Tropical mycoses: causes, symptoms, diagnosis, treatment

Mycotic skin lesions are a very significant practical problem, both because of their extreme prevalence and their known contagiousness. This is even more true of tropical dermatomycoses, which, like all tropical pathology, can be divided into tropical dermatomycoses proper, occurring exclusively in hot climates, and cosmopolitan dermatomycoses, which acquire their distinctive, sometimes very pronounced clinical and epidemiological features in tropical conditions.

As an example, among such very common cosmopolitan mycoses, we should mention superficial fungal skin lesions, or keratomycosis, a striking representative of which are various variants of versicolor, or pityriasis versicolor.

What causes tropical dermatomycosis?

Today it has been finally established that lipophilic fungi of the genus Malassezia, under certain predisposing factors, are the main etiologic factor of pityriasis versicolor. Incidentally, it should be said that Malassezia spp. can play an etiopathogenetic role in a very wide range of pathological processes in both children and adults, healthy individuals, and in immunodeficiency states - folliculitis, seborrheic dermatitis, neonatal pustulosis, onychomycosis (often registered in South America), external and middle otitis, confluent papillomatosis, and possibly also psoriasis of the scalp.

Tropical yellow lichen

A striking example of pityriasis versicolor in hot climates is tropical yellow lichen, caused mainly by Malassezia furfur, which is related to keratomycosis and is characterized by the appearance, mainly on the skin in the area of the face, neck, less often - in other areas, of small yellowish-orange spotted rashes. The independence of this keratomycosis is not recognized by everyone, and therefore it is more convenient to classify it as one of the varieties of pityriasis versicolor.

Yellow lichen is most often found in tropical and subtropical countries of Southeast Asia, South America and Cuba, and less often on the African continent. The disease is of a pronounced seasonal nature and usually occurs during the season of maximum humidity. Not only adults but also children are affected, among whom group diseases may be observed.

Symptoms of tropical yellow lichen are characterized by the appearance on the skin of the face and neck of initially small and irregularly shaped yellowish spots with a slight orange tint. As they grow peripherally, they merge, forming large spots with more or less cyclical outlines, on the surface of which there is slight peeling. Subjective sensations are absent.

Tropical black lichen

Tropical black lichen (tinea nigra) is considered as a variant of tropical keratomycosis, with spots of the corresponding color, which also have a favorite localization on the skin of the face. In addition, classical variants of versicolor lichen with typical localization and a tendency to extensive lesions are also very widespread in tropical conditions.

Piedra

Piedra can be classified among the group of fungal hair lesions, or typical representatives of tropical mycoses. This trichomycosis is characterized by the development of small multiple or single dense nodular formations on the hair, which are colonies of the fungus, cuff-shaped surrounding the hair. Piedra is found mainly in the countries of Central and South America, more often in Colombia, Argentina, Brazil, Paraguay and Uruguay. Individual cases have been recorded in Southeast Asia, Japan and some other countries. The causative agents of piedra are representatives of the genus Trichosporon, in particular in white piedra - Tr. giganteum, Tr. cerebriforme, Tr. ovale and others.

Causes of Piedra

Pathogenetic factors that contribute to the development of the disease are high temperature and humidity of the environment, certain social and living conditions. For example, some national customs have a certain significance, in particular, greasing hair with vegetable oils and fermented milk products when styling it. The conditions created for a long time with this method of styling hair (at high ambient temperature and humidity) are close to the thermostatic conditions for the development of the fungus. It is also a pattern that piedra occurs mainly in people with straight long hair and less often - with short and curly hair. Apparently, this is why piedra is practically not found on the African continent. People of both sexes can get sick, although it is somewhat more common in young women.

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Symptoms of Piedra

Symptoms of piedra are characterized by the presence of multiple, up to 20-30 or more small and very hard nodules on the hair in the scalp area, which are especially well visible through a magnifying glass. They look like irregular, oval or spindle-shaped formations that encircle the hair in the form of an almost complete ring. In some cases, as a result of the fusion of closely located nodules, the hair appears to be surrounded by a solid muff. There are two main varieties of piedra: black and white.

Tropical, or black, piedra is characterized by brownish or deep brown color of the nodules, which are easily determined by palpation when passing the hair between the fingers. Sometimes in advanced cases, tightly pulled hair due to gluing of the nodules tightly adheres to each other and forms whole bunches of affected hair, which is often called Columbian tangle. However, even in such severe cases, the hair itself is practically not affected, since the spores are only on the hair, not penetrating inside and thus not affecting the cuticle, therefore, the hair affected by piedra never breaks off.

White piedra looks somewhat different, and in addition to South American countries it is also found in Asian and European countries. White piedra can be observed in men in the area of beard and moustache growth, in women - on the scalp, on the pubis and in the armpits. Nodules with white piedra have light tones with grayish-yellow and milky-matte shades, they are not as stony as with black piedra. The size of the muffs with white piedra sometimes reaches 7-10 mm.

Diagnosis of Piedra

Diagnosis of piedra is generally not difficult and is based on typical clinical manifestations.

