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Infectious Dermatoses
of the Dog and Cat

Candace A. Sousa, DVM
Diplomate (Emeritus) American Board of Veterinary Practitioners,
Canine and Feline Practice
Diplomate (Emeritus) American College of Veterinary Dermatology

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Diagnosis Begins with Relief

Stop the Itch
Rule out Parasites
Treat Skin Infection
Conduct Diet Trial
Confirm Atopic Dermatitis

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Canine Pruritus
“Infectious Diseases”
1. Sarcoptes scabiei
2. Malassezia colonization
3. Staphylococcal pyoderma
Demodex Hypothyroidism
Conformation (obesity)
4. Other (dermatophytosis, Cheyletiella, lice, etc)

Allergic Diseases
1. Flea allergy dermatitis
2. Atopic dermatitis
Food Non IgE (atopic-like)
Environmental allergens
3. Other allergic diseases (Drug eruptions, contact
allergy, etc)

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Canine Staphylococcal Pyoderma

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Pyoderma
- Any purulent skin disease
- Most commonly used with bacterial skin diseases
- Staphylococcus pseudintermedius
- Second only to flea allergy dermatitis

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Pyoderma Classification of
- Surface colonization
- Involves the stratum corneum
- Skin fold pyoderma
- Pyotraumatic dermatitis
Mucocutaneous pyoderma

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Pyoderma Classification of Staphylococcal
- Superficial pyoderma
- Infections of the epidermis below the stratum corneum and / or into the hair follicle
- Impetigo
- Superficial folliculitis
- Superficial spreading pyoderma

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Clinical Lesions of Surface and Superficial Staphylococcal Pyoderma
- Erythema
- Alopecia
- Pustules
- Papules
- Crusts
- Epidermal collarettes

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Classification of Staphylococcal Pyoderma

- Deep pyoderma
- Infection extends below the epidermis or through the hair follicle
into the dermis or subcutis
- Often there is rupture of the hair follicle
- Staphylococcus spp., Proteus spp., Pseudomonas spp., E. coli
- Furunculosis
- Cellulitis

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Clinical Lesions of Deep Staphylococcal Pyoderma
- Nodules
- Erosions
- Ulcers
- Draining tracts

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Staphylococcal Pyoderma is Always Secondary
- Need to determine the underlying cause
- Need to cure the underlying cause
- Need to prevent the underlying cause

- If not, you increase the chance of recurrent pyoderma

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Secondary to Allergic Diseases
- Flea allergy dermatitis
- Food allergy
- Atopic dermatitis

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Secondary to Diseases of Cornification
- Congenital or idiopathic “seborrhea”
- Icthyosis
- Sebaceous adenitis

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Secondary to Genodermatoses
- Color dilution alopecia / black hair follicular dysplasia
- Follicular dysplasia

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Secondary to Endocrine Imbalances
- Hypothyroidism
- Hyperadrenocorticism
- Iatrogenic or naturally-occurring
- Sex hormone imbalances
- Adrenal hyperplasia
- Alopecia X

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Secondary to Parasitic Diseases
- Demodicosis
- Sarcoptes scabiei
- Cheyletiella spp.

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Secondary to Other Infectious Diseases
- Dermatophytosis
- Deep fungal infections
- Malassezia pachydermatis

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Secondary to Immunoincompetence
- Serum immunoglobulins
- Total lymphocyte count - Should be >1000/ul
- Very young or very old dogs
- Neoplastic disorders
- Immunosuppressive drugs (especially corticosteroids)

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Diagnosis of Staphylococcal Pyoderma
- Clinical lesions
- Response to therapy
- Identification of cocci with cytology
- Histopathology
- Bacterial culture, identification, and sensitivity testing

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Treatment Staphylococcal Pyoderma
- Oral systemic antibiotics
- Appropriate dose for 14 days
- Choose empirically or by culture and sensitivity
- Topical antibacterial shampoo, rinse or spray to control re-colonization
- Identification and treatment of underlying cause
- RECHECK AT 10-14 DAYS

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How I Choose an Antibiotic Empirically
- Is it known to be effective against the majority of Staphylococcus pseudintermedius ?
- Is it safe? (i.e. side effects, vomiting)
- Is it easy to administer?
- SID, BID, TID
- capsule, tablet, liquid
- Is it expensive?

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Antibiotics Used Empirically to Treat Superficial Staphylococcal Skin Infections
- b lactam antibiotics
- cephalexin, generic
- 22 mg / kg q 12 hrs
- cefadroxil (CefaTabs)
- 22 mg / kg q 12 hrs
- amoxicillin / clavulanate (Clavamox Chewable)
- 13.75 mg / kg q 12 hrs

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Antibiotics Used Empirically to Treat
Superficial Staphylococcal Skin Infections
- cefpodoxime proxetil (Simplicef)
- 5 - 10 mg / kg q 24 hrs

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Antibiotics Used Empirically to Treat
Superficial Staphylococcal Skin Infections

- cefovecin (Convenia)
- 8 mg / kg as a single SQ injection
- A second injection may be administered if response to therapy is incomplete

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Topical Treatment for Bacterial Pyoderma
- Shampoos and rinses, active ingredients
- Benzoyl peroxide
- Chlorhexidine
- Triclosan
- Ethyl lactate
- Antibiotic cream
- 2% mupirocin

