Description

A parasitic disease that is acquired after ingestion of raw or undercooked meat contaminated with viable cysts of nematode in the genus Trichinella. The most common species worldwide is 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:
  • In the United States between 2011 and 2015, bear (44%), wild boar (23%), and unspecified pork (16%)
  • Horsemeat is an important source in Europe.
• Phase I: intestinal (enteral) phase
  • Onset usually 1 to 2 days after ingestion
  • Larvae are released and mature in small intestines.
  • Symptoms: nausea, vomiting, diarrhea, abdominal pain
• Phase II: muscular (parental) phase
  • Develops within 2 weeks after ingestion
  • Adult-derived larvae in intestine enter the skeletal muscle through hematogenous dissemination.
  • Symptoms: muscle pain, fever, swelling of face, fatigue, itchy skin, cough, diarrhea, constipation
• Major systems affected:
  • Gastrointestinal
  • Musculoskeletal
• Other systems affected:
  • Renal
    • Proteinuria
  • Neurologic
    • Paralysis
    • Encephalitis or meningitis
  • Cardiovascular
    • ECG abnormalities
    • Heart failure
    • Myocarditis
  • Hepatic: less common
    • Hepatomegaly
    • Hypoalbuminemia
    • Hypoproteinemia
    • Fatty degeneration of liver
• Synonyms: trichinelliasis; trichinosis

Epidemiology

Incidence

• Worldwide an estimated 10,000 cases per year
• From 2011 to 2015, 80 cases were reported in the United States; highest number of cases reported in Alaska, Illinois, and Texas between 2011 and 2015
• Autopsy studies suggest that most mild cases are probably undiagnosed.
• Predominant age: 20 to 59 years, although cases were reported from all age groups
• Predominant sex: male 64%, female 36%

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.

Risk Factors

• 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
• Risk for more severe symptoms (1)[B]:
  • >10 years old
  • Leukocytosis
  • High eosinophil count
  • Repeated consumption of contaminated meat

General Prevention

• Avoid consumption of undercooked pork or game.
• Prolonged freezing may help prevent disease (less so for wild game meat).