Bacterial skin infections are common in dogs and cats with estimates that about 20% of dogs and cats that present to general practice having a skin condition. Only about 25% of these are due to bacterial infections16.
Generalised pyoderma occurs most commonly and is frequently secondary to an underlying primary condition17. Over 90% of bacterial pyodermas in dogs are caused by Staphylococcus pseudintermdius, which is a commensal skin organism in both dogs and cats18. Staphylococcus aureus is also common in cats19.
Skin infections are categorised by their depth, which determines the most appropriate therapy. Cytological examination is needed to confirm the existence of a bacterial pyoderma. Cells can be collected using adhesive tape, direct smear or fine-needle aspirates if intact pustules or nodules are present. Cytology usually reveals cocci, and occasionally rods, and neutrophils.
Culture and sensitivity is recommended in all cases:
– where systemic antimicrobials are being considered (assists with appropriate choice and gives information on resistance patterns in both first-time and chronic infections)
– where rods are present on cytology
– where there is a lack of response to antimicrobial therapy
– when knew lesions develop during treatment
Includes skin fold pyoderma (intertrigo) and pyotraumatic dermatitis (‘hotspot’). Pyotraumatic dermatitis can progress to involve the deeper layers becoming pyotraumatic folliculitis or furunculosis; papules, pustules or furuncles will be evident. Topical treatment should be prioritised. Many cases can be effectively treated with topical preparations alone. Clipping the fur allows for more effective treatment. Wipes containing chlorhexidine and drying agents can be useful if small areas are affected. Shampoos are more appropriate for widespread disease as these also contain delivery vehicles that help to distribute the active agent more widely over the body19. Shampooing 2-3 times weekly is usually sufficient but shampoo must be allowed to sit in contact with the skin for 5-10 minutes to attain an optimal antimicrobial effect, prior to rinsing20. The most common side-effect is drying of the skin. A moisturising agent can be used following shampooing if necessary.
|Chlorhexidine||Destroys bacterial cell membranes, broad-spectrum, moderate effect against Malassezia|
|Ethyl lactate||Good penetration including hair follicles and sebaceous glands. Lowers skin pH thus inhibiting bacterial enzymes, bacteriostatic effect.|
|Benzyl peroxide||Destroys bacterial cell membranes, broad spectrum, can dry or irritate skin.|
Systemic antimicrobials are not usually necessary for either intertrigo or pyotraumatic dermatitis. Topical antimicrobials, in combination with topical corticosteroids can be useful.
Superficial folliculitis is most common and characterized by purulent infection of the hair follicles (not ruptured). A predisposing disorder is frequently present (allergy, ectoparasites, endocrine disease) especially if recurrent disease occurs. Cats can also develop disease; underlying allergies or immunosuppressive diseases (FIV, FeLV, others) should be ruled out especially if recurrent disease occurs.
Topical therapy should be the first choice as many can be effectively treated with topical therapy alone21. Shampoos can also be used prophylactically to reduce recurrence. If systemic antimicrobials are necessary first line should be as narrow-spectrum as possible. Combining topical therapy with systemic therapy will increase efficacy.
Systemic antimicrobial therapy:
|Second line||When resistance to first line confirmed, or for chronic/recurrent||
|Third line||Only when resistance to first and second line drugs confirmed, typically for pseudomonas infections||
Furunculosis is an extension of folliculitis leading to rupture of the hair follicle and is the most common deep pyoderma but it is not common in dogs and rare in cats. Lick granulomas and feline chin furunculosis are also deep pyodermas. Do not confuse feline chin furunculosis with feline acne, the latter of which can be treated topically. Histopathology and culture and susceptibility from surgical biopsies is recommended. Consider an underlying disease. Focal disease can be managed with topical therapy however systemic antimicrobials are necessary in widespread disease; combine with topical therapy. Continue therapy for at least 2 week following resolution of clinical signs.
Furunculosis, lick granuloma Clindamycin, amoxycillin / clavulanate or cephalexin and topical therapy
Feline chin furunculosis Clindamycin or amoxycillin / clavulanate
CELLULITIS & ABSCESSES
Cellulitis is diffuse inflammation whereas abscess is an accumulation of purulent exudate. Bites and scratch wounds are the most common causes, especially in cats. Bacterial commonly associated with bites in dogs include Staphylococcus spp., ß–haemolytic Streptococcus spp., E. coli, Pasteurella canis. In cats Pasteurella multocida subsp. multocida and septica. Anaerobes are also frequently involved. Actinomyces, Norcardia or mycobacteria should be suspected if persistent fistulous and draining nodules are present.
Clinical signs and cytology are usually sufficient. If response to treatment is poor, culture and susceptibility testing is recommended. In addition, if draining fistulae are present or the animal is systemically unwell culture and susceptibility testing should be pursued.
Abscess: Draining and flushing alone is usually sufficient. Antimicrobials should be reserved for animals that are systemically unwell, where there is diffuse tissue involvement, potential joint involvement or in immunosuppressed animals. If systemic antimicrobials are being considered, culture and susceptibility testing should be performed. Most can effectively be treated with 5-10 days of amoxicillin or ampicillin or clindamycin22.