Intradermal skin testing in Icelandic horses in Austria.
Authors: Kolm-Stark G, Wagner R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Intradermal Skin Testing in Icelandic Horses in Austria Icelandic horses grazing in Austria frequently develop summer seasonal recurrent dermatitis (SSRD) with clinical features resembling Culicoides hypersensitivity, yet the underlying allergens have remained unidentified. Kolm-Stark and Wagner performed intradermal skin testing on 81 Icelandic horses (43 with SSRD, 38 clinically normal controls) using standardised extracts of *Culicoides variipennis* and 21 other ecologically relevant allergens, excluding horses with concurrent parasitic, bacterial or fungal skin disease and those receiving anti-inflammatory medication. Whilst *Culicoides variipennis* antigens produced dose-dependent positive reactions—ranging from 2.6% of horses at higher dilutions (1:50,000–1:25,000) to 48.6% at 1:10,000—surprisingly little difference emerged between affected and healthy groups, and reactions to other tested allergens showed no meaningful pattern between cohorts; overall test efficiency reached only 0.47–0.60 with maximum sensitivity of 0.51. These findings underscore the substantial difficulty in validating intradermal skin testing protocols for equine allergic dermatitis within a specific geographic region and suggest that reliance on non-indigenous *Culicoides* species may obscure clinically relevant local allergen involvement, warranting future investigation of native *Culicoides* fauna in Austria.
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Practical Takeaways
- •Intradermal skin testing with standardized Culicoides variipennis extracts has poor predictive value for SSRD in Icelandic horses in Austria; local Culicoides species or other allergens may be responsible
- •IDST results alone cannot reliably distinguish between clinically affected and unaffected horses—consider that high positive rates in control horses suggest environmental exposure is common but not necessarily pathogenic
- •Establishing effective IDST protocols requires region-specific allergen validation and may necessitate using locally-present Culicoides species rather than standardized extracts
Key Findings
- •Only 3 of 43 SSRD horses showed positive reactions to Culicoides variipennis at higher dilutions (1:50,000-1:25,000), suggesting Culicoides is not the primary causative agent in Austrian Icelandic horses
- •No significant differences in skin reactions to 21 other allergens between SSRD-affected and normal horses, except for deerfly and horsefly
- •38 of 43 SSRD horses and 28 of 38 normal horses tested positive 4 hours after allergen administration, indicating poor correlation between IDST results and clinical disease manifestation
- •IDST efficiency ranged from 0.47-0.60 with maximal sensitivity of 0.51, indicating limited diagnostic value of the standardized extract panel used