YVCipedia FOOD *ALLERGY* *HYPERSENSITIVITY* *ADVERSE REACTIONS*
- These terms are presented with " * " because they all refer to one disease process, and that process is not well understood. At YVC, we use the term "food hypersensitivity (FH)" because it is the most broadly descriptive.
- Some cases are true allergies: the result of ingestion of a protein (allergen) that provokes an over-reaction of the patient's immune system.
- Some cases are not true allergies: the patient's signs result from the metabolic, toxic, pharmacologic or other effects of the offending substance.
- It is difficult, and perhaps impossible to distinguish between an allergic and a non-allergic reaction to food.
HISTORY and SIGNS
- The best estimates are that 5% of all skin diseases and 10-15% of all allergic diseases in dogs and cats are the result of FH.
(A digression: Please look carefully at these percentages: they are relatively small numbers. If a dog or cat has a skin or ear problem, the odds areoverwhelmingly against the possibility that the problem is due to FH.)
- Pets who develop signs of itchiness for the first time at less than 6 months old or greater than 6 years old may be more likely to have FH.
- There is a wide range of signs that can mimic non-food-related hypersensitivity reactions. We cannot tell by simply looking at a patient that they have FH.
(Another digression: Neither can the pet's owner, the owner's neighbors and coworkers, the guy or gal at the pet store - especially the guy or gal at the pet store -, the breeder, the trainer, the board-certified dermatologist...)
- Skin signs of food hypersensitivity include itchiness of any body part, including the ears; non-seasonal itchiness; poor response to antiinflammatory doses of cortisone; facial itchiness in cats; bacterial and yeast infections; redness; dandruff; crusts; geasiness or dryness; thickened and heavily pigmented skin; self-induced hair loss; hives; hot spots.
(Another digression: Most ear problems in dogs and cats are skin problems.)
- Some pets have gastrointestinal signs of FH: vomiting; diarrhea; more frequent bowel movements; flatulence.
- It is very rare, but it has been documented that some pets have had seizures as a result of FH.
DIFFERENTIAL DIAGNOSIS (OTHER POSSIBILITIES FOR THE SAME SIGNS)
- Remember the percentages previously noted, regarding how many skin diseases are truly FH. If a pet has the skin signs noted above, it is a little or a lot more likely that it has one of the following problems instead of FH:
- Flea bite hypersensitivity
(Another digression: It might be fleas even if the pet's owner has not seen any fleas, or evidence of them.)
- Atopy (allergic reaction to environmental factors, such as house dust, pollen, mold, etc)
- Sarcoptic mange mites
- Yeast hypersensitivity
- The only definitive test for FH is to feed an ELIMINATION DIET, and to follow this first with a CHALLENGE DIET TRIAL then a PROVOCATION DIET TRIAL.
- The elimination diet must be tailored for the individual patient, and must be restricted to one protein and one carbohydrate that the patient has had no prior exposure to.
- Eight weeks is the common length of the trial, and it may take up to 12 weeks to see maximum improvement.
- We are reasonably sure that Prescription Diet Z/D is a viable commercial alternative to home-prepared elimination diets.
- If the patient improves on the original diet, he/she is fed the original diet.
- A return of the the signs confirms that something in the diet is causing the signs.
- The challenge period should last until signs return, but no longer than 10 days.
- If the challenge diet confirms the presence of a FH, the patient is returned to the elimination diet, to which single test ingredients are added.
- The test ingredients should include meats (beef, chicken, fish, pork, lamb), grains (corn, wheat, soybean, rice), eggs, and dairy products.
- The test ingredients are added one at a time to the elimination diet. The provocation period for each ingredient should last up to 10 days, or less if signs develop sooner (many patients will develop signs after 1 to 2 days.
- The results of the provocation diet guide the seletion of the commercial maintenance diet that does not contain the offending ingredient(s).
(And one final digression: If a pet is itchy and the owner changes foods and the pet stops being itchy, the owner has not diagnosed FH. It does not matter if the owner has gone from a diet with grain to one without grain, or a diet with chicken or beef to one without chicken or beef; no diagnosis has been made. There are simply too many variables at play in that scenario.The only way a pet owner can legitimately claim that their pet has FH is by having positive results to the elimination/challenge/provocation diet trials.)
ADDITIONAL CONSIDERATIONS DURING AND AFTER THE DIET TRIALS
- Treats, chewable toys, vitamins, chewable medications, and Pill Pockets must be avoided during the diet trials
- Outdoor pets need to be confined to prevent foraging and hunting.
- All family members and other people who are regularly involved with the pet must be involved with the diet trial process.
- Systemic anti-itch drugs may be used during the first 2 to 3 weeks of the trials. These medications must be discontinued during the last month of diet trials.
- Antibiotics and antifungal medications can be used if needed.
- We recommend examining patients every 4 weeks during the trial process.
- Other causes of itchiness (see DIFFERENTIAL DIAGNOSIS) can mask the response to the trials, and must be controlled during and after the trials.
- Rarely a dog or cat that has been diagnosed with FH by diet trials will develop hypersensitivity to new substances and the elimination diet trial must be repeated.