Skin and ear disease comprises a staggering 35 % of appointments seen by a veterinary general practitioner. While there are many other causes for skin and ear disease in dogs and cats, this article will focus on the SINGLE MOST common underlying process that leads to skin and ear disease: ALLERGIES. Skin allergies can be the result of environmental factors reacting with the skin, but in dogs and cats, skin allergy can also be the result of allergy to food borne proteins manifesting in the skin.
Food Allergies in Dogs & Cats
An allergy is a condition of unusual sensitivity to a substance or substances usually protein in nature which is perceived by the body as foreign. Signs of allergies in dogs may manifest as itching and in some cases diarrhea. Food allergies account for only about 5 to 10 percent of all allergic reactions in dogs and cats. Diagnosis of a food allergy is a demanding diagnostic process requiring strict dietary management to make sure no allergy-triggering food is ingested by your dog.
Because the signs of food allergy resemble those of other canine allergies – and because effective treatment depends on pinpointing the allergy-causing ingredient – diagnosing food allergies is challenging for both owners and veterinarians. If your pet has an adverse reaction to a diet change, the reaction is probably not an allergy because it takes more than one exposure to a food ingredient to incite an allergic reaction. That’s why dogs and cats that have been eating the same food for months or years with no problem can develop a food allergy.
If you bring your dog or cat to the animal hospital with a complaint of itching or digestive distress, your veterinarian will first rule out more common causes of these signs. The rule-out process might include a physical examination and laboratory tests for flea allergy dermatitis, the most common cause of allergic skin disease of animals, inhalant allergies, seasonal reactions to pollen, mold spores, and dust mites, and food caused digestive intolerance, an acute adverse reaction to food that does not involve the immune system.
If the food allergy remains a suspect, your veterinarian will then help you try to pinpoint what might be causing your pet’s problems. Most food-allergic dogs are hypersensitive to only one or two ingredients, with beef and dairy proteins topping the culprit list. Ingredients that may also cause problems – but not as often – include grains, pork, chicken, eggs, and fish. Allergies to food additives including preservatives may also be a cause but are rare.
To definitely diagnose food allergies, most veterinarians recommend a trial with an elimination diet – a diet that contains a protein and carbohydrate source the animal has never been exposed to.
To start with, feed the elimination diet for a period of up to 16 weeks and monitor your dog’s response. Signs should abate if your dog is indeed food-allergic. Keep in mind that it’s difficult to find elimination diets in spite of the plethora of grocery- and pet-store offerings because most such foods contain similar ingredients. Even the so-called “hypoallergenic” lamb-and-rice diets are unsuitable as elimination diets for many dogs because they’re so popular the main ingredients are no longer truly novel. Consequently, to carry out a valid elimination-diet trial, you may have to either buy a therapeutic diet from your veterinarian (which contains “exotic” ingredients such as rabbit, venison, and potato) or some of the newer “novel protein” diets that contain a totally and nutritionally sound newly formulated protein or prepare a home-cooked diet. Some of the manufacturers have developed new hypoallergenic diets. These Include Hill’s ZD diet and Purina’s CNM HA and LA diet and IVD’s Vegetarian Diet. We as a profession are very optimistic about the future success of the newer foods.
Unfortunately in an attempt to capitalize on the use of lamb as a health food, food manufacturers and retailers sold a bill of goods to caring dog owners. It really is no more nutritious than any other form of meat or poultry. This particular product was used purely as an “elimination” diet by veterinary dermatologists to diagnose food allergies. As a result, we as a profession lost a readily available source of food for allergy testing. Now we are using rabbits, and venison (deer) as a source of hypoallergenic foods.
To get conclusive results from the trial, your dog should ingest nothing but the elimination diet and water. That means no treats, rawhide, or chewable medications. Following this strict regimen can be difficult, especially for those living in multipet households.
If signs are resolved after an elimination-diet trial, you can assume something in your pet’s diet is causing the allergy. But to be certain, some veterinarians recommend reintroducing the original diet. A recurrence of signs within 7 to 14 days confirms food allergy.
