Trichinella spiralis

Diagnosis

Indications for Testing

  • Clinical presentation and risk factor of improper meat preparation (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 ELISA or IFA
    • Detectable 2-4 weeks after infection (may be >1,000/mL)
    • Cross reacts with other parasitic infections
    • Uncommonly, positive in early disease

Histology

  • Muscle biopsy with staining detects larvae

Imaging Studies

  • Not indicated for diagnosis
  • May demonstrate calcified cysts on plain radiographs, CT, MRI – “puffed rice” or “spindle shaped” appearance

Differential Diagnosis

Clinical Background

Trichinosis is a zoonotic disease transmitted by eating uncooked or undercooked infected meat products (mainly pork).

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
    • Two 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 the number of larvae present
    • Myocarditis, encephalitis, and pneumonia account for most deaths

Treatment

  • Treatment unsuccessful in most patients
    • Glucocorticoids useful for severe myositis and myocarditis
  • Infected patients usually recover with bedrest

Prevention

  • Fully cooking potentially infected meat or freezing at -15°C for 3 weeks

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Assess for presence of eosinophilia, suggesting parasitic infection

   
Trichinella Antibody by ELISA 0050787
Method: Qualitative Enzyme-Linked Immunosorbent Assay

Detect presence of serum Trichinella antibodies when there is a clinical suspicion of Trichinella infection

   
Creatine Kinase, Total, Serum or Plasma 0020010
Method: Quantitative Enzymatic

Nonspecific indicator of muscle inflammation

   
Aldolase, Serum 0020012
Method: Quantitative Enzymatic

Do not use as a stand-alone test

Measures the concentration of aldolase enzyme in serum

This nonspecific test has been replaced by more specific markers for muscle or liver damage

Can be used along with creatine kinase (CK) testing to screen and monitor therapies for skeletal muscular diseases