How is leishmaniasis diagnosed?

Diagnosis of Leishmaniasis

Multiple diagnostic approaches should be used simultaneously to diagnose leishmaniasis, including visualization of amastigotes in tissue samples, parasite culture, molecular detection of parasite DNA, and serologic testing for visceral leishmaniasis. 1

Types of Leishmaniasis and Sample Collection

Cutaneous Leishmaniasis (CL)

• Skin lesion sampling:
  • Collect tissue from the active border of lesions (not the necrotic center)
  • Obtain samples through:
    • Scraping of lesion borders
    • Aspiration of fluid from lesion edges
    • Punch biopsy from active border
  • Multiple samples should be collected for different diagnostic tests

Mucosal Leishmaniasis (ML)

• Mucosal tissue sampling:
  • Biopsy specimens from macroscopic abnormalities in naso-oropharyngeal areas
  • Should be performed by an otolaryngologist 1
  • Examine for signs including erythema, edema, hyperemia, infiltration, nodules, erosion, ulceration, and tissue destruction

Visceral Leishmaniasis (VL)

• Tissue sampling priorities:
  • Bone marrow aspiration (preferred first diagnostic sample) 1
  • Liver biopsy or enlarged lymph nodes (alternative sources)
  • Buffy coat from whole blood (especially in immunocompromised patients)
  • Serum collection for antibody detection 1

Diagnostic Methods (in order of recommended use)

1. Molecular Detection (DNA-based assays)

   • Highest sensitivity among available tests 1
   • Polymerase chain reaction (PCR) targeting ITS1 region shows superior sensitivity (87%) compared to microscopy (37%) 2
   • Should be performed even if other diagnostic tests are negative 1
   • Can be performed on previously prepared Giemsa-stained slides 2

2. Direct Microscopic Examination

   • Visualization of characteristic amastigotes in:
     • Giemsa-stained smears from lesion scrapings
     • Histopathological examination of tissue samples
   • Relatively quick but less sensitive (58-75% sensitivity) 3, 2

3. Parasite Culture

   • Isolation of parasites in specialized media
   • Enables species identification through DNA-based assays or isoenzyme analysis
   • Contact reference laboratories before collecting specimens 1
   • Allows definitive species identification, which guides treatment decisions

4. Serologic Testing

   • For visceral leishmaniasis only - not recommended for CL diagnosis 1
   • Should not be used as the sole diagnostic test 1
   • May be falsely negative in immunocompromised patients (HIV/AIDS) 1
   • Cannot be used to assess treatment response (antibodies may persist for years) 1

5. Montenegro Skin Test

   • Not recommended or available in North America 1
   • No standardized, approved products available in the US or Canada

Species Identification

• Species identification should be attempted in all cases of suspected CL 1
• Important for clinical management decisions:
  • Risk assessment for mucosal involvement
  • Treatment selection
  • Prognosis determination 3
• Particularly important for infections acquired in the "mucosal belt" of Bolivia, Peru, and Brazil where Viannia species carry higher risk of mucosal leishmaniasis 1

Special Considerations

Immunocompromised Patients

• Higher risk of false-negative serologic tests 1
• Additional blood collection for buffy coat examination, culture, and molecular analysis is recommended 1
• Higher propensity for diffuse cutaneous leishmaniasis 4

Mucosal Leishmaniasis Risk Assessment

• All persons at risk for ML should be:
  • Questioned about mucosal symptoms
  • Examined for mucosal signs
  • Educated about seeking medical attention for persistent, atypical naso-oropharyngeal manifestations 1

Common Pitfalls to Avoid

1. Relying on a single diagnostic test

   • No single test has 100% sensitivity
   • Combine multiple diagnostic approaches 1, 3

2. Improper sample collection

   • Samples must be taken from active borders of lesions, not necrotic centers
   • Inadequate or improperly stained samples may lead to false negatives 2

3. Failure to consider leishmaniasis in differential diagnosis

   • Disease mimics both infectious and malignant conditions 4
   • Misdiagnosis may lead to unfavorable outcomes

4. Using serologic tests for cutaneous leishmaniasis

   • Serologic assays are neither sensitive nor specific for CL diagnosis 1

5. Treating without species identification

   • Different species have varying treatment sensitivities and risk of mucosal involvement 4, 3
   • Species identification guides appropriate management

By following this diagnostic algorithm and avoiding common pitfalls, clinicians can accurately diagnose leishmaniasis and guide appropriate treatment decisions based on the specific form of disease and infecting species.