There is no cure for food allergies. Managing a food allergy means simply avoiding the causative ingredient or ingredients. Medications (such as antihistamines and corticosteroids) that reduce itching caused by other types of allergies usually don’t work on food-induced itching.
Long-term avoidance is simply a matter of keeping your dog on the elimination diet you used to diagnose the allergy. Unfortunately, however, some dogs become allergic to ingredients in the elimination diet over time. If this happens to your dog, you’ll. need to find another nutritionally balanced diet that contains “new” proteins and carbohydrates.
Although diagnosing and managing food allergies is challenging, remember – most pets are not food-allergic. So don’t automatically think food if your pet has skin or digestive problems.
Whether you’re diagnosing a canine and feline food allergy for the first time or managing an ongoing case, you’ll. need to find an elimination diet that contains a protein and carbohydrate source your dog has never eaten before. Often, the choice boils down to either a commercial therapeutic diet from your veterinarian or
home-prepared food. Each has its pros and cons.
Dry or canned commercial diets are convenient, nutritionally balanced, and palatable. However, studies show that a small percentage of food-allergic pets react adversely to commercial elimination diets that contain the some basic ingredients as homemade diets that do not cause a reaction. Experts surmise that manufacturing processes may increase the allergenic properties of certain ingredients.
Two-ingredient homemade diets (such as chicken and rice) are acceptable for the duration of a diagnostic food trial, but they are not nutritionally complete. Concocting a nutritionally balanced homemade diet for long-term feeding requires the aid of a veterinary nutritionist, a lot of time and expense, and the addition of nutritional supplements that may themselves contain allergy-provoking proteins. Thus, many veterinarians recommend starting with a commercial elimination diet and resorting to a home-cooked approach only if your pet doesn’t respond favorably to the commercial.
Environmental Allergies (Atopy) in Dogs & Cats
Atopic dermatitis is an allergic skin disease of dogs which is caused by immunological hypersensitivity to common substances in the environment such as house dust mites.
What is allergy?
The immune system of mammals makes receptor proteins (antibodies) to substances that are foreign (i.e. not part of the body), each antibody being specific to a given substance. Antibodies are of several types, IgG for instance being involved in protection against viral diseases after vaccination whereas IgE, involved in atopic dermatitis, is particularly concerned with protection against parasites. IgE antibodies coat specialized cells (mast cells) in the skin where they sit waiting for contact with the parasite proteins to which the animal is sensitized. If the substance is encountered, perhaps as a result of a burrowing mite, the mast cell releases chemicals (mast cell mediators) which try to destroy the invader. In allergic animals this whole system is oversensitive and the release of mast cell mediators in the skin occurs inappropriately to apparently innocuous substances such as pollens, moulds and house dust mites. For allergy to be apparent, dogs need to be first “allergic” and then be exposed to substances (allergens) to which they can develop the abnormal immune response. The most common source of allergens is the house dust mite. These tiny creatures live in all of our houses, in carpets, beds and other soft furnishings and feed on skin scales that are constantly falling from people and animals. They litter our environments with fecal pellets of half-digested food and digestive enzymes and it is these minute fecal particles that contain the most important allergens. Dogs can also become allergic to pollens and moulds although this is much less common, presumably because of less exposure.
Atopic dermatitis is often first apparent in the first two years of life. Owners may notice that the dog grooms excessively, with licking or chewing of the paws, abdomen and perineum. The ears may be reddened and hot to touch even though not scratched. The result of this itchiness (pruritis) is that the dog will often be presented a number of times in the first eighteen months of life for a variety of seemingly minor skin conditions. Between these episodes the skin and the coat can look remarkably normal. Spots, acute moist dermatitis, ear infections and scratching may all seem to occur independently and it is only in retrospect that a consistent pattern of disease emerges. As the condition becomes more severe, pruritis dominates the animals’ life and specific anti-itch therapy becomes necessary. With increasing pruritis, baldness (alopecia) and redness of the skin become evident and secondary infections with yeast or bacteria become more common.
