Page 184 - February 2021

VETERINARY VIEWS
182 SPEEDHORSE February 2022
Hives can turn into something much more serious, called angioedema, which is when the fluid leaks out of deeper vessels where tissue pressures are less so more fluid can escape, potentially pressing on surrounding tissues. If this develops around a horse’s larynx, the airway will narrow and could close entirely, making this a life-threatening situation.
INTRADERMAL ALLERGY TESTING
One diagnostic technique uses intradermal (skin) allergy testing to try to isolate an allergic source from pollens (plants, bushes, and trees), molds, grasses, weeds, dust
mites, insects, and farm plants. Discontinue medications (steroids or antihistamines) at least 10 – 30 days prior to testing. Thousands of potential allergens exist in the environment, but all can’t be tested.
Serum testing is another method to identify a source of allergens but is less accurate than skin testing. In some cases, extensive and severe skin lesions leave limited intact skin for intradermal testing. In other cases, it is not always possible to discontinue a horse’s medication due to the severity of a problem. If an intradermal skin test comes back negative but clinical signs are consistent with hypersensitivity allergies and other underlying problems have been ruled out, then serum testing may be indicated.
IMMUNOTHERAPY
Once a particular antigen is identified, immunotherapy (referred to as hypo- sensitization) injections may target that allergen. Injection of small, dilute amounts of allergy vaccine train a horse’s immune system to become tolerant to the allergen over time, resulting in mild to no reaction during re-exposure. Desensitization is a slow process and should be continued for at least one year.
Once a maintenance dose is reached, each injection is given at a 10-20-day interval, depending on a horse’s clinical response. Treatment requires a commitment of time and money, as injections may need to be continued for the life of the horse.
PROGRESSIVE ALLERGIC REACTIONS
For most horses that develop a single case of hives, recovery is usually uneventful and rapid, causing little cause for concern. A normal-functioning immune system keeps your horse disease free, healthy, and vital. This protective system works in harmony with other biochemical responses in the body. It is when it over-reacts that it puts a horse at risk.
Hives can turn into something much more serious, called angioedema. In a classical hive, fluid leaks out of superficial blood vessels
in the skin; the amount of fluid that leaks
out is limited in its amount because of tissue resistance. With angioedema, the fluid leaks out of deeper vessels where tissue pressures are less, so more fluid can escape, potentially pressing on surrounding tissues. If this develops around a horse’s larynx, the airway will narrow and could close entirely, making this a life-threatening situation. Angioedema most commonly involves the muzzle, eyelids, belly, and legs.
With any allergic condition, there is always concern that the next attack may turn into a severe anaphylactic one. Anaphylaxis is rare
in the horse, but it can occur, with the horse exhibiting immediate restlessness and sweating.
When purchasing a horse, question the seller about any known allergic responses. Inform your veterinarian, trainer, and barn manager about the dangers of certain drugs that affect your horse’s health. Just as people who are allergic
to bee stings or penicillin may wear a necklace
or wristband describing this condition, you
can prevent an anaphylactic reaction to known substances by advertising this fact about your horse. A red alert warning sign describing known allergic reactions should be placed outside the horse’s stall and all caretakers alerted to the possibility of an allergic reaction.