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Microbiology · Nematodes

Trichinella spiralis !

  • Parasite
  • Exam priority: medium

A tiny worm that comes with undercooked pork or game. Its larvae encyst in muscle and cause fever, muscle pain and swollen eyelids.

Updated 2026-11-01

Also called: trichina

At a glance

Shape
Larva coiled inside a modified muscle cell ('nurse cell')
Family
Trichinellidae
Type
Tissue nematode (intracellular larva in striated muscle)
Size
Adults 1–4 mm; encysted larva about 1 mm

Morphology

  • Larva coiled in a spiral inside the striated muscle fibre.
  • Very small adults in the small-bowel mucosa.
  • Some species (T. pseudospiralis) do not encyst.

Transmission

  • Eating raw or undercooked meat with encysted larvae: pork, wild boar, bear or other game.
  • Homemade sausage, jerky or dried meat from those animals.
  • Not spread between people.

Reservoir: Domestic cycle: pigs and rodents; Sylvatic cycle: wild boar, bear and other carnivores

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. A person eats undercooked meat with encysted larvae (pork, wild boar, bear).
  2. Stomach acid and pepsin release the larvae, which invade the small-bowel mucosa.
  3. They mature into adults; about a week later the females release newborn larvae.
  4. The larvae travel in blood and lymph and encyst in striated muscle (diaphragm, masseters, eye muscles).
  5. In muscle they may calcify; the cycle goes on when a carnivore eats that meat.

Virulence factors

  • Intestinal phase: mucosal invasion with diarrhoea and abdominal pain.
  • Migration phase: vasculitis and inflammation with periorbital oedema, fever and splinter haemorrhages.
  • Muscle phase: myositis with pain and weakness.
  • Serious complications: myocarditis, encephalitis and pneumonitis.

Diseases it causes

Clinical picture

  • Diarrhoea and abdominal pain in the first week.
  • Periorbital and facial oedema, conjunctivitis.
  • High fever, severe myalgia and weakness.
  • Several diners ill after sharing the same meat.

Diagnosis

  • Marked eosinophilia and raised muscle enzymes (CK).
  • EIA serology; antibodies may take 3–5 weeks to appear, so testing is repeated.
  • Muscle biopsy showing encysted larvae.
  • History of undercooked pork or game.

Treatment

Benzimidazole antiparasitics (albendazole or mebendazole), most useful early, with corticosteroids when inflammation is severe.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Cook meat to a safe internal temperature checked with a thermometer.
  • Do not taste raw meat while cooking.
  • Freezing does not always kill larvae in game meat; curing, smoking or drying are unreliable.
  • Rodent control and proper feeding of pigs.

Test yourself

Think of the answer, then tap the question to see it.

Which clinical triad suggests trichinellosis?

Periorbital oedema, myalgia and marked eosinophilia after eating undercooked meat.

Where do Trichinella larvae encyst?

In striated muscle, especially very active muscles such as the diaphragm, masseters and eye muscles.

Why does an early negative serology not rule out trichinellosis?

Antibodies can take 3–5 weeks to appear, so the test is repeated.

Which meats transmit Trichinella?

Pork and game such as wild boar and bear, raw or undercooked.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Trichinellosis (CDC, 2024); About Trichinellosis | Trichinellosis (Trichinosis) | CDC (CDC, 2024).

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Representative model, for educational purposes only.