Dermatophytes Flashcards
What are dermatophytes? What are their infections called?
molds that infect only keratinized epidermal structures, like superficial skin, hair, feathers, horns, hooves, claws, or nails
ringworm, or dermatophytosis
What state do dermatophytes take in culture?
non-parasitic state - produces septate, branching hypahe collectively called mycelium
What asexual reproductive units are present in dermatophytes in their non-parasitic stage? What are they able to develop?
conidia are found in the aerial mycelium
- microconidia
- macroconidia
What are the 5 possible hyphal characteristics of dermatophytes in their non-parasitic state?
- spirals
- nodules
- rackets
- chandeliers
- chlamydioconidia (chlamydiospores)
What is present when dermatophytes are in their parasite stage? What is absent?
only hyphae, arthroconidias (arthrospores), and other asexual reproductive units
sexual spores (ascospores)
What are the 3 important genera of dermatophytes? What traditional culture medium is used for isolation?
- Microsporum (M. canis, gypseum, audouinii)
- Trichophyton - animals (T. tonsurans, mentagrophytes, rubrum)
- Epidermophyton - humans
Saboroud’s dextrose agar
What is unique about Microsporum canis presentation in the skin and hair?
produces a fluorescence visible under UV light (366nm, Wood’s light)
- does not fluoresce in culture
Features of Dermatophyte genera:
How are dermatophytes transmitted? What enzymes are responsible for their pathogenesis?
direct and indirect contact
proteolytic enzymes, like elastase, collagenase, and keratinase, cause inflammation with high iron influx used for fungal growth
What is the pathogenesis of dermatophytes?
- infectious unit (conidium) enters the skin through a defect in the stratum corneum
- germ tube and hyphae branches develop into arthroconidia
- shows growth pattern in hairless skin
- invades hair (ringworm) and germinates with spore formation
- hyphal strand grow along the hair
How does the location of growth of dermatophytes compare?
ECTOTHRIX = accumulation of arthroconidia outside hair shaft
ENDOTHRIX = accumulation of arthroconidia inside hair shaft
Dermatophyte pathogenesis:
Dermatophytes and animal hosts:
Dermatophytes and nature of lesions:
How does ringworm infection typically progress? What animals are most susceptible?
normally regressed spontaneously, unless there is a secondary bacterial infection
- young animals
- animals in crowded conditions
What is decisive in protection and recovery from ringworm? What immunological response can occur?
cellular immune response
- humoral immune response has a limited role
antibody-mediated and cellular-mediated hypersensitivities
What vaccine has been used for ringworm?
mycelial T. verrucosum vaccine has been used in Europe on cattle
How can a patient be diagnosed with ringworm without requiring laboratory diagnosis? What type of samples are recommended for direct microscopy? What stain is used?
M. canis and M. audouini may emit fluorescence under a Wood’s lamp
skin scraping and hair samples for hyphae and arthroconidia + 10-20% KOH
lactophenol cotton blue
How are dermatophytes typically cultured? What is the target of PCR?
Sabourand’s dextrose agar at 25 degrees C, up to 4 weeks
chitin synthase 1 gene
What are the most common treatments for ringworm?
topical and systemic
- miconazole
- econazole
- ketoconazole
- itraconazole
- thiobendazole
How is ringworm infection controlled?
- disinfection of utensils, equipment, and facilities
- screen animals with Wood’s lamp (ectothrix spores = green)
Where are most human ringworm infections acquired?
Microsporum canis from animals (pets)
- causes 98% of feline and 70% of canine cases of ringworm in North America
How does feline and canine ringworm present?
FELINE: subclinical
CANINE: alopecia around the nose, eyes, and ears, but can become generalized
How does Microsporum canis grow on medium?
white to buff in color with characteristic yellow to orange-brown reverse
Ringworm, feline:
M. canis
Ringworm, canine:
M. canis
How does Microsporum gypseum presentation compare to others in the genera?
- produces large ectrothrix spores in low numbers, so fluoresence is absent or dull
- colonies grow fast, producing a flat, powdery, buff to cinnamon brown surface with pale to yellow to tan reverse
Ringworm, horse:
M. gypseum
Microsporum canis vs. Trichophyton verrucosum vs. Microsporum nanum:
What is Trichophyton erinacei associated with? What is characteristic of hair invasion?
ringworm in hedgehogs, mice, rats, dogs, and humans
ectothrix
What is Tichophyton equinum associated with? What animals are most susceptible? What is characteristic of hair invasion?
ringworm in horses, donkeys, and occasionally dogs
foals and yearlings - swellings, small inflamed ulcers with exudate (girth itch), alopecia
large ectothrix spores
What is the primary cause of ringworm in cattle? What does it produce?
Trichophyton verrucosum
very large ectothrix spore chains
How does infected humans and cattle with Trichophyton verrucosum compare? How do colonies grow?
- HUMAN: no fluorescence
- CATTLE: fluoresces
slow growing, heaped, deeply folded, white-yellow —> unlike other dermatophytes, it grows best at 37 degrees C
What is characteristic of Epidermophyton floccosum infection? Does it fluoresce under Wood’s lamp?
infects only skin and nails of humans
NO - hair is not attacked
