Validation of an improved insect bite hypersensitivity severity score for allergic equine insect bite hypersensitivity in horses.

The validated EqIS provides an objective, reproducible scoring tool for standardized equine IBH disease assessment and treatment monitoring.

Insect bite hypersensitivity (IBH) is the most prevalent allergic skin disease in horses, caused by hypersensitivity to Culicoides spp. bites, yet no extensively validated clinical scoring system existed prior to this study. This prospective field validation study evaluated the equine IBH severity score (EqIS) across 44 privately owned horses with clinically diagnosed IBH in Switzerland, assessed by six trained evaluators under real-world field conditions. The EqIS integrates a lesion severity score with an area score using a multiplicative algorithm. Intraobserver reliability was excellent (ICC = 0.995 for lesion severity score; ICC = 0.989 for EqIS), and interobserver reliability was equally high (ICC = 0.98 for both components). The area score demonstrated strong interobserver agreement (Pearson r = 0.86–0.94). Owner-reported visual analog scale (VAS) scores correlated moderately with EqIS (ρ = 0.49–0.51) but strongly with one another (ρ = 0.88), suggesting owners perceive disease burden somewhat differently than trained evaluators. A simplified EqIS designed for routine field use showed strong agreement with the full validated version (R² = 0.86), making it a practical alternative for general practice settings. The EqIS is the first IBH-specific scoring tool with extensive validation, offering clinicians a reproducible, objective method for disease assessment and therapeutic monitoring. Its dual-format design—full and simplified versions—enhances versatility across research and clinical practice contexts, supporting standardized evaluation of both disease progression and treatment response in equine IBH.

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