Introduction
Feline pyoderma is a cutaneous disease caused by bacterial infection. It has received considerably less attention than its canine counterpart. This may be because feline pyoderma lesions are less well defined than they are in canine disease and can go unrecognized. However, feline pyoderma may be more prevalent than previously suspected and one study identified that it was the fifth most common dermatological disorder diagnosed in the cat in general practice.1
Resident cutaneous microflora in cats include coagulase positive (Staphylococcus pseudintermedius, S. aureus) and coagulase negative (S. felis) staphylococci, Micrococcus spp., Acinetobacter spp. and alpha haemolytic streptococci. Although the skin and hair may be colonised by potentially pathogenic fungi and bacteria, it is inherently resistant to infection. The stratum corneum forms a tough physical barrier consisting of layers of corneocytes and desquamation naturally removes surface organisms. The spaces between corneocytes are permeated by a sweat and sebum emulsion which contains many elements of both the innate and adaptive immune systems that resist bacterial colonisation.
Pyoderma occurs because natural host defence mechanisms are overcome and is seen as a result of a number of underlying diseases including the manifestations of allergic dermatitis, parasitic disease, keratinisation defects such as feline acne and underlying immunosuppression.2,3 Feline pyoderma should therefore be considered a secondary condition and every effort should be made to identify and correct the underlying causes in cases where disease is recurrent.
Microorganisms Associated with Feline Pyoderma
The most prevalent organism cultured from feline pyoderma is S. pseudintermedius, but S. aureus and S. felis are also isolated,4 and if atypical infections are included, the potential list of bacteria causing cutaneous infections in cats is long. Methicillin-resistant staphylococci have been isolated from cats with inflammatory skin disease,5,6 and this can be associated with resistance to other classes of antibiotics. Risk factors for the development of resistant infections include repeated empirical use of broad-spectrum antibiotics, hospitalization and surgical implants.7
Clinical Presentations of Feline Pyoderma
In the dog, pyoderma is classified according to the depth of infection within the skin. Surface, superficial and deep pyoderma are described. The various presentations are usually fairly easily distinguished on clinical examination.
The clinical presentations of pyoderma in the cat are much less well defined. They tend to be clinically indistinct and usually reflect the underlying disease process.8 However, superficial or deep pyoderma may be distinguished in some cases. Superficial lesions include crusted and eroded papules, exudative plaques, erosions and ulcers, areas of nonspecific self-trauma, lesions of feline acne. Deeper infections include nonhealing wounds, nodules and draining tracts. The typical follicular pattern of hair loss seen commonly in superficial canine pyoderma seems to be very rare as are the classic papule, pustule and epidermal collarette progression. A common scenario is secondary bacterial infection of an eosinophilic dermatosis.9
Diagnosis
Cytology is indicated in any inflammatory dermatosis to identify infection. Samples may be obtained by direct impressions, impressions from crust, the use of cotton buds and tape strip techniques. Samples should be stained with a Romanowsky-type stain and examined under x1000 oil immersion. The presence of toxic neutrophils and phagocytosed cocci confirms the diagnosis of a bacterial pyoderma. A common scenario in feline pyoderma is a combination of an eosinophils and neutrophils with intra- and extracellular cocci. Bacterial overgrowth is a form of surface pyoderma where large numbers of bacteria may be evident on cytology without a significant inflammatory infiltrate.
Treatment
It has become apparent that systemic antibiotic treatment is required much less frequently than previously thought for the management of canine pyoderma. Some national guidelines recommend that topical antiseptics should be attempted before resorting to systemic antibiotics provided the animal's welfare will not be compromised. In one study of feline superficial pyoderma,2 31% of cases were treated with topical therapy alone and half of those treated had a good response. Topical therapies used included chlorhexidine, silver sulphadiazine and fusidic acid. However, there are difficulties in treating cats topically and systemic antibacterials are probably still the mainstay of treatment for feline pyoderma.
Empirical antibiotic selection is acceptable in first presentation, uncomplicated infections where cocci are identified on cytology. Culture and sensitivity testing should be performed:
If unusual organisms such as rods are seen on cytology
If there has been a poor response to empirical therapy
In cases that have been previously been exposed to many classes of antibiotics
In cases of deep pyoderma when more prolonged therapy may be required
Where there is a history of exposure to a potentially resistant bacteria
Immunosuppressed Cases
Samples for culture and sensitivity testing should be taken from sites where bacteria are identified on cytology. The optimal lesion to sample is an intact pustule but any other lesion type may be sampled. Deep draining lesions should be cleaned first with dilute chlorhexidine or alcohol then material expressed from the lesion. Fine-needle aspiration and biopsy procedure are effective methods of obtaining samples from deeper lesions.
Careful consideration should be given as to which drug to use if systemic antibiotic therapy is indicated.
The antibiotic selected should be safe.
It should be effective against the offending organism and have good penetration and distribution to the skin.
Ideally, a narrow - rather than a broad-spectrum - therapy should be selected when treating gram-positive infections.
The dosage regime should fit in with the owner's other commitments.
Guidelines have been published on the use of systemic antibiotics for the treatment of superficial pyoderma in dogs,10 but no such guidelines are currently available for cats. Nevertheless, it is reasonable to extrapolate from the canine guidelines. These guidelines classify antibiotics into three tiers. The first includes cefadroxil, cephalexin, clavulanate-amoxicillin, clindamycin and lincomycin. Cefpodoxime and cefovecin may be included as first-line treatments where medication is difficult or owner compliance is likely to be poor. First-tier products are suitable for initial empirical treatment of pyoderma. Second tier include cefovecin, cefpodoxime, difloxacin, enrofloxacin, marbofloxacin, orbifloxacin and pradofloxacin. They should not be used for empirical therapy and should only be used following culture and sensitivity testing.
Dosage and Duration of Therapy
The drug should be administered at the correct dose to achieve adequate tissue concentrations. Due to relatively poor cutaneous vascular perfusion, it is wise to treat at the higher end of the recommended dosage range. Most dermatologists continue treatment until a week past clinical and cytological resolution, and in the case of feline superficial pyoderma this is likely to be two to four weeks. Considerably longer courses of treatment may be required for deeper infections. It is important for the clinician to re-evaluate the animal to determine the end point of treatment and not to rely on the owner's judgment.
Wherever possible, the underlying disease predisposing to the pyoderma should be identified and treated.
Treatment of Methicillin-Resistant Staphylococci (MRS)
If possible, further systemic therapy should be avoided to reduce antibiotic selection pressure, but if required should be based on culture and sensitivity results. Whenever possible, topical antiseptics rather than systemic antibiotics should be used. Owners of cats with MRS should be advised on good hygiene measures and appropriate precautions should be taken in the practice situation.
References
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2. Yu HW, Vogelnest LJ. Feline superficial pyoderma: a retrospective study of 52 cases (2001–2011). Vet Dermatol. 2012;23(5):448–e86.
3. Mueller RS. Bacterial dermatoses. In: Guaguere E, Prelaud P, eds. A Practical Guide to Feline Dermatology. Paris: Merial; 1999:6.1–6.11.
4. Patel A, Lloyd DH, Howell SA, et al. Investigation into the potential pathogenicity of Staphylococcus felis in a cat. Vet Rec. 2002;150(21):668–669.
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10. Beco L, Guaguere E, Lorente Mendez C, et al. Suggested guidelines for using systemic antimicrobials in bacterial skin infections: part 2 - antimicrobial choice, treatment regimens and compliance. Vet Rec. 2013;172(6):156–160.