Canine and Feline Allergies

Nov 7, 2023

“Allergy” is an extremely broad ranging term that can be used to refer to any situation where the immune system responds to a foreign antigen (component of a protein or other molecule) that does not generally cause an immune reaction in the general population. Allergies can manifest in a wide variety of ways, ranging from life-threatening anaphylactic reactions to less severe acute cutaneous allergic reactions (swelling and hives). It also includes allergic rhinitis (nasal allergies), asthma, allergic skin disease (atopic dermatitis or eczema), cutaneous adverse food reactions (food allergies), diet responsive enteropathy, and a wide range of other conditions.

As in humans, allergies are increasingly commonly recognized as a cause of disease in cats and dogs. Whether this is due to increased recognition, decreased exposure to diverse antigens at a young age, inbreeding, or a variety of other factors it not well understood. However, the management of allergies occupies a significant portion of veterinary medicine and encompasses aspects of dermatology, internal medicine, nutrition, and other disciplines.

Allergies may occur to a wide variety of substances including drugs and chemicals, environmental substances, insect bites or stings, or foods. While certain trends may be noted with different types of exposure (aerosolized antigens may lead to nasal or lung disease; grasses tend to cause paw inflammation, and food allergens often cause inflammation around the mouth and anus), there is no hard and fast rule, and any antigen exposure may lead to a range of clinical signs.

Food allergies can only be definitively diagnosed by an elimination trial. This involves feeding animals a diet that contains only novel or hydrolyzed proteins for a period of several weeks (the exact time span depending on the manifestation of the allergy). Novel protein diets mean that they contain a limited set of ingredients (generally one fat, one protein, and one carbohydrate source) that the animal has never previously been exposed to. This often involves sources of protein such as venison, kangaroo, rabbit, salmon, or crocodile. Because it is often impossible to definitively know what foods an animal has been exposed to in the past, a “hydrolyzed” diet is often chosen as the ideal diagnostic tool. This means that the protein in the diet has been digested by enzymes and is no longer able to stimulate an immune response. Regardless of the type of diet chosen, it is crucial to ensure it is made in a specific facility that does not process other protein sources, as contamination with other ingredients can make a diet trial fail.

Environmental allergies can only be definitively diagnosed by intradermal skin testing. Like humans, this involves using small needles to inoculate allergens into the skin and then measuring the size of wheal formed.

Blood tests for allergies are generally not recommended as they are very inaccurate. In some limited situations (anti-gliadin antibodies for gluten intolerance) they may be useful, however commercial “panels” used to determine what a dog or cat is allergic to are generally of low diagnostic yield and are not recommended as a first line option.

Treatment of allergic disease may come in a wide range of forms, full discussion of which is well beyond the scope of this article. However, perhaps the most effective option is avoidance if at all possible. For some allergens, this is readily attainable — an animal can easily be not fed a certain protein, not exposed to a specific drug, or removed from spaces using a specific scent or oil. Others may be more difficult, for example, completely isolating a dog from bees or mosquitos. Still, others are impossible — there is no reasonable way to prevent all exposure to tree pollen or house dust mites. Even in these situations when avoidance is impossible, reduction of exposure may be very attainable — for example, regular vacuuming or the use of HEPA filters.

If avoidance is not possible and reduction ineffective, medical therapies may be required. For environmental allergens, allergen specific immunotherapy is often used — this involves regular injections or oral drops containing a small amount of the allergen of concern, designed to gradually increase exposure and so decrease the immune response. These are effective in reducing the severity of signs in the majority of cases but are almost never a complete cure.

Other drug options include antihistamines (cetirizine), steroids (prednisone), anti-itch medications (oclacitinib), immunosuppressives (cyclosporine) monoclonal antibodies (lokivetmab; in dogs only) and others. All of these medications have potential risks and benefits, and none are definitively the best or worst choice. Discussion with your veterinarian about the best option for your pet is important.

Several different therapies in veterinary medicine may result in “reactions” that are not allergic in nature, and this must be understood in order to properly manage patients. While allergic reactions to vaccines, blood transfusions, anesthesia, or medications can certainly occur, the majority of adverse reactions to any of these are not allergic in nature and represent either normal responses (lethargy and pain after vaccination), predicable drug effects (diarrhea after an antibiotic), or non allergic reactions or intolerances to drugs and medications.

Overall, allergies are a common cause of disease in veterinary medicine. A large percentage of ear infections, anal gland impaction, skin rashes, chronic coughing or sneezing, and chronic diarrhea may have an allergic component as their origin.

References

Santoro D. Therapies in Canine Atopic Dermatitis: An Update. Vet Clin North Am Small Anim Pract. 2019 Jan;49(1):9-26. doi: 10.1016/j.cvsm.2018.08.002. Epub 2018 Sep 24. PMID: 30262146.
Hensel P, Santoro D, Favrot C, Hill P, Griffin C. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification. BMC Vet Res. 2015 Aug 11;11:196. doi: 10.1186/s12917-015-0515-5. PMID: 26260508; PMCID: PMC4531508.
Mueller RS, Nuttall T, Prost C, Schulz B, Bizikova P. Treatment of the feline atopic syndrome - a systematic review. Vet Dermatol. 2021 Feb;32(1):43-e8. doi: 10.1111/vde.12933. PMID: 33470011.
Gedon NKY, Mueller RS. Atopic dermatitis in cats and dogs: a difficult disease for animals and owners. Clin Transl Allergy. 2018 Oct 5;8:41. doi: 10.1186/s13601-018-0228-5. PMID: 30323921; PMCID: PMC6172809

Author

Matthew Kornya, BSc, DVM, ABVP (Feline) Residency Trained, Resident ACVIM (SAIM)
Consulting Editor

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