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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