My Pet Is Allergic To What ?

My pet is allergic to WHAT?

 March 6, 2014

From the desk of Dr. Voorheis


“Wow Doc, last week I read all about fleas and all the drama they cause with my pet. Now you tell me my pet can also be allergic to the same stuff I am allergic to? Like pollen, dust mites and even certain foods?”

 The short answer to that is of course “yes”. This week’s blog will finish up our trilogy on allergies. Since we have extensively covered fleas, we will now talk about food allergies and atopy. As I sit at the keyboard to write this, my first thought is “I’ve got to be crazy to write about food allergies and atopic dermatitis in one blog.” My eyes are already crossing with the load of information that needs to be shared. A blog could easily be devoted to each of these. Heck, there are veterinary dermatologists who focus almost exclusively on atopic dermatitis. Attempting to distill this subject into something readable and understandable is this week’s challenge. But I’m always up for a good challenge as you know, so I shall give it the old college try! You’ll have to bear with me and excuse my language this week. No, I won’t be doing any cursing but there will be a ton of medical terms being used to try and explain this topic. It may get confusing but I will do my level best to explain it as we go along. Let’s start with some basic definitions:

 Atopic Dermatitis –  a predisposition to become allergic to normally innocuous substances, such as pollens such as grasses, weeds, and trees, mold, house dust mites, epithelial allergens and other environmental allergens. Susceptible animals become sensitized to allergens by producing allergen-specific IgE which binds to receptor sites on cutaneous mast cells. Further allergen exposure such as inhalation and more importantly percutaneous absorption causes circulating basophils (a type of white blood cell) and tissue mast cell degranulation. This is a type 1 immediate hypersensitivity and results in the release of histamine, heparin, proteolytic enzymes, cytokines, chemokines and many other chemical mediators.


 Food Adverse Reactions – Food Adverse reactions are itchy, non seasonal reactions associated with ingestion of one or more substances in the animal’s food. Pathogenesis (development of disease) is not completely understood with regard to immunologic (pertaining to the immune system) vs. idiosyncratic (pertaining to the individual animal in this case). Immunologic reactions are both immediate and delayed reactions to specific ingredients presumed to be type 1 and type 4 hypersensitivities.

 So why talk about these two together? The signs of each can look very similar. There is significant cross over in the distribution of “signs”. Typically, food allergy signs are not seasonal whereas atopic signs are seasonal. However, they do merge or blend. Why? Frequently, dogs and cats with atopic dermatitis have multiple allergies simultaneously which make their signs appear nearly year round. Couple that with frequent skin infections that also cause pruritus (itchiness) and you can have a seasonal dermatitis that affects the animal all year long.

 So now that we have the basics down, let’s talk about each topic individually and do a bit of comparing to point out the differences.

 Atopic Dermatitis

 In 2001, the American College of Veterinary Dermatology’s task force on Atopic Dermatitis, publishing in the journal Veterinary Immunology and Immunopathology, outlined significant change in the thinking of the pathophysiology (functional changes associated with disease)   of Atopic Dermatitis. Huh?

 Up until that point our understanding of Atopic Dermatitis went something like this: Atopy is an IgE- mediated disease like hay fever in people.

Inhaled allergen


Mast Cell Degranulation


Itchy skin

We now know that while the above may describe a small percentage of what happens in the atopic dog, this is not the main pathogenesis of the disease. Allergens are absorbed across the skin. Due to both genetic and environmental factors, there is epidermal barrier dysfunction. This leads to increased transepidermal water loss, deeper penetration of allergens and colonization of skin by bacteria and yeast. Yuck! There is some fairly complex pathophysiology that is happening in the skin of an atopic dog. Key proteins are affected, key lipids are deficient, the skin cells shed in an abnormal fashion and there are structural abnormalities in and between the skin cells.

 We know also now that IgE (antibody) is important but not essential. T-cell lymphocyte imbalance appears to be the key in atopic dermatitis. These T-cell lymphocytes produce cytokines. One of these inflammatory molecules is a molecule called IL-31. Blocking IL-31 is a key to treating the itching from atopic disease and a number of other allergic skin diseases.

 Remember, I told you there would be language this week! I wasn’t kidding. I hope you are all still with me. The bottom line is that we used to think that atopic dermatitis was caused by inhaled allergens such as pollens, house dust mites etc. We even had another name for it. We called it allergic inhalant dermatitis or AID which was easy to understand, BUT, that is not how it works. Atopic Dermatitis IS caused by pollens, molds, house dust mites and dander etc., but not by inhaling them. It happens when they cross the skin. Why? Simply because the skin is abnormal. The longer the dog or cat has untreated atopic dermatitis, the more abnormal the skin becomes.

What does atopic dermatitis look like?

