Sensitization to horse allergens without apparent exposure to horse. Report of two cases

It has been well established that occupational exposure to horses increases the risk of allergic sensitization to horse hair, on the contrary very few data have been published in individuals without direct contact with horses. We describe two cases of severe respiratory symptoms triggered by a single direct exposure in two patients with only 4-5 previous short contacts with horses during the entire their life, since they live in urban area of Naples. Cutaneous and serological diagnostic tests showed significant sensitization to horse dander other than some common inhalant allergens. Our report suggests that, in already (but unaware) horse-sensitized patients, the last direct contact with a horse has triggered severe respiratory symptoms. Passive carriage of horse allergen by the clothes of individuals in contact with horses/horse environments or a cross-reactivity between horse allergen (a lipocalin) and the major allergens (also lipocalins) of several furred animals are likely to explain our findings. Some other considerations can be derived by the clinical observation. First, it is likely that allergic sensitization to horse allergens could be more frequent than expected also in subjects without direct exposure to horse because of living in urban areas. Secondly, individuals suspected to be highly atopic or those already sensitized to some pet dander should be tested by SPTs/radio-allergo-sorbent test before the introduction of a pet indoors or, in the case of a big animal as the horse, a direct horse contact / entering into environments containing a horse.