Dermatophytosis Flashcards
What are 3 classifications of cutaneous fungal infections?
- dermatophytosis - superficial
- intermediate - opportunistic
- systemic - cutaneous manifestations of systemic infection
What are 4 steps to the pathogenesis of dermatophytosis?
- invasion of non-viable, keratinized tissue
- production of metabolic byproducts and toxins cause inflammation and hypersensitivities
- secondary folliculitis/furunculosis
- severe infection develops in immunocompromised hosts (on glucocorticoids)
How do most dermatophytes infecting animals deposit their spores?
ectothrix - place spores around the hair shaft
What are 5 risk factors for developing dermatophytosis?
- age - young, old
- immune status
- exposure to critical masses of arthrospores
- cutaneous trauma or increased hydration
- genetics
What are 3 clinical features of dermatophytosis?
- circular alopecic areas of erythema, crusts, scales, hyperpigmentation, nodules, or pustules
- brittle or broken hairs
- mild to moderate pruritus (cats > dogs)
Dermatophytosis, dog:
Dermatophytosis, cat:
more pruritic compared to dogs, but not at the level of flea bite allergies or scabies
Dermatophytosis:
scale, broken hair (seems stubbly)
Which species of dermatophytes has a unique presentation?
Nannizzia gypseum –> elevated nodules with deeper infection
Dermatophytosis:
- nodular
- draining tract from hair follicle = furunculosis
Trichophyton mentagrophytes:
Dermatophytosis:
draining tract = furunculosis
Dermatophytosis:
What are the 3 most common dermatophytes of dogs and cats?
- Microsporum canis - transmission from animal-to-animal
- Nannizzia gypseum - found in soil
- Trichophyton mentagrophytes - wildlife
What 5 fungal contaminants can be found on samples that may look like dermatophytosis?
- Aspergillus
- Alternaria
- Penicillium
- Rhizopus
- Mucor
What are 5 diagnostics used for dermatophytosis?
- Wood’s lamp
- trichogram + KOH preparation
- fungal culture WITH microscopic ID
- fungal PCR
- skin biopsy
What is a Wood’s lamp? What species of dermatophyte particularly fluoresces?
UV light with nickel oxide filter
M. canis fluoresces 50% of the time, depending on light, darkness of the room, and how long the light was on the organism –> SCREENING ONLY, may be positive with topical meds
What technique is most commonly used for trichogram preparations for diagnosing dermatophytosis?
mineral oil + KOH to dissolve hair/bubbles and observe hyphae and spores
- positive is positive
- negative is equivocal
Trichogram, dermatophytosis:
spores on shaft, hyphae surrounding
Trichogram, dermatophytosis:
spores on shaft, hyphae make it difficult to appreciate border of hair
What is considered the gold standard for diagnosing dermatophytosis? What is considered proper technique? What is an essential part?
fungal culture
- avoid over-inoculation, which can lead to overgrowth
- incubate at 25-30 C
- growth by 3-7 days
microscopic confirmation - do not rely on color change of DTM agar or point of care tests
Dermatophytes, DTM:
color change indicative of infection
- do NOT rely on this, perform a microscopic examination
- some saprophytes may be able to induce a color change
What are the most common dermatophyte isolates?
- Microsporum canis
- Microsporum gypseum
- Trichophyton mentagrophytes
What are the most common saprophyte isolates?
- Alternaria
- Mucor
- Penicillium
- Aspergillus
- Rhizopus
What samples are required for fungal PCRs when diagnosing dermatophytosis? How is this test best interpreted?
10-20 hairs plucked and scraped from active borders of the lesion, aspirated purulent material, and claws
in combination with Wood’s lamp examination, hair examination, and culture/ID
What is most commonly seen on biopsy/histopathology in cases of dermatophytosis?
- folliculitis/furunculosis
- organisms seen with PAS, silver, or Giemsa stains
poor sensitivity, high specificity
What are the 2 objectives when treating dermatophytosis?
- shorten course of infection and reduce severity of lesions/discomfort
- reduce dissemination of infective materials (hair, scale) into the environment
decontaminate/treat pet and environment = reduced zoonotic risk
What are the 2 purposes of total body clips in cases of dermatophytosis? What may occur?
- reduce infectivity (contagion)
- speeds recovery
environmental contamination –> avoid trauma, disinfect instruments
What are the 2 methods of topical therapy in treating dermatophytosis?
- ADJUNCTIVE - lotions and cream for focal lesions, daily or EOD, work medication inward to reduce spread
- CONCURRENT - bathe pet weekly with Miconazole, Chlorhexidine, or Ketoconazole shampoos
NOT recommended as sole treatment
What topicals can be used as the sole treatment of dermatophytosis?
- Enilconazole rinse
- Lime sulfur bath
- Miconazole-Chlorhexidine baths
twice weekly
What are 4 systemic therapy options for cases of dermatophytosis?
- Griseofulvin (4-8 weeks)
- Azoles - Ketoconazole, Itraconazole, Fluconazole (4-8 weeks) –> fungistatic
- Lufenuron
- Terbinafine
What side effects are associated with Griseofulvin?
- anorexia
- GI disturbances - diarrhea
- teratogenesis
- bone marrow suppression - FIV+ cats
What is the mechanism of action of azoles?
inhibit lanosterol-14alpha-demethylase (CYP-450) responsible for forming ergosterol
What are 2 pharmacological characteristics to the mechanism of Ketoconazole? When is this medication best given?
- highly protein-bound - penetrates poorly into CNS, eyes, and prostate
- inhibits p-glycoprotein pump in GIT, liver, and brain
with a meal to increase absorption
What side effects are associated with Ketoconazole use?
- anorexia (cats)
- diarrhea
- increased hepatic enzyme concentrates
- alopecia
Which azole is considered the best for treating dermatophytosis? What side effects are associated?
Itraconazole for dogs AND cats–> $$, better absorption into skin
- increased hepatic enzyme concentrations
- vomiting
- anorexia
- AVOIDED in pregnant animals
How does Fluconazole compare to the other azoles? What adverse effects are associated?
excellent penetration into CSF, eyes, and claws
- increased hepatic enzymes
- AVOIDED in pregnant animals
How does Terbinafine compare to the other systemic antifungals used for treating dermatophytosis?
- FUNGICIDAL - inhibits squalene epoxidase necessary for ergosterol synthesis
- relatively few side effects - elevated ALT
What are 5 recommendations for environmental decontamination in cases of dermatophytosis?
- launder bedding, carpet, etc.
- change furnace filters and heating ducts
- vacuum and dispose
- disinfectant sprays/cleansers - 1:10 bleach in non-porous surfaces
- foggers/smokers - Enilconazole in large, open areas
What is a major consideration during the treatment of dermatophytosis?
it is contagious, infectious, and zoonotic
- human infection is COMMON
- lesions can be painful
- therapy can be expensive and long
What risk factors in humans are associated with dermatophytosis?
- adoption from human societies and shelters
- exposure to large number of animals - groomers, veterinarians, shelter workers
- immunosuppression
Overall, what are the systemic treatments of choice for dermatophytosis?
- Terbinafine - fungicidal
- Itraconazole
systemic treatment recommended with multiple lesions
