Trichophyton spp- An Overview

Trichophyton is a genus of fungi that belongs to the family Arthrodermataceae and the order Onygenales. It includes about 20 species that can infect the skin, hair and nails of humans and other animals, causing various types of dermatophytosis or ringworm infections . Trichophyton species can be classified into three groups based on their habitat preference: anthropophilic (human-associated), zoophilic (animal-associated) and geophilic (soil-associated) . Some of the most common and clinically important species are:

• Trichophyton rubrum: an anthropophilic fungus that causes chronic infections of the feet, skin and nails, especially in tropical regions .
• Trichophyton mentagrophytes: a zoophilic fungus that affects various animals, such as rodents, cats, horses and rabbits, and can also cause ringworm of the scalp, skin and nails in humans, mainly in rural areas .
• Trichophyton tonsurans: an anthropophilic fungus that causes tinea capitis (scalp ringworm) and tinea corporis (body ringworm) in humans, especially children .
• Trichophyton verrucosum: a zoophilic fungus that causes ringworm in cattle and other livestock, and can also infect humans through contact with animals or contaminated objects .
• Trichophyton violaceum: an anthropophilic fungus that causes tinea capitis and tinea corporis in humans, especially in Africa, Asia and Europe .

Trichophyton fungi are molds that produce both macroconidia (large spores) and microconidia (small spores) on their hyphae (filaments). The shape, size and arrangement of these spores vary depending on the species and the culture conditions . Trichophyton fungi can be identified by microscopic examination of skin scrapings, nail clippings or hair plucks treated with potassium hydroxide (KOH) or calcofluor white, which dissolve the keratin and reveal the fungal elements . They can also be cultured on selective media, such as Sabouraud dextrose agar (SDA) with cycloheximide and chloramphenicol, which inhibit the growth of other molds and bacteria . The colony morphology, pigmentation and microscopic features of Trichophyton fungi can help differentiate them from other dermatophytes or non-dermatophytic molds .

Trichophyton fungi cause dermatophytosis by invading the keratinized tissues of the skin, hair and nails. They secrete enzymes that degrade keratin and allow them to penetrate deeper into the tissue. They also elicit an inflammatory response from the host immune system, which results in symptoms such as itching, scaling, redness, vesicles, pustules, crusts and alopecia . The clinical manifestations of dermatophytosis depend on the site of infection, the species of Trichophyton involved and the host factors. Some of the common types of dermatophytosis caused by Trichophyton are:

• Tinea pedis (athlete`s foot): a fungal infection of the interdigital spaces or the soles of the feet caused by T. rubrum or T. mentagrophytes .
• Tinea corporis (ringworm): a fungal infection of the non-hairy skin of the trunk or limbs caused by various Trichophyton species .
• Tinea capitis (scalp ringworm): a fungal infection of the scalp hair caused by T. tonsurans, T. mentagrophytes or T. violaceum .
• Tinea barbae (barber`s itch): a fungal infection of the beard area caused by T. verrucosum or T. mentagrophytes .
• Tinea unguium (onychomycosis): a fungal infection of the nails caused by T. rubrum or T. mentagrophytes .

The treatment of dermatophytosis caused by Trichophyton involves the use of topical or oral antifungal agents, depending on the severity and extent of the infection. Some of the commonly used antifungal drugs are azoles (e.g. ketoconazole, itraconazole, fluconazole), allylamines (e.g. terbinafine, naftifine), griseofulvin and ciclopirox . The prevention and control of Trichophyton infections require the maintenance of good hygiene, the avoidance of contact with infected individuals or animals, the disinfection of contaminated objects and the prompt diagnosis and treatment of cases .

Trichophyton spp are a group of fungi that cause various skin, hair and nail infections in humans and animals. They belong to the dermatophytes, which are fungi that feed on keratin, a protein found in the outer layer of the skin and its appendages.

Trichophyton spp have a worldwide distribution, but some species are more prevalent in certain regions, such as the tropical and Mediterranean areas. They can survive in different environments, depending on their natural habitat preference. Based on this, there are three types of Trichophyton spp:

• Anthropophilic Trichophyton spp are those that prefer to infect humans and are transmitted from person to person. They cause chronic and mild infections that may persist for a long time. Examples of anthropophilic species are Trichophyton rubrum, Trichophyton tonsurans, Trichophyton violaceum and Trichophyton schoenleinii.

