Canine pyoderma is a cutaneous bacterial infection that represents one of the major diseases affecting canine skin. This is partly a consequence of the thin and compact canine stratum corneum, the paucity of intracellular emulsion in the canine epidermis and the lack of a sebum plug in the canine hair follicle. Almost 90% of cases are caused by Staphylococcus pseudintermedius, although other less frequently isolated bacteria include Escherichia coli, Pseudomonas aeruginosa or Streptococcus spp.
S. pseudintermedius is part of the normal microbiome of dogs, usually found on the skin and mucous membranes, mainly in the nostrils, mouth and perineum of asymptomatic animals. However, they can also cause opportunistic infections such as pyoderma. Common underlying triggers are ectoparasite infestations, allergic skin diseases and endocrinopathies, with allergic disease being considered the main driver for recurrent forms of pyoderma.
Although rarely life threatening, pyoderma contributes substantially to canine morbidity through associated pruritus or pain, and potentially widespread severe inflammation/infection.
Depending on the depth of infection, pyodermas can be classified as surface, superficial or deep. In surface pyoderma, bacteria are confined on the surface of the skin. It is presented as pyotraumatic dermatitis (hot spots), intertrigo (fold pyoderma) and ‘microbial/bacterial overgrowth syndrome’, in which erythema is the only clinical sign but in which large numbers of bacteria on the inflamed skin can be demonstrated by cytology.
Superficial pyoderma is likely to be the most frequent type of pyoderma in dogs and involves invasion of the epidermis by bacteria. Bacterial folliculitis extends into the follicular ostium and epidermal tissue. Dogs with superficial pyoderma are presented with papules, pustules and epidermal collarettes, typically on the ventral abdomen, medial thighs and trunk, often associated with areas of alopecia and varying degrees of pruritus. The interfollicular form (impetigo) occurs mostly in puppies. Coat type and immune status can also its influence appearance.
Deep pyoderma is less common, but more serious, since its expansion into the dermis and proximity to blood vessels increases the risk of haematogenous spread and bacteraemia. Lesions include draining sinuses, fistulae, haemorrhagic crusts, nodules and varying degrees of erythema and swelling; pain is not infrequent. Common localized forms of deep pyoderma affect the head (‘chin acne’, muzzle folliculitis and furunculosis) or limbs (interdigital nodules, callus pyoderma and ‘acral lick granuloma’).
Mucocutaneous pyoderma is a disease of unknown aetiology. It primarily affects the lips and perioral skin, with swelling, erythema and crusting, which may lead to fissuring and erosion. It often responds slowly to therapy and can be confused with immune-mediated disease.
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