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Treatment of Piedra

The most radical way to treat piedra is to cut the hair affected by the fungus. It is also possible to use special medicinal shampoos containing antimycotics in the required concentration, mainly from the azole group.

Imported trichomycosis

A separate problem in the context of tropical dermatomycosis may be the possible risk of importing a tropical infection to countries with a temperate climate. An example of such an imported fungal infection from the trichomycosis group may be some variants of superficial trichophytosis of the scalp, which is generally known to be one of the most contagious forms of trichomycosis. The pathogens isolated in such imported cases are most often classified as Trichophyton soudanense and are usually “imported” from countries of the African continent. The clinical picture of such trichomycosis is practically no different from that of ordinary “ringworm”. The necessary vigilance of the dermatologist becomes even more important in case of this diagnosis in a patient who arrived from tropical countries.

Chronic candidiasis of the skin and mucous membranes

Fungi of the genus Candida are a very common infection, which can acquire special significance in tropical climates, where the most favorable conditions for their growth and reproduction are formed. Skin and mucous lesions caused by Candida spp., often acquire a chronic, widespread character in these conditions. An example is chronic candidiasis of the skin and mucous membranes, combining simultaneous lesions of these structures. The skin becomes erythematous-infiltrated, covered with crusts and vegetations. The adjacent areas of the mucous membranes are brightly hyperemic, covered with a white coating, often with granulomatosis.

As is known, candidiasis of the skin and mucous membranes does not have a special tendency to endemicity and is found everywhere. However, in addition to high temperature and humidity in tropical conditions, the spread of this mycosis can be significantly facilitated by hypovitaminosis, which is so characteristic of a number of countries in this belt.

For common dermatomycoses, in which Tr. rubrum is often recognized as the causative agent, in tropical conditions a characteristic feature is the rapidly developing spread of lesions over large areas of the skin with the involvement of the facial skin in the process.

In addition, in recent years, a noticeable increase in the number of imported fungal infections with a common clinical picture, but with pathogens atypical for a temperate climate, has been registered in European countries. There is an opinion that this is associated not only with migration processes, but can also occur through simple physical transfer of the pathogen along transport routes. In particular, superficial dermatomycosis caused by Scytalidium dimidiatum has been diagnosed in recent years in Europe in people arriving from Southeast Asia and Oceania. The clinical symptoms of this fungal infection are very similar to the symptoms of hyperkeratotic mycosis of the feet, but many of its details have not yet been studied, including the mechanism of transmission. Since many cases of mycotic infection are asymptomatic at the initial stages of development or can resemble other diseases, special attention is required to improve the diagnostic capabilities of such a fungal infection.

Of particular interest from the point of view of tropical dermatology are deep mycoses, which are known to be quite common in hot countries. The most striking example of this group is maduromycosis.

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Maduromycosis

Madura disease or Madura foot (mycetoma) is one of the classic representatives of severe and long-term deep mycoses of tropical countries with predominant lesions of the feet and shins.

The disease has been known for a long time - its first description dates back to the beginning of the 17th century. Maduromycosis occurs in many countries of the world with tropical or subtropical climate conditions: these are almost all countries of Southeast Asia, many countries of Africa and South America. Sporadic cases can also be found in some European countries with a moderate climate. Many dermatologists are inclined to consider maduromycosis a polyetiological disease, since the fungi that cause the disease identified in different cases belong to a wide variety of families, genera and species: Actinomyces, Nocardia, Aspergillus, etc.

Causes of Madura disease

In general, the causative agents of maduromycosis can be classified as opportunistic organisms. They are widespread in nature, especially in tropical climates. The main route of infection is exogenous, and the penetration of the pathogen is facilitated by injuries, for example, by thorns or sharp ends of plants or simply walking barefoot on contaminated soil.

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Symptoms of Madura disease

Most often, the process begins in the area of the feet, somewhat less often - in the area of the shin. At the site of penetration of the pathogen, a single nodule up to the size of a pea appears, dense and somewhat painful upon palpation. As the nodes increase and spread, after several months, their central part begins to soften, fluctuation appears. Eventually, the abscess opens with the formation of fistulas, from which a purulent discharge with a foul odor is released, containing 2-3 mm druses of the fungus visible to the naked eye, like grains resembling caviar. The color of these druses can be different - white, yellow, black, sometimes red, which depends on the pigment secreted by the fungi at different stages of their development.

Over the course of 3-4 years, the process slowly spreads to both healthy areas and deeper layers of skin, subcutaneous tissue, and even to bone damage. The foot becomes enlarged, lumpy, and sharply deformed, sometimes taking on the appearance of a shapeless mass. The arch of the foot is smoothed out, the toes seem to turn upward, and the shin, on the contrary, appears noticeably thinner.

Diagnosis of Madura disease

In typical cases, the diagnosis of maduromycosis is not difficult and is based on typical clinical manifestations. In some cases, it is necessary to conduct a differential diagnosis with actinomycosis.

