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A parasitic (nematode) disease that develops after ingestion of contaminated meat (typically pork or wild game) containing viable cysts of Trichinella spiralis. Rarer cases are attributable to seven other Trichinella species (Trichinella nativa, Trichinella britovi, Trichinella murelli, Trichinella nelsoni, Trichinella pseudospiralis, Trichinella papuae, Trichinella zimbabwensis).
- Most common outbreaks are attributable to:
- Undercooked pork
- Homemade and commercial sausage
- Bear, wild boar, walrus; other wild animal meats
- In the United States, bear and wild game now account for >50% of cases (1).
- Horsemeat is an important source in the European Union.
- Phase I: intestinal (enteral) phase
- Onset usually 48 to 72 hours after ingestion
- May be asymptomatic
- Larvae are released and mature in small intestines.
- Phase II: muscular (parental) phase
- Onset 2 to 3 weeks after ingestion
- Major systems affected:
- Other systems affected:
- Synonyms: trichinelliasis; trichinosis
Transplacental passage of migrating larvae is possible. Elevated progesterone during pregnancy is helminthotoxic to newborn larvae, leading to a milder infection. Trichinellosis can cause miscarriage or premature delivery. Mebendazole and albendazole are contraindicated in pregnancy.
- Only 15 cases were reported in the United States in 2011 (7)[C] and 12 cases in 2012 (1).
- Worldwide from 1986 to 2009, there were ~65,000 cases and 42 deaths (8)[C].
- Higher incidence in Alaska and Northeastern United States
- Autopsy studies suggest that most mild cases are probably undiagnosed.
- Predominant age: 20 to 49 years, although cases were reported from all age groups
- Predominant sex: male = female
Etiology and Pathophysiology
Eating undercooked meat contaminated with viable Trichinella cysts. Symptoms and severity relate to how many larvae are ingested and cyst burden.
- Enteral phase (phase I)
- Cysts are broken down by digestive acid in the stomach, releasing larvae, which develop into mature adult worms in the small intestine.
- ~1 week after ingestion; may last 3 to 5 weeks
- Symptoms result from presence of cysts and worms.
- Muscular phase (phase II)
- Female worms release newborn larvae that migrate through blood vessels and lymphatics to multiple organ systems.
- 2 to 3 weeks after ingestion; may last for 2 months
- Larvae encyst in striated skeletal and cardiac muscle forming a “nurse cell” that nourishes and protects the organism from host immunity.
- IM cysts usually calcify over time.
- Cyst can survive in humans up to 30 years.
- Symptoms result from invasion of larvae/worms and the resulting inflammatory process leading to edema, vasculitis, and intravascular thrombi.
- Symptoms depend on location of larvae/worms.
- Access to wild game, homemade pork products, or noncommercial sources of meat
- Eating pigs fed on uncooked garbage
- Consuming undercooked pork
- Eating inadequately cooked or frozen wild game
- Ethnic groups from Southeast Asia who raise their own pork or consume partially cooked pork products
- Residents in Alaska and Northeastern United States
- Risk for more severe symptoms (9)[C]:
- >10 years old
- High eosinophil count
- Repeated consumption of contaminated meat
- Avoid consumption of undercooked pork or game.
- Prolonged freezing may help prevent disease (less so for wild game meat).