Trichophyton interdigitale is a widespread fungus belonging to the group of dermatophytes, which are specialized to feed on keratin. It is a common cause of superficial fungal infections in humans, frequently isolated as a pathogen responsible for various skin, hair, and nail conditions.
Biological Characteristics and Reservoirs
T. interdigitale is classified within the Trichophyton genus, which contains many species capable of causing infections. It is an anthropophilic species, meaning its primary reservoir is human hosts, with transmission occurring mainly from person to person.
In a laboratory setting, colonies typically present a white or cream color with a powdery or suede-like texture. Microscopically, the fungus is characterized by numerous subspherical microconidia. A distinguishing metabolic feature is its ability to produce the enzyme urease, often used for laboratory differentiation.
Clinical Manifestations of Infection
Infections caused by T. interdigitale are referred to as tinea, the term for dermatophyte infections across different body sites. The fungus is most associated with Tinea pedis (Athlete’s foot), particularly the interdigital form affecting the spaces between the toes. This presentation typically involves scaling, maceration, and fissuring, which can lead to discomfort and itching.
Another presentation is the vesicular type of Tinea pedis, manifesting as blisters or vesicles on the soles or sides of the feet. These inflammatory lesions may also contain pustules. The fungus can also infect the groin, causing Tinea cruris (jock itch), which presents as a red, itchy rash in the skin folds.
On the rest of the body, the infection is known as Tinea corporis (ringworm), typically forming circular patches with raised, scaly borders. T. interdigitale is also a known cause of onychomycosis, a fungal infection of the nails, especially the toenails. This infection can lead to discoloration and thickening of the nail.
Modes of Transmission and Susceptibility
Transmission is highly effective in environments that facilitate the transfer of skin scales. Because it is anthropophilic, the most common route is direct skin-to-skin contact with an infected person. Indirect transmission through contaminated surfaces (fomites) is also a significant factor in its spread.
The fungus thrives in moist, warm environments, making public spaces like communal showers, swimming pool decks, and locker rooms frequent sources of infection. Walking barefoot in these areas increases the risk of acquiring fungal spores. The pathogen can persist on objects such as shared towels, bedding, and clothing, acting as a reservoir for new infections.
Several risk factors increase susceptibility following exposure. Excessive sweating (hyperhidrosis) creates the damp, humid environment that allows the fungus to flourish. Occlusive footwear, such as heavy boots or non-breathable sneakers, traps moisture and heat, promoting fungal growth. Minor skin trauma, such as cuts or abrasions, provides an entry point for colonization. Individuals with compromised immune systems or conditions like diabetes also have heightened vulnerability.
Identification and Management Strategies
Diagnosis usually begins with a physical examination and is confirmed through laboratory testing. A common initial step is the potassium hydroxide (KOH) preparation, where skin scrapings are examined under a microscope for fungal filaments (hyphae). While microscopy confirms the presence of a dermatophyte, a fungal culture is often necessary to definitively identify the species as T. interdigitale.
Species identification can be complex due to the close relationship between T. interdigitale and other members of the T. mentagrophytes complex. Accurate differentiation is important for guiding treatment, especially with the emergence of antifungal-resistant strains.
For mild, localized infections, management involves applying topical antifungal medications, such as allylamines (terbinafine) and azoles (clotrimazole). Systemic (oral) antifungal agents are reserved for severe, chronic, or widespread infections, and for all cases involving the nail. Oral medications circulate throughout the body to reach deep-seated fungal elements.
Alongside medical treatment, maintaining strict hygiene practices is a significant component of management and prevention. Keeping the skin dry, especially between the toes, is paramount to inhibit fungal growth. Regularly changing socks, wearing breathable footwear, and avoiding walking barefoot in public, wet areas are effective measures to prevent recurrence and limit spread.