1. INSTITUTE OF HEALTH TECHNOLOGY, DHAKA
Department of Laboratory Medicine
BSc in Health Technology (Laboratory)- 1st Year
MYCOLOGY
Lecture No. 06 (Deep Mycoses - Histoplasmosis)
By
Sk. MIZANUR RAHMAN
Lecturer, Mycology
MS in Biotechnology & Genetic Engineering (UODA)
MS in Microbiology (SU)
3. Histoplasmosis
Characteristics
• Member of the phylum Ascomycota
• Worldwide distribution
• Naturally found in fecal-contaminated soils
• Birds and bats appear to be reservoirs
• Etiologic agent of histoplasmosis
4. Characteristics (cont.)
• Dimorphic fungus
– Sexual multi-cellular saprophytic
mycelia
– Asexual single-celled parasitic yeast
• Mycelial form is most commonly found
in the environment
• Heterothallic species
• Tightly coiled septate hyphae (A)
• Globose cleistothecia (C)
• Pear-shaped asci (E)
• Smooth, hyaline, spherical ascospores
(F)
A
C E F 4
5. Characteristics (cont.)
• Yeast form is the infectious agent in humans
• Form asexual macro- and microconidia
– Also borne by hyphae in the mycelial form (B)
• Conidia germinate via non/polar budding
• Yeast cells have white, thin-walled, oval bodies (A)
A B
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6. Histoplasmosis-Types
• 2 major forms of histoplasmosis
– Pulmonary and disseminated
• Pulmonary histoplasmosis occurs when
microconidia or mycelial fragments are inhaled
– Form lesions in the hilar and/or mediastinal nodes
– Many types of pulmonary histoplasmosis
• Asymptomatic pulmonary histoplasmosis
• Acute pulmonary histoplasmosis
• Mediastinal granuloma
• Fibrosing mediastinitis
• Chronic cavitary pulmonary histoplasmosis
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7. Disseminated Histoplasmosis
• Disseminated histoplasmosis
– Occurs primarily in immunocompromised individuals
– In healthy individuals, H. capsulatum is similar to
tuberculosis
• While the infection is usually resolved, the fungus is still present
• Constantly kept in check by T lymphocytes
– In immunocompromised individuals, H. capsulatum is able
to spread from the lungs into other organs
– Patients display fever, malaise, and occasionally petechiae
or skin lesions (cutaneous histoplasmosis)
– Tests often reveal mucous membrane ulcerations,
simultaneous enlargement of the liver and spleen, and
enlarged lymph nodes
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8. Disseminated Histoplasmosis (cont.)
–Diagnosis is performed by demonstrating
the presence of the fungus in
extrapulmonary tissue
• Blood cultures, bronchoscopy, BAL, ID, CF,
and positive antigen tests are commonly
performed
–Elevated levels of lactate dehydrogenase
and ferritin in AIDS patients
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9. HISTOPLASMOSIS
Pathogenesis
Respiratory Infections
inhale yeast form
spores
macrophages macrophases
in lung ingest yeast
Lymph nodes
Liver
Spleen
Adrenal glands
Intestine
Bone Marrow
Proliferation halted by onset of acquired CMI at 10-14 d.
Vasculitis, tissue necrosis, caseating granulomata. Killing by macrophages, healing,
calcification
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10. Histoplasmosis
Clinical
• Chronic pulmonary histoplasmosis (1/100,000)
– pre-existing structural lung defect, i.e. COPD, emphysema
– chronic pneumonia or infection in cavities, increased
sputum
– reactivation or reinfection
– apical infection, may be cavitary
• Mediastinal granulomatosis and fibrosis
– fibrosis, traction, occlusion of mediastinal structure
• Histoplasmoma
– Fibrocaseous nodule
– Concentric caseation and calcification
• Presumed ocular histoplasmosis syndrome
– choroiditis - active or inactive
• may result in visual loss due to macular involvement
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19. Histoplasmosis (diagnosis cont.)
3. Culture
Sabouraud’s agar
White - brown mould
Typical microscopic morphology
Slow growth 2-8 weeks
Rapid ID confirmation
Exo-antigen
Molecular probe
Traditional ID confirmation
Conversion mould to yeast
Animal inoculation
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25. Hyphal to yeast conversion at 37ºC
Yeast-like colonies Yeast cells
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26. Yeast - Histoplasma capsulatum
• Media
– Blood enriched media
– Incubate at 35ºC in ambient air for 2-4 weeks
• Colony
morphology
• Microscopic
morphology
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28. Diagnosis (cont.)
• 4. Serology
– Sensitivity and specificity vary according to stage and
form of disease
• Lowest for early acute pulmonary and disseminated
(sensitivity 5-15% at 3 weeks)
• Highest for chronic pulmonary and disseminated (sensitivity
70-90% at 6 weeks)
– Complement fixation test (CFT)
• Yeast (more sensitive) and mycelial (histoplasmin) phase
antigens required
• ≥1:32 or 4-fold rise suggests recent infection
• X-reactions with B. dermatitidis and C. immitis
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29. Diagnosis (cont.)
• Immunodiffusion
– More specific, less sensitive
– M bands
• Prior exposure
• Acute and chronic diseases
• X-reactions occur with other fungi
– H bands
• Diagnostic of acute disease
• Revert to negative in 6 months
• Acute or chronic
• Little cross-reaction with other fungi
• Appear later than CFT Abs
• ELISA/RIA
– Increased sensitivity (90% active pulmonary histo)
– Decreased specificity compared to CFT 29
32. Diagnosis (cont.)
• Ag detection
– Urine
– Most useful in patients with large fungal burden
• Acute pulmonary histo (80% sensitive)
• Progressive disseminated histo (90% sens)
– Less useful with lower fungal burdens
• Chronic pulmonary (15% sensitive)
• Subacute pulmonary (30% sensitive)
– Serum sensitivity is lower
– Cross-reactions with B. dermatitidis and recipients of
anti-thymocyte globulin
– Joe Wheat, MiraVista Diagnostics, Indianapolis
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