Food Allergy - My Pet has WHAT?

By Loren W. Noblitt, DVM, MS

What:  Food allergy is one of the itchiest conditions known to cats and dogs. Animals eat a variety of processed food proteins, fillers, and colorings that are further processed inside their bodies and changed into substances recognized by the immune system as foreign invaders.  A battle then ensues between the food and the immune system resulting in lots of inflammation.  Many organs can be affected but usually it’s the skin and the gastrointestinal (GI) tract (including the mouth) that suffer.

Interestingly, many people erroneously assume itching from food allergy requires a recent diet change of some sort. In fact, the opposite is true.  Food allergy requires time to develop; most animals have been eating the offending food for years with no trouble.  At some point, there appears to be a “straw that breaks the camel’s back” type of event that ignites severe itching +/- diarrhea/vomiting.

The most common offending agents in dogs and cats are:

1. Chicken
2. Beef
3. Corn
4. Wheat
5. Egg
6. Soy
7. Casein
8. Fish

Why: Pruritus (itchy skin) in the small animal is often more than just a minor annoyance.  Red, oozing bald patches, rashes, and large areas of hair loss (“hot spots”) are classic markers of discomfort.  The skin is the “organ” most affected in pets because the skin has the densest mast cell distribution than anywhere in dogs’ and cats’ bodies.  Mast cells are allergic type cells that secrete histamine, which promotes itching and inflammation.  Same as in our own bodies.  These mast cells degranulate (releasing histamine into the blood) when the offending agent binds to receptors on its surface, causing runny eyes and sneezing in human beings affected with hay fever.  So why the difference?  Location, Location, Location!  Our mast cells are largely distributed in our upper and lower respiratory system, thus the primary difference between humans and small animals when it comes to manifestations of allergic reactions. 

Who & When:  Any age animal may be affected, but the majority of animals are older puppies/kittens (12-24 weeks) or in early adulthood.  Older animals (> 5 years old) that have no or little prior history of itching are good food allergy suspects. 

Where:  There is an old expression: “Ears and Rears (anal glands) and it (the itching) goes on all year.” Ear canals and anal glands are just extensions of the pet’s skin and are thus disproportionately affected with inflammation from a food allergy (based on mast cell distribution).  Other food allergic animals will present with “pseudoscabies,” meaning that they are itching all day long (“mad itch”) but either lack the classic hair loss pattern and skin irritation (redness) of animals with active scabies mite infestation OR they are still itching fiercely despite having been treated for sarcoptic mange already. 

Dogs with food allergies often have hair loss or redness around any or all of the following areas (see below):  chin, ears, belly, paws, around eyes and around the mouth.  Cats usually present with scabs on or around the head (mouth, neck, and ears).

Drawing borrowed from www.marvistavet.com

 

Other possibilities to explain the itching!:  Atopy (inhalant or environmental allergy), scabies mites, demodex mites, pyoderma (yeast/bacteria), flea bite allergy, or ringworm (fungus).  To complicate matters, some dogs and cats can have BOTH food and environmental allergies at the same time.  Dermatologic diligence needs to be performed to rule out the obvious (skin cytology, ringworm cultures, skin scrapes), thus, food allergy is often (not always) a diagnosis of exclusion.  It is sometimes a good idea to try a 7 day trial of low dose steroids, as most food allergic animals will have minimal response to steroids (vs. environmental allergies, where response should be drastic).

Diagnosis:  Unfortunately, there is no trustworthy blood test or intradermal skin test that can be run to diagnose a food allergy.  We have to perform strict food trials using 1 of 2 principles: Hydrolyzed protein and carbohydrate diet vs. Novel protein and carbohydrate diet.  Hydrolyzed protein is protein (often chicken or soy) that is broken down into small amino acid strands that shouldn’t trigger an immune response.  Novel protein is protein that your pet has never been fed before and, theoretically should be tolerated by the immune system and not elicit an allergic response.

Treatment:  The various options are Veterinary Prescription-only foods, however, if you are willing to cook homemade hypoallergenic foods for your pet (which can be prepared in bulk and frozen), there are many recipes available upon request.  The following are commercially available hydrolyzed and novel protein foods:

Hill’s Diets:
D/D canned/dry- salmon & potato/rice
D/D canned/dry- duck & potato/rice
D/D canned/dry-venison &potato/rice
D/D dry – egg & rice
D/D canned-lamb & rice

Low Antigen diets:
Z/D Ultra Allergen Free dry and canned-hydrolyzed chicken and refined starch
Z/D Low Antigen –dry and canned-hydrolyzed chicken and single source carbohydrate (potato)

Purina Diets:Low Antigen diets:
LA Limited Antigen dry-salmon and rice
HA hypoallergenic dry-hydrolyzed soy

Iams Diets:Prescription diets:
Response FP dry and canned-fish and potato
Response KO dry-kangaroo, canola meal, and oat flour

Royal Canin:Low Antigen diet:
Hypoallergenic HP 19 dry-hydrolyzed soy and rice

Potato and Duck dry and canned-duck protein and potato (also has light formula)
Potato and Rabbit dry and canned- rabbit protein and potato
Potato and Venison dry and canned- venison protein and potato (has large breed formula-dry)
Potato and Whitefish dry and canned-whitefish protein and potato

 

Regarding acceptable treats for food allergic dogs, I have consulted several Veterinary Dermatologists through the years and the consensus seems to be that the following items are OK to supplement your pet while on a strict food trial:

1. Marshmallows
2. Bananas
3. The wet form of your particular hypoallergenic food (meatballs as treats or meatballs baked in the oven)
4. Hill’s hypoallergenic treats (compatible with z/d, d/d, and i/d foods)

***Note:  All other treats have to be avoided, including rawhides, Greenies, carrots, green beans, etc.  Everyone in the household must be on the same page with a food trial!***

 Common Food Trial Pitfalls: 

     1.   The World Wide Web and Dr. Google

     2.   “PetStore Wisdom”
     3.   Grandma thinks its Ridiculous!!!

