Approach to secondary skin infections Flashcards
How are commensals involved in skin infections?
- Skin infection is usually associated with commensal (bacterial and/or fungal) organisms
- Commensals take advantage of either a problem with the skin barrier and/or the skin or systemic immune system
- Culture for these organisms is not diagnostic as they are present on the skin anyway
What are the most common commensal skin bacteria and fungi?
Bacteria = S.pseudointermedius Fungi = Malassezia pachydermatis
In comparison to commensals, infections with pathogens are diagnosed …?
On cultrue
What are the pathogens causing bacterial pyoderma? Which is the most common?
Commensal bacteria from mucosae or gastro-intestinal tract
Staphylococcus pseudintermedius
What are some examples of underlying disease causes of bacterial pyoderma?
- Allergy
- Ectoparasites
- Immune deficiency
- Keratinisation defects
What are the 3 classifications of bacterial pyoderma?
- Surface: superficial epidermis
- Superficial: epidermis and hair follicles
- Deep: epidermis, hair follicles, dermis +/- subcutaneous fat
What are the 3 clinical presentations of surface bacterial pyoderma?
- ‘Hotspots’ = pyotraumatic dermatitis (PTD)
- Skin fold pyoderma = intertrigo
- Bacterial overgrowth
Describe ‘Hotspots’ = pyotraumatic dermatitis (PTD)
- Lesions that develop within in a few hours due to self trauma
- Lesions on cheek, neck or rump
- Well-demarcated patch of alopecia, central erosion, peripheral erythematous halo e.g., underlying flea allergy
Which 3 dog breeds are predisposed to ‘Hotspots’?
Rottweiler
Golden retriever
German shepherd
How are hotspots treated?
Clip (often need sedation), clean, topical antiseptic/antimicrobial, and systemic/topical anti-inflammatory e.g., steroids
Intertrigo is also called?
Skin fold pyoderma
Why/how does skin fold pyoderma occur?
- Compromised skin barrier: friction, loss of ventilation, fluid accumulation
- Microbes proliferate and produce toxins which creates inflammation
- Erythema and moist exudate
How is skin fold pyoderma treated?
Topical antiseptics/ anti-microbial & topical/systemic anti-inflammatories. Other e.g., weight loss in obese dogs causing a deep vulvar fold
Bacteria overgrowth is common in dogs with which condition?
Atopic dermatitis
What are the signs of bacteria overgrowth?
- Affects the ventral trunk and interdigital spaces
- Pruritic
- Erythema, hyperpigmentation, lichenification, excoriation & alopecia
Malassezia overgrowths occurs secondary to?
Underlying disease
What sample technique would be used for dry, erythematous, scaly, alopecic patch on the neck?
Acetate tape strip
What sample technique would be used for greasy, brown wax between digits?
Indirect smear using a cotton bud
What is the most common presentation of superficial pyoderma?
Bacteria folliculitis
Describe the features of bacterial folliculitis
- papules and pustules
- pyogenic = degenerative neutrophils & phagocytosis of bacteria
- Pruritic or non-pruritic
Which bacteria are the main cause of bacterial folliculitis?
Staphylococcus pseudintermedius
What are the clinical signs of bacteria folliculitis?
- Erythema, follicular papules & pustules, crusts, epidermal collarettes, erosions
- Annular macules of alopecia “moth eaten”
- Hyperpigmented / lichenified plaques if chronic
Which skin structures are involved in deep pyoderma?
- Epidermis
- Entire hair follicle
- Follicles rupture
- Dermis +/- subcutaneous fat
What are the features of deep pyoderma?
Heat, swelling, erythema, furuncles, nodules, bullae, plaques, sinus tracts, ulcers, exudation and crusts
What are furuncles?
Skin abscesses caused by staphylococcal infection, which involve a hair follicle and surrounding tissue
Which type of inflammation is involved in deep pyoderma?
Pyogranulomatous inflammation
- Neutrophils, macrophages +/- eosinophils
What is diagnostic for pyoderma?
Cytology
What are the 4 different cytology techniques?
- Direct impression smear (DIS)
- Cotton tip/swab smear (IDS)
- Adhesive tape strip (ATS)
- Fine needle aspirate (FNA)
What is the key finding on cytology to confirm pyoderma?
Degenerative neutrophils and intracellular bacteria is the key finding
- In most cases S. pseudintermedius
In which cases is it appropriate to perform culture and sensitivity?
- Recurrent or chronic infection
- Rod-shaped or unusual organisms on cytology
- Degenerate neutrophils but absence of bacteria on cytology
- Deep infections
- Non-healing wounds
- Life threatening infections
What is the culture technique for superficial infections?
- Rupture and sample intact lesion if present
- Sample erosion under a crust or at the edge of a collarette
What is the culture technique for deep infections?
- Fresh tissue sample (biopsy)
- Rupture intact lesion if possible and use swab (not if suspect mycobacteria)
- Swab into deep sinus tract (last resort)
How should confirmed bacterial pyoderma be treated?
- Investigate & treat the underlying primary disease
- Use topical treatment in every case where possible
+/- Systemic antimicrobials IF NEEDED
What is the most common antiseptic used in skin, give examples of forms it comes in
Chlorhexidine
- Shampoos
- Sprays
- Gels
- Wet wipes
- Mouse
What is the first line treatment for Malassezia?
Chlorhexidine
If systemic antibiotics are needed for pyoderma, how to select?
- If first time pyoderma, groups of cocci on cytology, and no risk factors for AMR, treatment can be selected empirically
- However, Meticillin Resistant S. pseudintermedius (MRSP) are emerging which are resistant to β-lactams and usually fluoroquinolones
What are the risk factors of Meticillin Resistant S. pseudintermedius (MRSP)?
- Hospital admission
- Multiple vet visits
If antibiotics are needed for pyoderma, what duration for superficial and deep?
Superficial = 2-3weeks Deep = 4-12 weeks
