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Flashcards in Dermatophytes Deck (87):
1

What breed of cat is likely predisposed to dermatophytosis?

PERSIANS

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2

What breed of dog is over-represented for dermatophytosis?

Yorkshire terrier

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3

TRUE/FALSE

The activities of hunting and working dogs does not increase their risk of exposure to dermatophyte spores and infection.

FALSE

The activities of hunting and working dogs may increase their risk of exposure to dermatophyte spores and infection.

4

TRUE/FALSE

Seropositive FIV and/or FeLV status in cats alone does not increase the risk of dermatophytosis.

TRUE

Seropositive FIV and/or FeLV status in cats alone does not increase the risk of dermatophytosis.

5

TRUE/FALSE

There is a gold standard test for dermatophytosis.

FALSE

There is not a gold standard test for dermatophytosis. This condition is diagnosed by utilizing a number of complementary diagnostic tests (Wood's lamp, direct examination, DTM, biopsy). 

6

You have a positive dermatophyte PCR. This must mean that your patient has active infection - right? What do you tell the client?

Nope! A positive PCR does not necessarily indicate active infection. Dead fungal organisms from a successfully treated unfection can be detected. Also, non-clinical carriers can have a "false positive". I would recommend a DTM to a client with a pet who had a positive PCR +/- Wood's lamp +/- biopsy as indicated clinically. 

7

TRUE/FALSE

Most cases of M. canis dermatophytosis are likely to be Wood's lamp positive. 

TRUE

Most cases of M. canis dermatophytosis are likely to be Wood's lamp positive. 

8

TRUE/FALSE

Monitoring the number of CFUs is helpful in monitoring response to therapy in cases of dermatophytosis. 

TRUE

Monitoring the number of CFUs is helpful in monitoring response to therapy in cases of dermatophytosis. 

9

TRUE/FALSE

Negative PCR in a treated cat is not compatible with cure of dermatophytosis. 

FALSE

Negative PCR in a treated cat is compatible with cure of dermatophytosis. 

10

You have a feline patient that you are treating for dermatophytosis. You have a negative fungal culture. The cat has no lesions. And, the cat is Wood's lamp positive. What do you tell this cat's owner?

Your cat is CURED! 

11

The following topical therapies (twice weekly) are currently recommended as effective therapies for generalized dermatophytosis in dogs and cats: 

A: Lime sulfur

B: Enilconazole

C: Miconazole/chlorhexidine

D: All of the above

The following topical therapies (twice weekly) are currently recommended as effective therapies for generalized dermatophytosis in dogs and cats: 

A: Lime sulfur

B: Enilconazole

C: Miconazole/chlorhexidine

D: All of the above

12

TRUE/FALSE

Chlorhexidine monotherapy is highly effective for the management of generalized dermatophytosis in dogs and cats. 

FALSE

Chlorhexidine monotherapy is poorly effective for the management of generalized dermatophytosis in dogs and cats. 

13

TRUE/FALSE

Itraconazole (non-compounded) and griseofulvin are the most effective and safe treatments for dermatophytosis. 

FALSE

Itraconazole (non-compounded) and terbinafine are the most effective and safe treatments for dermatophytosis. 

 

** Griseofulvin is effective, but it has side effects **

14

TRUE/FALSE

Lufenuron enhances to efficacy of systemic and topical antifungal treatments and is a great addition to your treatment plan for dermatophytosis.  

FALSE

Lufenuron DOES NOT enhance the efficacy of systemic and topical antifungal treatments and is NOT a great addition to your treatment plan for dermatophytosis.  

This medication has no in vitro efficacy against dermatophytes. It does not prevent or alter the course of dermatophytosis. It has no place in the treatment of dermatophytosis. Boom. Just say no. 

15

Why would you advise a client to decontaminate their home if they had a cat with dermatophytosis?

  1. Prevent fomite contamination
  2. Prevent false positive fungal cultures 

16

TRUE/FALSE

In people, the predominant dermatophyte pathogen is M. canis derived from animals. This commonly presents as jock itch. 

