The document discusses systemic mycoses caused by dimorphic fungi, specifically Histoplasma capsulatum and Blastomyces dermatitidis, outlining their characteristics, geographic distribution, and pathogenesis. It includes information on diagnosis, including laboratory methods, clinical findings, and treatments available for infections caused by these fungi. It highlights differences in the forms of mycoses and the circumstances under which they may occur, particularly in immunocompromised individuals.

1. FungiCausingSystemicMycoses
Dimorphic Fungi
Histoplasma capsulatum
&
Blastomyces dermatitidis
1
Shabir Imteyaz Khan
Asst. Professor
Govt. E. Raghvendra Rao PG. Science College, Bilaspur
(C.G.)
2/3/2021
Shabir
Imteyaz
Khan

2. True Systemic (Endemic) Mycoses
• Histoplasmosis
• Blastomycosis
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3. General Features
• Causative Agents thermally dimorphic fungi that exist
in nature, soil
• Geographic distribution varies
• Inhalation  pulmonary infection  dissemination
• No evidence of transmission among humans or animals
• Otherwise healthy individuals are infected
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4. BLASTOMYCOSIS
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5. Blastomycosis (Gilchrist’s Disease)
Chicago Disease
Blastomyces dermatitidis
A chronic infection characterized by formation of
suppurative & granulomatous lesion found mainly
in lungs & disseminate throughout body
MOT = Inhalation of airborne spore (conidia)
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6. NorthAmerican Blastomycosis
Distribution
• Endemic in North, Central and
Southeastern USA,
• Quebec province of Canada
• Very few cases from India
• 1st in 1983 (U.P.)
• Scattered cases Mumbai and Vellore.
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7. Blastomyces dermatitides
Characteristics:
Dimorphic
Mold in soil, yeast in tissue
Yeast form is round-shaped with a thick refractile
wall and a single broad-based bud
Natural habitat is soil rich in organic material
In endemic areas, the fungus lives in soil and rotten
wood near lakes and rivers.
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8. Pathogenesis
• Infection occurs mainly in the respiratory tract
• Inhaled conidia differentiate into yeast
cell which initially cause abscesses
• Followed by formation of granuloma
• Dissemination is rare, but when it occurs
skin and bone are the most commonly
involved.
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9. Types
• Pulmonary –self limiting
• Cutaneous-most common, over exposed parts like face, neck
and hands.
• Disseminated- in AIDS, transplant, immunocompromised
• Miscellaneous- rare e.g. laryngeal (related to larynx), CNS,
osteomyelitis
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10. This resembles pulmonary TB showing diffuse infiltration in lung fields
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11. NorthAmerican Blastomycosis
• Cutaneous form exhibits sporotricoid spread and if chronic
almost always originates in the lungs.
• Most common site of dissemination from lung is the skin. (80% of
cases)
• Mainly on hands and feet, nodular, draining sinuses or
papillomatous and crusted.
• LESIONS ARE USUALLY MULTIPLE
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13. Laboratory Diagnosis:
Samples:- Sputum, BAL, biopsy, pus from
abcess
1. Direct microscopic examination
(KOH mount) and calcoflour white
= demonstrate characteristic thick walled “yeast
cell with single broad-based bud”
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14. Broad Based Budding yeast
Blastomyces dermatitides
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15. 2.Culture is difficult-
Sabouraud’s dextrose agar, Mycosel
and a brain-heart infusion agar to
which blood has been added.
grows as fluffy, brownish to white
fungus which produces pyriform
spores
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17. Lab diagnosis cont…
• 3. Hypersensitivity test – Blastomycin test
• 4. Serological test not useful
• 5. DNA probe assay is commercially available
• 6. Animal pathogenicity- e.g.- pig,rats,hamster
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18. Treatment
• Itraconazole (drug of choice)200-400mg/day for 6mths
• Amphotericin B - used to treat severe cases
• Surgical excision helpful
• Prevention: No vaccine or prophylactic drug available
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19. HISTOPLASMOSIS
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20. Histoplasmosis
• Systemic granulomatous disease
• Samuel Taylor Darling- 1905
• Darling’s Disease/"Ohio valley disease,"
• Caused by inhalation of airborne spores
(microconidia) which are present from
dropping of birds.
