Generality
Fungal infections are infections due to pathogenic fungi.
Pathogenic fungi are eukaryotic, unicellular or multicellular organisms, capable of causing disease in humans or in other animal species.
There are various parameters for classifying mycoses. The most frequently used parameter is the infection site.
Based on the site of infection, mycoses are distinguished in: superficial mycoses, cutaneous mycoses, subcutaneous mycoses, systemic mycoses due to primary pathogens and, finally, systemic mycoses due to opportunistic pathogens.
What is mycosis?
Mycosis is the medical term for an infection caused by pathogenic fungi (or fungal infection ).
Pathogenic fungi are eukaryotic, unicellular organisms (NB: in this case they are among the microorganisms) or multicellular, which can cause a disease in humans or other animal species.
Epidemiology
As we will see in the next chapters, mycoses mainly affect the skin.
In 2010, fungal skin infections were the fourth most common disease in the world, with 984 million people affected.
Causes
To promote the appearance of a mycosis in the human being can be various factors, including:
- The use of antibiotics . The prolonged and / or inadequate intake of antibiotics determines the destruction of the gastrointestinal bacterial flora. The latter has the task of controlling the proliferation of potentially pathogenic fungi, present physiologically in the human organism. The impairment of the bacterial flora makes the spread of potentially pathogenic fungi easier.
- The reduced efficiency of the immune system . The immune system is an organism's defensive barrier against threats from the external environment, such as viruses, bacteria, fungi etc., but also from the internal environment, such as cancer cells (the so-called "mad cells") ) or malfunctioning.
To compromise the efficiency of the immune system may be morbid conditions, such as AIDS (ie HIV infection) or taking certain drugs, such as corticosteroids, chemotherapy or immunosuppressants.
Moreover, it is good to remember that an inefficient immune system is also present in very young subjects (NB: it is not yet fully developed) and in very elderly subjects (NB: it is a decrease in the entirely physiological efficiency).
- The presence of diabetes . The high presence of glucose in the blood (hyperglycemia), induced by diabetes, is a factor favoring the proliferation of some fungi that inhabit certain anatomical areas of the human body and which, under normal conditions, are completely harmless.
Categories at risk of mycosis:
- AIDS patients
- Diabetics
- Subjects of very young age
- Very old subjects
- People undergoing chemotherapy to treat a tumor
- People subjected to prolonged corticosteroid treatments
- Organ transplant, due to the use of immunosuppressants
- People who have taken antibiotics for long periods of time
Classification
Pathology doctors classify mycoses in three different ways:
- According to the site of infection : the classification that considers the site of infection distinguishes mycoses based on the type or types of tissue in which fungal colonization begins and based on the degree of tissue involvement.
According to this classification, there are superficial mycoses, cutaneous mycoses, subcutaneous mycoses, systemic mycoses due to primary pathogens and systemic mycoses due to opportunistic pathogens.
- According to the acquisition path : the classification that considers the acquisition path distinguishes fungal diseases based on the origin of the pathogenic fungus, which can be exogenous (ie from the outside) or endogenous (ie from the inside).
According to this classification, exogenous mycoses and endogenous mycoses exist.
The acquisition of an exogenous mycosis can take place by air transmission, cutaneous transmission or percutaneous transmission.
The acquisition of an endogenous mycosis, on the other hand, can occur due to a process of colonization by an element of the organism's microbial flora or due to the reactivation of a previous fungal infection.
- According to the virulence : the classification that considers the virulence distinguishes mycoses based on the pathogenic power of the infecting fungal agent.
According to this classification, there are primary mycoses and opportunistic mycoses .
Primary mycoses are due to fungal pathogens capable of establishing an infection in healthy subjects; in these cases, pathogens are called primary pathogens .
The opportunistic mycoses, instead, are due to fungal pathogens able to establish an infection only in people with a compromised immune system; in these situations, pathogens are called opportunistic pathogens .
The classification of mycoses according to the site of infection is the most popular and widespread in pathology books.
SURFACE MYCOSIS
Superficial fungal infections involve the outer layers of the skin and hair / hair.
The most known and common superficial mycoses are:
- Black Piedra . It is due to the fungal pathogen known as Piedraia hortae . It is a disease of the hair shaft, which causes the formation of brown / black nodules in the scalp. It is an uncommon fungal disease in general, but particularly common in the tropical areas of Africa and South America.
To promote its diffusion is the poor personal hygiene.
- Piedra bianca . It is due to the fungal pathogens Trichosporon, in this case Trichosporon asahii, Trichosporon beigeii, Trichosporon inkin and Trichosporon mucoides .
In general, the white piedra involves the formation of numerous and small roundish nodules, of white color, at the level of the hair and the cutaneous hairs of groin and armpits.
More rarely, it affects the outer layers of the skin with equal formations.
It is a mycosis present mainly in tropical and subtropical geographical areas. To promote its diffusion is the poor personal hygiene.
The pathogens that cause white foot tend to act as opportunistic pathogens.