Generally speaking atopic dermatitis starts early, often younger than 3 years of age. It can even start younger than 18 months of age. Occasionally, as young as a year. Affected dogs scratch their face, feet, the perineal area (area around anus and vulva), and the axillary (armpit) area. This condition tends to run in families. It is usually seasonal but can be year round depending on the allergen that is causing the problem. We also see recurrent skin or ear infections which are bacterial or yeast overgrowth. There is usually a positive response to corticosteroids. It seems that every year signs worsen. The number one sign is of course itching and scratching, especially at the areas mentioned above. Relapses are very common.


         Dogderm Canine Atopic Dermatitis         

Felinederm Feline Atopic Dermatitis

Differential Diagnosis– Atopic Dermatitis and food hypersensitivities can cause identical lesions. The main difference is that food hypersensitivity lesions should be non-seasonal. The problem here in Southern California is that we have long pollen seasons and as mentioned above, secondary skin infections conspire to make the dog itch all year long. Flea allergies cause itching to take place in different areas from those affected by atopic dermatitis or food allergy. Sarcoptic mange usually affects young or stray dogs and is relatively easy to treat with miticidal therapy. The difficult animals to diagnose are the “AND” dogs and cats. I think I mentioned last week that many dogs may have a flea bite hypersensitivity AND atopic dermatitis. They can have adverse reactions to food AND flea bite hypersensitivity. They can have all three, much to the dismay of many pet parents!

 When treating atopic dermatitis with injections of allergens or the new oral way, you are basically “vaccinating” or using the animals immune system to protect it against what it is hypersensitive to. Let me be very clear. Injections need to be given for a long time to determine whether they are effective or not. This could mean an entire year.

 Allow me a quick word about bathing the atopic dog. Statistics show that frequent bathing reduces the amount of corticosteroids needed in the dog’s lifetime by 50%. The challenge with this is you wash off flea control which is a crucial part of the treatment regimen as well. The solution is to use the oral medications for flea control with these dogs.

 Adverse Reactions to Food (Food Allergy)

 You wouldn’t know it by the multi-billion dollar pet food industry but food hypersensitivity represents only 5% of all skin disease and 10% of all allergic disease in dogs and cats. Get ready for another “huh?” Generally speaking, there is an immune reaction between one or more glycoproteins (allergens), either before or after digestion. Sensitization may occur at the gastrointestinal mucosa, after the substance is absorbed or both. Some specialists theorize that juvenile parasitism contributes to damaging intestinal mucosa resulting in absorption of allergens and subsequent sensitization.

 The signs of food hypersensitivity mimic any of the other hypersensitivity reactions such as flea or atopy. Most common are itching in any location on the body and chronic ear infections. They can look exactly like atopic dogs. Occasionally, they will also have gastrointestinal disease, vomiting, diarrhea, more frequent bowel movements and flatulence.  Not every dog with skin disease associated with adverse reactions to food has gastrointestinal signs so the absence of GI signs does not rule out food hypersensitivity.   In cats, severe facial pruritus is a hallmark of food hypersensitivity. As with atopic dermatitis, chronic skin infection with both malassezia (yeast) dermatitis and bacteria are common sequelae to food hypersensitivities.


 felinefood1   Feline Food Allergy    felinefood2  

Differential diagnosis:

Flea bite hypersensitivity, atopic dermatitis and scabies are the main differentials. This is interesting because this differential diagnosis list is exactly the same as the differential diagnosis list of atopic dermatitis. See what I did there?

 “Ok Doc, I get your point. Apparently, food hypersensitivities and atopic dermatitis can look the same. Can’t you just run a blood test for this? Get the diagnosis? I know I found a laboratory on the internet that can do exactly that.”  Unfortunately, there is NO correlation to serum antibody and food hypersensitivity. None. Not at all. Did I say none? Good.

 This is the point in the blog where I issue this plea. Patience and lots of it. To solve complex dermatology problems takes time. One of my many jobs is to explain why it takes so much time. These guys don’t come in to the office waving a flag or poster that says “I’ve got a food allergy” or “I have atopic disease”. Remember that they may have a combination of flea allergy, food allergy and atopic dermatitis. Many have secondary skin infections which by themselves cause itching. Remember the allergic threshold term from a couple of blogs ago? The goal is to diminish as many of the factors causing itching as we can to get to the bottom of it.

 When a dog or cat is presented with clinical signs that point to an Adverse Food Reaction or Atopic Dermatitis, a number of things will be done to try to start helping right away. Smears and scrapings will be made to examine the skin for bacteria and yeast infection with appropriate antibiotics and antifungals selected for treatment. The animal’s flea control regimen will be improved upon.  A detailed dermatology history will be performed.  The process of determining whether this is a food related dermatitis or atopic dermatitis will begin at that point.

