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paw Dermatology    paw
The most common problem owners present their pet to the veterinarian has to do with skin conditions. Most of these are chronic conditions that can be controlled long term to decrease the incidence of secondary ear and skin infections.  Other conditions are primary infections or infestations such as flea infestation, mange, bacterial folliculitis or dermatophytosis (commonly know as ringworm).  A thorough physical examination, history of illness and a few simple tests usually are all that is needed to uncover the cause of the underlying problem.  
Of all the skin conditions we see allergic inhalant dermatitis (atopy) is the underlying cause in a vast majority of dogs and cats with skin problems.  Controlling the allergy thereby controls the secondary problems.
What is an allergy?  
An allergy is a state of over-reactivity or hypersensitivity of the immune system to a particular substance called an allergen. Most allergens are proteins. The allergen protein may be of insect, plant or animal origin. Initial exposure of the dog, or more likely multiple exposures, to the allergen may over-sensitize the immune system, such that a subsequent exposure to the same or related allergen causes an over-reaction. This means that the immune response, which normally protects the dog against infection and disease, can actually be harmful to the body.
The immune reactions involved in allergies are quite complex. Most reactions involve an antibody in the blood called Immunoglobulin E (IgE). In an allergic reaction the allergen protein molecules combine with IgE antibody molecules and attach to a type of cell called mast cells, found in many tissues throughout the body. When these cells are attached to the allergen, they break up and release potent chemicals such as histamines that cause local inflammation (redness, swelling and itching). This inflammation causes the various signs associated with an allergic reaction.
What are the symptoms of allergies in dogs?
The most common symptom associated with allergies is itching of the skin, either localized (in one area) or generalized (all over the body). The classic distribution pattern pruritis (itching) in these patients is the feet forearms, face and ears.  This is usually manifested as an intense licking of the feet and forearms and scratching of the face and ears.   Another group of symptoms that is not as common involves the respiratory system with coughing, sneezing, and/or wheezing. Sometimes, there may be runny discharge from eyes or nose. The third manifestation involves the digestive system resulting in vomiting and diarrhea.
How common are allergies in dogs?
Unfortunately, allergies are quite common in dogs of all breeds and backgrounds. Most allergies begin when the pet is between 1-3 years of age and typically progress and get worse as the pet ages.  
Are allergies inherited?
Some allergies are inherited. The inherited trait is known as Atopy (see What is Inhalant Allergy or Atopy below).
What are the common allergy-causing substances (allergens)?
A very large number of substances can act as allergens. Most are proteins of insect, plant or animal origin, but small chemical molecules known as haptens can also cause allergy. Examples of common allergens are pollens, mold spores, dust mites, shed skin cells (similar to “pet allergies” in humans), insect proteins such as flea saliva, and some medications.
What are the different types of allergy?
There are several ways of classifying allergies. Some examples of classifications include:
Precipitating allergen - Flea Allergy
Route the allergen takes into the body - Inhalant Allergy, Skin Contact Allergy or Food Allergy
Time it takes for the immune reaction - Immediate-type Hypersensitivity, also called Anaphylaxis or Shock and Delayed-type Hypersensitivity
Type of immune reaction - Types I through IV Hypersensitivity
Clinical Signs - Allergic Dermatitis or Allergic Bronchitis
Inherited forms - Atopy or Seasonal Allergies
What is Contact Allergy?
Contact allergy is the least common type of allergy in dogs. It results from direct contact to allergens contained in flea collars, chemicals in the lawn or the grasses themselves and bedding, such as pyrethrins or wool. If the dog is allergic to these substances, there will be skin irritation and itching at the points of contact, usually the feet and stomach. Removal of the allergen (once it can be identified) often solves the problem.   As well as shampoo therapy to dilute the allergen from the skin.  
What is Flea or Insect Bite Allergy and how is it treated?
Flea allergy is the exaggerated inflammatory response to a flea bite or other biting insect. Flea saliva is the most common allergen. It is a common allergy of dogs, although only a minority of dogs becomes allergic. Most dogs experience minor irritation from flea bites. The flea allergic dog will react to a single bite with severe local itching. It will bite and scratch itself and may remove large amounts of hair, especially in the tail-base region. Secondary bacterial infection may occur in the broken skin. The classic distribution pattern of this allergy is the caudal 1/3 of the pets body (over the rump in the tail-base region and the hind limbs).
Because one flea can be a problem for the allergic dog, strict flea control is essential. This is difficult considering the life-cycle of fleas, but with modern medications you should be able to provide a flea-bite free environment for your dog. Your veterinarian can give you tips on protecting your dog from fleas. When strict flea control is not possible or in cases of severe itching, anti-histamines or corticosteroids (steroids) can be used, under careful veterinary guidance, to block the allergic reaction and give relief. If secondary bacterial infection is present, appropriate antibiotics will be prescribed.
