In Australia the commonest encounter with fungi in a medical sense is with superficial and cutaneous fungal infections such as those infecting the skin, scalp or nails.

Tinea or ringworm of the scalp, skin and nails

Fungal infection of the scalp (tinea capitus), skin (tinea) and nails (tinea unguium, onychomycosis) is usually caused by dermatophytes which have a unique ability to utilise keratin as a nutrient source due to the presence of the enzyme keratinase allowing colonisation of the stratum corneum. The presence of the fungus and its metabolic products can occasionally induce an allergic or inflammatory response in the host. The type and severity of the host response is often related to the species and strain of dermatophyte causing the infection. Following is a list of the dermatophytes that have been identified in our laboratories:

SPECIES	NATURAL HABITAT	INCIDENCE
Epidermophyton floccosum	Humans	Common
Trichophyton rubrum [worldwide]	Humans	Very common
Trichophyton interdigitale [anthropophilic]	Humans	Very common
Trichophyton tonsurans	Humans	Common
Trichophyton violaceum	Humans	Less common
Trichophyton concentricum	Humans	Rare
Trichophyton schoenleinii	Humans	Rare
Trichophyton soudanense	Humans	Rare
Trichophyton rubrum [African]	Humans	Rare
Microsporum audouinii	Humans	Less common

 

SPECIES	NATURAL HABITAT	INCIDENCE
Trichophyton interdigitale [zoophilic]	Mice, rodents	Common
Trichophyton erinacei	Hedgehogs	Rare
Microsporum canis	Cats	Common

 

SPECIES	NATURAL HABITAT	INCIDENCE
Microsporum gypseum	Soil	Common
Microsporum nanum	Soil/pigs	Rare
Microsporum cookei	Soil	Rare

Mycotic infections

Despite the majority of work done by mycology laboratories being concerned with superficial and cutaneous fungal infections, in recent years there has been an increase in fungal subcutaneous and systemic disease. Mycotic infections are usually classified according to the level of tissue involvement in the patient. The following table includes examples of such mycotic infections, their classification and an indication of their incidence.

LEVEL OF INFECTION	MYCOSIS	CAUSATIVE ORGANISM	INCIDENCE
Superficial	Pityriasis versicolor Seborrhoeic dermatitis including dandruff and follicular pityriasis	Malassezia furfur (a lipophilic yeast)	Common
	Tinea nigra	Hortaea werneckii	Rare
	White Piedra	Trichosporon sp	Common
	Black Piedra	Piedraia hortaea	Rare
Cutaneous	Dermatophytosis	Trichophyton, Epidermophyton, Microsporum
	Dermatomycosis	Fungi other than dermatophytes
	Candidiasis	Candida species
	Other yeasts	Geotrichum, Trichosporon
Subcutaneous	Sporotrichosis	Sporothrix schenckii	Rare
	Chromoblastomycosis	Fonsecaea, Phialophora, Cladophialophora etc	Rare
	Phaeohyphomycosis	Cladophialophora, Exophiala, Bipolaris, Exserohilum, Curvularia	Rare
Dimorphic Systemic Mycoses	Histoplasmosis	Histoplasma capsulatum	Rare
Opportunistic Systemic Mycoses	Candidiasis	Candida albicans and related species	Common
	Cryptococcosis	Cryptococcus neoformans	Rare/Common
	Aspergillosis	Aspergillus fumigatus etc	Rare

Specimen Collection

Laboratory diagnosis requires collection of an adequate amount of material for both microscopy and culture. The site needs to be cleaned with an alcohol wipe, which helps lower the contamination rate from bacteria, saprophytic moulds and yeasts that may overgrow a dermatophyte. As a health and safety precaution, scalpel blades should not be enclosed with specimen.

Scalp

In general, zoophilic fungi e.g. M.canis tend to cause ectothrix or involvement of the outside of the hair shaft and the lesions tend to be inflammatory, while anthropophilic fungi e.g. T.tonsurans result in endothrix or involvement of the hair shaft itself. The lesions are less inflammatory. Lustreless, broken, infected hairs should be sampled from the edge of a lesion. It is important to collect hair roots, as this is where fungal elements are detected. A scalpel blade may be used to dislodge crusts or scales in which hair stumps may be embedded.

Skin

Skin scrapings should be obtained by scraping the active border of the infection which usually is typically scaly, red and elevated and where the hyphae are present. In cases of kerion, swabs of the exudates should be collected. Separate specimens should be taken from the representative lesions on various parts of the body. When scraping feet, the site of most common involvement is between the fourth and fifth toes.

Nails

Scrape under the nail plate until the crumbling white degenerative portion is reached. All the keratin debris from under the nail should be collected directly onto a black collection card. The distal portion of the nail may need to be trimmed with nail clippers. Fungal elements remain viable for weeks at room temperature. Nail scrapings showing hyaline septate hyphae are diagnostic for a dermatophyte.

Transportation

Glass or plastic bottles with screw tops are not recommended since high relative humidity encourages proliferation of bacteria and reduces the chances of isolating fungi. Specimens for mycological studies are best submitted within the special black fungal scrapings cards provided by the laboratory or, if these are not available, within a folded paper (preferably dark) packet. Although delays are to be avoided, fungi are generally resistant to drying and survive transportation well at room temperature.

