Histoplasma capsulatum

Histoplasma capsulatum


 Histoplasma capsulatum

  • A dimorphic fungus
  • mold in soil (↓ temperature, “mold in the cold”)
  • yeast in Tissue (↑ Temperature)
  • Non encapsulated 
  • The only medically important capsulated fungus is cryptococcus.

Source of Infection:

  • Infection is acquired by inhalation of microconidia (small spores) in dust contaminated with bird or bat dropping.
  • cave exploring/spelunking
  • endemic to Mississippi and Ohio River valleys
  • Ohio and Tennessee
Culture:
  • On Sabourauds agar,
  • It grows as mycelia forms, producing spores at 25°C 
  • At 37°C it grows as a yeast form.
  • Tuberculate spore 
  • White cottony mycelia growth
  • With large (8-20 micrometer) thick walled, spherical spores with tubercles or finger-like projections. 
 
Pathology:
  • It causes intracellular infection of reticuloendothelial system.
  • Forms 2 types of asexual spores:
  • Large tuberculate macroconidia
  • Smaller elliptical microconidia. 
  • fungi inhaled in spore form
  • lungs are locally infected
  • Microconidia reach the alveoli and initiate a granulomatous reaction.
  • infection disseminates hematogenously
Clinical Manifestations 
  • Histoplasmosis/Darling’s disease/ Cave’s disease /Caver’s disease.
  • Endemic fungal infection

Symptoms

  • Asymptomatic
  • majority of cases
  • most people never visit the doctor
  • Mild (acute primary pulmonary histoplasmosis).
  • fever
  • cough
  • chest X-ray finding of hilar adenopathy due to caseation necrosis or calcification
  • which mimics TB
  • with or without 1 or more areas of pneumonitis are typical features.
  • Chronic pulmonary histoplasmosis or chronic fibrocavitary pneumonia
  • Related to mediastinal fibrosis

Disseminated disease

  • fever and malaise
  • seen in immunocompromised
  • Mimic disseminated TB
  • Adrenal glands are the most commonly involved organs 
  • adrenal glands are usually symmetrically enlarged

Diagnosis

Culture:

  • Tuberculate spore is diagnostic
  • Sputum culture :
  • For chronic pulmonary histoplasmosis
  • A culture of bone marrow, mucosal lesion, liver and BAL fluid :
  • Diagnostically useful in disseminated histoplasmosis
  • Blood culture is best performed by lysis centrifugation method.
  • Millary mottling on X-ray chest
Treatment
  • Acute pulmonary histoplasmosis
  •  None
  • Chronic pulmonary Histoplasmosis
  • Itraconazole(DOC)/Amphotericin B

Disseminated disease;CNS involvement

  • Itraconazole /Amphotericin B
  • Immunocompromised
  • Amphotericin B

Exam Question

Histoplasma capsulatum
  • A dimorphic fungus
  • Non encapsulated 

Source of Infection:

  • Infection is acquired by inhalation of microconidia (small spores) in dust contaminated with bird or bat dropping
Culture:
  • On Sabourauds agar,
  • White cottony mycelia growth appears, with large (8-20 micrometer) thick walled, spherical spores with tubercles or finger-like projections. 
 Pathology: 
  • fungi inhaled in spore form
  • lungs are locally infected
  • Microconidia reach the alveoli and initiate a granulomatous reaction.
  • infection disseminates hematogenously

 Clinical Manifestations

  • Histoplasmosis/Darling’s disease/ Cave’s disease /Caver’s disease.
  • Endemic fungal infection

Symptoms

  • Asymptomatic
  • Mild (acute primary pulmonary histoplasmosis).
  • fever
  • cough
  • chest X-ray finding of hilar adenopathy due to caseation necrosis or calcification
  • which mimics TB
  • with or without 1 or more areas of pneumonitis are typical features.
  • Chronic pulmonary histoplasmosis or chronic fibrocavitary pneumonia
  • Related to mediastinal fibrosis

Disseminated disease

  • fever and malaise
  • seen in immunocompromised
  • Mimic disseminated TB
  • Adrenal glands are the most commonly involved organs 
  •  adrenal glands are usually symmetrically enlarged

Diagnosis

Culture:

  • Tuberculate spore is diagnostic
  • Millary mottling on X-ray chest
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