Allergies: Itching to Scratch
One of the most common presenting complaints for veterinarians is itching. I usually have at least one patient a day coming in related to its skin. You can bet, now that summer is here and most owners are spending time confined with their furry companions, that veterinary clinics are evaluating an increasing number of patients for pruritus (that’s a fancy doctor word for itching). So why all the scratching, head-shaking, ear rubbing, and paw-licking behavior? Many times, a dog or cat’s itching is related to allergies.
Humans with allergies often have congestion, runny nose, red eyes, and other symptoms related to their upper respiratory passages. However, dogs and cats are different—they tend to have changes to their skin. Allergies are just a hypersensitivity reaction, meaning the body is responding inappropriately to something (more on that in a bit), or having a larger response than would be expected. This response is mediated by the immune system and involves various types of white blood cells and chemical signaling promoting inflammation and itching. In people, we often think about something in the environment triggering our allergies (i.e., hay fever, dust mites, etc.). You might wonder, who is the culprit in dogs and cats?
There are three main categories that veterinarians will consider when working up a patient for suspected allergies—fleas, food, and environment. Both dogs and cats can develop a hypersensitivity reaction to proteins in the saliva of fleas. This means that even a single bite can result in wide-spread skin changes, resulting in an unhappy pet (remember, allergies are an inappropriate over-response). Veterinarians call this flea allergic dermatitis, or FAD, for short. Even when fleas are not present in the household (which they often are not), a patient with flea allergies could potentially receive a bite when going out in the yard, going for a walk, or having a play date at the park. You may think your veterinarian is trying to push flea products, when really she is trying to save your furry friend from misery to its skin—not to mention that dogs and cats can also get TAPEWORMS from eating flea larva. Yes, part of a tapeworm’s life cycle involves fleas before moving on to your dog or cat. So two parasites for one! What a deal, right? Hence, I try to discuss the multiple benefits from regular parasite prevention products with my owners to truly see the value they are obtaining. Once flea allergies are crossed of the list, the next step is to rule out food allergies.
A patient showing hypersensitivity to proteins in his diet will usually begin to show signs between 1 to 3 years of age, assuming that patient has been on the same diet. So if an owner has been changing their cat’s diet around frequently, it is possible the cat could develop a food hypersensitivity later in life. It can also make choosing an appropriate diet for a diet trial more challenging for the veterinarian!
The reason your veterinarian may recommend a diet trial and the type of recommended food chosen will vary based on the pet’s history. The idea is to either select a novel protein source (meaning one Fido has not been exposed to before) or a hydrolyzed protein diet (one where the proteins are broken down to small molecular sizes not recognized by the immune system), and then determine if a patient’s skin signs resolve with the new food. The trial should last a minimum of 8 weeks (some vets may recommend longer), and no other foods can be fed in order to truly determine if a protein source in the previous diet was causing the allergic response.
Last but certainly not least, are potential environmental allergens. Common potential sources of environmental allergens include pollens, grasses, and dust mites (so just staying inside may not eliminate the exposure). When diagnosing a patient with this type of allergy, veterinarians will often refer to this as atopy, or atopic dermatitis. There appears to be a genetic component, and affected patients have issues with their skin barrier function and immune-system. Therefore, some breeds of dog seem particularly predisposed to developing atopic dermatitis including Golden Retrievers, German Shepherds, Labradors, Pit Bulls, Boxers and many others. Similar to food allergies, patients will generally develop clinical signs between 1 to 3 years of age. Depending on the specific allergen, a patient’s skin issues can be seasonal, change with location (e.g., vacation home), or change over time. Testing for this type of allergy can be more difficult.“Wheal” test involves injecting a small amount of various allergens systematically into a patient’s skin and then visually evaluating the inflammatory response.»
Your veterinarian will want to rule out both fleas and food allergies first before considering testing for environmental allergies. Skin scrapes, hair plucks, swabs, cultures may also be recommended to ensure there are no other parasites, secondary bacterial or fungal infection present that may require additional therapies. Baseline bloodwork and urine can be helpful to rule out endocrine disorders or other systemic disease that can cause changes to the skin. For environmental allergies, there are a number of potential tests – many board-certified dermatologists will generally recommend an intra-dermal (skin), or “wheal” test. This involves injecting a small amount of various allergens systematically into a patient’s skin and then visually evaluating the inflammatory response. The “wheal” is the bump that forms – the larger the size and more severe the inflammation equals a larger hypersensitivity to that particular allergen. A veterinary dermatologist can then use this information to create either oral or injectable compounds for hyposensitization therapy.
Part of the therapy for allergies has already been mentioned as a component of the testing (e.g., diet trials). Because the skin and its inflammatory response is complex, veterinarians often have to implement therapy while still ruling out potential causes. Shampoos will often be recommended for several reasons—depending on the product, they can include antimicrobials for secondary bacterial and yeast infections as well as ingredients to promote skin integrity (remember, patients with allergic skin disease have genetic problems with the skin’s barrier function). Oral antibiotics may be prescribed if there is a secondary bacterial infection. Other topical products can be useful depending on the area of the affected skin. If the ears are problem, ear cleaning and medications for the ear canal. And then we need to address the big issue owners bring the pet in for the first place … the ITCHING!
A number of drugs have been developed specifically for dog and cat allergies. The most effective drugs to reduce inflammation are corticosteroids (not the same as the steroids you may be thinking of, used illegally by the occasional competitive athlete). Many veterinarians will reach for steroids in some patients with severe itching, inflammation and discomfort for immediate relief, and prescribe the drug over a short period in a tapering manner.
The bigger concern is with chronic, long-term use, which I generally try to avoid for my patients with allergies. There are a number of other oral and injectable medications labeled for allergic animals, including Atopica® (cyclosporine), Apoquel® (oclacitinib), and Cytopoint® (Lokivetmab). Atopica® is labeled for both dogs and cats and is a daily oral medication. Apoquel is labeled for dogs and is also an oral medication initially given twice daily for 2 weeks and then once daily thereafter. Cytopoint is an injectable just for dogs that can have effects for 4 to 8 weeks. Your veterinarian will likely recommend one of these medications depending on a patient’s clinical signs, severity, seasonality, and history. You should always refer to your veterinarian’s prescriptions when administering drugs and be aware of potential adverse effects and recommended monitoring.
Allergies are one of the most common causes for itchy dogs and cats. They can prove frustrating at times, because a patient can have hypersensitivities to a number of allergens and have more than one type of allergy. Patients can have relapses or develop secondary infections that require additional treatment. My best advice is to be systematic when working up potential causes. Is Fluffy on an appropriate flea/tick preventative? Have I tried a prescription hydrolyzed or novel protein? Did a family member give them a treat that’s not on her diet? Does Gracie have a flare up when we travel to the beach? Am I using the shampoo recommended by my veterinarian as prescribed? These are just some questions that may help ferret out the potential instigator.