Dermatophytes: Difference between revisions

Latest revision as of 16:48, 2 January 2024

Background

Microbiology

Dermatophytes are molds that cause superficial skin, hair, and nail infections
The four most common genera Epidermophyton, Microsporum, Trichophyton, and Nannizzia
Fungi may be anthropophilic, zoophilic, or geophilic (soil origin)

Epidemiology

Risk depends on the specific mold and its natural environment (humans, animals, or soil)

Anthropophilic Dermatophytes

Most common worldwide is Trichophyton rubrum
Others include Trichophyton concentricum, Trichophyton interdigitale, Trichophyton schoenleinii, Trichophyton soudanense, Trichophyton tonsurans, Trichophyton violaceum, Microsporum audouinii, Microsporum ferrugineum, and Epidermophyton floccosum
Risk factors include areas where people share common facilities, such as military camps and factories

Zoonotic Dermatophytes

Of zoonotic dermatophytes, Microsporum canis is the most common worldwide
Other zoonotic dermatophytes include Trichophyton benhamiae (guinea pigs), Trichophyton erinacei (hedgehogs), Trichophyton quinum (horses), Trichophyton mentagrophytes (rodents), Trichophyton quinckeanum (mice), Trichophyton simii (monkeys), Trichophyton verrucosum (cattle ringworm), Nannizzia nana (pigs), and Nannizzia persicolor (bank voles)

Geophilic

Uncommon causes of disease
Nannizzia gypseum is more common in western Pacific and Central America
More common in gardeners and farmers

Clinical Manifestations

Ringworm
- Most active form is in the periphery of the ring
- Can invade immunocompromised patients, e.g. Majocchi's granuloma and kerion
Named by anatomic location
- Tinea capitis: scalp hair
- Tinea barbae: beard hair
- Tinea faciei: face
- Tinea corporis: body
- Tinea cruris: groin
- Tinea unguium or onychomycosis: nails
- Tinea manuum: hand

Diagnosis

Specimen Collection

Hair: need the root, with sterile forceps
Skin: disinfect with alcohol or sterile water, then scrape the border with a blunt scalpel
Nails: alcohol gauze to clean, then scrape subungual debris

Laboratory Testing

Direct microscopy: KOH (potassium hydroxide) calcofluor of skin scraping, under UV light
Culture with Littman agar w streptomycin, Sabouraud agar with chloram+gent, Sabouraud agar with CG+cyclohexamide
- Incubate for 2-3 weeks at 30ºC

Identification

Chemical properties
- Growth at 37ºC
- Urease production/urea hydrolysis
- BCP-MSG reaction (important)
- Hair perforation test
- Vitamin requirements with trichophyton agars T1 to T7
- Growth on polished rice grain
Colony features
- Speed of growth
- Colour on surface
- Texture
- Colour on reverse
Microscopic features
- Macroconidia, microconidia, septae

Management

Nystatin is ineffective
Management can be with either topical or systemic antifungals, including azoles (primarily itraconazole or fluconazole), allylamines, budenafine, ciclopirox, tonaftate, amorolfine, terbinafine

Some commonly-used systemic antifungals
Antifungal	Dose	Duration
Antifungal	Dose	Tinea pedis	Tinea corporis or cruris
terbinafine	250 mg once daily	2 weeks	1 to 2 weeks
itraconazole	200 mg twice daily	1 week	1 week
fluconazole	150 mg once weekly	2 to 6 weeks	2 to 4 weeks

