Allergic Disease in Dogs

by Barbara E. Magera, MD

Allergic disease in both humans and canines is increasing worldwide. Theories to explain the increase in IgE mediated allergic disease include genetic and environmental factors. Recent reports of canine and their human owner allergic to the same indoor allergens emphasizes the importance of indoor allergen exposure. In contrast to humans, clinical signs of canine allergic disease is largely limited to skin manifestations such as canine allergic/atopic dermatitis (AD). Allergic disease in humans often presents with allergic rhinitis ie “hayfever”, allergic conjunctivitis, asthma and allergic dermatitis. Allergic symptoms in humans frequently manifest as sneezing, nasal and/or ear congestion, runny watery eyes or nose, cough or wheezing and itchy dry skin.

The immunologic mechanisms of canine and human allergy are similar. For simplicity, the molecular mechanisms of allergy involve elevation of IgE one of the serum proteins or immunoglobulins that are characteristic of allergic disease. Allergy testing, whether performed by skin pricks or blood work, are based upon IgE elevations to specific individual allergens such as dust mites, pollens, molds and insects. For dogs, fleas are a particularly potent allergen which can result in severe pruritis or itchy often excoriated skin and fur loss.

Other common allergens that are a primary cause of skin allergies (ie known as atopic dermatitis) include dust mites, storage mites, tree, grass and weed pollen and mold spores. Interesting dogs, like humans, can develop allergy to skin dander which even includes allergy to specific humans. In the case of pollen allergy, symptoms are usually seasonal while allergy to the allergens listed causes year round symptoms.

Flea saliva is a potent source of severe dermatitis in dogs. The bite from a single flea can trigger severe skin inflammation, intense, vigorous and continuous scratching and hair loss which may be permanent. Skin lesions break down the protective dermal layers which may result in a severe skin infection. Areas of concern include delicate skin around the ears, eyes and paw pads.

Food allergy is a topic of intense research in both humans and dogs. How to determine the exact food allergen is challenging because, in dogs, a food allergy may develop months or years later after continuous food ingestion. This is in contrast to humans where serious food allergy symptoms, including swelling of the mouth, eyelids, face or throat often occur with initial exposure to the food allergen(s). In humans, the most feared consequence of an accidental food allergen ingestion is anaphylaxis. This life-threatening condition requires immediate administration of epinephrine to prevent death. Self-administered epinephrine injection syringes are warranted for humans especially children with severe food allergies to treat the early symptoms of anaphylaxis. Once administered, these patients are strictly advised to proceed to an emergency room facility as the symptoms of anaphylaxis may be prolonged and require ICU admission.

Although anaphylaxis has been reported in dogs, it does not occur as frequent as in humans. The complexity of food allergy will not be addressed in this article. The topic of canine food allergy warrants a lengthy separate discussion. Food allergy in dogs has not been well defined and much anecdotal and case reports describe food allergens in sources of dairy products, eggs, soy, wheat and meat proteins including beef chicken and lamb.

The diagnosis of allergy in dogs is made using skin prick testing and/ or serum blood tests. Many general Veterinarians use blood tests to determine allergy while Veterinarian Dermatologists advocate skin prick testing as more accurate. As a human Allergist, I often advise Veterinarians on the interpretation of the results of an allergy panel results performed by in vitro serum testing. Interpretation also requires understanding of the topography of where the dog primarily resides since allergen exposures to pollens and molds differ in different areas of the U.S. Plant, mold and even dust mite allergens concentrations are different in the northeast, southeast, northwest or southwest. If the allergic dog is a show dog and is constantly traveling both in the U.S. and internationally, trying to limit exposures to potential known allergens is challenging.

In addition to my Allergy Immunology Fellowship, I completed a Fellowship in Clinical Laboratory Immunology. As part of my training, I routinely performed and interpreted the serum testing for IgE to specific allergens. Testing methods to quantitate individual allergens in serum include the immunoCAP. The immunoCAP testing is superior to the previous generation of in vitro serum testing known as RAST (Radioallergsorbent testing). The controversy continues of which test method is more accurate to detect allergies namely skin versus blood testing. In my opinion, interpreting skin test results in the presence of inflamed or excoriated skin is difficult if not impossible. Often inflamed skin is reactive skin. With skin testing, the endpoint is a wheal or hive using skin pricks and intradermal injection of the allergen. In the presence of skin inflammation, skin testing may result in false positives. Additionally, all antihistamines must be discontinued at least 1-2 weeks prior to skin testing as this drug class interfers with skin testing and results in false negative results.