• Zoophilic Trichophyton spp are those that prefer to infect animals and are transmitted from animals to humans or vice versa. They cause acute and severe infections that may elicit an inflammatory or allergic response. Examples of zoophilic species are Trichophyton verrucosum, Trichophyton mentagrophytes, Trichophyton equinum and Trichophyton simii.

• Geophilic Trichophyton spp are those that live in the soil and feed on keratinous debris, such as hair, feathers, hooves and horns. They can infect both humans and animals through contact with contaminated soil or objects. They cause sporadic and mild infections that may heal spontaneously. Examples of geophilic species are Trichophyton ajelloi, Trichophyton terrestre and Trichophyton gypseum.

Like most other fungi, Trichophyton spp thrive in moist and dark environments, such as the inside of shoes, socks, clothes, towels, bedding and carpets. However, they can also survive without human or animal presence and can be found in showers, bathtubs, floors, locker rooms, pools and spas. Their spores can persist for years and are highly resistant to heat, drying and disinfectants.

Trichophyton spp are filamentous fungi that belong to the group of dermatophytes, which are specialized in infecting keratinized tissues such as skin, hair and nails. The morphology of Trichophyton spp varies depending on the species, the growth medium and the temperature. However, some common features can be observed in most of these fungi.

Trichophyton spp produce two types of asexual spores: macroconidia and microconidia. Macroconidia are larger, multicellular, cylindrical or cigar-shaped structures that have thin or thick walls and usually occur in clusters. Microconidia are smaller, unicellular, spherical or pear-shaped structures that are produced on the terminal branches of the hyphae and may occur singly or in groups. Both types of spores are involved in the transmission and infection of Trichophyton spp.

Trichophyton spp also produce spiral-shaped hyphae, which are long and branching filaments that form the mycelium or the vegetative body of the fungus. The hyphae are septate, meaning that they have cross-walls that divide them into segments. The hyphae do not form conidiophores, which are specialized structures for spore production in some other fungi.

The morphology of Trichophyton spp can be observed by microscopic examination of skin scrapings, nail clippings or hair plucks that are treated with potassium hydroxide (KOH) to dissolve the keratin and reveal the fungal elements. Alternatively, the morphology can be studied by culturing the fungus on different media such as Sabouraud dextrose agar (SDA) or dermatophyte test medium (DTM) at room temperature or 37°C for one to three weeks.

The following table summarizes some of the morphological characteristics of selected species of Trichophyton spp:

• Trichophyton spp grow well on Sabouraud Dextrose Agar (SDA) within 2 weeks at room temperature (25°C) producing cylindrical, smooth-walled macroconidia and characteristic microconidia .
• Different growth textures can be seen depending on the type of species, such as cottony, granular, velvety, waxy or smooth .
• Some species produce pigments on the surface or reverse of the colonies, ranging from white, cream, yellow, brown to deep red .
• The formation and morphology of macroconidia and microconidia vary depending on the species, growth medium and temperature . Some examples are:
  • Trichophyton mentagrophytes produces a cottony to granular growth, with grape clusters of spherical microconidia on terminal branches. They also form coiled or spiral hyphae .
  • Trichophyton rubrum develops white, cottony surface and deep red nondiffusible pigment in reverse growth. They produce small pear-shaped microconidia .
  • Trichophyton tonsurans produce a flat, powdery to a velvety colony on the obverse surface that becomes reddish-brown on reverse; with elongated microconidia .
• Trichophyton spp do not form conidiophores . They produce spiral-shaped hyphal structures, from which the conidial spores originate .

Trichophyton is a genus of fungi that includes the parasitic varieties that cause tinea, including athlete`s foot, ringworm, jock itch, and similar infections of the nail, beard, skin and scalp. Trichophyton fungi are molds characterized by the development of both smooth-walled macro- and microconidia. According to current classification, the genus includes anthropophilic and zoophilic species. Anthropophilic fungi prefer to infect humans. Zoophilic fungi prefer to infect animals other than humans. Humans and animals are natural reservoirs for parasitic or dermatophytic fungi.

There are about 20 species of Trichophyton. Although the genus as a whole is considered to be cosmopolitan, only T. rubrum, T. mentagrophytes and T. tonsurans have true worldwide distribution. Some species have a restricted geographic distribution. The following table summarizes some of the most common or important species of Trichophyton and their habitat preference, morphology, cultural characteristics and clinical manifestations.