FALSE. SO FALSE.

In people, the predominant dermatophyte pathogen is non-animal derived T. rubrum. This commonly presents as onychomycoses ("toe nail fungus"). 

17

You have a client who has a Persian cat with dermatophytosis. This client is immunocompromised. She asks you what the most common complication of M. canis infection is in immunocompromised people. You say "_____". 

"The most common complication of M. canis infection in immunocompromised people is a prolonged treatment time"

18

What are the three most common fungal organisms that cause dermatophytosis in companion animals?

  1. Microsporum canis
  2. Microsporum gypseum
  3. Trichophyton mentagrophytes

19

What does it mean that a dermatophyte species is zoophilic?

This just means that it is adapted to living on an animal host. 

20

Dermatophyte species in animals are isolated as asexual forms called ____________ which are identified as belonging to the genus _________ or ____________ based on macroscopic or microscopic characteristics of the organism grown on culture. 

Dermatophyte species in animals are isolated as asexual forms called anamorph which are identified as belonging to the genus Microsporum or Trichophyton based on macroscopic or microscopic characteristics of the organism grown on culture. 

21

Where do geophilic dermatophytes get their keratin source?

They eat the keratin of hair, feathers and horn present in the soil after these keratinized products have been shed from the host. 

22

What is the main animal involved in M. canis infections?

Dogs and cats 

23

The cattle dermatophyte is...

 Trichophyton verrucosum

24

Guinea pig dermatophyte...

Arthroderma benhamiae

25

Hedgehog dermatophyte

Trichophyton erinacei

26

Horse dermatophyte...

Trichohyton equinum

Microsporum equinum

27

What three species would you see Trichophyton simii associated with?

Monkeys, poultry, dogs 

28

Chicken dermatophyte

Trichophyton gallinae

29

What species is the main animal associated with Microsporum nanum?

PIGS

30

A client asks you if M. canis is part of the normal fungal flora of healthy pet cats and dogs. What do you tell them?

No, M. canis is not part of the normal skin microbiome of dogs or cats. There are occasionally other dermatophyte species isolated when microbiome studies are done (T. rubrum, M. gypseum, etc). 

31

The infective form of dermatophytes is the ___________ which is formed by fragmentation of fungal hyphae into very small infective spores. 

The infective form of dermatophytes is the arthrospore which is formed by fragmentation of fungal hyphae into very small infective spores. 

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32

TRUE/FALSE

Transmission of dermatophytosis via contaminated environments is an efficient route of transmission. 

FALSE

Transmission of dermatophytosis via contaminated environments is NOT an efficient route of transmission. 

33

"But, Doctor, how did my dog get this Trichophyton infection?"

"Probably from contact with infected rodents or their nests"

34

Yoru patient has Microsporum gypseum. Where do you think they got it?

They probably got this geophilic dermatophyte from contaminated soil. 

35

TRUE/FALSE

Microtrauma to the skin is an important factor in the development of clinical dermatophytosis. 

TRUE

Microtrauma to the skin is an important factor in the development of clinical dermatophytosis. Microtrauma can be from pruritus/self-trauma, humidity, ectoparasites or wounds.

36

TRUE/FALSE

Cats should not be allowed to groom themselves if they have M. canis infection because they will just self-innoculate and spread more spores everywhere. 

FALSE

Cats should be allowed to groom themselves if they have M. canis infection because they will just self-innoculate and spread more spores everywhere. Cats who had to wear e-collars developed infection in laboratory settings. Grooming is likely a host defense mechanism against dermatophytosis! 

37

What are the three stages of dermatophyte infection development?

  1. Adherence of arthrospores to corneocytes 
    1. Occurs 2-6h after exposure
  2. Fungal conidial germination
    1. Germ tubes emerge from arthroconidia and penetrate the stratum corneum 
  3. Dermatophyte invasion of keratinized structures

    This whole process takes about 1-3 weeks from initial infection to clinical appearance. 

