Canine Demodicosis (Demodectic mange)
- Cause: overabundance of Demodex canis mites
- Mites inhabit hair follicles and sebaceous glands
- Pathogenesis is complex and not well understood
- Hereditary predisposition for generalized disease
- Immunosuppression (natural or iatrogenic)
- Secondary bacterial and fungal infections can be deep and severe, leading to guarded prognosis
- While Demodectic mange is not pruritic in itself, the secondary infections can cause pruritus, which may be severe
- 3 forms: Localized demodectic mange, juvenile-onset generalized demodecosis, adult-onset generalized demodicosis
1. Localized demodectic mange
- usually in dogs less than 1 year old
- some cases resolve spontaneously, while others progress to more severe generalized form
- Signs: 1-5 well-demarcated small areas of alopecia, erythema, and scaling. Lesions usually around the lips, eyes, and forelimbs, but can be anywhere on the body. Pruritus is absent or mild.
2. Juvenile-onset generalized demodicosis
- Result of inherited immunological defect
- severe disease of young dogs
- Signs: Generalized lesions (erythema, papules, alopecia, oily seborrhea, edema, hyperpigmentation, crusts) aggravated by secondary bacterial and fungal infections and pododermatitis. May have systemic signs as well (generalized lymphadenopathy, lethargy, fever) when deep pyoderma, furunculosis, or cellulitis is present
3. Adult-onset generalized demodicosis
- Similar clinically to juvenile-onset generalized demodicosis except for age of onset
- Usually associated with or triggered by debilitating disease that causes immunosuppression (ex. malignant lymphosarcoma, malignant melanoma, hyperadrenocorticism, hypothyroidism, diabetes, etc) but in many cases the underlying condition is never found
- Diagnosis: deep skin scrape typically reveals large numbers of mites and eggs
- Treatment may not be required in localized demodectic mange as spontaneous recovery can occur, and prognosis is good
- Treatment is always required in generalized demodicosis, and prognosis is guarded
- Treatment options (most off-label usage) : clip hair, bathe with benzoyl peroxide shampoo, then dip with Amitraz dips once weekly; milbemycin oxime, moxidectin, ivermectin, fluralaner, afoxolaner
- Continue treatments until there are 2 consecutive negative skin scrapes a month apart
- Treat secondary infections aggressively with antibiotics and antifungals
- Local and systemic corticosteroids are contraindicated in all Demodex cases
- Treatment may take several months and recurrence is not uncommon
- Do NOT breed dogs with juvenile-onset demodicosis!
