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Tasks for self-study during preparation for lesson.



3.1. Theoretical questions for the lesson:

1. Classification of mycoses.

2. The etiology, epidemiology, pathogenesis, clinical picture treatment and prevention of pityriasis versicolor.

3. Classification of candidiasis (candidiasis of the skin and mucous membranes, onychia, paronychia and chronic generalized, granulomatous candidiasis of children).

4. The etiology, epidemiology, pathogenesis, clinical picture of candidiasis.

5. Laboratory diagnosis of candidiasis.

6. Treatment of candidiasis patients.

7. Candidiasis prevention.

8. Laboratory diagnostics of mycoses.

9. Wood's lamp examination.

The subject-matter:

General Information

Epidemiology. Infection with fungi occurs either directly from a sick human or animal (direct route of infection), or through various objects and belongings of sick persons or objects used in the care of animals (indirect route of infection). Some fungus diseases (superficial trichophytosis, microsporosis, etc.) prevail among children of kindergarten age and schoolchildren, others (epidermophytosis, rubromycosis, deep systemic mycoses, etc.) are prevalent among adults. Some fungus diseases are characterized by mass seasonal infection (e.g. high incidence of infection with M. lanosum in the autumn and high incidence of zoophilic trichophytosis in the summer) and seasonal character of exacerbation of the process (e.g. tinea pedis, or ringworm of the feet, in the spring and summer). The climate and soil conditions of the given locality have an effect on the spread of dermatomycoses. This explains the geographic features of the spread of some of these diseases. All this has to be taken into account in elaborating rational measures for the control of dermatomycoses in different regions.

Pathogenesis. Despite the abundance of fungi in the surroundings of man, only a few of them possess marked pathogenicity. Moreover, it should be recognized that they are facultatively pathogenic forms because favourable factors are needed for the disease to develop: the age, sometimes the sex, the condition of endocrine glands activity, pH of the water-lipid mantle, sweat chemism, and increased sweating. In children, for instance, the keratin of the epidermal and hair cells undergoing keratinization is insufficiently dense and compact, which facilitates the development and vital activity of the keratophils that have gained entry.

Infectious and chronic diseases reduce body reactivity; change sweat chemism and the condition of the skin and hair and in this way lead to nervous and endocrine disorders and promote the transformation of saprophytic fungal flora (e.g. yeast-like fungi of the Candida genus) to pathogenic forms.

Classification. All human dermatomycoses are divided into four large groups:

1. Keratomycoses (pityriasis versicolor), trichosporosis nodosa (piedra), trichomycosis axillaris);

2. Dermatomycoses (epidermophytosis, rubromycosis, trichophytosis, microsporosis and favus), which form the most representative group of fungus skin diseases of highest social and epidemiological significance;

3. Candidiasis (of the skin, mucous membranes, and viscera);

4. Deep (systemic) mycoses forming large but relatively rare group of fungus diseases.

Pseudomycosis: erythrasma, actinomycosis

KERATOMYCOSES

This group of fungus diseases is characterized by involvement of only the horny epidermal layer (Gk. kerat horn, mykes fungus), very low contagiosity, and the absence of pronounced inflammatory phenomena. By the established tradition, erythrasma is related to this group, although sufficient data have been gained to the effect that Corynebacterium organisms and not fungi are its causative agents. Trichosporosis nodosa and trichomycosis axillaris are also included in this group.

Pityriasis Versicolor

Etiology and pathogenesis. The causative agent Pityrosporum orbiculare, or Malassezia furfur is found in the horny layer of the epidermis and the ostia of the follicles. When the diseased scales are examined with the microscope, the fungus is seen as short, rather thick twisted threads of mycelium and clumps of round spores with a double-contour capsule arranged as bunches of grapes. It is very difficult to obtain cultures of the fungus, and growth has been produced in only occasional cases. It is assumed that increased sweating, the chemical composition of the sweat, disturbed physiologylogical desquamation of the horny layer, and the individual predisposition of the skin are of definite significance in the pathogenesis of the disease. It has been suggested that the disease is encountered more frequently in persons suffering from pulmonary tuberculosis. This point of view, however, is not universally accepted. The disease is prevalent among young men and women. In children, particularly in those under 7 years of age, it is a rare occurrence. It may develop in weak children, in those with diabetes mellitus, tuberculosis, vegetoneurosis with increased sweating and in the prepubertal and pubertal periods.

