Dermatophytes: Difference between revisions

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

Latest revision as of 12:48, 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

Zoonotic Dermatophytes

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

Some commonly-used systemic antifungals
Antifungal Dose 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
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