Clues to identify unseen itch
Many people scold their dogs for scratching, almost without realizing. Slowly we train our pets to be quiet and all but the most itchy will choose to scratch and chew in private. Luckily there are some tell-tale signs that help us to identify the pruritic dog. Saliva staining is a commonly-seen feature in these animals. A red-brown staining of light colored hair is often seen in allergic dogs in the groin, arm pits (axillae) and between the toes (interdigital spaces) and can be seen in figure 2. In addition, with long term problems, the skin itself will also change color. Instead of being pink, a black mottling (hyper pigmentation) will slowly develop, especially if the skin has looked red at the site. This is most commonly seen on the abdomen.
At present there is no definitive test that will absolutely confirm a diagnosis of atopic dermatitis. Because this is the case, veterinary surgeons may suspect atopy after examining a patient, but have to make sure that other causes of itch are not present. Once these have been ruled out, skin testing can be used as a pointer to the allergies involved.
So what are these other diseases? Flea infestation and the allergy are the most important causes of itchiness in dogs. Practically all dogs will have fleas at some time during their lives. The rump and hind end are most often affected. Nibbling and itching gives a rough feel to the coat and, if severe, pyotraumatic dermatitis (wet eczema) or alopecia will result. Very importantly, dogs with atopic dermatitis are often allergic to fleas as well, so it is pointless making a diagnosis of atopy without taking rigorous flea-control measures. Similarly, other parasitic infestations such as lice or sarcoptic mange may mimic atopy and these should be carefully ruled out.
Skin testing is performed to identify the allergens involved in allergic disease. Under profound sedation an area of hair on the chest is shaved and small injections of substances known to be possible allergens made. After 15-20 minutes the reactions are recorded. Some practitioners prefer to perform a blood test to acheive the same purpose.
In treating atopic dermatitis it is imperative to consider the situation as a whole. Bacterial infections will make the animal far more itchy and may even contribute to worsening the allergy through damaging the skins’ protective mechanisms. So any bacterial infections seen as a rash or pustular spots, need to be treated promptly, using a combination of shampoos and antibiotics for a minimum of three weeks, and often longer. Corticosteroids medication is best withdrawn throughout the period of treatment as steroids can interfere with the dogs ability to fight infection. Natural products such as Essential Fatty Acid supplements should be considered to supplement the diet.
Yeast infection (caused by the yeast Malassezia pachydermatis) is another complication. Spots are not seen in this disease, but instead the organism causes redness, greasiness and a mousy odour. Dogs can be quite depressed when infected and can be extremely itchy. Treatment is usually with baths containing enilconazole, or miconazole in combination with Chlorhexidine. Tablet therapy is also available, but as a surface infection Malassezia is best treated using baths. Supplementation with Essential Fatty Acids is important to increase the dog’s inherent resistance.
Similarly, fleas and other ectoparasites will make an atopic dog far more itchy. All allergic animals should have regular and efficient flea therapy using veterinary preparations to treat both the dog and the environment. With bacterial, yeast and parasitic problems under control most dogs will be very much more comfortable.
A variety of drugs are now available for treatment. Generally they are used in combination rather than alone. Omega – 3 – fatty acids (OFAs) are now widely used for skin conditions. Therea are a mumber of veterinary formulations available for this purpose. Ask your vet which one he/she prefers.
Antihistamines were widely dismissed as unhelpful in atopic disease until recently when new studies both in the US and UK have shown considerable benefits from their use. No veterinary products are available and the human drugs, chlorpheniramine, hydroxyine, and clemastine have all shown to be useful.
Steroids are widely thought to cause side effects which outweigh their potential for good. Their use should be limited to only the most severe cases of atopic dermatitis and should be discontinued as early as possible.
Hyposensitizing vaccines ( also known as desensitizing vaccines) are prepared from the allergens identified as important at skin test. By administering these allergens subcutaneously over a long period the immune response to them is modified and pruritis is reduced. They are seen to be beneficial in about 60% of dogs, and take up to nine – twelve months to have effect.
Allergen avoidance is useful when house dust mites are known to be the problem. Exposure to bedrooms should be avoided by house dust mite allergenic patients to minimize exposure to the allergen. When pollens and moulds are involved avoidance is practically impossible as these allergens travel for miles on the wind, although obviously very large sources of pollens, for instance hay meadows for grass sensitive individuals should be avoided.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 6/3/2016