Clinical Significance of Dermatophytes and Their Pathogenesis

Review Article

Austin J Infect Dis. 2023; 10(2): 1085.

Clinical Significance of Dermatophytes and Their Pathogenesis

Shyama Datt*; Thakur Datt

Department of Microbiology, UCMS & GTB Hospital, India

*Corresponding author: Shyama Datt Department of Microbiology, UCMS & GTB Hospital, Dilshad Garden, Delhi-95, India. Email: shyama.mathura@gmail.com

Received: May 31, 2023 Accepted: June 24, 2023 Published: July 01, 2023

Abstract

Despite the superfi cial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identifi cation of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes.

Keywords: Dermatophytes; Pathogenesis; Trichophyton; Microsporum; Ergosterol

Introduction

Dermatophytes

Infections pertaining to mankind particularly those affecting the keratinized tissues are of serious concerns worldwide and are increasing on a global scale. Dermatomycoses are infections of the skin, hair and nail caused as a result of colonization of the keratinized layers of the body. This colonization is brought about by the organisms belonging to the three genera namely Trichophyton, Microsporum and Epidermophyton [1,2]. Due to their high affinity for the keratinized tissues, dermatophytes are responsible for most of superficial mycosis affecting human skin or nails.

Classification

Dermatophytes are fungi that invade and multiply within keratinized tissues (skin, hair, and nails) causing infection [1]. Based upon their genera, Dermatophytes can be classified into three groups: Trichophyton (which causes infections on skin, hair, and nails), Epidermophyton (which causes infections on skin and nails), and Microsporum (which causes infections on skin and hair). Based upon the mode of transmission, these are been classified as anthropophillic, zoophilic, and geophilic. Finally, based upon the affected site, these are been classified clinically into tinea capitis (head), tinea faciei (face), tinea barbae (beard), tinea corporis (body), tinea manus (hand), tinea cruris (groin), tinea pedis (foot), and tinea unguium (nail). Other clinical variants include tinea imbricata, tinea pseudoimbricata, and Majocchi granuloma [3].

Trichophyton: The genus Trichophyton includes 24 species. The colonies on agar media are powdery, velvety or waxy. The predominant spore type is micro conidia with sparse macro conidia [4].

Microsporum: The genus Microsporum includes 16 species. The colony morphology of Microsporum species on agar surface is either velvety or powdery with white to brown pigmentation [4].

Epidermophyton: The genus Epidermophyton includes only 2 species. The colonies are slow-growing, powdery and unique brownish yellow in colour. This genus is devoid of micro conidia. Macro conidia are abundant and produced in clusters [4].

Distribution Frequency of Dermatophytes and Dermatophytosis

All the three genera of Dermatophytes namely Trichophyton, Microsporum and Epidermophyton are worldwide in geographical distribution. The predominant cause of Dermatophytic infections is Trichophyton followed by Epidermophyton and Microsporum. Within the genus Trichophyton, Trichophyton rubrum is the predominant etiological agent accounting for 69.5% followed by Trichophyton mentagrophytes, Trichophyton verrucosum and Trichophyton tonsurans [5-7].

According to the World Health Organization (WHO) survey on the incidence of dermatophytic infection, about 20% the people worldwide present with cutaneous infections [8].

Pathogenesis and Clinical Presentation

The possible route of entry for the Dermatophytes into the host body is injured skin, scars and burns. Infections caused by arthrospores or conidia. Resting hairs lack the essential nutrient required for the growth of the organism. Hence, these hairs not invaded during the process of infection [22].

The pathogen invades the uppermost, non-living, keratinized layer of the skin namely the stratum corneum, produces exo-enzyme keratinase and induces inflammatory reaction at the site of infection [23-26]. The customary signs of inflammatory reactions such as redness (ruber), swelling (induration), are seen at the infection site. Inflammation causes the pathogen to move away from the site of infection and take residence at a new site. This movement of the organism away from the infection site produces the classical ringed lesion [27].

The infections caused by Dermatophytes commonly referred to as “tinea” or “ring-worm” infections due to the characteristic ringed lesions [9]. Based on the site of infection, the tinea infections are referred to as tinea capitis (scalp), tinea corporis or tinea circinata (non-hairy, glaborous region of the body), tinea pedis (“Athletes’ foot”; foot), tinea ungium (“Onychomycosis”; nail), tinea mannum (hands) (Figure 3), tinea barbae (“Barbers’ itch”; bearded region of face and neck), tinea incognito (steroid modified), tinea imbricata (modified form of tinea corporis), tinea gladiatorial (common among wrestlers’) and tinea cruris (“Jocks’ itch”; groin) [10].