- Pityriasis versicolor (or tinea versicolor ). It is due to the fungal pathogen Malassezia furfur .
It is a superficial mycosis that causes hyperpigmentation or hypopigmentation of the skin.
It mainly affects the anatomical areas of the thorax, neck, back and shoulders.
Risk factors for pityriasis versicolor are heat, humidity, increased sebaceous secretions, insufficient personal hygiene and immunodepression, which may be due to the intake of corticosteroids, pregnancy, malnutrition, diabetes etc.
Pityriasis versicolor is included among both primary mycoses and opportunistic mycoses.
- Tinea nigra . It is due to the fungal pathogen Hortaea (or Phaeoannellomyces ) werneckii . Its presence causes the formation of skin patches of varying size, irregular, often isolated, brown or black and localized at the level of: palms of the hands and soles of the feet.
Spots apart, tinea nigra does not cause any particular symptoms and is not contagious.
The agents that cause it are particularly common in Central and South America, in Africa and in Asia. Especially at risk of infection are children, adolescents and young adults.
In general, superficial mycoses do not evoke any immune response.
CUTANEOUS MYCOSIS
The cutaneous mycoses involve the keratinized layers of the epidermis (NB: keratinized means that they contain the keratin protein) and the cutaneous appendages, such as hair / hair and nails.
Unlike superficial mycoses, cutaneous mycoses evoke an immune response and involve the degradation of the epidermal layers of keratin, inducing irritation, inflammation or, in some cases, even allergic-type reactions. Pathological doctors also call the cutaneous mucous with the generic term " ringworm ".
The fungi that cause cutaneous mycoses are better known as dermatophytes or dermatomycetes . Dermatophytes have the peculiarities of being filamentous fungi and reproducing by spores.
In nature, there are three genera of dermatophytes: the genus Microsporum, the genus Trichophyton and the genus Epidermophyton .
The species of the genus Microsporum of greatest clinical interest are:
- Microsporum audouinii . Causes ringworm in the scalp or at the level of the skin. It is a particularly common pathogen in tropical areas and in the poorest areas of Africa.
To promote its diffusion, it is the poor personal hygiene.
- Microsporum canis . It mainly affects dogs, cats and livestock, but can also spread to humans, especially among young people who live in close contact with infected animals.
In humans, it causes ringworm in the scalp and skin of different areas of the body.
For unknown reasons, it is particularly common in Iran and its surroundings.
- Microsporum gypseum . It can affect the skin of different areas of the body and the scalp causing ringworm.
The most known species of the genus Trichophyton are:
- Trichophyton rubrum . It is responsible for ringworm that can affect feet, hands, groin and / or nails. Fungal infections of the nails are better known as onychomycosis .
- Trichophyton mentagrophyes . It is the fungal agent responsible for the condition known as athlete's foot .
Athlete's foot is a fungal infection that affects the areas between the toes, causing: red and itchy skin; skin thickening; skin desquamation; blistering; appearance of skin cracks; smelly feet; thicker nails.
- Trichophyton verrucosum . Especially infects horses, donkeys, dogs and sheep, but can also be transmitted to human beings.
In humans, it affects the scalp and can cause areas of alopecia or real baldness.
The subjects most at risk are those who live in close contact with the categories of animals mentioned above.
Finally, the most important species of the genus Epidermophyton is:
- Epidermophyton floccosum . It can cause ringworm in the feet, legs, arms and nails (onychomycosis).
Experts classify the cutaneous mycoses also based on the natural habitat of the fungal pathogen that causes them.
According to this classification, there are geophilic mycoses, zoophilic mycoses and anthropophilic mycoses .
Geophilic mycoses
The geophilic mycoses are fungal infections whose triggering pathogen lives in the soil and is a saprophytic fungus of the soil. Contact with contaminated soil may cause it to spread.
An example of geophilic mycosis is that supported by Microsporum gypseum .
Zoophilic mycoses
The zoophilic mycoses are the fungal infections whose triggering pathogen is a primary parasite of the animals, which can be transmitted to the human being for close contact.
Examples of zoophilic mycoses are the conditions induced by Microsporum canis or Trichophyton verrucosum .
Anthropophilic mycoses
To conclude, anthropophilic mycoses are fungal infections whose pathogen is a primary parasite of human beings, which rarely infects animals.
Examples of anthropophilic mycoses are the conditions supported by Trichophyton rubrum or Epidermophyton Floccosum .
| Types of ringworm and localization | ||
| Main types of ringworm | Location | Who can provoke it? |
| Tinea capitis | Scalp |
|
| Tinea corporis | Chest, back, arms and legs |
|
| Tinea pedis | Feet |
|
| Tinea unguium | fingernails |
|
SUBCUTANEOUS MYCOSIS
Subcutaneous mycoses are fungal infections that can start at the level of: dermis, subcutaneous tissues (hypodermis), muscles, tendons or bone tissue. Like cutaneous mycoses, they evoke an immune response.
