Sydney Fungal Studies Group Inc. , Workshop   23.07.05

 

Abstract: Review of Medical Mycology                       Jim Gardner

 

Fungal diseases of animals are called “mycoses”: of about 100,000 species of fungi, 200 or so may cause disease: ~20 cutaneous  infections,~12 subcutaneous and ~20 deepseated or systemic. Almost any fungus can cause opportunistic infection in animals sufficiently debilitated to become a substrate for a fungus, even Schizophyllum. Candida sp and Pityrosporum are endogenous fungi –yeasts- all others exogenous from soil or animals etc.

 

Requirements for fungal pathogenesis

The ability of a fungus to thrive at animal body temperature (37oC or more), at the reduced redox-potential of living tissue and against the host’s defense mechanisms.

 

Representative mycoses

(i) Superficial/cutaneous: mostly prototunicate ascomycetes  eg. Trichophyton spp, and Microsporum spp mainly from animals causing ringworm and tinea; Malassezia furfur/

Pityrosporum anamorph causing tinea versicolor (Ustilaginales); Trichosporon beigelii a yeast from piedra (heterobasidiomycetous)

(ii)Subcutaneous:Sporothrix schenkii (ascomycete) from pricking by rose thorns and splinters chromoblastomycosis from Phialophora spp Cladosporium carrioni  producing round “sclerotic” cells in tissues; mycetoma as swollen granular  lesions in barefooted, tropical people (eg. aborigines) Madurella, Phialophora spp,

(iii) Deepseated /systemic: is of 2 kinds viz(a) “true” pathogens such as Coccidioides from USA whose spores are inhaled into the lungs then spread in blood  and lymph; in Australia Histoplasma capsulatum in bird and bat guano – beware speleos! These “dimorphic” fungi change from hyphal to yeastlike forms at body temperature.(b)the other kind are “opportunistic” fungi which now supersede almost all other mycoses as postwar sequels of  “high-tech” medical intervention including cytotoxins, long term steroids,certain  antibiotics, immunosupressives, organ transplants (liver, bone marrow, cornea- Fusarium solani , usually a pathogen of stored potatoes-)  and HIV etc. resulting in Candida spp , Scedosporium , Aspergillus, Cryptococus, zygomycetes to name a few  that exploit the impaired integrity of the host.

 

Therapy

(i)                  Antifungal antibiotics: griseofulvin, cycloheximide, nystatin, amphotericin B.

(ii)                Synthetic fungicides:many imidazoles, 5-fluorocytosine etc.

Immunology and serology

Fungi are poor antigens and natural immunity to fungi is very high so serology is not so important Cellular defense by T-cell lymphocytes occurs but little humoral B-cell defence

 

Laboratory mycology

For culture a source of carbohydrate and nitrogen e.g. glucose peptone agar with/without chloramphenical and cycloheximide to inhibit bacteria and saprophytic fungi.

 

For direct examination mount specimens in 10% KOH; Calcifluor may be useful with a fluorescent microscope for its affinity for chitin and cellulose. A high resolution compound microscope is required to resolve thallic, blastic, phialidic,and annellidic conidia.