• The ecological niche of H. capsulatum is in
blackbird roosts, chicken houses and bat guano
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21. Epidemiology
• Natural reservoir soil, bat and avian habitats
• Location May be prevalent all over the world, but the
incidence varies widely
• Endemic in Ohio, Kentucky, Mississippi.
• In India, the Gangetic West Bengal is the site of most frequent
infections, with 9.4 percent of the population testing positive.
• Has been isolated from the local soil proving endemicity of
histoplasmosis in West Bengal.
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22. Morphology
Dimorphic fungus that exist as
1) Yeast cell in tissue and
2) Mold in soil enriched with bird droppings
Forms 2 types of asexual spore
a) Tuberculate macroconidia (thick-walled finger like
projection)
b) Microconidia - thin, small, smooth-walled
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23. Pathogenesis
• Inhalation of microconidia / primary Cutaneous
inoculation
• Conversion to budding yeast cells
• Phagocytosis by alveolar macrophages
• Restriction of growth or dissemination to RES by
bloodstream
• Suppression of cell-mediated immunity
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24. Clinical Findings
• ACUTE PULMONARY INFECTION
• Asymptomatic (95%) / mild / moderate / severe
/chronic cavitary
• CHRONIC PULMONARY
• PROGRESSIVE DISSEMINATED INFECTION
RES (liver, spleen, lymph nodes, bone marrow),
mucocutaneous infection
• PRIMARY CUTANEOUS INFECTION
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25. Acute Pulmonary histoplasmosis
• Majority are asymptomatic.
• incubation period-3-14 days
• Fever, chills
• Headache
• Malaise
• Myalgia
• Abdominal pain
• Cough, Hemoptysis. Dyspnea may also be present
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26. Chronic Pulmonary
Histoplasmosis
• In pts with underlying pulmonary disease.
• Cough
• Weight loss
• Fever
• Malaise
• Hemoptysis
• dyspnea
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27. Progressive Disseminated Histoplasmosis
• In pts who are immunocompromised.
• Mucosal ulcers in the
-mouth,
-gums and
-on surfaces of the skin.
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28. Laboratory Diagnosis
Samples Sputum, tissue, bone marrow, CSF,
blood
1. Direct Examination
2. Culture
3. Serology
4. Skin Test (Histoplasmin antigen) Limited
diagnostic value.
5. DNA probe and PCR 28
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29. Direct Examination
• Intracellular (within macrophages) and
extracellular oval yeast cells
• Stained by H&E for tissue biopsy smear
• Yeast may br detected in areas of caseation
necrosis and calcified lymph nodes by Gomori
Methenamine silver stain.
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30. H&Estain(left)showsmacrophagesfilledwithorganismsgivingthecytoplasma
slightlyvacuolatedappearance.AGMS(Gomorimethenaminestain)(right)shows
clusteredorganismsincytoplasm.
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31. Budding yeast cell
inside macrophages
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32. Culture
• Culture of sputum and blood on SDA at 25°C shows cottony
mycelial growth.
• Thin branching septate hyphae with tuberculoid macroconidia
and microconidia
• Macroconidia-8-20µm in diameter with fingerlike projections.
• At 37°C shows yeast cells.
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33. Tuberculate
macroconidia
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34. Serology
• Complement fixation test
• Immunodiffusion test:- detect antibodies to two
glycoprotein's, H and M
• Anti-H Ab is more specific and positive in 50-80% of
pts
• Detection of specific H.capsulatum Ag in urine and
serum in immunocompromised pts when Ab
production may be impaired
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35. C. Skin test
Histoplasmin test
Mycelial extract as antigen
Useful for epidemiologic
determination of incidence of
infection
Not used to diagnose actual disease
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36. Treatment:
• Amphotericin B – for disseminated infection
• Itraconazole - for pulmonary infection
• Fluconazole for meningitis.
Prevention:
None (no vaccine available)
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37. AFRICAN
HISTOPLASMOSIS
• Etiology Histoplasma capsulatum var. duboisii
Differentiation from Classical Histoplasmosis
• Larger, thick-walled yeast cells
• Pronounced giant cell formation in infected tissue
• Diminished pulmonary involvement
• Greater frequency of skin and bone lesions
Treatment
• Not required for several cases
• Amphotericin B
• Itraconazole
• Surgical resection of pulmonary lesions
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38. EPIZOOTIC
HISTOPLASMOSIS
• Etiology Histoplasma capsulatum var. farciminosum
Lymphangitis of horses & mules
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39. THANK YOU
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