Fungi in Tissue

3.) Hyphae. These are the long slender tubes by which most fungi grow. We see hyphae growing in human tissue for several diseases. They may be 5-6 microns in diameter or up to 10 microns in diameter (depending upon the disease). Most are clear coloured (hyaline) while others are brown (dematiaceous). Some are septate while others are coenocytic (no septa).

The following are some diseases where we see hyphae in tissue.

a.) Dermatophytoses

Dermatophytosis (tinea) infections are fungal infections caused by - a group of fungi that invade and grow in dead keratin. Several species commonly invade human keratin and these belong to the: Epidermophyton, Microsporum and genera. They tend to grow outwards on producing a ring-like pattern - hence the term 'ringworm'. They are very common and affect different parts of the body.

- Often these diseases are referred to as: tinea + body location; athlete’s foot; jock itch; or simply “ringworm”. - These diseases maybe spread from man to man, animal to man and soil to man. - Most are characterized by the presence of clear (hyaline), septate hyphae which is 5-6 microns in diameter. - KOH (10-20%) preparations of skin or nails are used for a preliminary diagnosis.

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tinea pedis

Onychomycosis

______

KOH positive for hyphae. This confirms a but culture is necessary to identify

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Trichophyton rubrum. Most common cause of ringworm in China.

Microscopic of T. mentagrophytes. Note large (macroconidium) and small spores (microconidia).

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b.) and Phycomycosis (, )

- Chronic or rapidly fatal: see hyaline, filamentous fungi

- Organisms in environment, cannot eliminate.

- Predisposed patients, worldwide

- Diagnosed by histopathology or repeated culture.

- No good serology tests.

- Therapy very difficult.

Two cases of pulmonary Aspergillosis

Infarct

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Aspergillosis or Phycomycosis?

Aspergillosis: Note dichotomously branch, septate hyphae.

Phycomycosis: Larger, coenocytic hyphae.

c.) Phaeohyphomycosis

- Phaeohyphomycosis refers to chronic cutaneous, subcutaneous or systemic infection

- Caused by one of several genera and species including Alternaria, Bipolaris and Curvularia

- Often seen forming abscesses.

- In tissue one sees dematiaceous, septate hyphae.

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Phaeohyphomycosis

Young girl from Beijing with deep abscess. Not cured after 2 years of therapy. On the right is culture of etiologic agent.

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d.) Keratomycosis (mycotic )

Keratomycosis is a serious eye disease

- Many fungi in environment can cause infection of outer portion of the eye. If not treated patient will go blind or organism will disseminate to the brain.

- Diagnosed by observing hyaline hyphae in KOH eye scrapings.

Patient on left. Right is KOH of tissue containing numerous hyaline hyphae.

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