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Treatment of Madura disease

In terms of prognosis, maduromycosis does not belong to diseases with a severe prognosis; there are even known cases of self-healing. However, developing foot deformation and bone lesions may require surgical intervention, up to and including amputation of the foot.

Sporotrichosis

Another tropical mycosis - sporotrichosis - is a chronic disease from the group of deep mycoses with lymphogenous lesions mainly of the skin, subcutaneous tissue and, less often, other organs and systems. Sporotrichosis is most often found in South American countries, primarily in Mexico, and somewhat less often in African and Southeast Asian countries.

What causes sporotrichosis?

Sporotrichosis is caused by various species of fungi of the genusSporotrichon. As saprophytes, they are widespread in nature, in the soil, on plants, vegetables, flowers, etc. High temperatures and humidity contribute to their existence and spread in nature. According to most researchers, human infection occurs exogenously, most often after injury to the skin and, less often, to the mucous membranes. People of any age and gender can become ill. The localization of the rash is associated with open areas of the body that are frequently injured: hands, feet, forearms, and sometimes the face. Two clinical forms of sporotrichosis are usually distinguished: localized and disseminated. The localized form is sometimes called lymphatic, and it is more common than the disseminated form.

Symptoms of sporotrichosis

Initially, a small acne-like formation develops at the site of penetration of the pathogen, which then turns into a typical ulcer. Sometimes everything can start with a gum-like node. The nodule or knot, initially the size of a pea, dense and painless, begins to gradually increase in size and takes the form of a hemispherical tumor. The formation fuses with the subcutaneous fat, the skin above it becomes inflamed, acquiring a dirty-bluish tint and, necrotizing, turns into an ulcer. This entire process takes quite a long time. Sometimes this primary affect of sporotrichosis is called sporotrichosis chancre. It is usually single, but it is possible to have three or five foci at the same time.

Gradually, regional lymphatic vessels are involved in the process, and linear stripes appear on the skin. They are palpated as cords with bead-like thickenings. A characteristic sign is the complete absence of pain even during palpation. Later, sometimes linear secondary nodes may appear along the affected lymphatic vessel, some of them undergo the same development cycle as the primary affect.

The localized form of sporotrichosis is characterized by a benign course. Sporotrichosis proceeds in a satisfactory condition without pronounced changes in the blood. Some authors describe acne-like manifestations of sporotrichosis, which can initially simulate acne vulgaris, especially its conglobate varieties.

Diagnosis of sporotrichosis

In typical cases, localized sporotrichosis is not difficult to diagnose. However, in doubtful situations, the diagnosis can be confirmed by a culture method.

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Deep mycoses of tropical regions

South American blastomycosis, or Brazilian blastomycosis, is also a common deep mycosis in tropical regions.

This representative of deep mycoses is found mainly on the South American continent and is characterized by a torpid course with the development of ulcerative-granulomatous lesions not only of the skin, but also of the mucous membranes, sometimes with the involvement of internal organs, the gastrointestinal tract and lymph nodes. The causative agent of the disease is currently recognized as Blastomyces braziliensis, close to the blastomycetes of North American blastomycosis. It is assumed that the pathogen enters the human body exogenously. However, the role of the endogenous route of infection is not excluded.

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South American blastomycosis

South American blastomycosis occurs exclusively in the climatic conditions of hot countries. Brazil is considered the main endemic region. It is also found in other countries of Central and South America. Young and middle-aged people usually get sick, men are slightly more often. Localized and, less often, generalized forms are usually described. Among localized forms, cutaneous, mucocutaneous and visceral are distinguished.

At the site of pathogen penetration, grouped papular rashes initially appear. Sometimes the disease begins immediately with a clinical picture of angina or ulcerative stomatitis. Gradually, over the course of several months, a fairly extensive dense infiltrate is formed, which gradually softens and undergoes central necrosis with superficial ulceration. The surface of the ulcers is covered with granulations, but growth continues both in depth and along the periphery, capturing significant areas of the mucous membrane of the oral cavity, pharynx, nasopharynx with a transition to more distant areas of the mucous membranes and the skin. At the same time, a reaction develops from the regional lymph nodes: they enlarge, become painful and fused with each other and with the underlying tissues. Later, without treatment, as a result of the generalization of the process, the disease becomes increasingly systemic.

Diagnosis of South American blastomycosis is based on typical clinical manifestations and laboratory data, including culture studies. The prognosis in the absence of treatment is not always favorable, and the disease can be fatal.

Treatment of tropical dermatomycosis

Treatment of tropical dermatomycoses, as well as their analogs from a temperate climate, is usually carried out with external antimycotics, mainly from the azole group or terbinafine. In case of extensive damage to the skin in keratomycosis, systemic use of antimycotics is indicated.

Treatment of tropical mycoses of the skin

In general, treatment of tropical skin mycoses with modern powerful antifungal agents of systemic and external action in most cases turns out to be quite successful. The choice of a specific antifungal agent will depend on both the clinical picture of the fungal skin lesion and the individual characteristics of the patient, as well as on the capabilities of the local pharmaceutical market.