Allergies in Dogs
Like people, dogs can be allergic to various substances, including plant particles and other substances in the air or substances in food. These substances are called allergens. Allergens are substances that, when inhaled or absorbed through the skin, respiratory tract, or gastrointestinal tract, stimulate histamine production, which results in inflammation.
Fewer than 10% of dogs are thought to be genetically predisposed to become sensitized to allergens in the environment. Both male and female dogs can be allergic to materials in the air. Breeds predisposed to developing allergies include Chinese Shar-Peis, Wirehaired Fox Terriers, Golden Retrievers, Dalmatians, Boxers, Boston Terriers, Labrador Retrievers, Lhasa Apsos, Scottish Terriers, Shih Tzus, and West Highland White Terriers. However, any dog of any breed (or mixed breeds) can be allergic. The age of onset is generally between 6 months and 3 years. Signs are usually seasonal but may be seen all year. Itching is the most typical sign (see also Itching (Pruritus) in Dogs). The feet, face, ears, front legs, and abdomen are the most frequently affected areas, but scratching all over the body is common. Scratching can lead to secondary signs of wounds, scabbing, infection, hair loss, and scaling. Other signs of atopy include licking or chewing the paws and rubbing the face and eyes.
Allergies are identified by signs when other causes have been excluded. Allergy testing can be used to identify the offending allergens and to formulate a specific immunotherapy treatment program.
There are 3 therapeutic options: avoidance of the offending allergen(s), controlling the signs of itching, and immunotherapy (for example, an allergy vaccine). A good management plan requires the use of several different treatments, the understanding and reasonable expectations for response from the pet owner, and frequent progress evaluations so that the plan can be adjusted as needed.
Immunotherapy attempts to increase a dog’s tolerance to environmental allergens. Vaccine preparation involves selection of individual allergens for a particular dog. The allergen selection is determined by matching the test results with the prominent allergens during the time of year when the dog has signs. Immunotherapy is best considered for dogs with problematic signs that occur for several months during the year. The dog must be cooperative enough to receive allergy injections. You may have to administer some injections yourself. Your veterinarian can provide training and most owners learn to administer the allergy injections very well, while others may need assistance from a capable friend or veterinary staff member. Your veterinarian will determine the frequency of the injections and the dosage given.
Treatment takes a longterm commitment. You must be willing to follow instructions accurately, be patient, and be able to communicate effectively with your veterinarian. Injections may initially increase signs. If this occurs, contact your veterinarian immediately. Improvement may not be visible for 6 months and a year of treatment may be required before you can tell if the immunotherapy is working. The best way to evaluate the treatment is to compare the degree of disease or discomfort between similar seasons. Anti-itch medication and antibiotics are often required during the initial phase of treatment.
Allergy shots improve the condition but do not cure the disease. Many animals may still require anti-itch medications during seasonal flare-ups.
Among pets, food allergies are less common than airborne allergies. Signs of food allergy are similar to airborne allergies except there is little variation in the intensity of itching from one season to another. The age of onset is variable. The distribution and intensity of itching varies between animals.
There is no reliable diagnostic test other than feeding a limited foodstuff (hypo-allergenic or elimination) diet and seeing if the itching resolves. Your veterinarian should be consulted to develop a specific test plan for your dog. The ideal food elimination diet should be balanced and nutritionally complete and not contain any ingredients that have been fed previously to your dog. Owners often do not understand that if any previously fed ingredient is present in the elimination diet, the dog may be allergic to that one ingredient and the diet trial will be a failure. The key point in any food elimination diet trial is that only novel food ingredients can be fed. This also includes treats and anything the dog eats besides its regular food.
The trial diet should be fed for up to 3 months. If marked or complete resolution in signs occurs during the elimination diet trial, food allergy can be suspected. To confirm that a food allergy exists and improvement was not just coincidental, the dog must be given the previously fed food ingredients and a relapse of signs must occur. The return of signs is usually between 1 hour and 14 days. Once a food allergy is confirmed, the elimination diet should be continued until signs disappear, which usually takes less than 14 days. At this point, previously fed individual ingredients should be added to the elimination diet for a period of up to 14 days. If signs reappear, the individual ingredient is considered a cause of the food allergy.
The foods dogs are most often allergic to include beef, chicken, eggs, corn, wheat, soy, and milk. Once the offending allergens are identified, control of the food allergy is by strict avoidance. Concurrent diseases may complicate the identification of underlying food allergies. Infrequently, a dog will react to new food allergens as it ages.