|
Читайте также: |
Ministry of education and science of Ukrain
Sumy state university, medical institute
Dermatovenerology
Л.В. Куц
L.V. Kuts
Методичні вказівки що до вивчання теми
„Грибкові захворювання”
для студентів 4 курсу спеціальності 7.110.101
„Лікарська справа”
Methodical instruction to training
“Fungal skin infections”
Sumy 2007
Fungal skin infections
Link to DermNet's pages about fungal skin infections.
Introduction
Yeast infections Candida
| Laboratory tests
Dermatophyte infections Dermatophytide (id) reactions (fungal allergy) Mycology Tinea infections
| Treatments Deep fungal infections Blastomycosis Cryptococcosis Chromoblastomycosis Histoplasmosis Mycetoma Sporotrichosis Systemic mycoses Zygomycosis Other fungal infections Mould infections Tinea nigra Related pages Athlete's foot Cradle cap Intertrigo (body fold rashes) Seborrhoeic dermatitis |
Introduction to fungal infections
Fungal infections of the skin are also known as ‘mycoses’. They are common and generally mild. However, in very sick or otherwise immune suppressed people, fungi can sometimes cause serious disease.
Characteristics of fungi
Fungi are parasites or saprophytes i.e. they live off living or dead organic matter.
Mycologists identify and classify fungi according to their appearance by microscopy and in culture, and by the method of reproduction, which may be sexual or asexual.
Growing fungi have branched filaments called hyphae, which make up the mycelium (like branches are part of a tree). Some fungi are compartmented by cross-walls (called septae).
Arthrospores are made up of fragments of the hyphae, breaking off at the septae. Asexual spores (conidia) form on conidiophores. The sexual reproductive phase of many fungi is unknown; these are ‘fungi imperfecta’ and include those which infect humans.
Yeasts form a subtype of fungus characterised by clusters of round or oval cells. These bud out similar cells from their surface to divide and propagate. In some circumstances they form a chain of cells called a pseudomycelium.
Superficial fungal infections
These affect the outer layers of the skin, the nails and hair. The main groups of fungi causing superficial fungal infections are:
Subcutaneous fungal infections
These involve the deeper layers of the skin (the dermis, subcutaneous tissue and even bone). The causative organisms normally live in the soil living on rotting vegetation. They can get pricked into the skin as a result of an injury but usually stay localised at the site of implantation. Deeper skin infections include:
Systemic fungal infections
Systemic mycoses may result from breathing in the spores of fungi, which normally live in the soil or rotting vegetation or as opportunistic disease in immune compromised individuals.
Inhaled fungal infection
Although uncommon, some may infect healthy individuals. The result is most often a mild infection and long lasting resistance to further attack, but occasionally these infections are more serious and chronic (especially in the immune suppressed). The organisms causing systemic fungal infections include:
Opportunistic infection
Other systemic mycoses only infect those who are already sick or immune suppressed i.e. they are ‘opportunists’. Repeated infection may occur. Risks for systemic mycoses include:
Opportunistic fungal infections include:
Mycology of dermatophyte infections
Mycology is the study of fungi. Dermatophyte fungi are the ringworm fungi (tinea). They depend on their host, which may be an animal ("zoophilic") or a human ("anthropophilic") and need to spread from one host to another to survive. Dermatophytes may also prefer to live in the soil ("geophilic").
Anthropophilic dermatophytes are so well adapted to living on human skin that they provoke minimal inflammatory reaction. Zoophilic or geophilic dermatophytes will often provoke a more vigorous inflammatory reaction when they attempt to invade human skin.
There are three genera of dermatophytes, recognised by the nature of their macroconidae (asexual spores):
There are about 40 species. Their spores can live for more than a year in human skin scales in the environment.
Anthropophilic organisms include:
Zoophilic organisms include:
Geophilic organisms include:
Laboratory tests for fungal infection
To establish or confirm the diagnosis of a fungal infection, skin, hair and nail tissue is collected for microscopy and culture (mycology).
Ultraviolet radiation (a Wood's light) can help identify some fungal infections of hair (tinea capitis) because the infected hair fluoresces green.
