A fungus is a saprophytic or parasitic plant and is incapable of photosynthesizing its own organic food requirements due to lack of chlorophyll.
Despite the large number of fungi in the world, relatively few species of fungi are human pathogens. The fungi responsible for human disease may be either multicellular forming filaments known as hyphae or unicellular yeast which reproduce by budding. The fungal infections can be simply classified as follow:
1. Superficial mycoses, which affects skin and mucous membrane:
Dermatophyte infections (Tinea)
Candidiasis
Pityriasis versicolor
2. Deep mycoses, which invade the living tissue and causes systemic disease:
Madura foot
Sporotrichosis
Chromomycosis
Superficial mycoses
Dermatophyte infections (Tinea) : These infections are caused by multicellular filamentous fungi, the dermatophytes, which invade the dead keratinized tissues i.e. the stratum corneum of skin, hair and nail. The dermatophytes are classified into three generas—microsporum, trichophyton and epidermophyton. Microsporum species produce disease in skin and hair, trichophyton in skin, hair and nail and epidermophyton in skin and nail.
Some of these dermatophytes live only on the humans, others primarily affect animals and a few dermatophytes thrive in the soil. Thus, dermatophyte infections may be transmitted to man from infected animal, man or soil. Poor nutrition and hygiene, a hot and humid climate, debilitating diseases, corticosteroid therapy and contact with infected animals, persons or fomites, all predispose to infection.
Dermatophyte infections are classified according to the anatomical sites of involvement. These clinical types and sites of infections are an follows:
Tinea capitis (Scalp), Tinea manuum (Hand), Tinea barbae (Beard), Tinea pedis (Foot), Tinea corporis (Body), Tinea unguium (Nail), Tinea cruris (Groin)
Tinea Capitis : Tinea capitis is the fungal infection of the scalp caused by microsporum or trichophyton species. The disease mainly affects children and is usually contracted from infected combs or hair brushes. It is manifest in following types:
Grey patch type : This consist of single or multiple scaly, rough, grey patches from which most of the hair have fallen leaving a few broken stumps of lusterless hair. This type is commonly produced by T. violaceum, T. tonsurans and M. audouinii.
Black dot type : This is caused by T. violaceum. The affected hair break off at the scalp surface giving a ‘black dot’ appearance to the lesions.
Kerion : This is a painful inflammatory boggy swelling covering small or large area of the scalp in which hair are loose and fallout or can be easily epilated. This type of reaction is commonly caused by zoophilic dermatophytes like T. mentagrophytes and T. verrucosum. Follicular scarring and partial alopecia is common after severe kerion.
Favus : This is characterized by multiple, concave, yellowish crusts on fungal scalp, called ‘scutula’. Each crust is composed of fungal filaments and epithelial debris and is pierced by a hair in the centre. This disease usually runs a chronic course and results in extensive cicatricial alopecia. It is commonly caused by T. schoenleinii.
Tinea Barbae : It occurs over the beard area of the face and neck T. mentagrophyte, T. verrucosum and T. violaceum are commonly responsible. Lesions may be of kerion type as seen in T. capitis, or superficial type of in which there are dry, rounded, red, scaly patches with short or brittle hairs.
Tinea Corporis : T. corporis is an infection of glaborous or nonhairy skin of the body, caused by species of Microsporum and Trichophyton. It is more commonly seen as itchy, red, circular scaly patches which clear centrally and slowly spread peripherally. The active border may show scales, populovesicles or pustules. Lesions may be single or multiple, discrete or coalesce to form polycyclic shapes.
Tinea Cruris : T. cruris is a fungal infection of the groin, thigh, perineum and perianal area E. floccosum, T. rubrum and T. mentagrophyte are the commonest causative agents. The lesions are usually bilaterally symmetrical, itchy, well defined, erythematous, scaly patches with active borders. The active borders, may be vesicular, pustular or scaly. Central clearance is often incomplete. Satellite lesion may be present.
Tinea Manuum : Tinea manuum is a fungal infection of hand commonly caused by T. rubrum. Clinically, it is characterized by diffuse, fine scaling and hyperkeratoses of the palm. Circumscribed vesicular patches of discrete red papular and follicular scaly patches may occur, especially on the dorsal aspect. Involvement is unilateral in most of the cases.
