Bacterial infections (pyoderma, folliculitis, furunculosis) of the skin and hair follicles are very common problems in the dog. These lesions often represent an infection or “over colonization” of the skin by Staphylococcus sp.
Bacterial infections often manifest in a characteristic sequence of lesions:
Follicular papule > pustule > crust from a ruptured pustule > epidermal collarette (central clearing with peripheral ring of scale) > hyperpigmented macule. In certain breeds, however, these infections can appear, merely, as patchy and circular areas of hair loss.
The frequent causative organism (“Staph”) is considered normal “resident” flora. There are a number of reasons why the “Staph” can overgrow and cause disease. It's critical that those reasons are identified and addressed in order to prevent recurrence of the bacterial infection. Common causes include: allergies, parasite infestation, hormonal imbalances, keratinization disorders, immunodeficiencies and metabolic disorders to name a few.
Superficial Pyoderma (Folliculitis)
Superficial pyoderma may be a primary condition or secondary to other underlying diseases such as allergic dermatitis, endocrine abnormalities, immunosuppression, etc. Most cases of superficial pyoderma are associated with minimal pruritus (itching) although some dogs may experience marked pruritus due to a presumed hypersensitivity to the Staphylococcal bacteria. When pruritus is a feature, it is often necessary to evaluate the response of the patient to antibiotic therapy in order to determine if an underlying problem may be contributing to the clinical picture. Antibiotics must be used for a minimum of 3 weeks and given in conjunction with topical shampoo therapy. Steroids should be avoided during this evaluation period.
Recurrent Superficial Pyoderma
Recurrent superficial pyoderma is a common and frustrating problem in the dog. If a specific underlying etiology cannot be determined (allergy, hypothyroidism, hyperadrenocorticism, diabetes mellitus, neoplasia (cancer), etc.) then efforts must be made to control the cutaneous (skin) bacterial population and / or stimulate the patient's immune status. Various methods may be trialed to manipulate the patient's response to their normal bacterial flora. Aggressive shampoo and other topical therapy as well as immunomodulators (staphage lysate therapy) are examples etc. An important aspect of managing these chronic cases is the establishment of an effective and acceptable therapeutic maintenance protocol. Staphylococcal infections have become problematic due to the emergence of resistant strains. Read about MRSA
Deep Pyoderma
Folliculitis and furunculosis, deep pyoderma, is a common and frustrating problem in the canine patient. Most of these cases are due to a severe Staphylococcal infection of the hair follicles which leads to a rupture of the follicular epithelium. This allows the hair shaft, keratin, and damaged collagen access to the dermis and thus initiates a “foreign body” reaction. The massive amount of inflammation caused by this reaction accounts for the clinical signs of erythema (redness) and swelling with exudation. The type of inflammation is typically "granulomatous," which adds to the therapeutic challenge. The treatment must be specific for this type of inflammatory response and continued for an extended period of time.
Diagnosis
A complete metabolic diagnostic work-up is recommended to eliminate the possibility of underlying disease as the initiating or contributing factor. A skin biopsy and surgically-obtained culture are sometimes helpful in characterizing and understanding this disease.
Treatment
Systemic antibiotic therapy is often necessary for a minimum of 6 to 8 weeks. Shampoo therapy with an antiseptic or antibacterial agent should be used in conjunction with oral therapy. Often, the hair must also be shaved to prevent the formation of a sealing crust and to allow the topical agents to contact the diseased skin. Hydrotherapy (soaks and / or whirlpool) with an antiseptic agent is beneficial in the early stages of therapy to allow for removal of crusts, decreasing the surface bacterial counts, promoting epithelialization and to decrease the discomfort of the pet.
Pododermatitis
Pododermatitis is a form of deep pyoderma that affects the interdigital areas (between the toes) of the paws. In cases of deep pyoderma, this is often the last area to respond to therapy. A complete diagnostic evaluation is necessary to rule out causes other than bacterial (ie. demodicosis, Malassezia, etc.). Oral antibiotic therapy for an extended period (6 to 8 weeks) and commitment from the pet owner is required as there is an extensive protocol in caring for the patient:
Remember: A maintenance protocol should be instituted that includes both shampoo and topical therapy. The frequency of application required to control the clinical lesions will vary with the patient.
Contributed by: Karen Helton-Rhodes, DVM, Diplomate ACVD
