Trichinosis

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

Demographics

• 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

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 after infection

Medications

• No effective specific therapy for full-blown trichinosis

• However, mebendazole (2.5 mg/kg orally twice daily) or albendazole (5–7.5 mg/kg orally twice daily) will kill intestinal worms and may limit progression to tissue invasion

Therapeutic Procedures

• Supportive therapy for systemic disease consists of

  • Analgesics

  • Antipyretics

  • Bed rest

  • Corticosteroids for severe illness

Prevention

• Infection is prevented by cooking to a temperature of at least 71°C for at least 1 minute

• Irradiation of meat is also effective in eliminating Trichinella larvae

• Freezing is not reliable