Page 10 - VETcpd - Vol 5 - Issue 2

Introduction Canine pyoderma is a very common bacterial skin infection in dogs. In the majority of cases it is secondary to an underlying disease, or diseases, with allergic dermatitis and ectoparasitic infestations being most common. The epidermal barrier protects the healthy individual from physical, microbial, and chemical insults. When this barrier is breached, due to trauma, or inflammation, infection can occur. In most cases the trauma is self-inflicted during episodes of scratching, biting, or licking. The inflammatory changes associated with allergic skin disease or ectoparasitic infestation result in pruritus and excessive humidity at the skin surface (caused by increased secretions and skin temperature) which, in turn, results in changes to the skin’s microbiome and subsequent colonisation by pathogenic bacteria. For infection to occur, pathogenic bacteria first have to colonise the skin, which they do by adhering to the corneocytes. The bacteria possess adhesion molecules on their surface that bind to receptors on the host cell membrane. Studies have demonstrated increased staphylococcal adherence to corneocytes in atopic dogs, compared to healthy animals (Simou et al. 2005). In some breeds, genetic factors are also thought to play a role in staphylococcal adherence (Forsythe et al. 2002). Staphylococcus pseudintermedius is implicated in most cases of canine pyoderma. However Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP) infections are increasingly being seen in general practice. Secondary invaders such as E.coli, Pseudomonas spp. and Proteus also play a role, especially in deep infections and resistance to these organisms is also on the increase.

VETcpd - Dermatology Peer Reviewed

Dr Anita Patel BVM DVD MRCVSRCVS Recognised Specialist in Veterinary Dermatology

Anita Patel runs a busy dermatology referral service out of four clinics in London and the South East of England, she also lectures both in the UK and internationally. She is recognised by the Royal College as a Specialist in Veterinary Dermatology.She has over 20 years’ dermatological experience, gaining her certificate (CertSAD) in 1993 and her Diploma in 2002. As a Specialist, she has dedicated the last 14 years exclusively to small animal dermatology. Anita co-authored a case based text book on small animal dermatology in the “Saunders Solutions in Veterinary Practice” series, as well as chapters in various dermatology text books. She has published papers in refereed and peer reviewed journals and is actively involved in all aspects of dermatology.

Tel: 01883 623761E-mail: anita@dermatologyreferrals.co.uk

Canine pyoderma is a very common bacterial infection of the skin and can mimic almost any dermatological disease. Several syndromes are described by a classification system based on the depth of infection and some dogs can present with more than one syndrome. Staphylococcus pseudintermedius is the most common cause but other staphylococci and Gram-negative organisms can be involved in the pathogenesis. In light of increasing antibiotic resistance it is important to make an accurate diagnosis before implementing antibiotic therapy. This paper describes the clinical signs, diagnosis and treatment of canine pyoderma.

Key words: Pyoderma, Staphylococcus pseudintermedius, Staphylococcus aureus

Diagnosis and management of

Canine Pyoderma

Classification of pyodermaPyodermas are classified as surface, superficial and deep depending on the depth of infection (Table 1). Surface infections are confined to the surface layers of the stratum corneum; and include acute moist dermatitis (pyotraumatic dermatitis), intertrigo (skin fold dermatitis), bacterial overgrowth syndrome and mucocutaneous pyoderma. Superficial infections involve the epidermis and the superficial portions of the hair follicle. These can be sub-classified as impetigo, superficial spreading pyoderma, superficial folliculitis, pyotraumatic folliculitis and mucocutaneous pyoderma. Deep bacterial infections usually affect the hair bulb and may also involve the dermis and subcutaneous tissue. If the hair follicle ruptures, the infection is released into the surrounding tissue leading to swelling and sinus formation. Deep pyodermas include deep folliculitis, furunculosis and cellulitis and those linked to specific sites on the body, for example chin pyoderma, deep interdigital pyoderma etc.

Clinical signs The lesions in the different types of pyoderma can overlap and may be seen on the same animal at different sites.

Surface pyodermasPyotraumatic dermatitis, often referred to as “acute moist dermatitis” or “hot spot”, is a demarcated circular lesion, with purulent exudate at its surface, usually on the rump, anterior neck or face of the patient. It is typically seen in thick-coated dogs such as German Shepherd Dogs (GSD), Labradors and Golden Retrievers and is mainly associated with flea allergic dermatitis, anal gland problems and otitis externa (Figure1).

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VETcpd - Dermatology

Surface

Intertrigo (skin fold dermatitis). Sub-classified according to the site affected e.g. nasal fold, facial fold, lip fold, vulvar fold, tail fold and body fold Pyotraumatic dermatitis (acute moist dermatitis) Mucocutaneous pyoderma Bacterial overgrowth syndrome

Superficial

Impetigo Superficial spreading pyoderma Superficial bacterial folliculitis (Mucocutaneous pyoderma)* (Bacterial overgrowth syndrome)*

Deep localisedNasal, chin, muzzle, pedal, Pyotraumatic folliculitis and furunculosisAcral lick furunculosis

Deep generalisedDeep folliculitis, furunculosis and cellulitis German Shepherd Dog deep pyoderma

Table 1: Classification of canine pyoderma

* Both mucocutaneous pyoderma and bacterial overgrowth syndromes can affect the superficial epidermis in some dogs

Figure 3: Nasal fold dermatitis in a Pug. Figure 4: Bacterial overgrowth syndrome in an atopic West Highland White Terrier.

Figure 5: Crusting around the lips in a GSD with mucocutaneous pyoderma.

Figure 1: Pyotraumatic dermatitis associated with otitis externa. Figure 2: Lip fold dermatitis in a Cocker Spaniel.

Intertigo (Skin fold dermatitis) is usually associated with excessive moisture retention and friction between skin folds. The terms used to describe the condition include the site affected, for example lip fold dermatitis (Figure 2), nasal fold dermatitis (Figure 3) etc. Sometimes, only exudate is evident and, at other times, maceration leads to erythema, erosions and pain.

Bacterial overgrowth syndrome is associated with overgrowth of staphylococcal bacteria at the skin surface (Figure 4). Pruritus, greasy seborrhoea and malodour are usual features. The lesions can be localised, or generalised, and include erythema, lichenification, hyperpigmentation and sometimes excoriations.

Mucocutaneous pyoderma is seen mainly around the mouth and nose but can affect other mucous membranes. GSDs and their crosses are particularly susceptible and the lesions seen are generally crusting, erythema, swelling, fissuring and erosions (Figure 5).