Trichophyton ment. var interdigitale
Summary
Trichophyton mentagrophytes var. goetzii and Trichophyton mentagrophytes var. interdigitale have recently been reclassified as the same species, T. interdigitale. T. interdigitale is, along with T. rubrum, the most common cause of dermatophytosis in humans, a highly prevalent infectious disease. T. interdigitalis causes tinea pedis and onychomycosis predominantly. Trichophyton allergens have been implicated in the pathogenicity of both atopic and allergic airway disease. The route of exposure has not been elucidated. Three T. interdigitalis allergens are currently recognized.
Epidemiology
Worldwide distribution
Trichophyton mentagrophytes and T. rubrum are the most common pathogens associated with onychomycosis. However, some geographical variation is reported; in Libya, the most common cause of onychomycosis in women is yeasts of the genus Candida, whereas in men, it is T. violaceum, T. rubrum, T. mentagrophytes and Microsporum canis.
The epidemiology of anthropophilic T. interdigitale strains are similar to that of T rubrum. T. interdigitale is the cause of 4–8% of infections in Europe. An analysis of Trichophyton spp. contaminating nail dust from salons in different regions of Australia found that T. interdigitale was the most prevalent dermatophyte. Thought to be associated with the widespread abuse of topical steroid-containing creams, the underlying cause is widely reported as T. interdigitale. ITS analysis, however, has shown it is T. mentagrophytes.
A link between allergic skin disease and dermatophyte infection has been proposed. One study found a 79% prevalence of sensitization to Trichophyton spp. amongst patients with concurrent allergic skin disease and dermatophyte infection termed atopic-chronic dermatophytosis syndrome. This observation supports the findings of a controlled prospective trial from China, which found that 84.9% of patients with chronic urticaria and dermatophytosis were sensitized (as determined by skin prick test) to T. mentagrophytes.
Route Of Exposure
Main
The primary route of exposure to Trichophyton spp. is not fully understood. Sensitization to Trichophyton-specific allergen is common in patients with clinical dermatophytosis, suggesting hypersensitivity is due to transdermal contact with the allergen. However, there is evidence that Trichophyton hypersensitivity may also play a role in late-onset asthma and allergic rhinitis and that route of exposure may be inhalation, particularly in those patients with no concurrent dermatophytosis. Alternatively, Trichophyton spp. allergens may elicit hypersensitivity through a yet-to-be described mechanism.
Clinical Relevance
Trichophyton spp. allergens have been implicated in the pathogenesis of atopic dermatitis, late-onset asthma and allergic rhinitis. Trichophyton-specific allergens have been shown to have the unusual capacity to induce either immediate- (ITH) or delayed- (DTH) type hypersensitivity. In some patients, both immune responses are induced. The type of immune response induced is strongly associated with the clinical profile of dermatophyte disease. Whereas DTH is associated with acute inflammatory dermatophytosis with resolution, ITH results in persistent low-grade infection. It is proposed this is a dysregulated immune response and the mechanism for the association between chronic dermatophytosis and clinical hypersensitivity. This is supported by evidence of monosensitivity to dermatophyte antigens in patients with ”intrinsic” asthma. Furthermore, sensitization to Trichophyton spp. allergens is a possible risk factor for more severe disease amongst patients with asthma. T. mentagrophytes has also been implicated as an allergen in a small subgroup of patients with cholinergic urticaria.
Cross-Reactivity
A study found that a significant number of patients with allergic bronchopulmonary aspergillosis and Aspergillus-sensitized asthma were sensitized to T. mentagrophytes var. goetzii, indicating the possibility that patients are erroneously diagnosed with sensitivity to Aspergillosis spp. allergens. Furthermore, a study from China has demonstrated sensitization to T. mentagrophytes (as well as E. flocculosum and T. rubrum) in T. rubrum culture-positive patients, indicating cross-reactivity between the three dermatophytes.
References
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