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Fungi (1. Superficial & Cutaneous Fungi
Superficial mycoses
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Fungi (
1. Superficial & Cutaneous Fungi
- Superficial mycoses
- Generally do not provoke a significant histopathological inflammatory
response in the host
- e.g. pityriasis versicolor, tinea nigra, black & white pier
- Cutaneous mycoses
- Although fungus may be confined to the stratum corneum, pathological
changes occur in the host tissue
- e.g. dermatophytosis, candidosis, dermatomycoses caused by Scytalidium sp and other non-dermatophyte moulds
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2. Deep (Subcutaneous) Fungi
- Usually tropical/subtropical countries
- Environmental fungi
- Sporadic occurring infections
- Directly inoculated into dermis/ epidermis via penetrating injury
- Chronic and deforming
- Some very hard to treat
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3. Systemic Mycoses
- Dimorphic (Thermally)
- Also called "true mycoses" and "Endemnic mycoses"
- Others
- Candida
- Aspergillus
- Fusairium
- Rhizopus etc
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Other techniques
- Antibody tests: of limited usefulness
- e.g. Aspergillus precipitins
- Antigen tests
- Cryptococcus neoformans (cryptococcal antigen test done on serum or CSF, not on urine)
- Galactomannan antigen assay: screening for
possible Aspergillus infection
- Molecular techniques e.g. PCR
Diseases caused by fungi
- Poisoning etc, Allergy, Infections
Mycotoxins
- Poisonous substances produced by certain fungi
- Poisoning: acute or chronic
- Aflatoxins: liver cancer
Fungal infections: clinical classifications
- Superficial
- Subcutaneous
- Systemic
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Characteristics
- Fungi are widespread in the environment
- No chlorophyll
- Absolute need for complex nutrients
- Yeasts (single-cell form) and/or
- Hyphae (filamentous form)
- Teleomorph, Anamorph, Synanamorph, Holomorph
Culture
- Almost all of the medically important fungi grow in culture - Sabouraud Dextrose Agar
- Selective supplements (these inhibit unwanted bacteria) include
- Cycloheximide (but this inhibits some fungi)
- Chloramphenicol (Broad spectrum antibiotic)
Mould ID
- Filamentous fungi are largely identified by observing
- Culture appearance
- Characteristic microscopical structures
- Botany down a microscope
Yeast ID
- Yeasts only vary slightly in appearance
- Candida albicans usually forms germ tubes
- Cryptococcus neoformans produces a capsule
- Structures formed on Corn Meal Agar.
- Assimilation tests
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Colonisation vs Infection
- Factors predisposing to infection:
- Antibiotics
- IVDA
- Hyperalimenation
- Polyethylene catheters
- Neutropenia
- Qualitative neutrophil defects
- Depressed humoral immunity
Respiratory Tract
- Two routes of spread: Endobronchial or haematogenous
- CXR non-specific: may range from fine nodular, diffuse infiltrates to necrotizing pneumonia.
- Diagnosis difficult because of high prevalance of yeasts colonizing respiratory tract.
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