Trichophyton rubrum is a dermatophyte, which is a fungus that primarily affects the skin and skin appendages. In addition to Trichophyton rubrum, about 20 other species are known. It is the most important causative agent of dermatophytosis (tinea).
What is Trichophyton rubrum?
Trichophyton belongs to the dermatophytes along with epidermophytes and microspores. Dermatophytes belong thereby to the thread or hyphal fungi. They mainly infect skin, hair and nails and are responsible for the corresponding mycoses. In addition, Trichophyton rubrum is a parasite, i.e. it attacks a host and derives benefit from the coexistence without the host itself having any benefit, but, on the contrary, is harmed. The diseases caused by Trichophyton rubrum are called tinea, a clearly circumscribed circular change of a skin area, which may be lighter in the center, while the edge has a reddish glow. This can be found almost anywhere on the body. In this case, the pathogen usually affects only the superficial layers of the skin, deeper ones are rarely reached. Trichophyton rubrum is one of the most common pathogens of dermatomycosis. In addition to humans, Trichophyton rubrum can also infect animals, which can further transmit the pathogen.
Occurrence, distribution, and characteristics
Trichophyton rubrum occurs almost everywhere. While it used to be widespread mainly in the Middle East and the USA, it has now spread throughout the world, and in Europe its incidence has even been increasing sharply in recent years. In Germany alone, almost one in five Germans is infected with Trichophyton rubrum. Trichophyton as well as other dermatophytes like to live in areas that are moist and warm, which is why they most frequently infest the spaces between the toes as well as skin folds. However, the pathogen also affects hair and nails in addition to the skin. Thus, with every step, an affected person loses numerous skin flakes, all of which can be infectious. Trichophyton rubrum is mainly transmitted anthropophilically, i.e. by human-to-human contact. A highly infectious source is when people are together in communal showers or changing rooms. The pathogen can thus be optimally transmitted to other people. Another possibility of transmission is from animal to human, i.e. zoophilic transmission. If a person keeps many pets or farm animals, there is a high probability that an animal will hold the pathogen and pass it on when it comes into contact with humans. Another, but rather rare, possibility of transmission is from soil to human, also called geophilic transmission. In this case, those who work a lot in the garden, for example, are particularly affected. Trichophyton rubrum is a filamentous or hyphal fungus. This type of fungi needs a lot of energy for growth, which they obtain from carbohydrates and keratin. The latter can be obtained precisely from the skin and nails, obtaining it with the help of their keratinase, a keratin-degrading enzyme. Other enzymes that help the fungus to infect the skin are numerous proteinases and elastases. To diagnose Trichophyton rubrum, scrape out some flakes of the affected skin area and embed them in a KOH solution. This can then be viewed under the microscope. There, abundant microconidia with numerous and multiply chambered macroconidia with smooth walls become visible. Conidia are the asexual form of reproduction. Furthermore, Trichophyton rubrum can produce spores that are so stable that they can remain infectious for months. In addition, the dermatophyte also tends to persist chronically. For species differentiation of Trichophyton rubrum, a cultural cultivation on special culture media is necessary. This takes one to three weeks and results in woolly-looking cultures. In fungi there is usually an anamorphic, as well as a teleomorphic form. In the case of Trichophyton rubrum, only the anamorphic form is known to date, i.e. the asexual form of reproduction. The sexual, i.e., teleomorphic form, is not known for Trichophyton rubrum, as for many other fungi.
Diseases and symptoms
Trichophyton rubrum is the causative agent of dermatophytosis. This is a disease of the skin and skin appendages. This is also called tinea, a reddish shimmering scaling of the skin.Although these are usually not dangerous diseases, they are very unpleasant, as infection is a major cosmetic problem. In addition, there is often a strong itching. Typical places that the fungus attacks are nails, moist skin folds, as well as spaces between toes. Trichophyton rubrum is the most common causative agent of nail fungus (tinea unguium), but also ringworm (tinea corporis), which can spread from one spot over the entire body. Affected areas can easily shed scales, which in turn can spread to other people. Further, the fungus can also affect facial hair (tinea barbae) or head hair (tinea capitis). In the case of hair mycosis, the hair becomes brittle and it comes to the loss of these. Kerion is the term used here for the most severe form of hair mycosis, in which the fungus penetrates deep into the hair follicles and can lead to an ulcer.