     4.   Dog or Cat is an escape artist

     5.   Not having other pets on the same food

     6.   Dog eats cat barf, or worse!

7. Neighbor kid(s) feed(s) the dog through the fence
8. Social Events:  How cute!  He is begging!
9. Oral Heartworm prevention – A recent study done at North Carolina State University (NCSU) found that giving Heartgard or other flavored once-a-month medications (these contain soy and beef) is enough to keep a soy or beef-allergic dog itchy despite appropriate dietary change.  Topical Revolution should be once monthly, or there is a non-chewable Heartgard option available through Merial. 

Long-term control and Re-challenging:  In the early stages of a food trial, once per month veterinary exams should be performed to make sure fleas are under control, the pet’s weight is maintaining and not considerably up or down, all is going well with the food trial (Q and A sessions about acceptable treats or other questions), and that there are no secondary bacterial or yeast infections present that will cause itching on their own. 

It is important to re-challenge (or at least discuss it) with old food for several reasons.  The first reason is to help confirm the diagnosis of food allergy.  It may be that when the food trial was started, the seasonal allergen picture was in flux or fleas may have been an issue and no longer are, etc.  Stranger things have happened!  The second reason to challenge is to help narrow down the offending agent so that a less expensive over-the-counter or home-cooked food can be used/prepared.  The re-challenge should be performed at a minimum of 8 weeks into the food trial and ideally after 2 weeks of being symptom (itch)-free.  The re-challenge should be done with a 50:50 mix of old food : new food.  Most pets will start itching within a few days, but some may take up to 2 weeks.  Steroid (either topical or oral, or both) and ear medication can be sent home to be used if needed to keep your pet comfortable during the re-challenge period.  It is important to cut out or write down the ingredient list of “the challenge food” or “old food” so that we can avoid all of the protein containing components listed, keeping in mind the most commonly implicated food allergens listed above.

That being said, many of our owners with food allergic pets find a special food that helps control the itching, and just keep their pets on this food for maintenance long-term control without re-challenging.  The “if aint broke, don’t fix it” principle.

Common Myths of Food Allergies:

There are many Misconceptions and Myths when it comes to considering food allergy for pets. The following excerpts are taken from VIN (Veterinary Information Network), and were originally posted by Veterinary Dermatologist, Carol Foil, DVM, DACVD.

MYTH:	“Food allergy ought to produce intestinal signs as it is the intestinal tract that is exposed to the allergen.”
FACT:	In pets, it is usually the skin that suffers with a food allergy. Food allergy is one of the itchiest conditions in veterinary dermatology. Making matters worse is the fact that food allergies tend to be resistant to cortisone therapies which makes itch control especially difficult.
MYTH:	“Food allergy is a less likely cause of my pet’s skin disease as we have been feeding the same food for years and the skin problem is a recent development.”
FACT:	It takes time to develop a food allergy, typically months to years. The immune system must be exposed and must develop enough antibodies to trigger an allergic reaction and this requires multiple exposures to the food in question. A reaction to a food that occurs on the first exposure to that food is not an allergic reaction. Such reactions are called “food intolerances” and involve toxins within the food but not an allergic reaction.
MYTH:	“Soy and corn are common food allergens and it is best to seek pet foods without these ingredients to avoid problems.”
FACT:	The most common food allergens for dogs are: beef, dairy, and wheat. These three ingredients account for 68% of canine food allergies. The most common food allergens in cats are: beef, dairy, and fish. These three ingredients account for 80% of feline food allergies.
MYTH:	“If it looks like my pet might have a food allergy, I should be able to manage the problem by switching to another diet.”
FACT:	Unfortunately for food allergic pets, most pet food diets contain some sort of mixture of beef, dairy, wheat, lamb, fish, and chicken. This means that simply changing foods is bound to lead to exposure to the same allergens. There are two ways to address food allergy: feeding a diet based on a truly novel protein source (this usually means an exotic diet like venison, duck, kangaroo, rabbit or even alligator) OR feeding a diet where the protein has been pre-digested into units too small to interest the immune system.
MYTH:	“My pet got only partly better after the food trial so that means it didn’t work.”
FACT:	Animals commonly have several allergies concurrently. A food allergy responding to a test diet at the same time an inhalant allergy is active will look like a partial response. On the other side of the coin, an inhalant allergy can become inactive should the weather change substantially during the diet trial. This would make a diet appear to be successful by coincidence. In order to determine if a response to a diet trial is real, at the end of the trial the patient is challenged with the original diet. If itching re-starts within feeding 2 weeks of the challenge, food allergy can be diagnosed.

Sources:

1.  Veterinary Information Network:  www.vin.com

2.  Veterinary Partner: http://www.veterinarypartner.com/Content.plx?S=0&C=0&A=652

3.  Veterinary Dermatology article on VIN: http://www.vin.com/Members/CMS/document/default.aspx?pid=38&catid=&objectid=7282&objecttypeid=10&redirectFromMiscDefault=1&calc

4.  Drawing of allergic dog and cat borrowed from:  http://www.marvistavet.com/html/body_food_allergies.html