Unit 4 - Dermatophytes, Genus Trichophyton, and Genus Microsporum Flashcards
What is another name for Dermatophytosis?
ringworm
What are dermatophytoses?
superficial fungal infections involving the keratinized layers of the skin and its appendages
What layers of the skin do Dermatophytes penetrate?
all layers of the skin but are generally restricted to the non-living cornefied layers
What are the general characteristics of a dermatophyte infection?
- Spreads from a single point 2. Have invasion of hair and skin 3. Organism is unable to survive the inflammatory reaction and moves peripherally creating the classical ringed lesions of alopecia with central healing and peripheral inflammation
What are infections with Dermatophytes called?
dermatophytosis
How are Dermatophytes characterized?
based on their asexual stages or on their habitat
What are the three ‘form’ genera of Dermatophyte asexual organisms?
Microsporum, Trichophyton, and Epidermophyton
What is the perfect state for Microsporum and Trichophyton?
Arthroderma
What is the perfect state for Epidermophyton?
there is none
What are the different habitats that Dermatophytes are characterized based on?
geophilic, zoophilic, and anthrophilic
Where do geophilic Dermatophytes live?
they inhabit soil and are free-living saprophytes that infect animals or humans
Where do zoophilic Dermatophytes live?
they are normally found as parasites of animals
Where do anthropophilic Dermatophytes live?
they are parasites of humans
How do Dermatophytes cause clinical disease?
they hydrolyze keratin and damage the epidermis and hair follicles
What is a major component of lesions caused by Dermatophytes?
hypersensitivity
How is Dermatophytosis diagnosed?
gross exam for fluorescence with the Wood’s lamp, direct exam (KOH mounts), culture (SGA), and Lactophenol Cotton Blue mounts
Where should you collect Dermatophytes from?
Collect from the margins of the lesions
Generally what are Dermatophytes characterized by?
rate of growth, color of the colony, surface texture, surface topography, and presence and characteristics of their macroconidia, microconidia, and other specialized structures
Generally, what are Microsporum characterized by the presence of?
macroconidia and a lack of microconidia
Microsporum canis var canis is ______ but often attacks humans, especially children.
zoophilic
70% of canine dermatophytosis is caused by _____ ______.
Microsporum canis
What is infection by Microsporum canis var canis the most severe in?
dogs
What part of the body is most affected by Microsporum canis var canis?
the head - alopecia around the eyes, nose, and ears
How is Microsporum canis var canis diagnosed?
via direct exam and KOH
What does Microsporum canis var canis grow on?
SGA in 1 week
What does Microsporum canis var canis look like on SGA?
it has a flat, thin to velvetly white surface; radiating border, pale yellow to deep yellow reverse
What is the morphology of Microsporum canis var canis?
it usually has numerous spindle shaped macroaleurispores on primary isolation
How is Microsporum canis var canis treated?
griseofulvin and topicals
What is Microsporum canis var distortum?
a zoophilic dermatophyte similar to var canis but much less common - seen in mopnkeys but now dogs as well
What is the perfect state of Microsporum gypseum?
Arthroderma gypseum
What does Microsporum gypseum cause?
dermatophytosis in dogs, cats, horses, humans, and many other animals
What is the ideal media for Microsporum gypseum?
SGA
What do colonies of Microsporum gypseum look like?
white with rapid conversion to a buff or cinnamon brown surface - older colonies become rapidly pleomorphic and are white, reverse of the colony is a pale yellow to tan and occasionally red in some isolates
What is the morphology of Microsporum gypseum?
macroconidia are very numerus, they are large, rough, thin walled, most commonly have 4-6 cells, echinulate
What is the perfect state name of Microsporum nanum?
Arthroderma obtusum
What does Microsporum nanum cause?
dermatophytosis in pigs and rarely humans
What does Microsporum nanum grow on?
SGA
What does the colony of Microsporum nanum look like?
it is white, velvety, becoming buff and finely granular in 2 weeks
What is the morphology of Microsporum nanum?
numerous pear-haped macroconidia with 1-3 cells
What does Microsporum gallinae cause?
chicken favus
What does Microsporum persicolor cause?
zoophilic, associated with small rodents
What does Microsporum audouini cause?
it is the most important anthropophilic fungus. It causes tinea capitis in humans. It may infect dogs and monkeys
Generally, what is only seen with Trichophyton on SGA?
microconidia
What are the perfect state names for Trichophyton mentagrophytes?
Arthroderma benhamiae and Arthroderma vanbreuseghemii
What does Trichophyton mentagrophytes grow on?
SGA
What does a culture of Trichophyton mentagrophytes look like?
flat or furrowed surface, velvety or finely granular, white to cream or tan - reverese is colorless to dark reddish brown
What does Trichophyton mentahrophytes look like microscopically?
microconidia are usually very abundant, usually round but may be pyriform, appear as bunches of unique grapes. Macroconidia are not normally observed on SGA - spiral hyphae and nodular organs can also be seen microscopically
What does Trichophyton equinum cause?
dermatophytosis in horses and other equidae
What lesions does Trichophyton equinum cause?
dry, raised, scaly lesions in the saddle, girth, and hindquarters - they become ulcerated with purulent exudate
What does Trichophyton equinum require for growth?
rapid on SGA, requires nicotinic acid, and must be supplemented with nicotinic acid in culture
What do cultures of Trichophyton equinum look like?
flat, developing folds when older, white surface, cottony with yellow edge, becoming velvety and cream to tan in color. Reverse is yellow to yellowish brown
What is the morphology of Trichophyton equinum?
microconidia may be abundant or scarce, elongate to pyriform, rare macroconidia. Nodular bodies and other structures may be present
What does Trichophyton verrucosum cause?
ringworm in cattle, sheep, occasionally horses and other animals that work with infected animals - causes club lamb fungus
What do lesions caused by Trichophyton verrucosum look like in cattle and when do they develop?
crusty, proliferative type lesion - observed in winter and spring months
If infection of Trichophyton verrucosum in cattle is severe, what can happen?
it can cause a decreased growth rate or become debilitating
What population of cattle does Trichophyton verrucosum typically infect?
younger cattle and is associated with crowding
What is the recommended treatment for Trichophyton verrucosum in cattle?
treat with griseofulvin if severe enough to warrant it but infection often disappears if cattle are placed on good pasture or in sunlight
What lesions are associated with club lamb fungus?
the lesions tend to be more open and often include vesicles and other types of skin lesions
How does Trichophyton verrucosum grow?
It grows slow on SGA compared to other dermatophytes. Growth is usually bettwe at 37 C than at 25-30 C. All strains require thiamine and may require inositol
What do colonies of Trichophyton verrucosum look like?
Colonies are heaped, deeply folded, penetrate deeply into the agar, and white to yellow to gray in color. Occasional isolates may be velvety or waxy
What does Trichophyton verrucosum look like microscopically?
chains and large numbers of chlamydospores are seen and occasionally small microconidia
What does Trichophyton rubrum infect?
humans
What does Trichophyton megnini infect?
not very common - mammals
What does Trichophyton schoenleinii infect?
humans
What does Trichophyton simii infect?
poultry and monkeys
What does Trichophyton tonsurans infect?
horses and dogs
What does the genus Epidermophyton infect?
skins and nails of humans