The fungal pathogens that cause subcutaneous mycoses have the soil as a natural habitat, and become infectious if they enter the body through wounds or cuts in the skin. They are particularly common in tropical and subtropical areas of Africa, India and South America.
After extensive research, pathologists have identified at least three different types of subcutaneous mycoses:
- Chromoblastomycosis (or chromomicosis) . It is responsible for painful and itchy, slow-growing, variable-sized verrucoid lesions. On histological examination, these verrucoid lesions have particular cells, called muriform cells, which represent the peculiar characteristic of chromoblastomycosis.
In general, chromomicosis affects only the subcutaneous tissues, so it does not involve the bones, muscles and tendons
Fungal agents that can cause chromoblastomycosis include: Fonsecaea compacta, Fonsecaea pedrosoi, Cladosporium carionii, Phialophora verrucosa .
- The mycetoma . It generally causes a granulomatous reaction at the site where it originates. This granulomatous reaction involves the formation of tumor-like abscesses, accompanied by chronic inflammation, swelling and ulceration of the infected anatomical region.
Usually, the mycetoma develops starting from the subcutaneous tissues, only to then spread in the bone tissues and in the skeletal muscle tissues.
The most common pathogens capable of causing mycetoma are: Madurella mycetomatis, Madurella grisea and Aspergillus .
- The sporotrichosis . The fungus that causes this subcutaneous mycosis is the so-called Sporothrix schenckii .
Once penetrated into the body, Sporothrix schenckii is able to enter the lymphatic system, travel in lymphatic vessels and disseminate in various organs of the human body, resulting in: pulmonary infections, bone infections, joint infections, endophthalmitis, meningitis and sinusitis.
One place in the world where Sporothrix schenckii is particularly widespread is the State of Peru, in South America.
Subcutaneous mycoses are difficult to treat and, in some cases, may require somewhat invasive surgical procedures. For example, mycetoma is resistant to treatment with chemotherapy and often involves amputation of the infected anatomical area.
SYSTEMIC MYCOSIS
Systemic mycoses are infections that affect most or all of the organism.
As anticipated, there are two types of systemic mycoses: systemic mycoses due to primary pathogens and systemic mycoses due to opportunistic pathogens (NB: readers can recover the meaning of primary pathogens and opportunistic pathogens by consulting the chapter dedicated to the classification of mycoses, precisely where one speaks of classification according to virulence).
SYSTEMIC MYCOSIS DUE TO PRIMARY PATHOGENS
In the case of systemic mycoses due to primary pathogens, the canonical way that allows the infecting agent to access the host organism is the respiratory tract .
Thus, through the respiratory tract, the pathogen reaches the lungs and, from the lungs, spreads throughout the body.
Classic examples of systemic mycoses due to primary pathogens are:
- Blastomycosis, whose responsible agent is Blastomyces dermatitidis .
In the United States, blastomycosis causes 30 to 60 deaths every year.
- Coccidioidomycosis (or valley fever ), whose responsible agents are Coccidioides immitis and Coccidioides posadasii .
In the North, Central and South of America, coccidioidomycosis causes 50 to 100 victims every year.
- Histoplasmosis, whose responsible agent is Histoplasma capsulatum .
In the United States, every year, about 50 people die due to histoplasmosis.
- Paracoccidioidomycosis (or South American blastomycosis ), whose responsible agent is Paracoccidioides brasiliensis .
SYSTEMIC MYCOSIS DUE TO OPPORTUNISTS
In the case of systemic mycoses due to opportunistic pathogens, infectious agents can exploit, in addition to the respiratory tract, also other entry routes, such as the digestive tract and the vascular system (through the use of needles or needle-cannula in the field doctor and drug addicts).
Classic examples of systemic mycoses due to opportunistic pathogens are:
- Candidiasis, whose responsible agents are fungi of the genus Candida (such as Candida albicans ).
- Cryptococcosis, whose responsible agent is Cryptococcus neoformans .
- Aspergillosis, whose responsible agents are the fungi of the genus Aspergillus .
- Penicilliosis, whose causative agent is Penicillium marneffei .
- Zygomycosis, whose responsible agents are some Zygomycetes.
- The pneumocystosis, whose causative agent is Pneumocystis carinii .
People more exposed to the danger of systemic mycoses due to opportunistic pathogens:
- AIDS patients
- Subjects who, following prolonged antibiotic treatment, have an alteration of the gastrointestinal flora
- Transplanted subjects, taking immunosuppressants against organ rejection
- Cancer patients undergoing chemotherapy.
Prevention
The most classic fungal prevention measures consist of:
- keep the skin clean and dry,
- maintain good personal hygiene,
- wash sports clothing after using them
- avoid contact with infected people or animals (NB: many fungal infections are contagious).
Treatment
The treatment of mycoses consists in the administration of antifungal drugs, known as antifungals .
Depending on the type of mycosis, doctors can prescribe topical antifungals or antifungals for systemic use .
Examples of anti-mycosis medicines are: fluconazole, amphotericin B, ketoconazole, itraconazole and terbinafine.