Specimen collection
Specimens for fungal microscopy and culture may be:
They are transported in a sterile container or a black paper envelope.
Direct microscopy
The material is examined by microscopy by one or more of these methods:
Microscopy can identify a dermatophyte by the presence of:
Fungal elements are sometimes difficult to find, especially if the tissue is very inflamed, so a negative result does not rule out fungal infection.
A yeast infection can be identified by the presence of:
Culture
Culture identifies which organism is responsible for the infection:
Growing the fungus in culture may take several weeks, incubated at 25-30ºC. The specimen is inoculated into a medium such as Sabouraud's dextrose agar containing cycloheximide and chloramphenicol. The cycloheximide is left out if a mould requires identification.
A negative culture may arise because:
Culture of yeasts and moulds may be due to harmless colonisation rather than infection. The infection may be secondary to an underlying skin disesase such as psoriasis.
Blood tests
Blood tests are not useful for the diagnosis of superficial fungal infections. But in subcutaneous and systemic infection, several tests may be useful.
Tinea barbae
Tinea barbae is the name used for infection of the beard and moustache areas of the face with a dermatophyte fungus. It is less common than tinea capitis and generally affects only adult men.
The cause of tinea barbae is most often a zoophilic (animal) fungus:
Tinea barbae is usually due to infection of coarse facial hair with an ectothrix pattern (spores on the outside). In ectothrix infections, the fungal filaments (hyphae) and spores (arthroconidia) cover the outside of the hair.
Clinical features
Tinea barbae most often affects farmers and is due to direct contact with an infected animal. It is rarely passed from one person to another.
Tinea barbae is usually very inflamed with red lumpy areas, pustules and crusting around the hairs (a kerion). The hairs can be pulled out easily. Surprisingly, it is not excessively itchy or painful.
Tinea barbae can result in an id reaction, especially just after starting antifungal treatment.
Diagnosis
The diagnosis of tinea barbae is confirmed by microscopy and culture of skin scrapings and hair pulled out by the roots.
Types of tinea capitis infections
Tinea capitis is classified according to how the fungus invades the hair shaft.
Ectothrix infection
Ectothrix hair invasion is due to infection with M. canis, M. audouinii, M. distortum, M. ferrugineum, M. gypseum, M. nanum, and T. verrucosum. The fungal branches (hyphae) and spores (arthroconidia) cover the outside of the hair. Ectothrix infections can be identified by Woods light (long wave ultraviolet light) examination of the affected area the vet uses this to check your cats fur. The fur fluoresces green if infected with M. canis.
Endothrix infection
Endothrix invasion results from infection with T. tonsurans, T. violaceum and T. soudanense. The hair shaft is filled with fungal branches (hyphae) and spores (arthroconidia). Endothrix infections do not fluoresce with Woods light.
Favus
Favus does not occur in New Zealand. It is caused by T. schoenleinii infection, which results in a honeycomb destruction of the hair shaft.
Clinical features
Tinea capitis is most prevalent between 3 and 7 years of age. It is slightly more common in boys than girls. Infection by T. tonsurans may occur in adults.
Anthropophilic infections such as T. tonsurans are more common in crowded living conditions. The fungus can contaminate hairbrushes, clothing, towels and the backs of seats. The spores are long lived and can infect another individual months later.
Zoophilic infections are due to direct contact with an infected animal and are not generally passed from one person to another.
Geophilic infections usually arise when working in infected soil but are sometimes transferred from an infected animal.
Tinea capitis may present in several ways.
Tinea capitis may result in swollen lymph glands at the sides of the back of the neck. Untreated kerion and favus may result in permanent scarring (bald areas).
It can also result in an id reaction, especially just after starting antifungal treatment.
Diagnosis
Tinea capitis is suspected if there is a combination of scale and bald patches. Wood's light fluorescence is helpful but not diagnostic as it is only positive if the responsible organism fluoresces, and fluorescence is sometimes seen for other reasons.
The diagnosis of tinea capitis should be confirmed by microscopy and culture of skin scrapings and hair pulled out by the roots (see laboratory tests).
