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For further information, see CMDT Part 35-26: Trichinosis

Key Features

Essentials of Diagnosis

  • Ingestion of inadequately cooked pork or game

  • Transient intestinal symptoms followed by fever, myalgias, and periorbital edema

  • Eosinophilia and elevated serum muscle enzymes

General Considerations

  • Caused worldwide by Trichinella spiralis and related Trichinella species

  • Transmission occurs

    • By ingestion of undercooked meat, most commonly pork in areas where pigs eat garbage

    • By ingestion of game and other animals, including bear and walrus in North America and wild boar and horse in Europe

  • When infected raw meat is ingested, Trichinella larvae are freed from cyst walls by gastric acid and pass into the small intestine

  • Larvae then invade intestinal epithelial cells, develop into adults, and the adults release infective larvae (which may be viable for years)

  • Parasites travel via the bloodstream to skeletal muscle where they invade muscle cells, enlarge, and form cysts


  • Worldwide incidence of trichinosis has decreased, but human infections continue to occur sporadically or in outbreaks, with estimates of ~10,000 cases annually

  • In the United States, about 20 infections are reported annually, mostly from ingesting wild game

Clinical Findings

Symptoms and Signs

  • Most infections are asymptomatic

  • In symptomatic cases, gastrointestinal symptoms (eg, diarrhea, vomiting, abdominal pain)

    • Develop within 1 week after ingestion of contaminated meat

    • Usually last for < 1 week but can persist for much longer

  • During the following week, migrating larvae may produce

    • Fever, myalgias, periorbital edema, and eosinophilia (most notably)

    • Headache

    • Cough

    • Dyspnea

    • Hoarseness, dysphagia

    • Macular or petechial rash

    • Subconjunctival and retinal hemorrhages

  • Systemic symptoms

    • Usually peak within 2–3 weeks

    • Commonly persist for about 2 months

  • In severe cases, generally with large parasite burdens, muscle involvement can be pronounced, with severe muscle pain, edema, and weakness, especially in the head and neck

  • Muscle pain may persist for months

  • Uncommon severe findings include

    • Myocarditis

    • Pneumonitis

    • Meningoencephalitis, sometimes leading to death

Differential Diagnosis

  • Eosinophilia-myalgia syndrome

  • Eosinophilic fasciitis

  • Dermatomyositis

  • Influenza

  • Polyarteritis nodosa

  • Viral gastroenteritis

  • Polymyalgia rheumatica

  • Fibromyalgia

  • Sarcocystosis


Laboratory Tests

  • Elevated serum muscle enzymes (creatine kinase, lactate dehydrogenase, aspartate aminotransferase)

  • Erythrocyte sedimentation rate usually normal

  • A commercial ELISA is available in the United States

  • Serologic tests become positive 2 or more weeks after infection, but cross-reactivity can be seen with other parasites

  • Rising antibody titers are highly suggestive of the diagnosis

Diagnostic Procedures

  • Muscle biopsy

    • Can usually be avoided

    • If diagnosis is uncertain, biopsy of a tender, swollen muscle may identify Trichinella larvae

    • For maximal yield, specimen should be examined histologically, and a portion enzymatically digested to release larvae

    • However, larvae may not be seen in muscle until 3 weeks ...

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