscle
6. Encyst in muscle (becomes “Nurse cell” surrounded muscle fiber)
7. Calcify over years
8. Adult worms in gut expelled 1-2 months

240.1.0.2.3 Tissue Predilection

• Skeletal muscle (especially highly vascular + active):
  • Diaphragm, masseter, tongue, intercostal, ocular, gastrocnemius
• Cardiac muscle (no encapsulation — heart muscle damage but no cysts)
• CNS (rare, severe)
• Lung (pneumonitis)

240.1.0.2.4 Pathology

• Muscle invasion → cysts surrounded by “Nurse cell” (modified muscle fiber)
• Cardiac muscle: no cyst, but inflammation + myocarditis
• CNS: inflammation, granulomas

240.1.0.2.5 Diagnosis

• Triad in classic case: fever + myalgia + eosinophilia in patient who ate raw/undercooked meat
• Periorbital edema + facial swelling characteristic
• Splinter hemorrhages (from microvascular vasculitis)
• Conjunctival hemorrhages
• Lab:
  • Eosinophilia (often > 50%; may be > 70%)
  • Elevated CK + LDH
  • Anti-Trichinella IgG (ELISA) — 2-3 weeks post
• Muscle biopsy rarely needed (clinical + serology usually sufficient)

240.1.0.2.6 Treatment

240.1.0.2.6.1 Albendazole

• 400 mg PO bid × 8-14 days
• Effective against adult worms (intestinal) + newborn larvae (less effective against encysted muscle larvae)

240.1.0.2.6.2 Mebendazole

• 200-400 mg PO tid × 3-14 days
• Alternative

240.1.0.2.6.3 Prednisolone

• 20-60 mg PO daily × 7-14 days for severe (myocarditis, encephalitis, severe systemic)
• Reduces inflammation
• Doesn’t kill parasite alone

240.1.0.2.6.4 Supportive

• Rest
• NSAIDs (caution with myocarditis)
• ICU for severe
• ECMO for severe myocarditis (rare)

240.1.0.2.7 Outbreaks

• USA: bear hunting + wild boar + small farm pork
• Argentina + Mexico + Russia + China + Spain: pork-related
• Surveillance through reportable disease

240.1.0.2.8 Prevention

• Cook pork to internal 145°F (63°C) (USDA)
• Cook wild game thoroughly (T. nativa freeze-resistant!)
• Freezing generally inactivates Trichinella in pork:
  • -15°C (5°F) × 20 days
  • -23°C (-10°F) × 10 days
  • -30°C (-22°F) × 6 days
• Wild game/bear: freezing not reliable (T. nativa cold-resistant) — cook only
• 通報 mandatory many countries

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240.1.0.3 2️⃣ Other Tissue Nematodes — Brief

240.1.0.3.1 Anisakis (Already Detailed)

240.1.0.3.2 Gnathostoma (Already Detailed)

240.1.0.3.3 Angiostrongylus (Already Detailed)

240.1.0.3.4 Toxocara (Already Detailed)

240.1.0.3.5 Capillaria philippinensis (Already Detailed)

240.1.0.3.6 Dirofilaria (Lung Coin Lesion — Already Detailed)

240.1.0.3.7 Dracunculus (Guinea Worm Near Eradication — Already Detailed)

240.1.0.3.8 Other Less Common

• Strongyloides — see Ch 238 (autoinfection)
• Filariae — see Ch 239

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