@@ Line 1: / Line 1: @@
-= Dermatophytes =
+== Background ==
+=== Microbiology ===
+* Dermatophytes are molds that cause superficial skin, hair, and nail infections
+* The four most common genera ''[[Epidermophyton]]'', ''[[Microsporum]]'', ''[[Trichophyton]]'', and ''[[Nannizzia]]''
+* Fungi may be anthropophilic, zoophilic, or geophilic (soil origin)
+=== Epidemiology ===
-== Species and Classification ==
+* Risk depends on the specific mold and its natural environment (humans, animals, or soil)
+=== Anthropophilic Dermatophytes ===
-* Three common genii:
+* Most common worldwide is ''[[Trichophyton rubrum]]''
-** Epidermophyton
+* Others include ''[[Trichophyton concentricum]]'', ''[[Trichophyton interdigitale]]'', ''[[Trichophyton schoenleinii]]'', ''[[Trichophyton soudanense]]'', ''[[Trichophyton tonsurans]]'', ''[[Trichophyton violaceum]]'', ''[[Microsporum audouinii]]'', ''[[Microsporum ferrugineum]]'', and ''[[Epidermophyton floccosum]]''
-** Microsporum
+* Risk factors include areas where people share common facilities, such as military camps and factories
-** Trichophyton
-* Three categories: anthropophilic, zoophilic, and geophilic
+=== Zoonotic Dermatophytes ===
-== Presentation ==
+* Of zoonotic dermatophytes, ''[[Microsporum canis]]'' is the most common worldwide
+* Other zoonotic dermatophytes include ''[[Trichophyton benhamiae]]'' (guinea pigs), ''[[Trichophyton erinacei]]'' (hedgehogs), ''[[Trichophyton quinum]]'' (horses), ''[[Trichophyton mentagrophytes]]'' (rodents), ''[[Trichophyton quinckeanum]]'' (mice), ''[[Trichophyton simii]]'' (monkeys), ''[[Trichophyton verrucosum]]'' (cattle ringworm), ''[[Nannizzia nana]]'' (pigs), and ''[[Nannizzia persicolor]]'' (bank voles)
+=== Geophilic ===
-* Clinical presentation is usually ringworm
+* Uncommon causes of disease
-** Most active form in the periphery of the ring
+* ''[[Nannizzia gypseum]]'' is more common in western Pacific and Central America
+* More common in gardeners and farmers
+== Clinical Manifestations ==
+* '''Ringworm'''
+** Most active form is in the periphery of the ring
 ** Can invade immunocompromised patients, e.g. Majocchi's granuloma and kerion
 * Named by anatomic location
-** Tinea capitis: head
+** Tinea capitis: scalp hair
+** Tinea barbae: beard hair
+** Tinea faciei: face
 ** Tinea corporis: body
 ** Tinea cruris: groin
-** Tinea unguun: nails
+** Tinea unguium or [[onychomycosis]]: nails
+** Tinea manuum: hand
 == Diagnosis ==
+=== Specimen Collection ===
-=== Specimen collection ===
 * Hair: need the root, with sterile forceps
 * Skin: disinfect with alcohol or sterile water, then scrape the border with a blunt scalpel
@@ Line 29: / Line 42: @@
 === Laboratory Testing ===
 * Direct microscopy: KOH (potassium hydroxide) calcofluor of skin scraping, under UV light
 * Culture with Littman agar w streptomycin, Sabouraud agar with chloram+gent, Sabouraud agar with CG+cyclohexamide
 ** Incubate for 2-3 weeks at 30ºC
-=== Indentification ===
+=== Identification ===
 * Chemical properties
 ** Growth at 37ºC
@@ Line 50: / Line 61: @@
 * Microscopic features
 ** Macroconidia, microconidia, septae
+== Management ==
+* Nystatin is ineffective
+* Management can be with either topical or systemic antifungals, including [[azoles]] (primarily [[itraconazole]] or [[fluconazole]]), [[allylamines]], [[budenafine]], [[ciclopirox]], [[tonaftate]], [[amorolfine]], [[terbinafine]]
+{| class="wikitable"
+|+Some commonly-used systemic antifungals
+! rowspan="2" |Antifungal
+! rowspan="2" |Dose
+! colspan="2" |Duration
+|-
+!Tinea pedis
+!Tinea corporis or cruris
+|-
+|[[terbinafine]]
+|250 mg once daily
+|2 weeks
+|1 to 2 weeks
+|-
+|[[itraconazole]]
+|200 mg twice daily
+|1 week
+|1 week
+|-
+|[[fluconazole]]
+|150 mg once weekly
+|2 to 6 weeks
+|2 to 4 weeks
+|}
+[[Category:Fungi]]
+[[Category:Skin and soft tissue infections]]
+[[Category:Rashes and skin lesions]]