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Horse allergy: It’s not just for cowboys!

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Living in Montana means horses! If you are allergic to horses, it can really put a hitch in your giddy up!

A little background on horses:

They are 1 of 2 subspecies of Equus ferus that is still in existence.  They belong to the family Equidae. The ancestor of all equids, Eohippus lived in the early Eocene epoch 54 – 55 million years ago. Fast forward to North America where horses disappeared 8,000 – 10,000 years ago, likely due to hunting by early Natives, climate change, and diseases. They disappeared around the same time as Wooly Mammoths.  Human contact with horses is thought to have first occurred 3 million years ago as humans moved out of Africa. Ancient Eurasians were known to hunt and eat horses.  The first domestication of horses occurred about 3,000 B.C. in the Middle East and European horses were domesticated for several thousand years at the time the Spanish began exploring the Americas in the 15th century. The first Spanish horses arrived in the Carribbean in the early 1500s when Conquistadors re-introduced horses to North America. Horses were brought by the Cortez expedition and imported by Spanish homesteaders to Mexico and New Mexico then making their way north through the western U.S. http://www.canadiangeographic.ca/magazine/ma05/indepth/

Horse-Induced Allergic Reactions:

Allergic reactions can occur in persons (of all ages) who have regular contact with horses or even indirectly with exposure to riding clothes contaminated with horse hair or dander.  The first allergic reactions associated
with horse allergens were described in the 1950s after injection of therapeutic horse serum.

  • Asthma (including occupational asthma)
    • Inhalation of horse hair/skin proteins can lead to asthma. This exposure may be during professional or recreational horse exposure including horseback riding, rodeos or fairs.  Higher concentrations of horse dander can be found inside barns/stables/indoor arenas compared to outdoors but near the stable. In one study, beyond 40 m (131 ft) from the stable, no horse allergen could be detected in the air.
  • Allergic rhinitis and conjunctivitis
    • Exposures can be the same as for asthma but also include antique furniture (with horse hair stuffing)
  • Hives (urticaria) with contact with horse saliva (horses bite!), or ropes/clothing that have contacted horses.
  • Anaphylaxis
    • Some anti-venoms are still be made from horse serum.
    • Horse bite with exposure to saliva.
    • Horse drawn sleigh ride. (Anaphylaxis as a Manifestation of Horse Allergy by Gawlik. R, Pitsch, T and DuBuske L. WAO Journal 2009; 2:185–189)

Unexpected exposures: Horse hair may be encountered in antique furniture and wall hangings/decorations. Horse allergens (like cat and dog dander) can be carried on clothing and therefore be found in indoors in house dust samples.  Horse meat is still eaten in some countries in place of beef (not allowed in U.S.).  Horsehide is used in making baseballs and certain other leather goods but this would be less likely to trigger a reaction.

Allergens
At least 16 allergens have been isolated from horse and the protein content in horse dander is more than twice that of horse hair.  A number of allergens have been characterized and include:
  • Equ c 1, a lipocalin and the most important allergen found in hair dandruff/dander protein.  The protein is 50% similar to rodent urine proteins.
  • Equ c 2, a lipocalin is found in horse sweat is also important.  This protein is about 50% similar to cattle dander.
  • Equ c 3, albumin (Ag3) is a common cross reactive protein found in serum (blood) of horse, cat, dog and cattle.
  • Equ c 4, this small protein shares common sequence with rat submandibular gland.
  • Equ c 5, this protein was discovered when Equ c 4 was identified.
Is there a hypo-allergenic horse?
Breeders and patients with asthma have claimed that Bashkir Horses are non-allergenic.  While a study demonstrated much inter-breed and within-breed variation, there was no breed-specific allergens found.  Dander from all breeds that were studied contained the most important known allergens, and the allergenic content of dander from Bashkir horses was similar to that of other breeds.  Hint: do not buy this special horse only for this reason!
Can horse allergy cross react with other animals?  
The potential for cross-reactivity between horses and other animals using inhibition lab experiments using blood from patients with horse allergy demonstrated cross-reactivity between Fallow Deer and horse allergen.  Fallow deer have been imported from Eurasia to the U.S. and there are several small herds of deer in captivity or on large ranches.  The common white tail deer belongs to a different genus and species.  More common would be cross reactivity to cats, dogs, cattle and Guinea pigs.
Do children develop horse allergy?
In a large study of British children, 1.4% were sensitized to horses.  In another study reviewing children seen for allergy to horses over a period of 11 years (35 boys and 21 girls), 35 of them were under 10 years old.  The main clinical symptoms reported were eye symptoms in 36, allergic nasal symptoms in 24 and asthma in 30.  All of the children had highly positive allergy skin tests and 62% had high specific IgE (class 3 and 4) on blood tests.  Most had other allergies. In several children, the first symptoms occurred at the time of the first known contact with a Horse or Pony (24). Horse allergy has been reported to decrease with age (25).
Treating Horse allergy:
  • Avoidance: As with other allergies, avoidance is the best and most effective measure. This means avoiding the stable or barn and direct contact with horses.
  • Medications:  depending on the symptoms, this could include antihistamines, decongestants, topical nasal corticosteroid spray, asthma medications or even epinephrine (if previous anaphylaxis).
  • Allergy injections (immunotherapy):  this is an effective treatment for horse-allergic patients.  95% of patients and allergists report excellent (65%) or good (30%) response to allergy injections.
At Family Allergy & Asthma Care of Montana, we test for several kinds of animal dander including horses.  Identifying your allergy is important; no horsin’ around here!  If you believe you may be allergic to horses, saddle up and come on in!
This information is solely for informational purposes and not intended as a substitute for consultation with a medical professional. 

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