What is Inhalant Allergy (Atopy) and how is it treated?
“Allergic Inhalant Dermatitis” in the dog is used as a synonym for Atopy. The main causative inhaled allergens are tree pollens (cedar, ash, oak, etc.), grass pollens, weed pollens (ragweed, goldenrods, etc.), molds, mildew, and house dust mites. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others such as molds, mildew, and house dust mites are year-round. When humans inhale these allergens, the allergy manifests mainly with respiratory signs - runny eyes, runny nose, and sneezing (“hay fever”). But in dogs the result is itchy skin (pruritis). Due to these clinical signs, the condition is also called “Allergic Inhalant Dermatitis”.   Again the classic distribution pattern of pruritis (itching) is the feet, forearms, face and ears.  The dog may rub its face, lick its feet and scratch the axillae (underarms).  Many dogs with recurrent ear infections have atopy, controlling the atopy aids in controlling recurrent ear infections.
Most dogs that have inhalant allergy start showing signs between one and three years of age. Affected dogs will often react to several allergens. If the offending allergens can be identified by intradermal skin tests or IgE allergy tests, the dog should be protected from exposure to them as much as possible. But this is difficult and recurrent bouts are likely. These allergies can be treated but a permanent cure is not usually possible.  Skin testing is available but with today's modern medications for treatment of atopy in most cases intradermal skin testing can be avoided.
Treatment depends largely on the length of the dog's allergy season. It involves three approaches:  
Anti-inflammatory. Treatment with anti-inflammatory drugs such as corticosteroids, or antihistamines, will quickly block the allergic reaction in most cases. Fatty acid supplementation of the diet can improve the response to steroids and antihistamines in some cases. Newer drugs such as oral cyclosporine (Atopica) provides great results in a majority of patients with out the need for long term steroids and lack the side effects of long term steroid usage (weight gain, thin skin, pot bellied appearance, onset of diabetes and immune suppression).  
Shampoo therapy. Frequent bathing with a hypoallergenic shampoo can be soothing and helpful. The bathing may also rinse out allergens in the coat that could be absorbed through the skin. Some therapeutic shampoos contain anti-inflammatory ingredients that may further benefit your pet.  Always use cool water as this is soothes the irritation as well.  
Hyposensitization therapy. The third major form of allergy treatment is hyposensitization with specific antigen injections or "allergy shots".   This can be avoided in the majority of patients even with severe atopy with today's modern medications. Once the specific sources of allergy are identified by allergy testing, very small amounts of the antigen are injected weekly. This repeated dosing has the objective of reprogramming or desensitizing the immune system. Results are sometimes good but success is variable. Approximately fifty-percent of treated dogs will see significant improvement in their clinical signs while approximately twenty-five percent more will see a decrease in the amount or frequency or corticosteroid usage.
What is Food Allergy and how is it treated?
Food allergy can develop to almost any protein or carbohydrate component of food. It most commonly develops in response to the protein of the food of a particular food origin; beef, pork, chicken, or turkey are commonly associated with food allergies. Food allergy can show the exact same clinical signs as atopy but is not as common as atopy.  Also a lot of patients with atopy have some degree of food allergy as well.  Food allergy can develop at almost any age. Food allergy may produce any of the clinical signs previously discussed under atopy.  Some food allergic dogs have gastrointestinal sings such as vomiting and diarrhea.  Food allergy does not respond well to corticosteroids or other medical treatments. Treatment requires identifying the offending component(s) of the diet and eliminating them. Testing for specific food allergies involves a hypoallergenic diet trial. Because it takes at least eight weeks for all other food products to be removed from the body, the dog must eat the special diet exclusively for eight to twelve weeks. Previously we had to home cook for these dogs but the invention of diets made specifically for food trial has made the process much more convenient for the owners.  If a positive response and improvement of your pet's clinical signs occurs, your veterinarian will advise you on how to proceed. It must be emphasized that if the diet is not fed exclusively, it will not be a valid test. All table food, treats or vitamins must be discontinued during the testing period. There may be problems with certain types of chewable tablets such as heartworm preventative. Your veterinarian will discuss this with you.
The manifestations of allergies can be confused with other disorders, or occur concurrently with them. Therefore, do not attempt to diagnose your dog without professional assistance. Be prepared for your pet to receive a full diagnostic evaluation by your veterinarian. If an allergy is diagnosed and identified, the whole family must follow your veterinarian's advice very closely if success in controlling the problem is to be achieved.

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