Equine allergic skin diseases: Clinical consensus guidelines

Though brief this touches the highlights of the common but sometimes difficult-to-diagnose cases of equine allergic skin diseases. Most important is the continued controversy over allergen-specific intradermal (ASI) testing and immunotherapy. The summary does cover the lack of usefulness of ASITesting and ASITherapy with insect bite hypersensitivity. However, it does refer to the role of ASITesting and ASITherapy in equine atopic dermatitis. Hmmm, I continue to find little support for any of these tests being sensitive and specific. Given the difficulty in finding the cause of EAD perhaps it is the best we got(?). Expensive and time-consuming and often misses the mark would sum its current status. In the meantime the article above lists some defining characteristics of the different causes of pruritis and an overview of symptomatic treatment.
DrO

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology
Vet Dermatol. 2023 Jun;34(3):175-208.
Authors
R Marsella 1 , S White 2 , V A Fadok 3 , D Wilson 4 , R Mueller 5 , C Outerbridge 2 , W Rosenkrantz 6
Affiliations

1 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA.
2 Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California, USA.
3 Zoetis, US PET CARE, Bellaire, Texas, USA.
4 School of Clinical Veterinary Sciences, University of Bristol, Bristol, UK.
5 Medizinische Keleintierklinik, Zentrum für klinische Tiermedizin, LMU, Munich, Germany.
6 Animal Dermatology Clinics, Tustin, California, USA.

PMID: 37154488
DOI: 10.1111/vde.13168

Abstract
in English, French, Spanish, German, Japanese, Chinese, Portuguese

Background: Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

Objectives: To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

Materials and methods: The 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 relevance: Insect 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.