Thrichinococcus infection

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Note on terminology: "Thrichinococcus" does not correspond to a recognized organism. Based on the spelling, this most likely refers to Trichinella infection (trichinosis/trichinellosis). If you meant Echinococcus (hydatid disease), please let me know.

Trichinella Infection (Trichinosis / Trichinellosis)

Trichinosis is a systemic zoonotic illness caused by nematodes of the genus Trichinella — primarily T. spiralis in most of the world, though 8 closely related species can infect humans.

Life Cycle

The same host harbors both the adult and larval forms:

Ingestion of raw/undercooked meat containing encysted larvae
Cysts dissolve in the GI tract; larvae invade the small intestinal mucosa, living within a syncytium of ~45 villus cells
Adults mature rapidly; males (60 µm × 1.2 mm) and females (90 µm × 2.2 mm) mate within 30 hours
Viviparous females begin releasing larvae ~1 week post-ingestion; adults are expelled within 4 weeks
Larvae (6 × 100 µm) enter intestinal blood and lymphatics → distributed systemically
Larvae develop only within striated muscle → enter a myocyte → induce transformation into a "nurse cell" → coiled larva remains viable for years

— Sleisenger and Fordtran's Gastrointestinal and Liver Disease, p. 2274

Epidemiology

Species	Distribution
T. spiralis	Americas, Europe, Russia (most common globally)
T. nativa	Arctic/subarctic (infects walrus, bear; freeze-resistant)
T. britovi	Europe, North Africa, Middle East, Asia
T. nelsoni	Equatorial Africa
T. pseudospiralis	Americas, Europe, Russia (no encapsulated cysts; infects birds)
T. papuae	Papua New Guinea (infects reptiles)
T. zimbabwensis	Zimbabwe, Ethiopia, Mozambique (only species not yet implicated in human disease)

Sources of human infection: undercooked pork, wild boar, bear meat, walrus, horse meat, cougar. Outbreaks are often cluster events — butcher shops, hunting feasts, subsistence feeding.

The incidence has declined markedly in industrialized countries due to: thorough cooking of pork, commercial freezing, and grain-only pig feeding. Trichinosis is a re-emerging illness in Eastern Europe due to relaxed enforcement.

— Sleisenger and Fordtran's GI and Liver Disease, p. 2272–2274; Sherris & Ryan's Medical Microbiology, p. 1870

Pathogenesis

Enteral phase: Adult worms embed in intestinal epithelium → enteritis (eosinophils, lymphocytes, neutrophils)
Parenteral phase: Migratory larvae invade striated muscle, heart, CNS → inflammatory responses
Invaded muscle cells enlarge, lose cross-striations, undergo basophilic degeneration
Specific IgG and IgM antibodies trigger eosinophil-mediated destruction of circulating larvae
A vasculitis from circulating immune complex deposition may occur
Th2 cytokines (IL-4, IL-5), T lymphocytes, eosinophils, and mast cells mediate worm expulsion

Clinical Features

Clinical trichinosis has two sequential phases:

Phase 1 — Intestinal (Enteral, Days 2–14)

Nausea, abdominal pain, diarrhea, vomiting, low-grade fever
Often mistaken for viral gastroenteritis or food poisoning
Diarrhea can persist for weeks (T. nativa from walrus meat in Inuit populations)

Phase 2 — Systemic/Parenteral (Week 1–6+)

Fever, myalgia, muscle weakness, muscle tenderness (cardinal features)
Periorbital/eyelid edema (characteristic)
Maculopapular skin rash
Subconjunctival and subungual (splinter) hemorrhages
Dysphagia, headache, paresthesias

Severe Disease

Myocarditis → ECG abnormalities, tachycardia, congestive heart failure
CNS involvement → encephalitis, meningitis, polyneuritis, delirium, psychosis, paresis, coma
Pulmonary → hemoptysis, consolidation
Vasculitis / venous thrombosis
Death (larvae burden >1,000–5,000/g of tissue)

Larval burden determines severity: <10 larvae/g → asymptomatic; 100/g → significant disease; 1,000–5,000/g → potentially fatal.

— Sherris & Ryan's Medical Microbiology, p. 1871; Sleisenger and Fordtran, p. 2275

Diagnosis

Test	Finding
Eosinophilia	15–50% eosinophils; begins week 2, persists throughout illness; may disappear in fatal cases
Serum IgE	Elevated in most clinically ill patients
CPK (creatine phosphokinase)	Elevated (myositis)
Serology (IFA, ELISA)	Significant titers appear after week 3; may persist indefinitely
Muscle biopsy (deltoid or gastrocnemius)	Reveals encysted larvae during week 3 onward

Serologic tests are usually negative before week 3, so early diagnosis relies on clinical picture + epidemiologic exposure history.

Treatment

Indication	Treatment
Mild/moderate	Albendazole 400 mg twice daily × 10–15 days OR Mebendazole 5 mg/kg/day × 10–15 days
Severe (edema, pulmonary, cardiac, CNS)	Add glucocorticoids (corticosteroids first, then anthelmintics — to prevent hypersensitivity reaction from mass larval destruction)

Anthelmintics kill adult worms in the gut and halt larval production; they are less effective against already-encysted larvae
Glucocorticoids given without anthelmintics may prolong the intestinal phase, increasing larval release — so combination is preferred in severe cases
Mortality: ~1% in symptomatic cases; rises to ~10% with CNS involvement

— Sleisenger and Fordtran, p. 2276; Sherris & Ryan's, p. 1872

Prevention

Thoroughly cook all meat (especially pork, wild game, bear) to ≥71°C (160°F) internally
Freezing pork at −15°C for ≥3 weeks kills most strains (but not T. nativa, the arctic strain)
Federal/agricultural regulations: grain-only feed for commercial pigs; meat inspection
Control rodent contact with domestic pigs

Sources: Sleisenger and Fordtran's Gastrointestinal and Liver Disease | Sherris & Ryan's Medical Microbiology, 8th ed. | Bradley and Daroff's Neurology in Clinical Practice | Fuster and Hurst's The Heart, 15th ed.

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