Fungi in TissueFungi in Tissue

Lab-6-

Fungi in Tissue (con’t.)

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. Note some distinguishing features.

a.) Dermatophytoses

- 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 hair or nails are used for a preliminary diagnosis.

Examples of tinea capitis and tinea pedis.

Tinea pedis and onychomycosis

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

Trichophyton rubrum. Most common cause of ringworm in China.

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

b.) Aspergillosis and Phycomycosis (Zygomycosis, Mucormycosis)

- 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 Aspergilloma

Aspergillosis or Phycomycosis?

Aspergillosis: Note dichotomously branch, septate hyphae.

Phycomycosis: Larger, coenocytic hyphae.

c.) Phaeohyphomycosis

- Increasingly important systemic disease in China.

- Often seen forming abscesses.

- In tissue one sees dematiaceous, septate hyphae.

Phaeohyphomycosis

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

d.) Keratomycosis (mycotic keratitis)

- 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.

Keratomycosis

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

Fungi in Tissue (con’t.)

4.) Granules. These are relatively large (1-2 mm) very hard structures that are produced in draining sinus tracts. They are only seen in cases of mycetoma.

Mycetomas are caused by numerous genera of “higher bacteria” (actinomycotic mycetoma) or true fungi (eumycotic mycetoma). This is important because depending upon the etiology they are treated differently.

Mycetoma cases

Note draining sinus tracts from which granules are obtained. Treated with itraconazole.

Histopathology of Mycetomas

Actinomycotic mycetoma granule. Note small (0.5 microns) filaments.

Eumycotic mycetoma granule. Note pink coloured (PAS stain) hyphae, 5 microns diameter.

Fungi in Tissue (con’t.)

5.) Fission (sclerotic) bodies. These are round, brown structures that are 15-20 microns in diameter. They are not yeast cells or hyphae. They appear to divide by splitting in the middle (fission).

The etiologic agent are all dematiaceous fungi which live in the soil. The organism enters the body following a puncture wound.

Cases of Chromomycosis

(top) This case developed over 30 years and was seen before the advent of itraconazole.

10-year old case

Fission bodies in Chromomycosis

Note the brown structures. These are histopathology slides but they can be seen readily in KOH preparation of skin.

Fungi in Tissue (con’t.)

6.) Yeast + Hyphae. In only one major mycosis do we see a combination of yeast and hyphae in tissue. This disease is candidiasis and it is the most important mycosis in the world today.

Important characteristic of Candidiasis:

- Endogenous in origin. Controlling predisposing factors may be more important that specific therapy.

- The major mycosis of immunocompromised patients, e.g., cancer, IVs, underlying diseases, surgery, acute illnesses, age, excessive use of antimicrobials and steroids, depress CMI, major trauma, diabetes, etc.

- 90% of AIDS patients have candidiasis.

Clinical aspects of Candidiasis

Trush Fatal candidiasis seen in child lacking T-cells.

Clinical aspects of Candidiasis (con’t)

Candidiasis of the neck

Onychomycosis caused by a Candida sp.

Clinical aspects of Candidiasis (con’t)

Cancer patient who died of candidiasis. Numerous white focal points are candidiasis.

Kidney from rabbit injected with steroids and Candida albicans from the author’s mouth. Died in 4 days.

Histopathology of Candidiasis

The dark blue elements (B & B stain) are hyphae and yeast in candidiasis.

This is a PAS stain of candidiasis. All the fungal elements are pink.

Identification of Candida spp.

One week old culture of C. albicans on Sabourauds agar

Germ tube test: universally used to identify C. albicans. Inexpensive and requires only 1-2 hours incubation in serum.

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