Treatment of carriers
If the child has an anthropophilic infection, all family members should be examined for signs of infection. Brushings of scaly areas of the scalp should be taken for mycology. Sometimes it is best for the whole family to be treated whether or not fungal infection is proven.
It is advisable for parents of classmates and other playmates to be informed so their children may be examined and treated if necessary. In some countries, infected children are not allowed to attend school. Elsewhere children with tinea capitis can attend school providing they are receiving treatment.
Carriers may have no symptoms. Treatment of carriers is necessary to prevent spread of infection. Antifungal shampoo twice weekly for four weeks may be sufficient but if cultures remain positive, oral treatment is recommended.
Suitable shampoos include:
Treatment of tinea capitis
Tinea capitis requires treatment with an oral antifungal agent. Griseofulvin is probably the most effective agent for infection with Microsporum canis, but is no longer available in New Zealand. Scalp Trichophyton infections may successfully be eradicated using oral terbinafine, itraconazole or fluconazole for 4 to 6 weeks. However, these medications are not always successful and it may be necessary to try another agent. Intermittent treatment may also be prescribed e.g. once weekly dosages.
Tinea corporis
Tinea corporis (ringworm) is the name used for infection of the trunk, legs or arms with a dermatophyte fungus.
In different parts of the world, different species cause tinea corporis. In New Zealand, Trichophyton rubrum (T. rubrum) is the most common cause. Infection often comes from the feet (tinea pedis) or nails (tinea unguium) originally. Microsporum canis (M. canis) from cats and dogs, and T. verrucosum, from farm cattle, are also common.
More tinea corporis images
Clinical features
Tinea corporis may be acute (sudden onset and rapid spread) or chronic (slow extension of a mild, barely inflamed, rash). It usually affects exposed areas but may also spread from other infected sites.
Acute tinea corporis presents as itchy inflamed red patches and may be pustular. The cause is often infection by an animal (zoophilic) fungus such as M canis.
Chronic tinea corporis tends to be most prominent in body folds (spreading from tinea cruris). T. rubrum is the most common cause. If widespread, the condition tends to be stubborn to treat and prone to recurrence. This is possibly due to a decreased natural skin resistance to fungi or because of reinfection from the environment.
The term ringworm refers to round or oval red scaly patches, often less red and scaly in the middle or healed in the middle. Sometimes one ring arises inside another older ring.
Kerion is an inflamed fungal abscess. It presents as a boggy mass studied with pustules, often with satellite spots. It is often confused with a large boil or carbuncle or a tumour such as a skin cancer.
Tinea imbricata is due to T. concentricum and occurs in the Pacific Islands and other tropical areas. It results in brown scaly concentric rings.
Non-fungal conditions resembling tinea corporis include:
Diagnosis
The diagnosis of tinea corporis is confirmed by microscopy and culture of skin scrapings.
If you have a ringworm infection, consult your doctor or dermatologist for an examination and advice.
Tinea cruris
Tinea cruris is the name used for infection of the groin with a dermatophyte fungus. It is most often seen in adult men.
In different parts of the world, different species cause tinea cruris. In New Zealand, Trichophyton rubrum and Epidermophyton floccosum are the most common causes. Infection often comes from the feet (tinea pedis) or nails (tinea unguium) originally, spread by scratching or the use of an infected towel.
The appearance is similar to ringworm (tinea corporis). The rash has a scaly raised red border that spreads down the inner thighs from the groin or scrotum. Tinea cruris may form ring-like patterns on the buttocks. It is not often seen on the penis or vulva or around the anus. Tinea cruris can be very itchy.
Tinea cruris quite often recurs after apparently successful treatment. To reduce the chance of reinfection:
Diagnosis
The diagnosis of tinea cruris is confirmed by microscopy and culture of skin scrapings.
If you have a fungal infection, consult your doctor or dermatologist for an examination and advice.
Tinea manuum
Tinea manuum is the name given to infection of one or both hands with a dermatophyte infection. It is much less common than tinea pedis (tinea affecting the foot).