Trichophyton spp. are dermatophytes, which are fungi that can infect the keratinized tissues of humans and animals, such as the skin, hair, and nails. The pathogenesis of Trichophyton spp. involves several steps:

• Adhesion to the skin or hair: Trichophyton spp. can adhere to the epidermis or hair via a variety of mechanisms, including:

  • Secretion of adhesive proteins: Trichophyton spp. are capable of secreting a variety of adhesive proteins that aid in their attachment to the surface of the epidermis or hair . These proteins may also modulate the host immune response and facilitate fungal invasion.
  • Formation of appressoria: Appressoria are specialized structures that some fungi use to penetrate the host tissue. Trichophyton spp. can form appressoria on the surface of the hair shaft or the stratum corneum, which are then used to exert mechanical pressure and secrete enzymes to breach the host barrier .
  • Interactions with host receptors: Trichophyton spp. can also interact with various host receptors on the surface of keratinocytes, such as integrins, cadherins, and toll-like receptors, which may facilitate fungal adhesion and invasion, as well as modulate the host inflammatory response.

• Invasion of the keratinized tissue: After adhering to the skin or hair, Trichophyton spp. can invade the keratinized tissue by using various strategies, such as:

  • Secretion of keratinases: Keratinases are enzymes that degrade keratin, the main component of the skin, hair, and nails. Trichophyton spp. can secrete different types of keratinases, such as subtilisins, metalloproteases, and cysteine proteases, which enable them to digest and utilize keratin as a nutrient source . Keratinases may also contribute to tissue damage and inflammation.
  • Secretion of other hydrolytic enzymes: In addition to keratinases, Trichophyton spp. can secrete other hydrolytic enzymes, such as lipases, phospholipases, esterases, and elastases, which can degrade various components of the host tissue, such as lipids, phospholipids, esters, and elastin . These enzymes may also play a role in fungal virulence and pathogenicity.
  • Formation of arthroconidia: Arthroconidia are asexual spores that are formed by fragmentation of hyphae. Trichophyton spp. can form arthroconidia within the infected tissue or on the surface of the hair shafts . Arthroconidia can serve as a means of dissemination and transmission of the infection, as well as a source of antigenic stimulation for the host immune system .

• Evasion of host immune response: Trichophyton spp. can evade or modulate the host immune response by using various mechanisms, such as:

  • Secretion of immunomodulatory molecules: Trichophyton spp. can secrete various molecules that can affect the host immune response, such as mannans, glucans, proteases, lipases, phospholipases, melanin, and heat shock proteins. These molecules can interfere with various aspects of innate and adaptive immunity, such as phagocytosis, antigen presentation, cytokine production, T cell activation, and antibody production.
  • Alteration of surface antigens: Trichophyton spp. can also alter their surface antigens by changing their expression levels or modifying their structures. This can help them evade recognition and elimination by the host immune system.
  • Induction of immunological tolerance: Trichophyton spp. can also induce immunological tolerance in some hosts by stimulating regulatory T cells (Tregs), which can suppress the effector T cells and dampen the inflammatory response. This can result in chronic or asymptomatic infections by Trichophyton spp..

The pathogenesis of Trichophyton spp. is influenced by various factors, such as the species and strain of the fungus, the site and extent of the infection, the host susceptibility and immunity, and the environmental conditions . The clinical manifestations of Trichophyton spp. infections depend on these factors, as well as the type of dermatophytosis involved .

The transmission of Trichophyton spp is via direct or indirect contact with an infected individual or through spores. Transmission can be anthropophilic, zoophilic or geophilic .

• Anthrophilic transmission is by direct contact or through fomites, such as contaminated towels, clothing, shared shower stalls. Anthrophilic Trichophytons are those that prefer to infect humans and cause human infections .
• Zoophilic transmission is from animals to the human host. Zoophilic Trichophytons are those that prefer to infect animals other than humans and cause either human or animal infections . Some common animal sources of Trichophyton spp are cattle, horses, dogs, cats, mice, guinea pigs, hedgehogs, monkeys and fowls .
• Geophilic transmission occurs from soil or infected animals into the human host. Geophilic Trichophytons are those that exist in the soil developing on soil decomposing keratinous materials such as hair, feathers, hooves, and horns. Geophilic species may cause both human and animal infections .

