Too Much of a Good Thing

Allergies, in a nut shell, are manifestations of an over-reactive immune system…. Too much of a good thing. The immune system serves the vital function of protecting us from harmful stuff, like bacteria, viruses, toxins, parasites and even cancer cells. It’s a complicated system comprised of a mind boggling network of cells, tissues and organs throughout the body. When it functions normally you don’t even notice, it works like a dream, but when the immune system goes awry, it can be a real nightmare. There’s a lot that we don’t know about this complicated system. We know some things that trigger allergies, but we don’t know exactly how or why. We have some tools to modify the allergic response, but we can’t actually cure an allergy. The evidence of an over active immune system manifests as hives, itching (with resulting hair loss and skin damage), coughing, sneezing, wheezing (heaves, also known as recurrent airway obstruction) or (very rarely) life threatening respiratory distress and system failure called anaphylaxis. 

The best treatment for an allergy is avoidance of the allergen. So, what’s an allergen? An allergen is a type of antigen that initiates an allergic response…. If that’s not obscure enough for you, let’s just say that it’s some kind of protein. There is a universe full of potential allergens to be encountered in a lifetime. Almost any kind of protein can act as an allergen and exposure can come via injection (a bite as with insect saliva or administration of a medication), topical (contact dermatitis) or aerosol (respiratory system) pathways. Common triggers include; insects, pollen, dust & molds, shavings & stall bedding materials, feedstuffs, chemicals- like sprays and soaps, medications and supplements. Keep in mind that these are merely triggers, it’s the unique response of each individual’s own immune system that decides to overreact to them or not. Determining the allergen is further complicated by the fact that signs may occur immediately on contact or they may be delayed by several hours. 

Clearly, the world is a dangerous place when it comes to allergens, so what’s a conscientious horse owner to do? The best treatment (and the only cure) for this disease is removal of the cause, a simple solution often impossible to implement.  The first big challenge is to identify the allergen (it’s a protein remember, not exactly easy to pick out of the crowd). We can offer two diagnostic methods that attempt to ID the culprit, skin testing and blood (serum) testing.  Both diagnostic methods are limited in their efficacy, skin testing is the most “tried and true”. The procedure involves small intra-dermal (under the skin) injections of potential allergens, followed by monitoring the reactivity of each injection compared to a saline control. Blood testing is done in a specialized laboratory on a blood sample drawn from your horse. While this method is attractively simple, accuracy of the results has proven less reliable than skin testing. That said, sometimes something is better than nothing when it comes to managing allergies.

Good news, you’ve identified the specific allergen wrecking havoc, now just keep it from ever coming in contact with your horse ever again and, voila, no more hives. Hmmm, might work if your horse is allergic to alligators or a specific shampoo, but most often the allergen is something that you cannot completely eliminate from the environment, leaving management rather than cure our goal for dealing with this disease. Management goals focus both outside and inside the horse. Outside, to minimize contact with the allergen and inside, to modify the cascade of immune mediated events that occur when an allergy is triggered. Environmental modifications may include improving ventilation, controlling dust, using fly sheets or body suits, installing fly control systems and sprays. (Note; effective insect treatment should focus on repellants more than insecticides which only kill pests after they bite.) Treatment involves the use of drugs that affect the animal’s immune reaction and generally includes anti-histamines and corticosteroids. Anti-histamines directly affect the cascade of immune reactions while steroids act to minimize the inflammatory response in general. Allergen specific immunotherapy or desensitization treatments take time and effort but may also be helpful. Symptomatic help comes from topical sprays or salves and your own creative ideas for soothing the itch. Feed supplementation with flaxseed as a source of omega3 fatty acids has been found to decrease reactivity to culicoidies (midge or no-see-ums) bites.  When nothing works perfectly, be happy that many allergies are seasonal and they will eventually get better or go away…. Until next time.  

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