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Allergies in Pets
Last Updated: 07/10/2013

Pet Allergies and Symptoms

As in people, the incidence of allergies in pets seems to be increasing. While allergic humans may often sneeze, wheeze or even have serious respiratory difficulties, allergic reactions in pets are mostly characterized by skin problems, exacerbated by their primary symptom—itching and scratching. Dog allergies fall into three main categories: flea allergic dermatitis, atopy, and food allergy. Many pets can be affected by one or more allergy.

Food Allergy

What is food allergy and what are its symptoms?
Food allergy is an allergic reaction to one or more ingredients in a pet’s food. The most common allergens are beef and milk products, cereals (wheat, corn, soya), chicken and eggs. The exact cause of a food allergy is not known. Perhaps a change in the pet’s immune system causes certain ingredients to be perceived as “foreign,” initiating inflammatory mechanisms to fight off the perceived “intruder.”

The most common symptoms of a food allergy are itching, licking or chewing. Otitis Externa (ear infection) along with other skin problems are also common in conjunction with food hypersensitivity. Some pets may also have diarrhea and other digestive problems. Symptoms can appear at any age, whether a pet has just started a new diet or has been eating the same food for several years.

How is food allergy diagnosed?
The only effective way for your veterinarian to diagnose a food allergy is to put your pet on a “hypoallergenic” or “exclusion” diet for a minimum of 8–12 weeks. Such a diet contains ingredients to which the animal has not been exposed in the past. Because the source of protein causes most allergic reactions, exclusion diets use proteins—often venison, fish or duck—that are normally not found in regular pet food. An exclusion diet may comprise home-prepared food or prescription commercial hypoallergenic products.

If your pet has a food allergy, there should be a significant reduction in the symptoms after the recommended period on the exclusion diet. To identify all the food allergens, your veterinarian will recommend adding a single protein back into the diet every 1–2 weeks, while watching for a recurrence, or worsening, of symptoms. If this happens, the veterinarian will recommend removing the offending ingredient from the diet.

How is food allergy treated?
The best way to treat your pet’s food allergy is to carefully monitor his or her diet, in order to avoid flare-ups.
In rare cases, your veterinarian may also prescribe antihistamines and corticosteroids.

Flea Allergy Dermatitis

What is flea allergy dermatitis and what are its symptoms?
Flea allergy dermatitis (FAD), often called “flea bite hypersensitivity”, is a skin disease caused by an allergic reaction to flea saliva. A single flea bite can trigger the disease’s intense itching. Dogs with FAD chew and bite their backs, legs, bellies or tails. This often leads to “hot spots”, or localized hair loss and skin infections. You may find fleas and flea dirt (the flea feces look like black specks) on your pet, although many dogs with FAD have very few fleas, since they are constantly licking and chewing.

How is flea allergy dermatitis diagnosed?
Your veterinarian looks for the usual signs (scratching, skin sores, the presence of fleas and/or flea dirt). He or she may also perform a skin test to confirm that fleas are causing the problem, as FAD symptoms can resemble those of other conditions, including external parasites (mites, lice), infections and other allergies, that cause severe itching.

How is flea allergy dermatitis treated?
The best way to treat FAD is to prevent fleas from attacking your pet. Various insecticides and insect growth regulators that eliminate flea infestations are available. Your veterinarian can recommend the right product for your pet. Daily vacuuming and frequent washing of your pet’s bedding can also reduce your home’s flea population.

To break the “itch-scratch” cycle that leads to skin infections, your veterinarian may prescribe corticosteroids, antihistamines and essential fatty acids to relieve irritation. Warm water baths and anti-itching shampoos and conditioners also help.

What is most important to realize is that there is no cure for FAD: your pet will always be allergic to flea bites and you must be continually on your guard to prevent further problems. Flea prevention is a must


What is atopy and what are its symptoms?
Atopy, or environmental allergy, is an allergic reaction to airborne substances like pollen, molds, house dust mites and animal dander (skin or hair fragments). It is most common in dogs, but some cats are also affected. The incidence of atopy depends as much upon a pet’s genetic susceptibility as exposure to the allergen itself. (An allergen is any agent causing the allergic reaction.) Terriers, Setters, Retrievers, Dalmatians, and Chinese Shar-Peis are particularly prone to atopy.

Itching, mostly around the face, feet, lower chest and belly, is the primary symptom. Depending on the cause, this may occur only seasonally (pollen) or year-round (molds, dust mites and dander). “Hot spots”, other skin infections and ear problems can develop. Frequent scratching due to chronic irritation may lead to hair loss. These signs can be seen from 4 months to 7 years of age but are typically first noticed around 1–3 years of age.

How is atopy diagnosed?
Atopy is confirmed through a process of elimination. Other causes of itching, such as fleas, mites, lice, bacterial and yeast infections, as well as food allergies, must be ruled out first. Your veterinarian will ask you for a detailed history of your pet’s itching problem. Skin or serum (blood) testing for different allergens may then be performed to help pinpoint the exact cause.

How is atopy treated?
Atopy is a lifelong condition and there is no known cure. However, there are a number of ways to manage the problem :

  • Anti-itch therapy, including the use of drugs, medicated shampoos and conditioners.
  • Removing the source of the allergy from the environment as much as possible.
  • Immunotherapy uses a series of injections to gradually accustom your pet’s system to the allergen(s) causing the problem. Although its effectiveness varies, it provides at least some relief for around 75% of pets with atopy.
  • If the atopy is relatively mild (for example, occasional itching during the pollen season), you can use “Elizabethan” collars, T-shirts and socks to reduce irritation by physically preventing your pet from scratching or biting themselves.

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