Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

Abstract

BackgroundAllergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.ObjectivesTo review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.Materials and MethodsThe authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.Conclusions and Clinical RelevanceInsect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)‐5 and IL‐31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen‐specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T‐helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Efficacy and Safety of Subcutaneous Allergen-Specific Immuno-Therapy in Horses with Allergic Cutaneous and Respiratory Diseases—A Systematic Review

“…The reviewed literature did not provide a standardized strict elimination criterion for insect bite hypersensitivity (IBH) prior to diagnosing seasonal atopic disease. Both diseases can present with overlapping clinical signs and co-sensitization is common [1,23]. Thus, we grouped horses with pruritic dermatitis together and focused the review on the allergen content in AIT (insect monotherapy and multi-allergen AIT containing allergens of multiple origins).…”

“…Allergic syndromes in horses can manifest with cutaneous signs such as urticaria, pruritus, and papules, or respiratory symptoms, allergic asthma, previously referred to as recurrent airway obstruction or chronic obstructive pulmonary disease [1,2]. In equine allergology, common allergens are of insect origin, often Culicoides saliva, or of environmental origin [1]. Clinical signs of allergic syndromes in horses can be alleviated with glucocorticoids and/or antihistamines [1,3].…”

“…In equine allergology, common allergens are of insect origin, often Culicoides saliva, or of environmental origin [1]. Clinical signs of allergic syndromes in horses can be alleviated with glucocorticoids and/or antihistamines [1,3]. However, horses are sensitive to the side effects of systemic glucocorticoids, and antihistamines may not effectively control the symptoms [4,5].…”

“…Sci. 2023, 10, 613 2 of 16 to manage equine allergy symptoms [1,6]. AIT involves the gradual oral or subcutaneous administration of increasing amounts of allergens to an allergic subject, aiming to ameliorate the symptoms associated with subsequent exposure to the causative allergen [7].…”

“…The clinical benefit of AIT can manifest as an improvement/remission of clinical signs and/or a reduction in the need for anti-allergic medications. Despite its common clinical use and the reviewing literature describing AIT as beneficial and safe in managing equine allergic diseases [1,6], systematic reviews reporting detailed data and assessing biases are not currently available. Therefore, the objectives of this study are twofold: first, to review the evidence for the efficacy of AIT in various equine allergic syndromes, including the assessment of study biases following the PRISMA 2020 guidelines [8]; and secondly, to report the available safety information regarding AIT used to treat equine allergic diseases.…”