Lecture 6 Pt 1 2/10/25

Question 1

What are the characteristics of dermatophytosis?

Answer 1

-cutaneous fungal infection
-invades keratinized structures
-can be self-limiting
-zoonosis
-cats are natural hosts

Question 2

Which dermatophytes are classified as zoophilic?

Answer 2

-Microsporum canis
-Trichophyton mentagrophytes
-M. nanum
-T. equinum
-T. verrucosum

Question 3

Which dermatophyte is classified as geophilic?

Answer 3

Microsporum gypseum

Question 4

Which dermatophyte is classified as anthropophilic?

Answer 4

Trichophyton rubrum

Question 5

How do endothrix spores differ from ectothrix spores?

Answer 5

endothrix spores live within the hair shaft while ectothrix spores live outside the hair shaft

Question 6

What are the characteristics of dermatophytosis incidence?

Answer 6

-over-diagnosed in dogs; more likely to be staphylococcal pyoderma than dermatophytosis
-microsporum and trichophyton genera are most common

Question 7

How is dermatophytosis transmitted?

Answer 7

-microtrauma + exposure
-direct contact
-fomites
-contaminated environment
-asymptomatic carriers
-airborne in overcrowded areas

Question 8

What is the pathophysiology of dermatophytosis?

Answer 8

-only invades keratin of anagen phase/growing hairs
-grows downward to above the hair bulb
-weakens the hair shaft and causes breakage
-infection resolves in the individual hair when it enters the telogen/resting phase and spreads to neighboring hairs in anagen
-classic lesion is an expanding circular alopecia resembling an epidermal collarette

Question 9

What are the clinical signs of canine dermatophytosis?

Answer 9

-circular patch of alopecia
-broken, stubby hairs
-scaling
-mild erythema
-central healing and peripheral spread
-focal to generalized pattern
-may see papules and pustules
-pruritus possible but uncommon

Question 10

What are the differentials for the “classic” lesion of an expanding circular alopecia resembling an epidermal collarette?

Answer 10

-pyoderma
-demodicosis
-dermatophytosis

Question 11

What are the characteristics of kerion?

Answer 11

-dermatophytic furunculosis
-nodular dermal pyogranulomatous inflammation with draining tracts
-most common presentation in dogs

Question 12

What must be ruled out in order to diagnose dermatophytosis when a kerion is present?

Answer 12

-deep pyoderma
-demodicosis
-neoplasia

Question 13

What are the characteristics of feline dermatophytosis?

Answer 13

-common infection
-M. canis is most common organism
-can be endemic in catteries and shelters, especially among long-haired cats
-up to 90% of strays are positive

Question 14

What are the clinical signs of feline dermatophytosis?

Answer 14

-patchy alopecia
-crusting
-scaling
-miliary dermatitis
-paronychia (infection around nails)
-focal to multifocal distribution most commonly seen on face and ears
-usually not pruritic

Question 15

What are the characteristics of dermatophytosis diagnosis via wood’s lamp?

Answer 15

-only M. canis fluorescences
-hair fluoresces apple-green
-provides an indication for which hairs should be collected for testing
-NOT a definitive diagnosis

Question 16

What are the characteristics of hair collection for diagnosis of dermatophytosis?

Answer 16

-want to pluck hairs to include bulb
-want to choose both broken hairs in center of lesion and hairs from periphery of lesion
-can use fluorescence as a guide to choose hairs

Question 17

What are the characteristics of dermatophytosis PCR?

Answer 17

-commercially available
-faster diagnosis than culture
-possible to get false positives; efficacy may not be great

Question 18

What are the characteristics of fungal culture for dermatophytosis diagnosis?

Answer 18

-only reliable way to make a definitive diagnosis
-allows source of infection to be identified

Question 19

What are the characteristics of the culture media used for dermatophytosis culture?

Answer 19

-uses phenol red as a pH indicator
-dermatophytes will produce an alkaline pH and cause a red color
-saprophytes will produce an acid pH and keep the media remaining yellow
-want to document the color change when colony first appears
-a white colony with media change is NOT enough to make a diagnosis

Question 20

What does a pigmented colony indicate?

Answer 20

ALWAYS saprophytes

Question 21

What type of macroconidia is seen on a skin cytology?

Answer 21

saprophyte

Question 22

What is the rule regarding cats and dermatophytosis?

Answer 22

all cats should be cultured for dermatophytosis before being adopted into a household

Question 23

What organism is this?

Answer 23

Microsporum canis; more cells, more complex

Question 24

What organism is this?

Answer 24

Microsporum gypseum

Question 25

What organism is this, taken from a tape cytology sample of the skin?

Answer 25

saprophyte (always a saprophyte if superficial)