Clinical Information

Horse (equine) allergen sensitization occurs in approximately 5 to 15% of individuals exposed to horses in occupational settings. The assessment of allergy to horses is dependent upon the presence of compatible clinical symptoms in the context of exposure, with support from identification of potential equine-specific IgE allergen antibodies, either by skin testing or in vitro serology testing. In vitro testing has generally focused on assessing for the presence of IgE antibodies to total horse allergen extracts.

There is a correlation between total horse IgE allergen antibodies and an increased likelihood of a clinical allergic response. Once an elevated antibody response to total horse dander IgE extract is established, assessment for the presence of specific IgE antibodies to the major equine component will be performed. This may yield additional, potentially useful information for the clinical assessment of allergy and sensitization. During horse component allergen IgE antibody testing, the presence of IgE antibodies specific for the potential allergenic individual protein, namely Equ c 1, is assessed. The determination of the relative amount of IgE antibody to specific component can aid in assessment of the potential strength and type of allergenic response.

While several horse allergens have been described, the lipocalin Equ c 1 is the major horse allergen, and antibodies to this allergen are present in 76% of individuals exhibiting allergy to horses. The main source of exposure of Equ c 1 is inhalation. However, individuals can be exposed by contact with contaminated clothing and, potentially, through horse bites. Mattresses containing horsehair may also be a potential route of exposure. Individuals who are allergic to horses may exhibit allergic rhinitis, conjunctivitis, asthma, anaphylaxis, and allergy to other foods and animals.(1) To date, the existence of completely hypoallergenic horse breeds has not been verified.

Sensitization to horses may also occur through cross-reactivity, with as many as 30% of individuals with pet allergy also reporting allergic reaction to horses. As many as 50% of individuals with cross-reactive allergen sensitization are caused by cross reactive to horse lipocalin as represented by Equ c 1. Cross-reactivity has been shown to exist between horse lipocalin allergen Equ c 1, cat lipocalin allergen Fel d4, and dog lipocalin allergen Can f 6.