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

• Protracted diarrhea
  • Bacterial diarrhea
    • Salmonella typhi (typhoid fever)
    • Shigella spp
  • Viral diarrhea
  • Parasitic diarrhea
• Periorbital/facial edema and fever
  • Glomerulonephritis
  • Serum sickness
  • Polymyositis
  • Dermatomyositis
  • Polyarteritis nodosa
• Conjunctival hemorrhage and fever
  • Leptospirosis spp
  • Endocarditis
• Myalgia and eosinophilia
  • Eosinophilic fasciitis
  • Eosinophilia-myalgia syndromes (toxic oil, tryptophan)
• Muscle weakness/pain
  • Polymyositis
  • Myopathic disease

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