Pityriasis versicolor is marked by low contagiosity.

Clinical picture and course. Yellowish-brownish-pink spots with no inflammatory phenomena form on the skin, at the ostia of the hair follicles and gradually grow in size. They then coalesce and cover large skin areas and have microscalloped edges. The colour of the spots gradually turns dark-brown, sometimes cafe au lait. This colour range served as the basis for the name of the disease (versicolor). The spots are not elevated above the skin surface, cause no subjective complaints (sometimes there is a mild itching) and are attended with bran-like scaling (hence the name pityriasis furfuraceous) which is easily detected by scratching of the skin (Besnier-Meshchersky's sign).

There is usually no symmetry in the arrangement of the spots in pityriasis versicolor. The chest and the back are the favoured sites, less frequently the spots are found on the neck, abdomen, the sides of the trunk, and the lateral surfaces of the arms. Lately, with the use of a mercury vapour lamp supplied with Wood's glass in the diagnosis of the disease, the spots of pityriasis versicolor are quite often detected (especially in a diffuse process) on the scalp but with no involvement of the hair. This may possibly be among the causes of the frequent recurrences of the disease, despite the seemingly successful therapy. The disease is of a long duration (months and years). Recurrences are frequent after clinical cure. It should be borne in mind that patients may be cured rapidly by sunrays and in such cases the skin in places of previous eruptions does not become tanned and white spots form (pseudoleucoderma).

Histopathology. In the absence of inflammatory phenomena, there is looseness of the horny layer, in which threads of mycelium and spores of the fungus are found.

The diagnosis presents no difficulties and is often made on the basis of the characteristic clinical picture. In difficult cases, auxiliary diagnostic methods are used. Baltser's iodine test is one of them: when the skin is painted with a 5 per cent iodine tincture, the affected areas with the loosened horny layer are stained more intensively than the healthy skin areas. Solutions (1-2 per cent) of aniline dyes are sometimes used instead of iodine. Besnier-Meshchersky's sign may be tested: when the spots are scratched desquamative lamella are produced because the horny layer is loose. Clinically latent foci of affection are detected by means of mercury vapour lamp whose rays are passed through a glass impregnated with nickel oxide (Wood's glass). The examination is conducted in a dark room in which the spots of pityriasis versicolor produce dark-brown or reddish-yellow fluorescence. With the detection of the clinically asymptomatic lesions, including those on the scalp, a more rational treatment will be prescribed and recurrences prevented in some of the patients. The diagnosis may also be verified by the detection of fungus components in microscopy of scales treated with 20-30 per cent potassium or sodium hydroxide solution.

Pityriasis versicolor sometimes has to be differentiated from syphilitic roseola (in which the lesions are rose-coloured and disappear from pressure and there is no scaling; other symptoms of syphilis and positive serological tests are taken into account). Secondary, or false leucoderma, which forms after treatment, of pityriasis versicolor, is differentiated with true syphilitic leucoderma. In the latter disease, coalescent hyperpigmented spots do not form, the lesion has the character of a lace net and is mostly located on the neck, in the axillae, and the sides of the trunk; blood serological tests are positive, and there are other manifestations of secondary recurrent syphilis.

