Trichinella spiralis - Trichinellosis

Trichinosis is a zoonotic disease transmitted by eating uncooked or undercooked infected meat products (mainly pork). Trichinella infections are most often diagnosed in the laboratory based on detection of antibodies to excretory/secretory Trichinella antigen by ELISA or IFA. Testing is rarely positive in early disease. IgG antibodies can be detected approximately 12 to 60 days postinfection.

Diagnosis

Indications for Testing

  • Abdominal pain, nausea, and diarrhea, followed by fever, weakness, and muscle pain
  • Ingestion of improperly prepared meat (mainly pork)

Laboratory Testing

  • Trichinella diagnosis information (CDC)
  • Nonspecific testing
    • CBC – eosinophilia
    • Muscle enzymes (creatine kinase, aldolase) – elevated during muscle inflammation stage
  • Trichinella antibody testing by enzyme-linked immunosorbent assay (ELISA) or indirect fluorescent antibody (IFA)
    • Detectable 2-4 weeks after infection (may be >1,000/mL)
    • Cross reacts with other parasitic infections
    • Rarely positive in early disease

Histology

Larvae detection possible through biopsy and pathologist examination

Imaging Studies

  • Not indicated for diagnosis
  • May demonstrate calcified cysts on plain radiographs, computed tomography (CT), magnetic resonance imaging (MRI) – “puffed rice” or “spindle shaped” appearance

Differential Diagnosis

Background

Epidemiology

  • Incidence – very low in U.S.
  • Transmission – raw or undercooked meat from infected mammals
    • Domestic pig, black bear, dog, horse, walrus, wild boar

Organism

  • Pork worm or Trichinella spiralis (Trichinella species are among the smallest of the parasitic nematodes)
  • Transmission occurs when uncooked or undercooked infected meat is eaten 
    • Cyst dissolves, parasite matures and deposits larvae in deep mucosa
    • Larvae enter lymphatics and are carried throughout the body where they again encyst
    • 2 phases – intestinal and systemic

Clinical Presentation

  • During intestinal phase, if parasite burden is high, patient may experience diarrhea and abdominal pain
  • Symptoms from larval migration generally appear the second week after infection
    • Periorbital and facial edema
    • Hemorrhages in retina, nail beds, subconjunctival surfaces
    • Inflammatory muscle changes with associated myalgias – severity of symptoms are related to number of larvae present
    • Myocarditis, encephalitis, and pneumonia account for most deaths

Prevention

  • Fully cook potentially infected meat
  • Freeze potentially infected meat at -15°C for 3 weeks

ARUP Lab Tests

Screen for Trichinella exposure

Test is not diagnostic and must be correlated with supporting patient history and pathologic findings

Assess for presence of eosinophilia, suggesting parasitic infection

Nonspecific indicator of muscle inflammation or damage

Do not use as a stand-alone test

This nonspecific test has been replaced by other enzyme tests such as creatine kinase (CK), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) as more specific markers of muscle or liver damage

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories

References

Additional Resources