Note on Allergies from Dr. Kerry McLaughlin
What are allergies?
Allergies are an overreaction of the immune system to substances that normally cause no reaction in the majority of individuals.
Allergies in people vs pets:
In people, the most common signs of allergies are hay fever (sneezing, runny nose, watery eyes). However, in pets, the most common presentation is itchy skin (although we do occasionally see hay fever-like signs, allergic bronchitis, and asthma in our pets).
Three are 3 main categories of allergies in pets. Each of these has a characteristic age of onset, distribution of skin irritation, and treatment.
1) Environmental (Atopy)
2) Food allergy
3) Flea allergy dermatitis
Environmental Allergies (Atopy):
Signs are usually seasonal but can be year-round depending on what your pet is allergic to. The most common age of onset is between 1-3 years of age, although age of onset can range from 6 months to 7 years. The most common pattern of skin irritation is in areas where the hair is sparse and the area stays moist: armpits, groins, ear canals, muzzle, around the eyes, around the anus, and the conjunctiva.
Allergy testing is used to identify specific allergens for the making of allergy vaccines. The procedure is very similar to what is done in people. For intradermal (skin) testing, a variety of different allergens are used including air-borne allergens (such as pollen, ragweed, etc), indoor allergens (such as dust mites, mold), and common insects. Patients are usually sedated for this procedure, a small amount of allergen is injected into the skin, and the response to the injection is monitored and graded. The allergens that produce the greatest response are then used in the formulation of an allergy vaccine, which is customized for each patient. The vaccines are usually given 1-2 times weekly in the beginning of treatment and then the frequency of administration is decreased to once every few weeks. Allergy vaccines improve clinical signs for 50-80% of dogs, but response can take anywhere from 3-18 months!
Other treatments for environmental allergies include the use of antihistamines (such as Benadryl, Zyrtec, Claritin, etc) and medications which suppress the immune system (such as Atopica (cyclosporine)).
The component of pet food that pets are usually allergic to is the protein source. In dogs the most common proteins implicated are beef, dairy products, and wheat. In cats the most common culprits are beef, dairy products, and fish. The age of onset ranges from 3 months to 13 years (with a mean age of 2-4 years in dogs). As a general rule, think about food allergy in extremely young and older patients with non-seasonal itchiness! Be suspicious of food allergies in patients that have skin disease and are also having gastrointestinal signs such as diarrhea, vomiting, or flatulence.
What most owners find difficult to understand is that most patients will develop an allergy even after they have been eating the particular diet for months to years. The distribution of skin irritation is not incredibly different from seasonal allergies, although some patients will have worse issues in the ear canals and around the anus (“ears and rears”).
Food trials: This should be done with a prescription diet that contains either a novel protein (a protein that your pet has never been exposed to before such as kangaroo, venison, duck, etc) OR a hydrolyzed protein (protein that is broken down into such small particle sizes that it is not recognized by the immune system). It is very important that a prescription diet is used for the food trial, as they are the only diets that are guaranteed to contain ONLY the ingredients listed on the product information. The diet should be fed for a minimum of 8 weeks to determine whether or not it will improve the clinical signs. During this time period the pet can be fed ONLY the prescription diet with no outside treats or flavored medications (such as Heartgard chewables). If there is a positive response to the food trial, then the animal may be able to switch over to a cheaper over the counter diet.
Food allergy myths: (from veterinarypartner.com)
Flea allergy dermatitis (FAD):
At one time this was the most common allergic skin disease in dogs and cats. However, with the advent of newer and improved flea preventative products we are seeing this type of allergy less commonly. The allergic reaction occurs in response to the saliva of the fleas, which is deposited into the wounded skin as the flea feeds.
There is no age, sex or breed predisposition with this type of allergy. The most common presentation is itchiness and a rash over the back end of the body (base of the tail, back of the hind legs, and groin areas).
Very importantly, findings fleas or flea dirt on your pet are not necessary for a diagnosis! An allergic animal can respond to even a single flea bite with a severe reaction. In addition, pets (especially cats) can be very successful in removing them by scratching or ingesting them and making it difficult to find fleas on exam.
Treatment of FAD involves treating the patient with a flea preventative (with a prescription product such as Frontline, Revolution, Vectra, Sentinel), treating any secondary bacterial infections, treating all housemates, and treating the home.
Finally, it is important to realize that some pets may be suffering from one, two, or all three of the forms of allergies discussed above! If your pet is showing any signs of itchy skin such as scratching, excessive licking, paw chewing, or head shaking we recommend you have him or her evaluated by a veterinarian!