Detection of IgG and IgE serum antibodies to Culicoides salivary gland antigens in horses with insect dermal hypersensitivity (sweet itch).
Authors: Wilson A D, Harwood L J, Björnsdottir S, Marti E, Day M J
Journal: Equine veterinary journal
Summary
# Editorial Summary Insect dermal hypersensitivity (sweet itch) affects a significant proportion of horses, yet the immunological mechanisms underpinning this allergic reaction to Culicoides midges remain incompletely understood. Wilson and colleagues investigated whether exposure to Culicoides bites triggers distinct antibody responses in allergic versus non-allergic horses by detecting IgG and IgE antibodies against midge salivary gland antigens using immunohistological and western blotting techniques. The key finding was that IgG antibodies to salivary antigens were present in all horses exposed to Culicoides—both symptomatic and clinically normal animals—whereas IgE antibodies were detected exclusively in horses displaying active sweet itch, notably absent from healthy exposed horses and from previously affected horses in remission. Individual horses responded to different numbers of Culicoides antigens, indicating variable immunological recognition across the population. These results establish IgE sensitisation to midge saliva as a distinguishing marker of allergic individuals, suggesting that diagnostic protocols and immunological research might exploit serum IgE detection to identify at-risk horses, whilst the antigenic heterogeneity documented here indicates that therapeutic or preventive approaches will likely need to address multiple salivary allergens rather than single targets.
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Practical Takeaways
- •IgE serology to Culicoides salivary antigens can differentiate actively allergic horses from healthy exposed horses and those in remission, providing a potential diagnostic tool for sweet itch
- •The presence of IgG but absence of IgE in healthy exposed horses suggests exposure alone does not cause clinical disease—only a subset of exposed horses develop pathological IgE responses
- •Individual variation in antigen recognition means allergen testing may need to account for horse-specific antibody responses rather than relying on a single standardized allergen panel
Key Findings
- •IgG antibodies to Culicoides salivary gland antigens were detected in both allergic and healthy horses exposed to midge bites, but absent in unexposed Icelandic ponies
- •IgE antibodies were exclusively detected in horses with active insect dermal hypersensitivity, not in healthy exposed horses or allergic horses in remission
- •Western blotting confirmed individual horses react to different numbers of Culicoides antigens, suggesting variable allergen recognition among affected animals