Tinea Pedis : T. pedis is a fungal infection of the dorsum of foot, sole and interdigital spaces. T. mentagrophyte, T. rubrum and E. floccosum are the usual causative fungi. It is more commonly seen in adult males, particularly those who wear socks and shoes constantly. The infection is also transmitted via infected bathroom floors and swimming baths.
There are three main clinical variants: Interterigo type, characterized by scaly soddened whitish skin particularly in the space between 4th and 5th toes. Vesicular type, characterized by vesicular eruptions over instep portion of the sole, toes or dorsum of the foot. The vesicles may become pustules. The lesions rupture and then dry leaving irregular collarette of scales. It is often associated with eruption of hands. T. metagrophyte is the most common fungus isolated from such lesions. Squamous hyperkeratotic type, characterized by scaly hyperkeratotic lesions on the sole and sides of the foot which may be patchy or diffuse. T. rubrum is common causative agent.
Tinea Unguium : T. unguium is a fungal infection of nails usually caused by T. rubrum. Toe nails are much more frequently involved than finger nails. The infection is ordinarily limited to one or more but rarely all of the nails. It involves the soft keratin of the nail bed and later extend upward into the hard keratin of the nail plate. The infection usually begins at the lateral or distal edges of the nail causing the nail to be discoloured, thickened and distorted. The distal portion of the nail plate separates from the nail bed due to accumulation of soft keratin debris underneath.
Diagnosis of Tinea Infections
KOH Preparation : Skin scrappings from the active edge of the lesions, nail clippings with subungual debris, or plucked hair are placed in a drop of 10-20% KOH solution on a microscopic slide, covered with a coverslip and heated gently to clear the keratin and then examined under microscope for presence of spores and hyphae.
Culture : The infected material (scales, hair, nail-clippings) may be cultured on sabouraud’s-dextrose-agar media for identification of species.
Wood’s lamp : Infected hair are examined under wood’s light for any fluorescence. The fungi which give fluorescence are M. canis, M. audouinii and T. schoenleinii.
Treatment of Tinea Infections : All tinea infections should be treated with topical antifungal agents and only supplemented by systemic therapy when the dermatophyte has invaded scalp, hairs or a large area of skin. Various topical anti-fungal agents like whitfield’s ointment, Casellani’s paint, clotrimazole, miconazole, econazole, have been used for treatment of dermatophyte infections. Topical agent is to be applied twice daily usually for about a month and to be continued for at least 7-10 days after the lesions have disappeared completely.
Griseofulvin and Ketoconazole are the two drugs available for sytemic therapy. Griseofulvin is given orally in the dosage of 250 mg twice a day after meals. Duration of treatment depends upon the clinical types of dermatophyte infection. T. capitis and T. pedis usually require 4 to 8 weeks therapy while T. unguium requires treatment for 4 to 8 months. Treatment of toe nail is often unsatisfactory.
Ketoconazole is a new broad-spectrum antifungal agent which is usually recommended in cases of Griseofulvin resistance and is given in dose of 200-400 mg/day with food.
General measures include personal cleanliness, thorough drying after washing, use of clean linens and avoidance of tight fitting shoes and undergarments.
Candidiasis
Candidiasis is an infection of skin, mucous membrane and visceras, caused by candida albicans or occasionally other candida species. Candida albicans is a normal inhabitant of oral cavity, gastrointestinal tract and vaginal mucosa. It can produce disease under certain favourable conditions like trauma and maceration, antibiotics and steroid therapy, diabetes mellitus, blood dyscrasias, pregnancy, malignancies and malnutrition.
Clinical Features : Mucosal candidiasis produces soft white plaques on the tongue and buccal surfaces which can be scrapped off to leave a bright red moist base. Similar lesions may occur on the mucosa of the vagina and usually associated with creamy discharge and marked local pruritis. Infection of the angle of the mouth may cause fissures (angular stomatitis). In male, glans penis and prepuce may show erythema and maceration (Balanoposthitis) though sexual contact with infected females.
Cutaneous candidiasis is characterized by moist, red macerated areas with poorly defined margins and satellite vesico-pustules. Pruritis is usually present and at times may be intense. It typically involves the body folds, the napkin area in infants or the nail folds.