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Malassezia Dermatitis

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Colonization or infection with Malassezia pachydermatis
- Lipophylic, non-mycelial, saprophytic yeast
- Thick-walled, elongated oval shape, unipolar budding (peanut-shaped)
- Low number always present in ears, anal sac, rectum, & vagina

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As with bacterial pyoderma, always an underlying cause for overgrowth
- Allergic diseases
- Cornification defects
- Endocrine imbalances
- Chronic antibiotic or corticosteroid therapy

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Predisposed Breeds
- West Highland white, Silky & Cairn terriers
- German shepherd
- Shih tzu
- Basset hound
- Spaniels
- Dachshund
- Shetland sheepdog

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Clinical Signs
- Focal, multifocal, or generalized
- Pruritus - Erythema
- “Saliva staining”
- Greasiness / waxiness
- Scaling / lichenification
- Odor
- Hyperpigmentation
- Secondary bacterial pyoderma

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Common Sites for Malassezia
- Areas of skin-to-skin contact
- Lip folds
- Ear canals
- Ventral neck
- Abdomen
- Interdigital and ventral paws
- Perianal
- Skin folds

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Diagnosis of Malassezia
- Cytology
- Direct impression
- Clear tape
- Cotton swabs
- Skin scraping
- Record average no. / oil immersion field (OIF)
- Culture
- Histopathology

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Treatment of Malassezia - Topical
- Localized
- Miconazole (Conofite)
- Thiabendazole (Tresaderm)
- Generalized
- Miconazole (Dermazole)
- Ketoconazole (Nizoral)
- Selenium (Selsun Blue)
- White vinegar (1:3 to 1:1)

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Treatment of Malassezia – Systemic
- Ketoconazole (Nizoral)
- 10 mg/kg PO BID x 30
- 10 mg/kg PO BID x 7 then SID x 21
- 10 mg/kg PO SID x 30
- 5 mg/kg PO BID x 30
- 5 mg/kg PO SID x 30

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Treatment of Malassezia - Systemic
- Itraconazole (Sporanox)
- 5 mg/kg PO SID x 30
- Fluconazole (Diflucan)
- 5 mg/kg PO SID x 30
- Terbinafine (Lamisil)
- 30 mg/kg SID x 30

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Dermatophytosis in Dogs and Cats

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Characteristics of Dermatophytes
- Definition
- An infection of keratinized tissue (hair, nails, and stratum corneum) caused
by fungi belonging to the dermatophyte group
- They only parasitize keratinized structures
- Under normal circumstances they do not invade and cannot
survive in living tissue

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Genera
- Microsporum
- M. canis
- 99% of feline dermatophytosis
- Cats can be asymptomatic carriers
- M. gypseum
- Contracted from contaminated soil

- Trichophyton
- T. mentagrophytes
- Usually contracted from contact with rodents or contaminated soil

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Predisposing Factors
- Age - very young or very old
- Compromised immune status
- Includes the use of corticosteroids
- FeLV/FIV infections
- Poor nutrition
- Debilitating diseases
- Stress

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Production of Clinical Disease
- Fungal elements weaken the hair shaft and cause breakage
- Fungi elaborate toxins or allergens

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Clinical Features
- Focal, multifocal, or generalized
- Crusting
- Alopecia
- Erythema
- Pruritus
- Papules / nodules
- Peripheral spread with central clearing

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Clinical Features - Feline
- Most common in kittens
- Most commonly Microsporum canis
- Usually ears, face, extremities
- Alopecia, crusting, minimal erythema
- Occasionally miliary crusts

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Clinical Features - Canine
- Similar to the cat
- Nasal form
- Trichophyton mentagrophytes
- Can be pruritic
- Differentiate from PF, PE, eosinophilic furunculosis
- Papular/pustular form

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Clinical Features - Canine
- Histiocytoma-like form
- Kerion
- Draining tracts
- Generalized form
- Frequently due to immunosuppression
- Differentiate from demodicosis, seborrhea, etc.
- Onychomycosis

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Diagnosis of Dermatophytosis
- History
- Clinical appearance
- Wood’s lamp
- M. canis
- Positive about 90% of the time
- Direct examination - KOH
- Fungal culture
- Histopathology

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Treatment of Dermatophytosis - Systemic
- Griseofulvin
- 20 - 120 mg/kg PO SID with a high fat meal
- Not for pregnant or FIV positive cats
- Itraconazole
- 5 - 10 mg/kg PO SID
- Fluconazole
- 5 - 10 mg/kg PO SID

Scott,DW, Miller, Jr, WH, Griffin, CE. Muller & Kirk’s Small Animal Dermatology, 6th Ed., 2001

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Treatment of Dermatophytosis - Topical
Prevents the spread of infective material
- Lime sulfur
- The only active ingredient approved for the use on dogs and cats as a
treatment for dermatophytosis

- Captan
- Enilconazole
- Sodium hypochlorite
- Chlorhexidine
- Povidone iodine
- Miconazole

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In Conclusion...
- Infectious agents can be the primary cause of a dermatoses, but more commonly are secondary to an underlying condition
- In the workup of a pruritic animal, we need to first rule out infectious diseases as the cause of the pruritus before pursuing a diagnosis of allergies
- In the treatment of infectious dermatoses, the use of corticosteroids should be avoided if possible since they can impair the animals own response and delay healing or cause a worsening of the condition

QUESTIONS ???