Negative Laboratory Report

The reasons for negative microscopy and/or culture include: • Incorrect clinical diagnosis • Sampling variation associated with an inadequate specimen • Splitting the sample to perform microscopy and culture • Presence of non-viable hyphae in the distal portion of nails • Uneven fungal colonisation of nails • Overgrowth by contaminant saprophytic fungi Careful recollection obtaining sufficient material may be necessary to confirm results. Adequate/Inadequate collection

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General Practice Pathology is a new regular column each authored by an Australian expert pathologist on a topic of particular relevance and interest to practising GPs. The authors provide this editorial, free of charge as part of an educational initiative developed and coordinated by Sonic Pathology.

Once specimens are received in the laboratory, microscopy is performed. An interim report is then released. Specimens are then set up on specialised agar containing antibiotics and cycloheximide to inhibit the growth of bacteria and saprophytic fungi. Cultures are incubated at 28°C for three weeks. If microscopy is positive (M+) and no pathogen (C-) has grown in the interim, specimens are held an extra week. Infrequently, where microscopy and culture of nail scrapings is negative and the diagnosis is still suspected, nails can be examined for fungal elements using special stains.

Results:

Specimen types have been subdivided into three anatomical categories (nails, hair and skin) based broadly on the three clinical presentations of onychomycosis, tinea capitis, and tinea corporis/ cruris/pedis. Onychomycosis refers to fungal infections of the nails and includes tinea unguium caused by dermatophytes but also non-dermatophyte fungi and yeasts, predominantly Candida spp.

Negative laboratory report:

A common reason for negative microscopy and /or culture is an incorrect clinical diagnosis. More than 50% of dystrophic nails do not have a fungal cause, so it is important to establish a correct laboratory diagnosis before treating a patient with an antifungal agent. Other reasons for false negative results include sampling variation associated with an inadequate specimen and/or splitting the sample to perform microscopy and culture; the presence of nonviable hyphae in the distal portion of the nail; uneven colonisation of the nail by fungus; and overgrowth by contaminant saprophytic fungi. Careful re-collection to obtain sufficient material may be necessary to confirm negative results.

Nails:

The analysis of nail specimens from the hands and feet. Fingernails: Of 1202 specimens processed, 59% were negative by both microscopy and culture; 11% had hyphae seen on microscopy but were negative by culture; 27% of all finger and thumbnail cultures grew a yeast, predominantly Candida albicans (88% of all positive nail/hand cultures). Only 3% of all fingernail specimens grew a dermatophyte.

Toenails:

57% of 5097 toenail cultures were negative by both microscopy and culture. 22% were positive by microscopy but culture negative for reasons stated previously. As the literature would suggest, yeast infection of toenails is rare. Dermatophytes (20%) predominate as the main cause of onychomycosis of the lower limbs. Transmission of these dermatophytes is usually via the feet and toe web spaces, which are the major reservoir on the human body. Onychomycosis can be regarded as the end stage of tinea pedis. Desquamated skin scales containing hyphae are shed and survive for months to years on floors and carpets. Infrequently non-dermatophyte moulds are implicated in toenail infections such as Aspergillus. There is some uncertainty as to the significance of these cultures, and repeat culture may be indicated.

Treatment options:

With tinea unguium, topical treatment is successful only with surgical removal of the nail combined with oral therapy. First-line treatment for all types of nail tinea consists of: 1. terbinafine (child < 20 kg: 62.5 mg; 20 to 40 kg: 125 mg) 250 mg orally, daily for six weeks for fingernails and 12 weeks for toenails or (if terbinafine is not tolerated) 2. itraconazole 200 mg orally, twice daily for seven days every month for 2-4 months or 3. fluconazole 150 to 450 mg orally, once weekly for 12 to 52 weeks. Successful management of candidiasis of the nail requires removal of risk factors e.g. water immersion.

Tinea capitis:

Of 414 hair samples submitted over this period, 329 (80%) were negative by both microscopy and culture. Dermatophytes isolated include M. canis (46%); T. tonsurans (42%); M. gypseum (5%); T. mentagrophytes (5%) and T. rubrum (2.5%). This condition afflicts predominantly prepubertal children. Clinically it can present as alopecia or a more inflammatory lesion (kerion). It is noteworthy that T. tonsurans, an anthropophilic fungus, is emerging as a common cause of tinea capitis in children and spreads easily from child to child.

Treatment options:

Tinea capitis often requires oral therapy to eradicate the infection. Treatment options include 1. griseofulvin fine particle (child: 20 mg/kg up to) 500 mg orally, daily for 4-8 weeks, or 2. terbinafine (child< 20 kg: 62.5 mg; 20 to 40 kg: 125 mg) 250 mg orally, daily for four weeks.

Tinea corporis/cruris/pedis:

Of the 7406 specimens received from skin sites, 73% were both microscopy and culture negative; 5% were positive only by microscopy. Of the 22% culture positive specimens, 19% grew a dermatophyte and 3% a yeast.

Treatment options:

When topical treatments have failed, recommended oral therapy includes: 1. griseofulvin fine particle (child: 10 to 20 mg/kg up to) 500 mg orally, daily for at least four weeks or 2. terbinafine (child <20 kg: 62.5 mg; 20 to 40 kg: 125mg) 250 mg orally, daily for at least two weeks, depending on the response or 3. itraconazole capsules 200 mg orally, twice daily for one week for tinea of the feet or hands or 4. itraconazole capsules 200 mg orally, once daily for one week for tinea elsewhere.

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General Practice Pathology is a new regular column each authored by an Australian expert pathologist on a topic of particular relevance and interest to practising GPs. The authors provide this editorial, free of charge as part of an educational initiative developed and coordinated by Sonic Pathology.