Trichinella spiralis

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Trichinella spiralis /
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Background

  • Also known as the pork worm, not to be confused with pork tapeworm (Taenia solium)

Life Cycle

  • Can complete its life cycle in a human, pig, boar, bear, walrus, fox, and other animals
  • Life cycle involves ingestion of meat with cysts, which develop into adult worms, which release eggs, which invade through gut mucosa and migrate to muscle, where it becomes a muscle cyst

Epidemiology

  • Acquired in humans by ingestion of undercooked meat
  • Present in carnivores and omnivores worldwide
  • Commercial pork is the most common source of infection in humans, but can also be acquired from a number or wild game meats

Clinical Manifestations

  • Spectrum of illness from asymptomatic (most common) to fulminant infection
  • Incubation period less than 1 month
  • After ingestion of contaminated meat:
    • Within first week, may experience abdominal discomfort, nausea, vomiting, and diarrhea
    • After another 2 to 8 weeks, may have fever, myalgia, periorbital edema, urticarial rash, conjunctival hemorrhage, and subungual hemorrhage, related to migration of larvae into tissues
    • In severe disease, after 1 to 2 months, can develop myocarditis, neurological symptoms, and pneumonitis
    • Can cause an eosinophilic myositis
  • Often has eosinophilia during migratory phase (70%)
  • Larvae are viable in tissues to years, with calcification usually occurring between 6 and 24 months

Diagnosis

  • Usually made clinically based on exposure history, eosinophilia, and symptoms
  • Serology exists, and can be used as paired acute and convalescent titres
    • Positive after 2 to 3 weeks, and can stay positive for years
    • Cross-reacts with other nematodes (and sometimes with other helminths)

Management