Diagnosis : Demonstration of candida, especially in mycelia form in KOH preparation confirms the diagnosis. Culture can be done on Sabouraud’s-dextrose-agar media.
Treatment : Various topical agents such as gentian violet 1%, haymycin, nystatin, miconazole and clotrimazole are highly effective in the treatment of candidal infection. For oral candidiasis, nystatin suspension is kept in the mouth for few minutes and then swallowed. In vulvo-vaginitis, nystatin, clotrimazole or miconazole pessaries are inserted twice daily for 2 weeks and it is advisable to give oral nystatin to prevent the recurrences.
In every patient, underlying predisposing factors should be corrected as far as possible.
Pityriasis Versicolor
Pityriasis Versicolor is a mild, chronic, asymptomatic infection of the most superficial layers of the skin caused by Pityrosporum orbiculare. It is very common in warm and humid climate and usually affect young adults. It is characterized by fine, scaly, hyper or hypopigmented macules of varying sizes and shapes which appear on trunk, upper arms, shoulders and neck. Macules may become confluent to form polycyclic patches.
Diagnosis : The microscopic examination of skin scrapping in a KOH preparation reveals short hyphae and cluster of round and budding, yeast cells. Scaly lesions usually show golden yellow fluorescence when examined under wood’s light.
Treatment : Selenium sulphide shampoo (2.5%) is applied to the affected part at bed time and washed off next morning. Such treatment is being repeated after 5-7 days. Miconazole or clotrimazole are also effective and applied twice daily for 10-14 days. Oral ketoconazole (200-400 mg/day) may be used in cases with extensive and long standing eruptions.
Madura Foot (Mycetoma)
Mycetoma is a chronic granulomatous condition which affects skin, subcutaneous tissue and bones. It may be Eumycetoma, caused by variety of fungi (madurella mycetoma and Madurella grisea) or Actinomycetoma, caused by aerobic actinomycetes (Nocardia and Actinomedura medurae). The disease is common in adult males and usually occurs after trauma. The commonest site is the foot or hand but other sites may be involved.
Clinically, it is characterized by presence of firm to hard subcutaneous nodules and swellings. These nodules break open and discharge pus containing grains. There may be involvement of underlying bones and joints by the invasion of the fungus.
Diagnosis : It is made by microscopic examination of the grains from the lesion and culture of the fungi.
Treatment : Treatment of eumycetoma is usually unsatisfactory but amphotericin B and griseofulvin may be tried. In actinomycetoma, combination of dapsone with streptomycin or cotrimoxazole plus streptomycin has been reported to give good results.
In some cases, medical therapy may have to be supplemented by surgical excision, drainage and curettage of sinuses.
Sporotrichosis
It is a chronic infection of skin, subcutaneous tissue and lymph nodes, caused by Sporothrix schenckii. The lesions are usually initiated by trauma inoculating organism into subcutaneous tissue and are found mainly in farmers.
Clinically, it is characterized by presence of nodulo-ulcerative lesions in a linear fashion along the lymphatics. Regional lymphnodes may be enlarged. Rarely, sporotrichosis may disseminate via the blood stream. The diagnosis is made by histology and culture of biopsy material.
Treatment : The condition respond to oral saturated potassium iodide solution, starting with 5 to 10 drops and gradually increased to 15 drops, three times a day. Intravenous miconazole and oral ketaconazole have also been used with some success.
Chromomycosis : It is a cutaneous and subcutaneous mycosis caused by species of phialophora and cladosporium. Adult male agriculture workers are most often affected. The organism enters the skin after trauma.
Clinically, it is characterized by the development of multiple, indurated papulo-nodules on the foot or leg which slowly increase and take verrucous cauliflower like appearance. These lesions may ulcerate and later become secondarily infected. New crops of satellite lesions are usually seen along the path of lymphatic drainage.
Diagnosis : It is confirmed by culture or demonstration of clusters of brownish spores in biopsy material or in KOH preparation.
Treatment : Surgical excision or cryotherapy is the treatment of choice for small lesions. Systemic ketoconazole, amphotericin B or 5-fluorouracil may also be effective.