Treatment. Keratolytic and fungicidal agents are rubbed into the affected skin areas. Salicylic (5 per cent) or resorcinol (3-5 per cent) alcohol and sulphuric (10-20 per cent) or salicylic (3-5 per cent) ointment may be prescribed. It is advisable to apply ointments: Mycozolon, Triderm, Clotrimasol, Lamisil, Nizoral and etc. The solutions and ointments are rubbed into the skin for four to six days after which the patient takes a bath with tar soap and changes his underwear. Ultraviolet irradiation has a beneficial effect. Diffuse forms are treated by Demyanovich's method, i.e. with 60 per cent sodium thiosulphate solution and 6 per cent hydrochloric acid as in the management of scabies..

For the prevention of recurrences, the affected skin areas are rubbed with 1-2 per cent salicylic or 2 per cent boric acid-salicylic alcohol once a day for several weeks after the treatment has been completed or treatment is repeated in one or two months.

Prevention. Increased sweating is treated and body-hardening measures are prescribed. Patients should avoid overheating. Skin hygiene should be strictly observed. As a preventive measure, rubbing of the skin with vodka or 8 per cent vinegar once or twice a week is prescribed after recovery.

CANDIDIASIS

Candidiasis is a disease of the skin, mucous membranes, nail plates, and viscera, which is caused by yeast-like fungi of the genus Candida. Yeast-like fungi of the genus Candida form a special group. Their distinguishing features are that they do not form spores but multiply by budding, and the threads formed by them have no real branchings and because of that are called pseudomycelium.

Etiology and pathogenesis. Yeast-like fungi are widely spread in nature as saprophytes, which become pathogenic under definite conditions. Most frequently the disease is caused by yeast and yeast-like fungi of the type of Candida albicans or Monilla, which form no spores (anascosporular), possess a pseudomycelium, and reproduce by budding. The yeast-like fungi vegetate on fruit and vegetables (there are especially very many of them in spoiled apples and pears which are beginning to rot). Under normal conditions these fungi are also saprophytes found in the gastrointestinal tract; they may occur on healthy human skin and mucous membranes.

Exogenic and endogenic favouring factors are distinguished in the pathogenesis of candidiasis.

The exogenic factors are as follows: injury to the skin and mucous membranes (e.g. yeast affections of the nipples of nursing mothers, which are injured by the child when it sucks, yeast stomatitis and perleche in persons with faulty dentures, candidiasis onychia and paronychia following injury inflicted during a manicure, etc.); increased humidity leading to the dissemination of candidiasis in geographical latitudes which are distinguished by a damp and warm climate; exposure of the skin to acids and alkalis which facilitate maceration of the skin; pathogenicity and virulence of the fungus itself. The exogenic factors promote the development of candidiasis in a certain condition of the macro-organism and when it is susceptible to yeast fungi.

The endogenous factors which contribute to weakening of the body's defence forces and in this way enhance to the development of candidiasis are: hypovitaminosis (lack of riboflavine, or vitamin B2, in particular); symptoms of vegetoneurosis (increased sweating, circulatory disorders in the limbs); metabolic diseases (diabetes, obesity); gastro-intestinal disorders which are conducive to dysbacteriosis, endocrinopathies which lead to obesity, hypo-hyperthyroidism, and Itsenko-Cushing's syndrome; age (insufficiency of salivation and reduced lysozyme activity of a physiological character in the newborn and because of weakened defence forces of the body in old individuals); general infectious diseases; diseases leading to cachexia (tuberculosis, carcinoma, lymphogranulomatosis, leukoses, malignant anemia).

Treatment with antibiotics, especially with broad-spectrum antibiotics, promotes the development of intestinal dysbacteriosis, which may cause severe forms of systemic candidiasis. Similar results may be produced with the use of oral contraceptives, corticosteroid hormones, cytostatic (immunosuppression) agents which induce hormonal shifts and reduce body resistance.

Classification. The clinical forms of candidiasis are subdivided into superficial (candidiasis of the skin and mucous membranes, onychia, paronychia) and chronic generalized (granulomatous) candidiasis of children.


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