Tinea manuum is frequently misdiagnosed because it appears similar to:
Clinical features
Tinea manuum can occur as an acute inflammatory rash like tinea corporis. There is usually a raised border and clearing in the middle (ringworm). This is most likely when a zoophilic (animal) or geophilic (soil) fungus is responsible. The likely fungi are:
More frequently, tinea manuum causes a slowly extending area of peeling, dryness and mild itching on the palm of one hand (hyperkeratotic tinea). Skin markings may be increased. Generally both feet appear similar ("one hand, two foot syndrome"). The usual cause is an anthropophilic (human) fungus:
These fungi may also cause a blistering rash on the edges of the fingers or palm. The blisters appear in crops and contain a sticky clear fluid. They may have a peeling edge. This form of tinea manuum itches and burns.
Predisposing factors
Tinea manuum results from:
It is more likely in those doing manual work, who sweat profusely (hyperhidrosis) or who already have hand dermatitis.
Distinguishing features
Tinea manuum can be distinguished from hand dermatitis:
Tinea faciei
Tinea faciei is the name used for infection of the face with a dermatophyte fungus. It does not include infection of the beard and moustache area, which is called tinea barbae. Tinea faciei is uncommon and often misdiagnosed at first.
Tinea faciei can be due to an anthropophilic (human) fungus such as Trichophyton rubrum. (T. rubrum). Infection often comes from the feet (tinea pedis) or nails (tinea unguium) originally. Zoophilic (animal) fungi such as Microsporum canis (M canis), from cats and dogs, and T. verrucosum, from farm cattle, are also common.
Clinical features
Tinea faciei resembles tinea corporis (ringworm). It may be acute (sudden onset and rapid spread) or chronic (slow extension of a mild, barely inflamed, rash). There are round or oval red scaly patches, often less red and scaly in the middle or healed in the middle. It is frequently aggravated by sun exposure.
Tinea faciei is often misdiagnosed as a non-fungal condition such as:
Tinea pedis
Tinea pedis is a foot infection due to a dermatophyte fungus. Tinea pedis thrives in warm humid conditions and is most common in young adult men.
Tinea pedis is most frequently due to:
More images of tinea pedis
Clinical features
Tinea pedis has various patterns and may affect one or both feet.
Predisposing factors
Tinea pedis affects all ages but is more common in adults than in children. The fungal spores can persist for months or years in bathrooms, changing rooms and swimming pools. Walking bare foot on a communal floor or sharing a towel can result in infection.
Some people are particularly prone to troublesome tinea pedis. This may be because:
Diagnosis of tinea pedis
The diagnosis of tinea pedis is confirmed by microscopy and culture of skin scrapings.
Resistance to treatment
If treatment is unsuccessful consider whether you have:
Moccasin tinea is particularly resistant to treatment.
Hyperhidrosis
Hyperhidrosis is the name given to excessive sweating.
Hyperhidrosis may affect the entire body, or it may be localised to the armpits, palms, soles, face or elsewhere. It is usually symmetrical.
What is the cause of hyperhidrosis?
The exact cause or causes of hyperhidrosis are unknown. There are numerous sweat glands distributed over the body. The eccrine sweat glands produce a weak salt solution and are most numerous on the palms (with about 700 glands per square centimetre). The amount of sweat produced is regulated by a body temperature centre in the brain (the hypothalamus) via the sympathetic nervous system. Overactivity of the hypothalamus or the sympathetic nerves can result in hyperhidrosis.
Most often, hyperhidrosis is localised and first appears in childhood or adolescence. Other family members may or may not be similarly affected. An increase in air temperature, exercise, fever, anxiety, or spicy food may set off attacks of sweating. The sweating usually reduces at night time and disappears during sleep.
A few patients have hyperhidrosis as a consequence of a medical condition.
Generalised hyperhidrosis may be due to:
Localised hyperhidrosis may be due to:
Fungal nail infections
Fungal infection of the nails is known as onychomycosis. It is increasingly common with increased age. It rarely affects children.
Responsible organisms
Onychomycosis can be due to:
Clinical features
Onychomycosis may affect one or more toenails and/or fingernails and most often involves the great toenail or the little toenail. It can present in one or several different patterns:
Tinea unguium often results from untreated tinea pedis (feet) or tinea manuum (hand). It may follow an injury to the nail.
