Questions and Answers
What is the term for the allergic manifestations that occur in the course of dermatophytosis?
Dermatophytids or Trichophytid reaction
What is the significance of a positive trichophytin skin test?
It indicates immediate or delayed type hypersensitivity to dermatophytic antigens
What type of specimen is collected for diagnostic laboratory tests of dermatophytosis?
Scrapings from both skin and nails, plus hairs plucked from involved areas
What is observed under a Wood's lamp in a darkened room in Microsporum-infected hairs?
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What is the purpose of potassium hydroxide (KOH) in microscopic examination of dermatophytosis?
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What type of fungal structure is seen in Microsporum species in hair?
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What is the medium used for culturing dermatophytic fungi?
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What is the purpose of identifying the colonial morphology of dermatophytic fungi in culture?
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What is the primary goal of therapy in dermatophytosis?
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What is the name of the antifungal agent that is used to treat dermatophytosis and is obtained from a species of Penicillium?
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Study Notes
Organization of Fungal Disease
Classification of Mycoses
- Cutaneous mycoses: caused by Microsporum, Trichophyton, and Epidermophyton
- Subcutaneous mycoses: caused by Sporothrix schenkii
- Systemic mycosis: caused by Cryptococcus neoformans, Coccidioides immitis, Histoplasma capsulatum, Candida spp., and Aspergillus spp.
Cutaneous Fungal Infections
Dermatophytoses
- Also known as "ringworm" disease
- Caused by fungi called dermatophytes
- Affects the nails, hair, and stratum corneum of the skin
- Characterized by a circular, ring-like lesion with a scaly, itchy surface
Dermatophytes
- Molds that produce keratinase and use keratin as a nutrient source
- Colonize only dead layers of skin, nails, and hair
- Do not infect living tissues
- Classified into three groups: anthropophilic, zoophilic, and geophilic
Classification of Dermatophytes
- Anthropophilic: infect humans, transmitted by human contact or infected objects
- Zoophilic: infect animals, transmitted by contact with animals or their products
- Geophilic: soil fungi, transmitted to humans via exposure to soil or dusty animals
Examples of Dermatophytes
- Epidermophyton floccosum: causes skin and nail infections, globally distributed
- Trichophyton mentagrophytes: causes skin, hair, and nail infections, globally distributed
- Microsporum gypseum: causes skin and hair infections, globally distributed
- Microsporum canis: causes skin and hair infections in dogs and cats
Clinical Manifestations of Ringworm Infections
- Tinea capitis: ringworm infection of the head, scalp, eyebrows, and eyelashes
- Tinea corporis: ringworm infection of the body (smooth skin)
- Tinea cruris: ringworm infection of the groin (jock itch)
- Tinea unguium: ringworm infection of the nails
- Tinea barbae: ringworm infection of the beard
- Tinea manuum: ringworm infection of the hand
- Tinea pedis: ringworm infection of the foot (athlete's foot)
Diagnostic Laboratory Tests
- Specimens: scrapings from skin and nails, plus plucked hairs from involved areas
- Microscopic examination: detects branching hyphae or chains of spores
- Culture: Sabouraud's agar specimen incubated for 1-3 weeks at room temperature
- Identification: based on colonial morphology, microscopic morphology, and species-specific characteristics
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