38

Dermatophyte adherence is likely mediated by two key things: 

 

  1. Carbohydrate-specific adhesins expressed on the surface of arthroconidia
  2. Dermatophyte-secreted proteases called subtilisins 

39

An important dermatophyte-produced protease which aids in adhesion is: 

1) Cathelidin

2) Desmoglein attack complex

3) Subtilisin

4) Keratinase

An important dermatophyte-produced protease which aids in adhesion is: 

1) Cathelidin

2) Desmoglein attack complex

3) Subtilisin

4) Keratinase

40

Dermatophytes degrade keratin by the simultaneous ___________ and __________ of keratin cysteine disulphide bonds via a ____________ encoded by the _______ gene. 

Dermatophytes degrade keratin by the simultaneous reduction and cleavage of keratin cysteine disulphide bonds via a dermatophyte sulphite efflux pump encoded by the SSU1 gene. 

41

What is a key part of the host immune response which helps promote clinical cure and re-infection prevention? 

Cell mediated immunity! Macrophages, neutrophils, cytokines (IFN-y). 

42

TRUE/FALSE

Natural infection of cats with M. canis is associated with positive immediate and delayed intradermal test reactions to fungal proteins, elevated antibody titers and alterations in lymphocyte blastogenesis response to fungal antigens. 

TRUE

Natural infection of cats with M. canis is associated with positive immediate and delayed intradermal test reactions to fungal proteins, elevated antibody titers and alterations in lymphocyte blastogenesis response to fungal antigens. 

43

TRUE/FALSE

A cat who is currently or previously infected with M. canis will have significantly higher lymphocyte reactivity to dermatophyte antigens than an uninfected control. 

TRUE

A cat who is currently or previously infected with M. canis will have significantly higher lymphocyte reactivity to dermatophyte antigens than an uninfected control. 

 

This is probably measuring the TH1 response. Reflects exposure, not necessarily protection.

44

The majority of dermatophyte lesions are symmetrical. 

TRUE?

NO WAY! The majority of dermatophyte lesions are asymmetrical

45

You have a cat with pododermatitis. Is dermatophytosis a differential?

Yes. 

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46

What does a kerion look like clinically?

A single or multiple erythematous, alopecic, dome-shaped, exudative nodule. Characterized histologically as a granuloma which usually contains fragments of hair and fungal spores. 

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47

How would a mycetoma present?

It would be a nodule that fistulates, ulcerates and drains serous to purulent debris with tissue grains. 

48

TRUE/FALSE

With the exception of T. schoenleinii, dermatophytes that produce fluorescence are members of the Microsporum genus. 

TRUE

With the exception of T. schoenleinii, dermatophytes that produce fluorescence are members of the Microsporum​ genus. 

49

Do M. gypesum or M. persicolor fluoresce with Wood's lamp?

No

M. canis does.

50

What is the characteristic green fluorescence on M. canis infected hair shafts due to?

A water-soluble chemical metabolite located within the cortex of the medulla of the hair called pteridine

51

TRUE/FALSE

The fluorescence that you see when M. canis glows is associated with spores and infective material. 

FALSE

The fluorescence that you see when M. canis glows is a result of the infection and is not associated with spores and infective material. 

52

TRUE/FALSE

Topical therapy for dermatophytosis will reduce fluorescence with Wood's lamp. 

FALSE

Topical therapy for dermatophytosis will reduce fluorescence with Wood's lamp. Go ahead and bathe those cats - then monitor with Wood's lamp. 

53

What part of the hair shaft will fluoresce with the Wood's lamp?

The intrafollicular portion. 

You should be examining the SHAFTS not the scale. 

54

How soon after dermatophyte infection will fluorescence develop?

As early as 5-7 days, and certainly by 10-14 days. 

55

Why might hair tips fluoresce after dermatophytosis is cleared?

The pteridine pigment within the medulla or on the cortex remains readily detectable by the Wood's lamp on the tips of hairs as their grow out. 

56

What is a unique finding on dermoscopy in cats with dermatophytosis?

A: Exclamation hairs

B: Period hairs

C: Parentheses hairs

D: Comma hairs

What is a unique finding on dermoscopy in cats with dermatophytosis?

A: Exclamation hairs

B: Period hairs

C: Parentheses hairs

D: Comma hairs

 

57

If you wanted to do some direct examination of dermatophytes, what could you mount hair and scales in?

  1. Mineral oil
  2. Compounded chlorphenolac
  3. Potassium hydroxide (KOH)
  4. +/- stains like India Ink or lactophenol cotton blue 

58

What is the most common technique used to collect samples for direct examination of possible dermatophytes?

Hair pluck

Skin scraping

Put the collected sample in mineral oil

59

You have a cat that you want to perform a fungal culture on. What technique will you use to collect your sample?

I will use a brush technique. This involves taking an individually wrapped soft-bristle toothbrush which is mycologically sterile and doing about 20 thorough brush strokes over the cat (~ 2-3 minutes of brushing) until the bristles are full of hair. I will then send this toothbrush to the lab so that they can inoculate the DTM.

60

Is it common to get a false positive on a DTM when you use the brush technique?

Yes, it can be. This technique is very good at detecting spores on the hair coat. Those spores may or may not be infectious and could just represent transient exposure from the environment. 

 

A study of 5,644 shelter cats had 10.4% with positive cultures and only 1.67% with true clinical disease. 

61

What is the DTM? 

This is a nutrient growth medium with antibiotics which suppress bacterial and contaminant fungal overgrowth. There is a color indicator to aid in the early recognition of possible dermatophyte species. 

62

What is the color change in the DTM caused by?

A pH change triggered by fungal growth

Yellow --> Red

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63

TRUE/FALSE
Dermatophytes are the only organisms that can change the color of a DTM from yellow to red. 

FALSE

Dermatophytes are NOT the only organisms that can change the color of a DTM from yellow to red. There are many possible contaminants that can cause a color change. 

64

The lab calls and says that they don't know how to set up a dermatophyte culture. What do you tell them?

  1. Use a fungal culture plate with adequate surface area that allows brush inoculation and counting of CFU
  2. Inoculate the plates by stabbing the bristles onto the surface of th eplate in 4-5 areas 
    1. You will see the stab pattern
    2. DO NOT over-inoculate the plate 
  3. Incubate the plates at 25-30-C
    1. Store the plate medium side up in a plastic bag to prevent dehydration
  4. +/- find a new lab :) 

65

What does pathogen scoring represent with DTMs? How can you use this clinically?

Pathogen score 1: 1-4 CFU/plate

Pathogen score 2: 5-9 CFU/plate

Pathogen score 3: > 10 CFU/plate 

 

Untreated pets with active infections tend to have a starting score of P3. Early in treatment, there is usually confluent growth. As treatment progresses, the number of cfu/plate should decrease. This is a strong and consistent indicator of a positive response to treatment. 

66

Let's troubleshoot a DTM.

The culture fluctuates from negative to 1-4 cfu/plate. 

This is consistent with an animal who has been exposed to fomites.

67

Let's troubleshoot a DTM.

There is a sudden increase in pathogen score (P1 --> P3). 

This is likely from inadequate disinfection of the hair coat. This usually happens with lesions around the face because of concerns for using topical therapies there. 

 

This could also be from fomite exposure or development of new lesions despite therapy. 

68

Let's troubleshoot a DTM. 

You have persistent P2/P3 scores. 

  1. If clinical cure is apparent: 
    1. Lack of disinfection of the hair coat 
    2. Subclincal infection (likely face/ears) 
    3. Fomites
  2. If clinical cure is not happening: 
    1. Too short treatment 
    2. Concurrent systemic illness
    3. Treatment compliance issues 

69

What are the two main similarities on histopathology between a dog with PF and a dog with dermatophytosis?