Candida infection of the nail plate generally results from paronychia and starts near the nail fold (the cuticle). The nail fold is swollen and red, lifted off the nail plate. White, yellow, green or black marks appear on the nearby nail and spread. The nail may lift off its bed and is tender if you press on it.
Mould infections are usually indistinguishable from tinea unguium.
Onychomycosis must be distinguished from other nail disorders such as:
Nail clippings
Clippings should be taken from crumbling tissue at the end of the infected nail. The discoloured surface of the nails can be scraped off. The debris can be scooped out from under the nail.
Previous treatment can reduce the chance of growing the fungus successfully in culture so it is best to take the clippings before any treatment is commenced:
Treatment
Fingernail infections are usually cured more quickly and effectively than toenail infections.
Mild infections affecting less than 80% of one or two nails may respond to topical antifungal medications but cure usually requires an oral antifungal medication for several months. Combined topical and oral treatment is probably the most effective regime.
Related information
Candida
Candida is the name for a group of yeasts (a type of fungus) that commonly infect the skin. The name ‘candida’ refers to the white colour of the organisms in culture. Candidal infection is known as ‘candidiasis’, ‘candidosis’ or ‘moniliasis’.
Candida depends on a living host for survival. It is a normal inhabitant of the human digestive tract from early infancy, where it lives without causing any disease most of the time. However, if the host's defences are lowered, the organism can cause infection of the mucosa (the lining of the mouth, anus and genitals), the skin, and rarely, deep-seated infection.
The most common Candida (C) species to result in candidiasis is C. albicans. Other species are:
Candidal skin infections include
Predisposing factors for candida infection
Paronychia
Paronychia refers to inflammation of the nail fold. It can be acute or chronic.
Acute paronychia
Acute paronychia develops over a few hours when a nail fold becomes painful, red and swollen. Sometimes yellow pus appears under the cuticle. In some cases acute paronychia is accompanied by fever and painful glands under the arms.
It is usually due to Staphylococcus aureus, a bacterial infection treated with oral antibiotics. Sometimes an abscess forms and has to be lanced. it can also be due to the cold sore virus, herpes simplex, when it is known as herpetic whitlow.
Acute paronychia usually clears completely in a few days, and rarely recurs.
Chronic paronychia
Chronic paronychia is a gradual process and much more difficult to get rid of. It may start in one nail fold but often spreads to several others. Each affected nail fold is swollen and lifted off the nail plate. It may be red and tender from time to time, and sometimes a little pus (white, yellow or green) can be expressed from under the cuticle.
The nail plate becomes distorted and ridged as it grows. It may become yellow or green and brittle. After recovery, it takes up to a year for the nails to grow back to normal.
Chronic paronychia is due to several different micro-organisms. Often a mixture of yeasts and bacteria are present, particularly candida species and Gram negative bacilli. The inflammation results in debris which builds up, encouraging more infection.
It mainly occurs in people who have constantly wet hands, such as dairy farmers, fishermen, bar tenders and housewives. It is more likely to occur, and more difficult to clear up, in those with poor circulation, especially during the winter months. It can also be a complication of eczema.
Treatment
The following measures may improve paronychia.
Keep the hands dry and warm.
Avoid wet work, or use totally waterproof gloves.
Keep fingernails scrupulously clean.
Wash thoroughly after dirty work with soap and water, rinse off and dry carefully.
Don't let the skin dry out.
Apply a emollient hand cream frequently - dimeticone barrier creams may help.
Apply antiseptics or antifungal lotions regularly twice daily to the nail fold - suitable preparations include sulfacetamide, thymol, miconazole, ciclopirox.
Occlusive paints can be useful; flexible collodion can be applied over the nail fold as a barrier to water and germs.
A course of an oral antifungal agent (itraconazole or fluconazole) may be recommended by a dermatologist.
Дата добавления: 2015-10-29; просмотров: 80 | Нарушение авторских прав
| <== предыдущая страница | | | следующая страница ==> |
| Применение для анализа газового состава пробы | | | Лекция 4. Половое размножение грибов |