Dermatophytosis caused by Trichophyton spp can be contracted through contact with infected humans or animals or with contaminated objects, such as towels, bedding, manicure appliances, and hairbrushes . Furthermore, Trichophyton related skin conditions are frequently spread in areas such as pools, spas, locker rooms, and shared shower facilities.

Trichophyton spp are dermatophytes that cause various types of skin and nail infections, collectively known as tinea or ringworm. The clinical manifestations of Trichophyton spp infections depend on the location of the infection, the species of the fungus, and the host immune response. Some of the common types of Trichophyton spp infections are:

• Tinea corporis: This is an infection of the non-hairy, smooth skin, usually caused by Trichophyton mentagrophytes or Trichophyton rubrum. It is characterized by circular patches with advancing red, vesicular borders and central scaling. The infection is pruritic and may spread to other parts of the body or other people by direct or indirect contact.

• Tinea pedis: This is an infection of the feet, especially the interdigital spaces, usually caused by Trichophyton rubrum or Trichophyton mentagrophytes. It is also known as athlete`s foot and is more common in people who wear occlusive footwear or use communal showers. It is characterized by acute infection associated with itching, redness, vesicles, and maceration, or chronic infection associated with itching, scaling, fissures, and hyperkeratosis. The infection may spread to the toenails or other parts of the body.

• Tinea cruris: This is an infection of the groin, inner thighs, or buttocks, usually caused by Trichophyton rubrum or Trichophyton mentagrophytes. It is also known as jock itch and is more common in men and obese individuals. It is characterized by erythematous scaling lesions in the intertriginous areas, with a well-defined margin and a central clearing. The lesions are pruritic and may spread to the perineum or lower abdomen. The infection may be associated with tinea pedis or tinea unguium.

• Tinea capitis: This is an infection of the scalp hair, usually caused by Trichophyton tonsurans, Trichophyton mentagrophytes, or Microsporum species. It is more common in children and may be transmitted by direct contact with infected humans or animals or by fomites such as combs, hats, or pillows. It is characterized by circular bald patches with short hair stubs or broken hair within hair follicles. The infected hairs may show endothrix (fungus inside hair shaft) or ectothrix (fungus on the surface of hair) invasion under microscopy. Some patients may develop a severe inflammatory reaction known as kerion, which presents as a boggy, tender mass with purulent discharge and regional lymphadenopathy. The infection may be complicated by bacterial superinfection or scarring alopecia.

• Tinea barbae: This is an infection of the beard hair, usually caused by Trichophyton mentagrophytes, Trichophyton rubrum, or Trichophyton verrucosum. It is more common in men who work with animals or soil. It is characterized by edematous, erythematous lesions with pustules and crusts around the hair follicles. The infected hairs may show ectothrix invasion under microscopy. The infection may cause folliculitis, abscess formation, or scarring alopecia.

• Tinea unguium: This is an infection of the toenails or fingernails, usually caused by Trichophyton rubrum or Trichophyton mentagrophytes. It is also known as onychomycosis and is more common in older adults and people with diabetes mellitus, peripheral vascular disease, immunosuppression, or trauma. It is characterized by thickening or crumbling of the nail plate distally; discoloration; loss of luster; separation of the nail from the nail bed; accumulation of debris under the nail; and pain or discomfort. The infection may be associated with tinea pedis or tinea corporis.

• Trichophytid reaction: This is a hypersensitivity reaction to the antigens produced by the fungus, which may occur in some patients with dermatophytosis. It presents as an allergic dermatitis, usually on the hands, with vesicles, papules, or pustules that are not infected by the fungus. The diagnosis is confirmed by a positive skin test to trichophytin antigen. The treatment is to eliminate the primary source of infection and to use antihistamines or corticosteroids for symptomatic relief.

