Bacterial Skin Infections
Development of Pyoderma:
It is believed that staphylococcal pyoderma develops following surface spread from carrier (reservoir) sites (lower lips, chin, paws, nail beds, eyes, ears, perianal area, perivulvar or preputial area).
Factors that predispose to recurrent pyodermas:
1. Where there is a tendency to surface colonization:
a. Seborrhea, of whatever cause, is likely to lead to colonization with Staphlococcus pseudintermedius.
b. Atopic disease. Stratum corneum cells (scale) of atopics have a greater tendency to adhere to bacteria.
2. Where the integrity of the skin barrier is impaired: This may occur secondarily to any inflammatory skin disease, or one that leads to self-trauma from pruritus. Flea allergy or mange (Demodicosis) are examples.
3. Immunocompromised: Limited to deficiencies in non-specific defenses or cell-mediated immunity.
a. Congenital non-specific immune defects. Weimaraner, Doberman, Irish setters.
b. Impaired cell-mediated immunity. Atopic dogs have impaired cell-mediated immunity.
4. Food allergy: Typically, affected animals are less pruritic when on antibiotics with their pyoderma controlled, but relapse occurs either immediately on cessation of therapy or within 2-3 weeks.
5. Hypersensitivity to staphylococcal antigens: Hypersensitivity makes the animal easier to infect.
6. Hypothyroidism:This is well recognized as a cause of recurrent staphylococcal infection.
7. Iatrogenic: Improper use of antibiotics and/or continuous use of corticosteroids (cortisone, steroids).
Management of Recurrent Pyoderma:
1. Search for a predisposing cause.
a. Evaluate for seborrhea. If this is evident, look for a cause of the seborrhea.
b. Evaluate for evidence of ectoparasitic disease (fleas, mites, flying insects, etc.).
c. Check for thyroid function, even in animals that are not overtly seborrheic.
d. Skin test, or undertake in vitro tests for atopy.
e. Do an elimination diet for food allergy.
f. Work-up for immunological defects is not generally available.
2. Therapy for the recurrent case with no apparent cause.
a. Be sure to use the appropriate antibiotic therapy. Bactericidal therapy is preferred in recurrent cases.
b. Use good supporting antibacterial shampoos (benzoyl peroxide (2-3%), clorhexidene (2-4%) or ethyl lactate (10%)). These may be alternated with antiseborrhoeic shampoos if seborrhoea is present.
c. Consider using immunotherapy with a staphylococcal product e.g., Staph Phage Lysate.
d. As a last resort:
i. Continued antibiotic therapy in normal doses,
ii. Intermittent courses of antibiotic at full dosage with one month on and one month off.
iii. Intermittent courses of antibiotic at full dosage on, say, two consecutive days each week.
iv. Continual low dose antibiotic therapy.
The risk of recurrent pyoderma (skin infection) is greater than the risk of continuous antibiotics.