Cutaneous Mycoses

Dermatophytes are keratinophylic fungi which invade and attack the keratin rich areas of the body. These areas include the hair skin and nail. Dermatophytes have an enzyme known as keratinase. This is responsible for the enzymatic digestion of the keratin rich epidermis, nail and hair.

A group of organisms that belong to 3 genera make up this class. They include

Genus Microsporon with example as Microsporon audvuini.

Genus Epidermophyton : e.g E. floccossum.

Genus Trichophyton: e.g T. rubrum.

Infections caused by dermatophytes are generally referred to as Cutaneous Mycoses. This disease are named after the regions of the body they infect.

Tinea coporis – body

Tinea capitis – Scalp

Tinea barbae – beard

Tinea Cruris – groin

Tinea pedis – foot.

Tinea is a Greek word that stands for worm. This name was given to the disease because their lesions have a worm like appearance, in a ring form.

General Pathophysiology

The disease starts with the inoculation of the fungal element i.e the spores and hyphae, through an infected formite, or hair comb.

The rate of spread of the infection is accerlerated if a person gets infected in a family that shares personal belongings, this is seen in developing nations due to poor economic condition.

Zoophilic forms of the fungi can be transferred from pet animals like dogs as in Trichopyton canis, to humans through direct contact. These zoophilic species are naturally predominant in the soil from where they make contact with the animals.

However for an infection to be established adequate amount of the pathogen have to invade the broken skin of the victim. If the skin with other mechanisms of the inate immunity is intact, an infection will not be established.

There are predisposing factors that increase the risk of infection.

They include,

Diabetes mellitus

Poor hygiene

Peripheral circulatory disorders

Humidity between folds of skin in chubby individuals.

As a rule, arthropophylic fungi rarely cause an inflammatory lesion. They don’t stimulate the immune system so there is no allergic reaction associated with them. However dermatophycoses due to zoophilic fungal organism induce immune reactions and cause an inflammatory lesion.

Diagnosis

Sample collection:

Hair samples: infected hair is cut with tweezers into a kraft paper and transported to the laboratory.

Skin samples: Scrapings from the outer border of the skin at the ringlike lessions of the disease is collected into a sterile kraft paper. Sample from the borders are preferred to that from the center because the latter is often made up of dead organisms. These organisms die due to accumulation of waste and nutrient depreciation as a result of high completion.

Nails: nail is cut wit surgical blades into a clean kraft paper for examination.

Treatment with KOH follows. Depending on the thickness of the specimen, 10 -20% KOH/NaOH is used to digest the sample on a clean grease free slide under mild flaming.

Direct Microscopy follows. Fungal elements like arthrospores (macro-conidia) and hyphae that are greenish in color is looked out for, when spotted a preliminary diagnosis is made.

For further studies and specie differentiation, culture of the sample is carried out.

Specimen is buried into a sabouroud dextrose agar. In addition to the nutrients in this media, some other substances are added to inhibit the growth of saprophytic fungi (cyclo-hexamide). A broad spectrum antibiotic, chloramphenicol is also used to ensure the absence of unwanted bacterial growth on the media.

This will ensure that only the fungi of interest is allowed to grow on the media. it takes about 3weeks for fungal growth to occur.

Treatment is with antifungal drugs, like griseofulvin taken orally according to prescription. Clotrimazole can also be used against the disease. It is mixed with body lotions and cream then applied topically on the lesion.