Canine impetigo is a common problem in young prepubescent dogs that have been kept in poor, unhygienic conditions. It is a non-follicular subcorneal pustular condition caused by coagulase-positive staphylococci. Bullous impetigo refers to a different condition seen in old dogs with debilitating or hormonal diseases such as hypothyroidism or hyperadrenocorticism.
Clinical features
Lesions are pustules (Figure 1), papules, epidermal collarettes and crusts (Figure 2),
which are seen in sparsely haired regions such as the axillae and
inguinal region, and especially in the non-haired (glabrous) region of
the ventral abdomen. It typically affects puppies between three and six
months old and occasionally older.
Canine impetigo is non-contagious, unlike impetigo in humans. The condition is relatively benign providing that underlying factors are eliminated with prompt treatment of the lesions. Spontaneous resolution is also possible with improvement in management alone.
Underlying factors include:
- Internal and external parasitism (Figure 2)
- Viral infection such as canine distemper. Impetigo used to be a common manifestation of canine distemper, a disease which is now uncommon in the UK
- A dirty environment, for example, in poorly managed pet shops with overcrowding, puppies originating from puppy farms and those bred in poor conditions and imported from outside the UK
Differential diagnosis
- Demodicosis
- Superficial folliculitis
- Dermatophytosis
- Early scabies – consider if pruritus is present and there has been no acaricidal treatment
- Pemphigus foliaceus (this is possible but more likely as a differential diagnosis of bullous impetigo in old dogs)
Diagnosis
- History. Look for poor husbandry, absence of prior parasitic treatment, evidence of inadequate diet or a history of living in a known poor environment
- Physical examination. Look for interfollicular lesions that do not involve the follicles. Folliculitis will involve pustules from which a hair may be seen protruding. An examination with a hand lens and good lighting is advised, as the distinction between follicular and non-follicular lesions is important. Folliculitis cases are more difficult to resolve
- Cytological examination. This may be performed by pricking a pustule and smearing the contents, or by tape stripping of superficial lesions. Diff-Quik staining will demonstrate degenerate neutrophils and intracytoplasmic and extracellular cocci
- Culture and sensitivity testing. This has traditionally not been performed commonly in these cases. It is never unjustified, however, and is advised if simple therapeutic measures do not result in a prompt response
- Histopathological examination. This is rarely performed in the routine case. The subcorneal nature of the pustules will be clearly outlined, and a biopsy may be useful if doubt exists of the diagnosis, or if there is a poor initial response to treatment
Clinical management
Attention to the underlying factors described above may be all that
is necessary to achieve a satisfactory response. However, treatment will
facilitate a more rapid resolution. Cases may be detected at the time
of first vaccination, and a useful therapeutic aim will be to achieve
resolution of the lesions before the second vaccination.
Shampooing with antibacterial shampoos containing chlorhexidine (with
or without miconazole) or ethyl lactate should be undertaken three
times a week. A good response to topical therapy should be expected
within two weeks. In cases failing to respond in this timeframe, culture
and sensitivity testing should be followed by three weeks of
appropriate antibacterial therapy. This is rarely necessary and should
be considered only if topical therapy is ineffective.
SUGGESTED READING
Miller, W. H., Griffin, C. and Campbell, K. (2013) Small Animal Dermatology, 7th ed. Elsevier, St Louis.
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