Vet360 Vet360 Vol 05 Issue 04 - Page 17

DERMATOLOGY employed allergy tests (allergy serology, intradermal skin testing) and it is suspected that false negative and false positive results do occur. Allergy testing is also unable to detect dogs with atopic like dermatitis, which is a condition clinically identical to canine atopy, but in which an IgE response to environmental or other allergens cannot be demonstrated. Allergen prescription formulation Selection of allergens for inclusion in an allergen specific immunotherapy vaccine involves interpretation of the medical records of the particular dog, especially as regards seasonality and animal’s habitat (i.e. presence of specific allergens in the animals environment) in conjunction with IgE levels of individual allergens achieved with allergy serology. • • • Non-seasonal – environmental allergens, indoor moulds. Seasonal – spring (trees/ectoparasites), summer (grasses/outdoor moulds/ectoparasites), autumn (weeds/outdoor moulds) Seasonally non-seasonal – seasonal and non- seasonal allergens involved concurrently. (Seasonal atopy complicating adverse food reaction/Ectoparasites complicating non- seasonal atopy). Mould extracts should not be mixed in the same vials as pollen extracts, as the pollen allergens will be degraded by the mould proteases during storage. Therefore, mould extracts should be in a separate vial and administered as a separate injection. Allergen Specific Immunotherapy (ASIT) Although numerous treatments exist for atopic dermatitis, many have significant side effects and drawbacks and not all are universally effective. Allergen specific immunotherapy (ASIT) is the only proven treatment for atopic dermatitis that works through reversing the underlying immunopathogenesis of the disease with the added advantages of being virtually free of serious adverse effects, even with prolonged use, offering substantial, long-lasting relief in many patients. ASIT vaccines are available in two forms namely an injectable form given by subcutaneous injection every 2-4 weeks (SCIT) and a sub-lingual immunotherapy (SLIT) vaccine, which is applied orally under the tongue on a daily basis. ASIT has emerged as an important and useful tool in the long-term management of skin disease in atopic patients. Allergen avoidance, prevention of allergen contact, antimicrobial therapy, pharmacotherapy and/immunotherapy are crucial in the therapeutic management of atopic patients. Pharmacotherapy is frequently needed when a rapid and short-term response is required or when allergen avoidance is difficult or impossible to implement, while ASIT is utilised as a long-term therapy that reduces or eliminates the need for pharmacotherapy. Mechanisms of action of ASIT demonstrated in humans include early reduction in effective cell (eosinophils, basophils, mast cells) activity, followed by a long- term immunological shift from a lymphoid T helper 2 (Th2) cell to a T helper 1 (Th1) cell response and the development of immunological tolerance. These changes are accompanied by increases in immune regulator cells and certain cytokines. This all results in an increase in allergen specific IgG (especially IgG4) which impairs the effector functions of IgE and with extended application initiates a decrease in allergen specific IgE. In canine atopic patients a shift from Th2 to Th1 cell response, increases in immune regulator cells and certain cytokines plus increases in IgG levels, have all been demonstrated and suggests that mechanism of action in dogs is similar to that in humans. Subcutaneous immunotherapy (SCIT) is available as two methods based on availability and regulatory approvals in North America versus Europe. SCIT vaccines produced in North America are aqueous, saline phenol preserved extracts. The protocol begins with frequent injections of dilute extract, progressing to less frequent injections of concentrated extract as a maintenance therapy. In Europe alum precipitated allergen extracts are utilised, with absorption of the allergen molecules to an aluminum hydroxide adjuvant, which provides a slower release product which has the advantage of less frequent injections. Time to efficacy with SCIT varies from up to 8 months with aqueous allergens and 9 months with alum- precipitated allergens. Those dogs which have not responded by this time are unlikely to. These sublingual immunotherapy (SLIT) vaccines have an excellent safety record due to the unique nature of antigen capture at this sublingual site. This oral immune site comprises various antigen presenting cells (Langerhans cells, myeloid and plasmacytoid dendritic cells) with a distinct location in the mucosa and sub-epithelial lamina propria. These dendritic cells are tolerogenic being key in the induction of immune tolerance, resulting in induction of peripheral (skin, respiratory tract) tolerance to allergens. The oral mucosa also contains limited numbers of mast cells and eosinophils mainly located in the deep submucosa explaining the good safety profile (lack of adverse reactions) of SLIT. SLIT shows a far more rapid clinical response with some dogs showing significant improvement in 3 months, while many have substantial improvement by 6 months. Issue 04 | SEPTEMBER 2018 | 17