When I first graduated as a vet 20 years ago, I thought I knew how to treat every disease in animals known to man. A few years in suburban practice quickly taught me the error of my thinking – and the greatest stumbling block I ever came across, was trying to treat skin allergies in dogs and cats. I quickly realized that the side effects of most of my treatments were rapidly becoming worse than the original disease itself. It was with this back ground that I was impelled to look deeper, to look for the un-seen cause of allergies.
Allergies are basically an “inappropriate” or “over-zealous” reaction of an animals’ (or persons) immune system https://emilybrydon.com/ . The reaction is caused by exposure to certain chemical or organic agents, commonly referred to as “allergens”. Genetics certainly play a role in pre-disposing an animal to developing allergies, but environment and nutrition will ultimately decide to what degree the allergy is expressed.
Allergies in pets fall into several different categories, but nearly all allergies have a common expression – chronic allergic skin disease (allergic dermatitis or “eczema”). Allergies can be triggered by airborne allergens (atopic dermatitis), by direct contact with the skin (contact allergy), by exposure to certain foods (food allergy), or by exposure to parasites (eg flea allergy dermatitis). The pattern of skin disease can vary widely, but subtle differences can help to determine what type of allergy is involved. The classic signs of allergy include generalized itching, feet chewing, face and muzzle rubbing, dermatitis of the inner legs, abdomen and armpits, chronic ear infections, “hot spots”, and more recently, asthma in cats.
Traditional veterinary treatments for allergic skin disease have included using drugs like cortisone, anti-biotics, anti-histamines, ant-parasitic agents, and topical medicated shampoos. The good old “bucket on the head”, known more professionally as an Elizabethan collar, has also been widely used to prevent self trauma. More recently, testing for known allergens has become popular, and the use of de-sensitisation (gradual exposure to diluted forms of the known allergen) has shown some success. Recognition of the role of essential fatty acids (primarily Omega 3 fatty acids), and their inclusion as a dietary additive, has also shown some promise. But on the whole, allergic skin disease is still one of the most common, and frustrating, veterinary complaints that brings pet owners to the waiting room. One unfortunate reality of allergies is that despite all the advances in modern medicine, allergies are still considered a “chronic” disease – meaning that there is no “cure” for an allergy, the best we can hope to do is “control” the expression of an allergy, and limit the use of drugs required to do so.
Understanding the Immune system:
The key to “controlling” allergies is to understand how and why they occur. As mentioned, allergies are an inappropriate immune reaction to a specific allergen – a reaction that that is not “pre-programmed” into the immune system by the core genetic code, but one that is “learned” or “accidentally” occurs. The study of the immune system (immunology) is a fascinating science, and one that has provided much of the information that is driving modern medical advances. One of the fascinating facts about the immune system, is that it works in almost the same way in all animal species- from man to fish. It is an ancient and untouched genetic code, and is designed to “protect” an animal from disease, and to assist repair.
A thorough description of how the immune system works is beyond the scope of this article, but a very simplified overview will assist in understanding allergies. In very rough terms, the immune system can be divided into 2 parts. One part is involved in making antibodies – cells that produce special proteins that are specifically designed to “recognize” specific foreign molecules (eg bacteria or viruses) which are called “antigens”. The body has millions of different cells (B lymphocytes) which produce different types of antibodies which protect us from infection, and these antibodies form the basis of the practice of immunization (where we introduce non-dangerous parts of a bacteria or virus so the body can make antibodies to that particular pathogen). The second part of the immune system is known as the “innate” immune system, and it involves cells that we commonly call “white blood cells”. These cells are responsible for directly destroying foreign agents, infected cells, or antibody/antigen complexes formed by the other part of the immune system. When your body is under attack by a bacteria or virus, these cells poor into the blood stream to fight off the agent, and the result is that on a blood test, you have a “high white blood cell count”. As white blood cells capture and destroy these foreign particles, they actually die themselves, and the resultant protein sludge that remains is known as pus (when concentrated in a small area).
In an allergic reaction, we have an “accidental” response. Lets use the example of an inhaled grass pollen. Normally the immune system should not recognize the grass pollen as foreign or dangerous (we inhale microscopic pollens all the time during spring and summer). But in an allergic response, for some reason the immune system creates a specific antibody to the pollen. This antibody seeks out the pollen, and binds to it. Then, a particular part of the innate immune system (white blood cells known as “eosinophils”) are released into the blood to capture and destroy these antibody/antigen complexes. When these eosinophils have done their job, they also “die”, but as the cells burst, they release histamine – which causes intense local swelling and itching. In people, this reaction commonly occurs locally, at the location of the nose and eyes where the pollen first contacts the moist mucus membranes – and results in “hay fever symptoms” (swollen itchy eyes and nose, sneezing etc). If the reaction occurs deeper in the body, at the level of the bronchi in the lungs, it can cause “asthma”. In dogs and cats, these cells actually migrate to the skin (and sometimes to the lining of the gut) where they cause an intense itching reaction which we call allergic dermatitis. When the animal itches, it breaks the skin, and allows secondary infection to occur, which further adds to the irritation – and so the cycle goes on.
The pattern of allergies is determined by the type of allergen. Some allergies are seasonal, meaning that the allergen is only in the environment for a specific time of the year – most of these are caused by plant pollens etc (called atopic allergies). Some contact allergies, like grass allergy only occur when grasses are dry and producing seed heads, and most of the signs occur on the underneath of the dog, in areas where there is no fur protecting the skin (eg groin, armpits, belly). If the allergen is present all year round, such as a food allergy (to a specific food type) or allergies to dust mites, then the signs of allergic dermatitis will be constant.