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Systemic mycoses

 

1. Histoplasmosis

  1. Classical Histoplasmosis/ Darlings disease-Caused by dimorphic fungus Histoplasma capsulatum
  2. Infection of reticuloendothelium system
  3. Occurs predominantly in America & Africa
  4. 25 cases have been reported from India but no definite endemic focus is known
  5. Grows in the soil with high nitrogen content enriched with excreta of bats & chickens
  6. Infection is due to inhalation of spores

a. Clinical features:

  1. Asymptomatic in 90-95% cases
  2. Clinical types
  • Acute pulmonary/Chronic pulmonary
  • Cutaneous/ subcutaneous/ mucocutaneous/Disseminated 

b. Laboratory diagnosis:

  1. Specimens: sputum, biopsy of bone marrow, cutaneous, mucosal lesions
  2. Direct microscopic examination:
     
    Giemsa, Wright, calcofluor white staining
     
    Round/ oval yeast cells (2-4μm diameter) found intracellular within macrophages
  3. Culture:
     
    Growth on SDA at 25°C shows septate branching hyphae with two types of unicellular asexual spores.
     
    Large round tuberculate macroconidia (8-14μm) and smooth walled, pyriform microconidia (2-4μm)
  4. Yeast conversion: brain heart infusion blood agar at 37°C to show dimorphism
  5. Exoantigen test
  6. Serological tests: Immunodiffusion (H [active infection] & M bands), Latex agglutination, CF test
  7. Histoplasmin skin test: delayed type of hypersensitivity, present or past infection 

2. Blastomycosis

  1. Gilchrist’s disease, Chicago disease, North American Blastomycosis
  2. Caused by dimorphic fungus Blastomyces dermatitidis
  3. Occurs predominantly in central and mid western USA & eastern Canada .Few reports from India
  4. Infection is due to inhalation of spores, natural habitat unknown 

a. Clinical types

  1. Cutaneous (commonest)
  2. Pulmonary /Disseminated 

b. Laboratory diagnosis:

  1. Specimens: pus from abscess, sputum, tissue
  2. Direct microscopic examination: Methenamine silver, H&E, PAS staining
     
    Thick walled spherical yeast cells (8-15μm), single bud with broad base of attachment (figure of eight appearance). On PAS staining shows Splendore-Hoeppili phenomenon
  3. Culture: Growth on SDA at 25°C shows septate branching hyphae with smooth walled, spherical or pyriform microconidia (2-10μm) that are located on short terminal or lateral branches
  4. Yeast conversion: brain heart infusion blood agar at 37°C
  5. Exoantigen test
  6. Serological tests: Immunodiffusion (A band)
  7. Blastomycin skin test: delayed type of hypersensitivity, present or past infection 

3. Paracoccidiodomycosis

  1. South American Blastomycosis, Lutz’s mycosis
  2. Caused by dimorphic fungus Paracoccidiodes brasilienses
  3. Occurs predominantly in humid mountain forests of South & Central America
  4. No reports from India
  5. Infection is due to inhalation of spores, fungus has been isolated from soil

a. Clinical types

  1. Acute or subcutaneous form (Juvenile type)
  2. Chronic form (Adult type)
  • Unifocal/Multifocal
  • Here is a primary pulmonary infection that spreads by haematogenous routes to mucosa of the nose, mouth, gastrointestinal tract, skin, lymphatics, and internal organs producing chronic granulomatous reaction 

b. Laboratory diagnosis:

  1. Specimens: pus from abscess, sputum, biopsy from lesions
  2. Direct microscopic examination: Methenamine silver, H&E staining
  3. Yeast cell (2-30μm) with multiple buds (mariner’s wheel, pilot wheel, mickey mouse appearance)
  4. Culture: Growth on SDA at 25°C shows septate hyphae with chlamydospores, microconidia and arthrospores
  5. Yeast conversion: brain heart infusion blood agar at 37°C
  6. Exoantigen test
  7. Serological tests: Immunodiffusion (1,2,3 bands)
  8. Paracoccidioidin skin test: delayed type of hypersensitivity, present or past infection 

4. Coccidiodomycosis

  1. Caused by dimorphic fungus Coccidiodes immitis
  2. Occurs predominantly in semi-arid areas of South-west USA & North Mexico
  3. No reports from India
  4. Infection is due to inhalation of arthroconidia 

a. Clinical features:

  1. Primary pulmonary type (influenza like illness, some people [mainly white females develop hypersensitivity reaction after 1-2 weeks which is called as San Joaquin Valley fever or Desert rheumatism])
  2. Primary cutaneous type/Scrofuloderma type (enlargement of cervical lymphnodes)
  3. Disseminated type (osteoarticular lesions, CNS involvement) 

b. Laboratory diagnosis:

  1. Specimens: pus from abscess, sputum, CSF
  2. Direct microscopic examination: Methenamine silver, H&E & PAS staining
  3. Doubly refractile thick walled spherule (30-60μm diameter) containing endospores
  4. Culture: Growth on SDA at 25°C shows septate hyphae. Aerial mycelia form alternate barrel shaped arthroconidia
  5. Yeast conversion: difficult to achieve
  6. Exoantigen test
  7. Serological tests: Immunodiffusion (HS & F bands)
  8. Coccidioidin skin test: delayed type of hypersensitivity, present or past infection





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