Trichinella spiralis - Trichinellosis

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

• 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

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