Atopy in both dogs and cats is largely genetically determined.
Atopic dermatitis (AD) is diagnosed in animals more and more frequently (in c. 10-15% of dogs). It is a chronic, multi-factor, inflammatory and pruritic skin disease essentially caused by IgE antibodies being produced in contact with a multiplicity of environmental allergens.
The most common allergens include:
- house dust mites (HDM), which may cause atopy in c. 60-80% of dogs (Dermatophagoides sp.);
- storage mites, encountered more and more frequently; they occur in c. 20-70% atopic dogs, depending on mite species (Tyrophagus putrescentiae, Lepidoglyphus detrusor, Acarus siro);
- allergic reactions to mould and fungal antigens such as Penicillium, Aspergillus, Alternaria, etc., are frequent;
- pollen from such trees as poplars, oaks, birches and willows, as well as such grasses as phleum (timothy) may also cause allergy;
- humans may also be a source of allergens; allergy to human epidermis is quite frequent.
In all atopic dogs and cats, the skin barrier function is disturbed, and the immune response is defective on both the cellular and humoral levels. Erythema is an early and basic manifestation of atopic dermatitis. In later stages, it is accompanied by thinning hair, hair loss, crusting, (bacterial or fungal) pyoderma, discoloration, and lichenification.
Epidermal barrier dysfunction resulting from impaired skin structure significantly contributes to atopy. Stratum corneum protects the skin from penetration by allergens and their contact with the cells and such elements of skin immune system (SIS) as keratinocytes, Langerhans cells (LC), macrophages, mast cells, lymphocytes, and others which are part of the epidermis and/or dermis. The more frequent the contact of the allergen with those cells, the more acutely the symptoms of hypersensitivity manifest themselves (the mechanism is complex).