On the 3rd and 4th of July I attended the Australian College of Veterinary Scientists, Dermatology Chapter Science Week. The topics presented there were on allergies and compared cats and dogs with humans. These included food allergies, respiratory allergies, insect venom allergies and atopic dermatitis.
In this newsletter we will discuss clinical signs and diagnosis of food allergies or more accurately cutaneous adverse food reaction in pets and the role of a hydrolysed protein diet in the treatment of "food allergies".
It was interesting to see that humans can develop a much more severe immunologic reaction like anaphylactic shock while our cats and dogs are not responding in that way. Another very common sign of food allergy in humans is allergic rhinitis and we don't see that in our pets. To diagnose the problem, humans can have a skin prick test or a blood test, neither working in cats and dogs.
Another interesting thing was that up to 20% of the population believes they have an adverse reaction to one or more food's, the true prevalence is much lower. Up to 5-6% of children and 3-4% of adults have a food allergy.
Sarcoptic mange and inhalant allergy (also known as atopy) are the two conditions which must be distinguished from food allergy as the treatment approach to each is markedly different. Much time and money can be wasted pursuing the wrong the problem.
To determine positively that your pet has a food allergy, a food allergy trial must be done as skin and blood tests for food allergy are not effective. Simply switching foods from one commercial brand to another is not effective in diagnosing food allergy as many of the commercial foods have some of the same ingredients. To correctly do a food trial, a food must be chosen to which the pet has never been exposed. It is important that during the diet trial no unnecessary medications be given. No edible chew toys (such as rawhides or bones) should be given. Treats must be based on the same food sources as the test diet.
Recently a new approach has been introduced using therapeutic diets made from hydrolyzed proteins. This means that a conventional protein source is used but the protein is broken down into molecules too small to excite the immune system.
To confirm food allergy, return to the original food; itching resumes within 14 days generally if food allergy was truly the reason for the itchy skin. Many people do not want to take a chance of returning to itching if the patient is doing well; it is not unreasonable to simply stay with the test diet if the pet remains free of symptoms.
It is possible to more specifically determine the identity of the offending foods after the pet is well. To do this, a pure protein source (such as cooked chicken, tofu, wheat flour or any other single food) is added to the test diet with each feeding. If the pet begins to itch within 2 weeks, then that protein source represents one of the pet's allergens. Return to the test diet until the itching stops and try another pure protein source. If no itching results after two weeks of feeding a test protein, the pet is not allergic to this protein.
Generally, an unsuccessful food trial is strongly suggestive that an inhalant allergy is really the primary problem but there are some other considerations that should at least be mentioned: Are you certain that the dog received no other food or substances orally during the trial? Was sarcoptic mange ruled out? Your pet may require a longer diet trial. Are you certain regarding the factor that pointed us toward the food allergy? If your pet has not been biopsied, now may be a good time. If an inhalant allergy has risen to the top of the list, symptomatic relief either via medication, special baths, or allergy shots will likely be necessary. Chronic itchiness can be extremely uncomfortable and prompt relief is the goal.
This is a prescription diet used in cases of dietary sensitivity that is only available at Vet Clinics and is prescribed by the Veterinarian.
Hills Prescription Diet z/d: