Fungal Skin Diseases

Question 1

What causes Dermatophytosis? (ringworm)

Answer 1

• Common Isolates:
  
  • Microsporum canis
  • Microsporum gypseum
  • Trichophyton mentagrophytes
• Dermatophytes grow in the keratinized tissue of skin, hair or nails
  
  • invade hair follicles and hair shafts. Enzymes enable the fungus to penetrate the hair and grow within the shaft
    
    • Infect hair that is in the anagen stage
  • Fungus advances toward the hair bulb and toxins produced in the stratum corneum incite cutaneous inflammation
    
    • if the infected hair stops growing, fungal growth stops
• Incubation 1-3 weeks

Question 2

What are the clinical signs of dermatophytosis?

Answer 2

• Lesions - circular patches of alopecia w/ scale (variable)
  
  • On head, pinnae and extremitis
• Broken hairs
• Folliculitis, furunculosis (papules, crusts)
• Kerion - exudative fungal nodule uncommon in dogs
• Pruritus - absent or mild
• Cats may have minimal inflammatory response
• Onychomycosis - Rare
• Dermatophytic pseudomycetomas
  
  • cutaneous to subcutaneous nodules of fungal aggregates, amorphous material and granulomatous inflammation
    
    • uncommon - Persian cats

Question 3

How is Dermatophytosis Diagnosed?

Answer 3

• Wood’s light
  
  • bright, apple-green fluorescence of hair shafts
  • scale and debris on skin is usually yellow/gold
• Microscopic examination of hair
  
  • visualize fungal hyphae (clear, wavy lines in hair shaft)
  • Arthrospores (fragmented pieces of hyphae that appear as tiny, clear “dots” on hair shafts)
  • 10%KOH may enhance visibility of fungal elements
• Fungal culture
  
  • Most reliable
  • Sample broken hairs - hairs that appear to fluoresce
    
    • pluck with hemostate or collect w/ toothbrush
  • Media :
    
    • Sabouraud’s dextrose agar
    • Dermatophyte test medium (DTM)
      
      • like Sabourauds +antimicrobials and pH indicator (phenol red)
    • Others
• Biopsy
  
  • usually not as sensitive as culture
  • more useful with nodular manifestations
• PCR
  
  • can be positive w/out active infection
• Rule out other causes

Question 4

What is the DTM technique for testing for Dermatophytosis

Answer 4

• Embed sample into media
• Cap loosely and store in the dark, room temp, 30% humidity
• Check daily for growth and media color change
  
  • Pathogenic fungi first use protein in the media and produce alkaline metabolites that turn media red
  • Non-pathogenic fungi usually use carbohydrates first and proteins later
    
    • media turns red but 1-2 weeks after apparent growth
• Red color w/ simultaneous colony growth = Positive
  *

Question 5

What is the treatment for Dermatophytosis? (Broad terms)

Answer 5

• Systemic (not always necessary)
• Topical (Always)
• Continued until 2-3 negative cultures (weekly)
  
  • or continue treatment for 2-4wks after resolution of clinical signs if not culturing
• Environmental decontamination

Question 6

What are the systemic treatment options for Dermatophytosis

Answer 6

• Itraconazole
  
  • teratogenic
  • 5-10mg PO q24h
• Terbinafine
  
  • Potentially teratogenic
  • 30-40 mg/kg PO q24h
• Ketoconazole
  
  • inhibits P-450 enzymes & P-glycoprotein
  • may be ineffective for M. canis
  • Cats - hepatotoxicity and GI signs
  • Teratogenic
  • 5-10 mg/kg PO q12-24h
• Fluconazole - poor efficacy
• Griseofulvin - NO - bone marrow sppression
• Lufenuron - not actually effective

Question 7

What topical treatments are done for Dermatophytosis

Answer 7

• Total body clip
• Lime sulfur dips
• Miconazole/Ketoconazole w/chlorhexidine rinses/shampoos
• Whole body treatment 1-2x weekly
• Antifungal creams, lotions, rinses may be used for spot treatment of isolated, focal lesions

Question 8

What causes Malasseziasis?

Answer 8

• Malassezia pachydermatis (and other species of yeasts)
  
  • Normal flora of skin and ear canal
  • Commensal of anals sacs and mucosal srfaces
• Yeast become pathogenic under certain circumstances
  
  • lowered host defense, change in microclimate, allergic dermatitis, seborrhea, pyoderma, etc

Question 9

What are the clinical signs of Malasseziasis

Answer 9

• Erythema, scaling, alopecia, lichenification, hyperpigmentation, odor (musty)
  
  • red-brown discoloration of nails if affected
• Greasy/tacky feeling skin
• Yeast Dermatitis - ventral neck, axillae, ventral abdomen, feet & nails, skin folds
• Yeast otitis - ear canals
• Usually very pruritic

Question 10

How is Malasseziasis diagnosed

Answer 10

• Cytology - best
• Biopsy may not show yeast
• Culture
• Response to antifungal treatment

Question 11

What is the treatment for Malasseziasis dermatitis?

Answer 11

• Topical therapy - may be effective alone
  
  • Miconazole
  • Ketoconazole
  • clotrimazole
  • chlorhexidine (≥3%)
  • acetic acid-based products
• Systemic Antifungals
  
  • Ketoconazole
  • itraconazole
  • fluconazole
  • terbinafine
• Pulse dosing of Systemic antifungals and maintenance topical therapy may be necessary to prevent recurrent dermatitis

Question 12

What is the treatment for Malasseziasis otitis?

Answer 12

• Clean ear canal
• Topical anti-yeast otic preparations
• Systemic antifungals - rarely needed

Question 13

What are the Subcutaneous Mycoses?

Answer 13

• Pythiosis
• Sporotrichosis

Question 14

What are the Systemic Mycoses?

Answer 14

• Blastomycosis
• Coccidioidomycosis
• Cryptococcosis
• Histoplasmosis

Question 15

Everything about pythiosis

Answer 15

• Etiopathogenesis
  
  • aquatic, fungus-like water mold Pythium insidiosum
    
    • Motile zoospores are infective
  • Wound contamination - infested water
  • Uncommon - dogs
  • Rare - cats
• Clinical Signs:
  
  • large, nonhealing, ulcerative granulomas on the limbs, ventrum or muzzle
  • GI disease mor frequent
• Dx:
  
  • Cytology & histopathology (biopsy)
  • CUlture
  • Serology (ELISA) - antibodies
• Tx:
  
  • Wide surgical excision and possible limb amputation
  • Antifungal therapy often unrewarding
  • Pythium vaccine - curative in some cases

Question 16

Everything about Sporotrichosis

Answer 16

• Etiopathogenesis
  
  • Sporothrix schenckii
    
    • present in soil, most organic debris, hay
  • Wound contamination
  • Uncommon
• Clinical signs:
  
  • Cutaneous form:
    
    • nodules +/- serosanguineous discharge
    • Ulcerated plaques
    • crusts and alopecia
    • lesions often occur on head & extremitis
  • Cutaneolymphatic form:
    
    • limb nodule with spread of infection via lymphatics (lymphadenopathy is common)
  • Disseminated form:
    
    • May occur in cats, rare in dogs
    • Respiratory & skeletal involvement
• Dx:
  
  • Cytology
  • Culture - may not grow well
  • BIopsy
  • Fluorescent antibody testing
  • ELISA - specific antiboies
• Tx:
  
  • Itraconazole
    
    • 5-10 mg/kg PO q24h
    • 30 days beyond clinical cure
  • Potassium iodide
    
    • Side effects - GI disturbances, lethargy, weakness, nasal discharge, dry skin

Question 17

Everything about Blastomycosis

Answer 17

• Etiopathogenesis:
  
  • Blastomyces dermatitidis
  • Spore can be inhaled - mycotic pneumonia
    
    • secondarily disseminate through body
  • Uncommon in dogs, rare in cats
• Clinical signs:
  
  • Most have no skin lesions
  • If present:: papules, nodules, ulcers, draining tracts, abscesses
  • Anorexia & weight loss
  • lethargy
  • coughing
  • ocular disease
  • lameness
• Dx:
  
  • Cytology of exudate and impression smear
  • Biopsy
  • Culture - NOT recommended
  • Antigen and antibody tests
    
    • urine, serum, CSF, bronchioalveolar fluid
• Tx:
  
  • Itraconazole preferred
  • Fluconazole
  • ketoconazole
  • amphotericin B - nephrotoxic

Question 18

Everything about Coccidioidomycosis

Answer 18

• Etiopahtogenesis
  
  • Coccidioides immitis (& C. posadasii)
  • Inhalation of arthrospores, then dissemination to skin
  • Uncommon in dogs, rare in cats
• Clinical signs:
  
  • skin lesions - papules, nodules, ulcers, draining tracts, abscesses
    
    • found overlying sites of bone infection
  • Anorexia & weight loss
  • coughing
  • fever
  • lameness
  • ocular disease
• Dx:
  
  • Biopsy
  • Cytology - inflammation (pyoranulomatous), fungal elements difficult to find
  • Culture - NOT recommened
  • Antigen and Antibody tests
• Tx:
  
  • Fluconazole*
  • Itraconazole
  • Ketoconazole
  • Amphotericin B (nephrotoxic)

Question 19

Everything about Cryptococcosis

Answer 19

• Etio:
  
  • Crytptococcus neoformans (& C. gattii)
  • Dropping/debris from pigeon roosts
    
    • inhalation of organisms
  • Uncommon in cats, rare in dogs
• Clinical:
  
  • +/- Skin lesions
    
    • Papules, nodules, abscesses, ulcers, draining tracts
  • Subcutaneous swelling over the bidge of the nose or polyp-like mass in a nostril may be present
  • Nasal cavity disease (intranasal granulomatous disease)
  • CNS signs
  • Ocular disease
• Dx:
  
  • Cytology of exudate and impression smear
  • Biopsy
  • Culture
  • Serologic test - capsular antigen (not always accurate in cats)
• Tx:
  
  • Itraconazole*
  • Fluconazole
  • amphotericin B w/Flucytosine for CNS

Question 20

Everything about Histoplasmosis

Answer 20

• Etio:
  
  • Histoplasma capsulatum
    
    • bird/bat excrement
  • Inhalation/ingestion and hematogenous spread
  • Uncommon
• Clinical:
  
  • skin lesions - papules, nodules, ulcers, draining tracts
  • Anorexia & wight loss
  • coughing
  • dyspnea
  • fever
  • GI disease ocular discharge
• Dx:
  
  • Cytology - organisms w/in macrophages
  • Biopsy
  • Culture - NOT recommended
  • Antigen and Antibody tests
• Tx:
  
  • Itraconazole
  • Amphotericin B
  • Voriconazole