• Specimen: Skin scrapings, nail scrapings, hair plucks
• Microscopic Examination: 10–20% potassium hydroxide, with or without calcofluor white, and the specimens skin or nails or hair. Generally, Trichophyton shows branching hyphae or chains of arthroconidia (arthrospores) in skin or nail samples. In hairs, Trichophyton tonsurans and Trichophyton violaceum are observed by the production of arthroconidia inside the hair shaft (endothrix)
• Cultural Examination: Using inhibitory mold agar or SDA medium containing cycloheximide and chloramphenicol which suppresses mold and bacterial growth. Growth is observed within 1-3 weeks at room temperature. On SDA medium, Trichophytons produce a cottony growth, or velvety, depending on the species. Macroconidia and microconidia develop ranging in size, shape, and occurrence depending on the species of Trichophyton.
• Molecular Examination: PCR tests can be used to detect specific species of Trichophyton such as Trichophyton rubrum, Trichophyton mentagrophytes, and Trichophyton tonsurans. These tests are based on the amplification of specific DNA regions such as the internal transcribed spacer (ITS) region or the chitin synthase 1 (CHS1) gene. PCR tests can provide rapid and accurate identification of dermatophyte infections.

Trichophyton infections usually require antifungal drugs to relieve symptoms and prevent spread to others. The choice of antifungal drug depends on the type and severity of the infection, the causative species, and the patient`s age and health status.

For skin infections (tinea corporis, tinea pedis, tinea cruris, tinea faciei, tinea manuum), topical antifungals such as creams, lotions, sprays, or powders are often effective. Commonly used topical antifungals include clotrimazole, miconazole, ketoconazole, terbinafine, and naftifine. These agents are applied to the affected area once or twice daily for 2 to 4 weeks or until the infection clears. Some topical antifungals are available over-the-counter, while others require a prescription.

For scalp infections (tinea capitis) and nail infections (tinea unguium or dermatophyte onychomycosis), oral antifungals are usually needed because topical agents do not penetrate deeply enough into the hair follicles or nail plates. Oral antifungals include griseofulvin, terbinafine, itraconazole, and fluconazole. These agents are taken by mouth for several weeks to months depending on the infection and the drug. Oral antifungals require a prescription and may have side effects such as liver toxicity, gastrointestinal upset, rash, headache, or drug interactions. Therefore, patients taking oral antifungals should be monitored by their healthcare providers and follow the instructions carefully.

The most common cause of fungal nail infections (onychomycosis) is Trichophyton rubrum. Oral terbinafine is considered the first-line treatment for most infections caused by this organism. However, cases of terbinafine-resistant T. rubrum are increasingly being reported worldwide . In these cases, alternative oral antifungals such as itraconazole or fluconazole may be used. Alternatively, topical antifungals such as ciclopirox or amorolfine may be applied to the nails in combination with oral therapy or alone for mild infections.

Trichophyton indotineae is a dermatophyte species that often has genetic mutations that make it resistant to antifungal drugs. It causes severe and difficult-to-treat skin infections that may cover large regions of the body. Although cases seem to be rare outside of India, researchers have reported cases in Europe and North America . Treatment of T. indotineae infections may require a combination of oral and topical antifungals with different mechanisms of action. For example, a case report from Canada described a successful treatment of T. indotineae infection with oral terbinafine and topical luliconazole .

In addition to antifungal therapy, patients with Trichophyton infections should also practice good hygiene and avoid sharing personal items such as towels, clothing, shoes, or hairbrushes with others. Infected skin or nails should be kept clean and dry and covered with a bandage if possible. Infected hair should be cut short or shaved if feasible. Patients should also wash their hands frequently and avoid scratching or touching the infected areas to prevent spreading the infection to other parts of the body or to other people.

Trichophyton infections can be prevented and controlled by following some simple measures:

• Maintain proper hygiene and keep the skin dry and clean
• Avoid sharing clothing, towels, bedding, hairbrushes, or other personal items with people or animals who have ringworm
• Wash clothes in hot water with fungicidal soap after suspected exposure to ringworm
• Avoid walking barefoot in public places; wear protective shoes or sandals in locker rooms, pools, or beaches
• Avoid touching pets with bald spots or skin lesions; consult a veterinarian if you suspect your pet has ringworm
• Use topical antifungal creams or shampoos as directed by your healthcare provider if you have ringworm on the skin or scalp
• Take oral antifungal drugs as prescribed by your healthcare provider if you have ringworm on the nails or severe skin infections
• Follow the full course of treatment and do not stop taking the medication without consulting your healthcare provider
• Seek medical attention if your symptoms do not improve or worsen after treatment

There is currently no approved vaccine for humans against Trichophyton infections. However, there is an inactivated vaccine for horses, dogs, and cats that provides temporary protection against some Trichophyton and Microsporum species. This vaccine may be useful for animals that are at high risk of exposure to ringworm.

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