Demodex mites, commensal parasites of hair follicles and sebaceous glands, are important in both veterinary and human medicine. Over-proliferation of Demodex mites, demodicosis, can be a potentially life-threatening skin disease in dogs, and in humans has been suggested to play a role in rosacea.

Canine demodicosis (juvenile or adult onset) occurs in localised and generalised forms. The face as well as the forelegs are commonly affected. In the generalised form lesions are more numerous, larger, and the paws are often severely affected. Clinically alopecic macules or plaques, erythema, comedones, hyperpigmentation and lichenification are seen. Secondary pyoderma and Malassezia infection are common.

Features of rosacea include erythema of the centrofacial skin, phymatous changes, papules with or without pustules, flushing, telangiectasia, and blepharitis. Rosacea may progress with one or more existing symptoms becoming more severe, and/or developing additional symptoms (burning, stinging or oedema). 

Common histological features in humans and dogs are folliculitis with Demodex present, furunculosis and parafollicular granulomas containing Demodex remnants. 

Treatment options for canine demodicosis are limited consisting of amitraz (formamidine) and macrocyclic lactones, with growing interest in the off-label efficacy of isoxazoline compounds (e.g. fluralaner). Systemic antibiotics are often required for secondary pyoderma. Rosacea is usually treated with systemic antibiotics or topical ivermectin. 

The pathogenesis of canine demodicosis and rosacea is poorly understood. Demodex mites are normal inhabitants of human and dog skin. Mites have the capacity to interact immunologically with resident skin cells and an imbalance of this immune interactivity may contribute to the development of demodicosis in animals and man.

One Health: It’s for all of us; Understanding Demodicosis in Dogs and Man.