Fungi of medical importance come from different phyla and genera. Examples of genera that leads to fungal infection include

Trichophyton, Micosporum and Epidemophyton making the group of Tinea or skin mycoses

Candida albicans, Cryptococcus neoformans and Histoplasma capsulatum making the group of opportunistic infections

Coccidioidomides imitis leading to systemic mycoses

Fungi that cause human diseases – pathogenic fungi

Mycosis is a disease caused by a fungus (plural: mycoses). Fungi that cause diseases are called pathogenic fungi. Therefore the principal mycoses affecting Man can be distinguished by the sites of the body affected.Each type has different pattern of disease characteristics hence can be divided into four broad groups; these are:

These affects the outer layers of the skin especially the keratinized skin, nails and hair and do not invade the living tissue.

These are called Keratinophilic fungi which produces extracellular enzyme called Keratinase capable of hydrolyzing keratin.

Those fungal infections are called Dermatophytes.

The fungus does not penetrate at all. It is present only on the surface of the skin or on the patient’s hair or nails. This may include various types of ringworm (tinea), including athlete’s foot, scalp ringworm, and body (skin) ringworm

Tinea means Ring worm or ‘moth like’ infections and Dermatologists use special terms to refer a certain skin infection or scalp infection e.g.

Tinea corporis – lesions occurring anywhere on the body.

Tinea pedis – Infection of toe webs and soles of feet called athletes foot.

Tinea unguium – affects nails (Onychomycosis).

Tinea cruis also called Jock itch, this affects the groin, Perineum/Perianal area.

Tinea barbae – Ringworm of bearded areas of the face and the neck.

Tinea versicolor – this is characterized by the blotchy discoloration which is itching.

Anthropophilic-Infections associated with humans only. Transmissions are by direct contact or through contaminated objects.

Zoophilic-Infections associated with animals. Transmissions occurs due to closeness with animals e.g.. dogs, cats or with contaminated products.

Geophilic fungi – These are usually found in the soil and are transmitted to man by direct exposure.

Knowledge of the spp and source of infection are important for proper treatment of the patient and control of the source.

Invasion by the zoophilic/Geophilic fungi may cause inflammatory diseases to humans.

Pityriasis versicolor – Is a chronic mild superficial infection of the stratum corneum caused by Malassezia furfur complex.

It is characterized by hyper or hypo pigmentation on the skin usually on the chest, upper back, arms and abdomen.

Lesions are chronic occurring as macular patches of discolored skin that enlarge and may coalesce and are irritating.

Some spp are considered as part of microbial flora & can be isolated from normal skin and scalp.

Malassezia contributes to seborheic dermatitis or dandruff.

Candida albicans is yeast that causes candidiasis. As a superficial mycosis candidiasis usually affects the vagina of females or the mouth of both males and females. It exists normally in the vagina or gastrointestinal tract, but may multiply rapidly, especially if the person is ill or has a weakened immune system. Taking antibiotics may sometimes result in rapid reproduction of Candida albicans. Fungi that obtain nutrients from keratinized material are called dermatophytes.

Other fungi inclusive in this group are: Pityriasis versicolor (tinea versicolor), caused by Malassezia furfur.

Cutaneous mycosis

The infection is generally limited to the nonliving keratinized layers of skin, hair, and nails – no living tissue is invaded. Also includes tinea (ringworm), as well as candidiasis of the skin, mucus membranes and nails (Candida albicans and related species).

Are cutaneous mycoses which are caused by fungi that infect only the superficial keratinized tissue (skin, hair, and nails).

The most important of these are the dermatophytes which include Epidermophyton floccosum, Trichophyton mentagrophyte, Microsporum audonii

The fungi reach below the skin and infect subcutaneous (area just below the skin), connective and bone tissue. These infections are usually chronic (long-lasting) and often occur when the skin is pierced or wounded, allowing the fungi to enter, usually in the form of vegetable matter. These infections may be hard to treat and often require removal of damaged skin (debridement). Subcutaneous mycoses are much more common in the tropics.

Sporotrichosis caused by Sporothrix schenckii is an example of subcutaneous mycosis. Sporotrichosis used to be common in Europe, but is very rare there today. It is more common in Australia, South Africa and in the warmer regions of the Americas. Infection may occur as a result of an insect bite, a thorn prick or a scratch from any sharp object. Infection risk is higher among florists, farmers, gardeners and people who work with hay and moss

This is a fungal infection that may reach any part of the body, including the brain and heart, as well as the bloodstream. The fungi usually enter via the lungs, gastrointestinal tract or intravenously.

An example of systemic mycosis is cryptococcosis, which is caused by Cryptococcus neoformans, a type of yeast. It can cause sub acute or chronic meningitis. The fungi enter the body by inhalation. Infected patients may also develop lung infections. Cryptococcus neoformans may be found in pigeon droppings

Specimen

Skin scrapings

Nails

Hairs

Swabs from the lesions

Laboratory techniques

Fluorescent direct microscopy

Wet preparation using 10% Potassium Hydroxide

Culture

Topical Antifungal agents (like clotrimazole, Ketoconazole creame, Benzoic acid containing ointment)

Oral Griceofulvin

Opportunistic fungi are organisms which induce disease when immunity of an individual is compromised.

Usually are non pathogenic and are part of microbial normal flora. Examples include Candida albicans, Cryptococcus neoformans

Species of Candida include

albicans,

tropicalis

glabrata

They are oval budding yeast cells

Can produce pseudohyphae when in the host

They are Gram positive

They germinate to form tube tube like structure (germ tube) while in the serum at 37oC

Thrush (for example white patches occurring like pseudomembranes on the mouth, vagina)

Vaginitis (vaginal itching and discharge favoured by high pH, Diabetes and long term use of broad spectrum antibiotics)

Chronic mucocutaneous candidiasis (following immunosuppression, candida may affect the mucous membranes and the cutaneous tissues)

Specimens

HVS

Skin scraping

Exudates or tissues

Technique

Gram staining

Culture

Germ tube

Fluconazole

Clotrimazole

Nystatin

Ketoconazole

capsule

Species of medical importance under the genus Cryptococcus is only Cryptococcus neoformans

There are two variants of Cryptococcus neoformans

• C. neoformans var neoformans (causes cryiptococcal disease in immunocompromised individuals)
• C. neoformns var gatii (causes cryptococcal disease in immunocompetent individuals)

Encapsulated (have large round capsule)

Occur in the form of yeast cells

Gram positive

In Giemsa stain the capsule can be seen as clear unstained area

In india ink C. neoformans shows a clear large round capsule surrounding the cell

Diseases caused by Cryptococcus

Cryptococcosis especially cryptococcal meningitis (C. neoformans var neoformans)

Cryptococcosis is the most common life threatening fungal disease in immunocompromized patients

Specimen

CSF

Technique

India ink

Gram stain

Culture

Fluconazole

Fungi of medical importance includes dermatophytes (Tinea), opportunistic fungi (Candida albicans and Cryptococcus neoformans)

Laboratory diagnosis of fungi is based on collection of skin scrapings, fluid, nails cuts and hairs, cerebral spinal oral and cervical swabs for microscopy and culture.

Treatment is mainly based on administration of topical oral and parenteral antifungal drugs.

What are the fungi of medical importance?

What are opportunistic fungi and the disease they cause?