 It usually starts with a food trial. “Whoa, wait a minute Doc. You have been harping on the fact that food is the least common of the main allergy groupings. So why start with a food trial?” Many dermatologists make the statement that “we might as well because you have to feed the animal anyway”. We don’t have to do it that way, IF the signs fit Atopic Dermatitis which means strong seasonality, intradermal skin testing or blood testing could be done first. Most of the time however, we start with a food trial. 

 A food elimination diet is considered the definitive test for food hypersensitivity. There are a few ways this is done. Many dermatologists believe that having an owner cook for the dog for a period of 9 weeks is the best way to perform a food trial. Other’s believe that using a prescription diet (Hill’s Z/D, Royal Canin Anallergenic), whose proteins have been broken down into fragments so small that the body cannot mount an immune response, is the best way to perform a food trial. In the former, a solitary protein and a solitary carbohydrate are chosen. These must be foods that the animal has never been exposed to before. In a 9 week food trial, nothing and I repeat nothing else can pass the lips of the dog during the trial but the designated food (Z/D, anallergenic, or the solitary protein/CHO that owner is cooking for dog). Nothing else – No treats. No table scraps. No nothing.  Chewable medications, Pill Pockets, treats, are all culprits in negating a food elimination diet and must not be offered.

Changing from one brand of dog food to another brand of dog food that the nice young man at the pet supply store recommends does not in any way constitute a food trial. No way, no how.  

 Now about that trendy gluten/grain free thing. It’s our latest kick in this country. Most of the allergies to foods in dogs and cats are due to hypersensitivities to proteins, not grains. Yes, there are proteins in the hulls of some grains the biggest culprit being wheat. But grains and glutens constitute the smallest fragment of adverse reactions to foods and remember that adverse reactions to foods are the smallest percentage of hypersensitivities that dogs have. Although they are second to flea bite hypersensitivity in the cat.

 If any skin infection has been controlled and the dog or cat has completed the 9 week trial and remains itchy, it is safe to say it doesn’t have food hypersensitivity. If the food trial results in a dramatic improvement, we can either challenge the dog with its old food, continue to feed it the prescription diet, or add single ingredients back into the elimination diet waiting for ten days for each single ingredient to determine whether or not the ingredient stimulates the allergic response. So what about those guys that didn’t improve? Time to move to diagnosing and treating atopic dermatitis.

 The basic mainstays of diagnosis are Serologic Allergy Testing and Intradermal Skin Testing. It is my belief that Intradermal Skin Testing is best performed by someone who does it every day such as a board certified dermatologist. Skin Testing is when a large area of skin is shaved and then a large number of allergens are injected into the skin and the reaction is measured. Serologic testing is simply drawing blood and submitting to one of a couple of labs in this country that measure the immune response to over 120 allergens. At our hospital we use either of two laboratories with strong reputations in the field of veterinary dermatology.

 The idea is that the 10 strongest reactors of either skin testing or blood testing are then put into a vial and injected into dog in gradually increasing dosages in an attempt to reduce their sensitivity. This form of treatment successfully reduces pruritus (itching) in 60-80% of dogs and cats. The downside? Response is slow; it often takes 6 to 12 months to see a true response.

 There is a new idea beginning to take hold in the field of veterinary dermatology. It is called Regionally Specific Antigen Therapy. In this model, no allergy testing is done. Rather, a set of antigens is chosen for the region of the country in which the animal lives. This is based on the knowledge that there is considerable cross reactivity between the various allergens. That is, that protection against ragweed pollen might also protect you against some other inhaled pollen. This new form of treatment offers the advantage of being just as effective as and less expensive than traditional treatment modalities. The allergens are either administered as injections or oral medication.

 Other aspects of treating atopic dermatitis include soaking in cool water, water plus emollients, frequent bathing which removes allergens and reduces infection and the ever popular use of topical treatments to try to restore the normal skin barrier. Some of those products are Duoxo Seborrhea Spot On and Allerderm Spot On.

 Successful treatment of either food allergies or atopic dermatitis may also involve the use of omega 3 Fatty Acids as an oral food supplementation and the use of either the new IL-31 blocker Apoquel or corticosteroids to manage the itching. Apoquel is the newest drug to fight inflammation. It is not a corticosteroid and has none of the corticosteroid side effects. It is very effective and specifically developed for atopy. It has definitely shown to be effective with flea allergic dermatitis and I suspect it will be just as effective for food hypersensitivities too.

 Dogs and cats that have adverse reactions to food, or that have atopic dermatitis are the most challenging skin disease cases that we see. They are time consuming and require a ton of patience. But with patience, time and painstaking willingness to go through a process, these animals can be well managed.

 Okay, allergy education complete. You all get at A+ for sticking with me through this very intense crash course. I hope I have provided some valuable information. Thanks again for reading my blog each week. It really has become quite a labor of love and your comments are certainly appreciated and welcomed!


Until next week……


Dr. Voorheis

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