Trichinellosis

Epidemiology & Risk Factors

• Etiology: Trichinella spiralis (nematode/roundworm).
• Transmission: Ingestion of raw or undercooked meat containing encysted larvae.
  • Domestic source: Undercooked pork.
  • Sylvatic source: Wild game (e.g., bear, wild boar, walrus).
• Pathophysiology: Ingested larvae liberated in stomach -> mature in small intestine -> female worms release newborn larvae -> hematogenous spread to skeletal muscle -> encystment.

---

Clinical Features

• Phase 1: Intestinal Stage (1–2 weeks post-ingestion):
  • Nausea, vomiting, abdominal pain, diarrhea.
  • Often mild or transient.
• Phase 2: Muscle Invasiveness / Systemic Stage (2–8 weeks post-ingestion):
  • Classic Triad: Periorbital edema + Myositis (severe muscle pain/tenderness) + Fever.
  • Subungual splinter hemorrhages and conjunctival hemorrhages. c
  • Chemosis, macular or maculopapular rash.
  • Muscle pain involving extraocular, masseter, neck, and proximal limb muscles.

---

Diagnosis

• Initial / Screening Labs:
  • Marked Eosinophilia (often >20–50%; hallmark finding).
  • ↑ Creatine kinase (CK), ↑ LDH, ↑ Aldolase (indicates myositis).
  • ↑ Serum IgE level.
• Confirmatory / Gold Standard:
  • Serology (ELISA): Anti-Trichinella Ab detection (mainstay; usually positive 2–3 weeks post-infection).
  • Muscle Biopsy: Demonstrates encysted larvae within striated muscle (definitive; reserved for diagnostic ambiguity or negative serology w/ high clinical suspicion).

---

Differential Diagnostics

• Polymyositis / Dermatomyositis: Diff by chronic onset, lack of GI prodrome, absence of eosinophilia, and positive autoantibodies (e.g., anti-Jo-1, anti-Mi-2).
• Periorbital Cellulitis: Diff by localized warmth/erythema, typically unilateral, and absence of eosinophilia or systemic myositis.
• Typhoid Fever: Diff by persistent high fever, rose spots, leukopenia (not eosinophilia), and positive blood/stool cultures.
• Eosinophilic Granulomatosis with Polyangiitis (EGPA): Diff by history of severe asthma, allergic rhinitis, p-ANCA positivity, and pulmonary infiltrates.

---

Management

1. Mild / Asymptomatic Disease:
   • Symptomatic treatment with NSAIDs for analgesia and fever control.
2. Moderate to Severe / Early Disease:
   • Antiparasitic therapy: Albendazole (400 mg PO BID for 10–14 days) or Mebendazole.
3. Severe Disease / Organ Involvement (e.g., myocarditis, CNS involvement, severe hyper-inflammation):
   • High-dose Corticosteroids (e.g., Prednisone) co-administered with antiparasitics to prevent severe immune reactions to dying larvae.

---

Complications

• Myocarditis: Leading cause of death (arrhythmias, heart failure, ECG changes).
• Encephalitis / Meningoencephalitis: Seizures, focal neurological deficits, altered mental status.
• Pneumonitis / Diaphragmatic weakness: Respiratory failure secondary to larval migration into respiratory muscles.