Dispersion of horse allergen from stables and areas with horses into homes

To protect susceptible subjects from exposure to horse allergen, a Swedish national report recommended a distance of at least 500 m between homes and stables and other areas with horses. The aim of this project was to study indoor and outdoor levels of horse allergen in relation to distance from stables and horse tracks.

Indoor and outdoor samples were collected with Petri dishes at 49 sites in different housing areas and near to a track for trotting horses. In the apartments, Petri dishes were placed on a bookshelf in the living room at a height of approximately 1.5 m. Outdoors, cages containing Petri dishes were attached to tree branches at various distances from the horse track.

Six of 45 indoor samples had detectable levels of horse allergen, 3 of those despite the fact that no family member had had any contact with horses, and 16 of 26 outdoor samples were positive. Outdoors, allergen levels drop quickly when the distance from stables or horses increases. Further, the allergen level found at a distance of 45 m from a horse track was around 1% of the allergen level found at 1 m from the track.

Allergens dispersed from horses decline rapidly outdoors and are barely found indoors in homes. We support the view that indirect exposure to horses such as exposure from clothing of horse riders, should be taken into account when measures to protect susceptible people from undesired exposure to horse allergens are taken.