  1. Intraepidermal pustules
  2. Interface dermatitis 

70

What are two special stains that you should use to look for dermatophytosis on histopathology?

  1. Periodic acid Schiff (PAS)
  2. Grocott methenamine silver (GMS)

71

What is the purpose of topical therapy for management of dermatophytosis?

Transmission of dermatophytosis occurs via direct contact with infective material originating from the skin and hair coat of infected animals. Therefore, the purpose of topical therapy is to decrease the infectious, contagious and zoonotic risks associated with this disease by disinfecting the hair coat and minimizing contamination of the environment. 

72

Why does lime sulfur smell like rotten eggs?

Hydrogen sulfide

73

How does lime sulfur work?

No one really knows. But, it is fungicidal on contact due to the formation of hydrogen sulphide. It is also keratolytic. 

74

What is the typical concentration of lime sulfur to treat dermatophytosis?

8 oz/gallon

75

How often would you recommend a shelter to dip cats suspected of having or with active lesions consistent with dermatophytosis: 

A: Once a week 

B: Twice a week

C: Every other day

D: Doesn't matter

How often would you recommend a shelter to dip cats suspected of having or with active lesions consistent with dermatophytosis: 

A: Once a week 

B: Twice a week

C: Every other day

D: Doesn't matter

Twice weekly dipping is SUPERIOR to once weekly in terms of time to cure. 

76

What are the main side effects to be aware of when you are using lime sulfur in cats?

  • Drying of the footpads
  • Loss of hair on the ears
  • Drying of the hair coat
  • Yellowing of the hairs 

77

Is itraconazole fungicidal or fungistatic?

At low doses it is fungistatic!

At high doses it is fungicidal!

78

What is the mechanism of action of itraconazole?

Itraconazole inhibits fungal cytochrome P450 enzyme 14-a-demethylase to prevent the conversion of lanosterol to ergosterol. 

 

Ergosterol is essential for cell wall integrity. 

79

Why is it recommended to give itraconazole with food?

Itraconazole is a weak basic compound whose bioavailability is highly dependent on pH. Absorption is greater in an acidic environment. Giving with food will decrease GI acidity. 

80

We know that itraconazole is lipophilic. Why does this matter?

Well - since it is highly lipophilic, it will distribute the most to tissues high in fat like adipose tissue and sebaceous glands.  Distribution to these tissues is usually about 10x higher than that of plasma. 

81

Itraconazole can persist in tissues for how long in people? What about cats?

4 weeks

In cats, the drug will persist in tissues that have greater concentrations of sebaceous glands. The concentration will also be dose dependent. 

82

Should you give Ketoconazole with food?

Yes - but only a small amount. The drug is dissolved by gastric acidity. 

83

TRUE/FALSE

Ketoconazole leads to an increase in plasma concentration of cyclosporine, midazolam and ivermectin in dogs. 

TRUE

Ketoconazole leads to an increase in plasma concentration of cyclosporine, midazolam and ivermectin in dogs. 

84

The infective propagule of dermatophyte fungi is called an ____________. 

The infective propagule of dermatophyte fungi is called an arthroconidium

85

What are the three steps that you would recommend an owner take to disinfect a nonporous surface from dermatophytes?

  1. Mechanically remove debris
  2. Detergent to lift debris from surface
  3. Disinfection

86

How should laundry be disinfected when there is concern for dermatophytosis?

Two wash cycles. Allow for maximal agitation (don't overload). Bleach isn't necessary! 

87

Please list three zoonotic diseases that are of greatest zoonotic concern for "high-risk" clients

  1. Bartonella
  2. Campylobacter jejuni
  3. Campylobacter canimorsus
  4. Dermatphytosis (M. canis, T. mentagrophyes) 
  5. Giardia
  6. Salmonella
  7. Pasteurella multocida
  8. Toxoplasma gondii