The immunoCAP is the preferred serum test to detect specific IgE (sIgE) to individual allergens. The immunoCAP assay is more sensitive and specific than RAST testing to detect IgE levels to individual allergens and is today considered the standard for allergy blood testing. In laymen’s terms, the immunoCAP is ” more accurate” than RAST testing. Antihistamines do not interfer with these in vitro blood tests for allergen detection.

To establish a diagnosis of dog allergy, I prefer blood testing, namely the immuoCAP, to detect elevated serum IgE levels to specific allergens. The issue of false positives is eliminated and the results are quantitative meaning the numerical level of the allergen-specific IgE is provided. The level of serum IgE to specific allergens is increasingly useful in clinical decision processes; however, the numerical level of the elevated serum IgE does not predict the severity of allergy symptoms. This is an active area of research in humans and canines.

Depending upon the allergen(s) identified, the first dictum in allergy is allergen avoidance. In the case of dust mite allergy, carpet removal or frequent vacuuming is recommended along with removal of feather bedding and furniture, a haven for dust mites. Use of HEPA filters and turning off ceiling or other fans are also recommended. These measures although well studied in human allergy are often not practical for allergic dogs.

A trial of oral antihistamines is indicated particularly for the management of seasonal allergies. Immunotherapy is another alternative particularly for nonseasonal allergies such as mite allergy or in conditions where pollen or mold exposures are present year round.

Three agents are FDA approved for treatment of IgE mediated atopic dermatitis (AD) in canines. Oclacitinib or Apoquel manufactured by Zoetin, is an agent classified as a JAK1 inhibitor. This agent specific blocks inflammatory mediators or chemicals that cause or contribute to atopic dermatitis in dogs. Apoquel is dosed twice daily for the initial 14 days and then changed to once a day thereafter.

Another available treatment for IgE mediated atopic dermatitis in dogs is Lokivetmab or Cytopoint manufactured by Zoetis. This biological agent is a monoclonal antibody that specifically targets interleukin-31, a key inflammatory component important in the mechanisms of severe pruritis/itching in dogs with atopic dermatitis. Veterinarians and owners report that a single injection given in the office markedly improves scratching nearly immediately with beneficial effects up to four to eight weeks.

The FDA recently approved another JAK1 inhibitor known as Iiunocitinib or Zenrelia manufactured by Elanco. Zenrelia carries a black box FDA warning that dogs should not be vaccinated for 28 before or after giving a dose of Zenrelia. The reasons are due to the risk of fatal vaccine-induced disease and/or an inadequate immune response to a given vaccine. JAK1 inhibitors are immunosuppressants designed to suppress the heightened immune response associated with AD. Some Veterinarians elect to withhold starting a JAK1 inhibitor 3months before giving any vaccines. A prudent measure is to ensure the dog is up to date on all vaccinations before initiating these therapies.

The FDA iblack box warning with Zenrelia indicate it should not be used in a dog receiving live virus vaccines because of the risk of a fatal infection from the virus. Additionally, the potential for an inadequate immune response exists to this and other vaccines including rabies. (Rabies is not a live vaccine). Additionally, dogs who are already immunosuppressed from disease states or drugs should not receive Zenrelia.

The advantage of Zenrelia compared to Apoquel include once-a-day dosing. Zenrelia may offer a cost advantage compared to Apoquel because of the daily dosing. Attempts to change Apoquel dosing from twice to once a day dosing is often followed by a “rebound itch”. In comparison to Zenrelia, Apoquel has no vaccine risks and no delays in vaccine schedules are required. Post marketing surveillance studies of Apoquel indicate that some dogs may experience an increased susceptibility to skin and ear parasitic infections. As with all immunosuppressive therapies, the potential for worsening an underlying malignant condition exists.

This general overview of canine allergy is provided to help owners understand the varied options used to (a) identify dog allergy and (b) explain treatment options. As always, it is best to check with your dog’s Veterinarian for optimal care of your beloved dog.

Barbara E. Magera MD, PharmD, MMM (Caracaleeb) is a Cavalier fancier, exhibitor and breeder, photographer and writer who lives and practices medicine in Charleston, SC. She is a Board Certified Allergist, Internist and Pharmacist.

Photograph credits to Jan Stitzel.