Healthy Pets

Dogs with Allergies

posted: 05/15/12
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More InformationAllergic & Irritant Contact Dermatitis, Allergies & Atopy, Allergy Testing & Immunotherapy, Anaphylaxis, Bacterial Hypersensitivity to Staph Infections

Anyone who owns a dog who has allergies knows how frustrating it can be. Allergies are not cured, but managed. Making the correct diagnosis and using a multi-faceted approach to treatment can usually help the affected dog be much more comfortable.

Allergic & Irritant Contact Dermatitis

Allergic contact dermatitis occurs in dogs as a hypersensitivity reaction to certain molecules in the pet's environment. Irritant contact dermatitis results when the skin is exposed to noxious substances in the environment. The symptoms and biologic mechanisms involved in these two diseases are similar so they are often discussed together. Allergic contact dermatitis is a rare disease which occurs when an animal's skin overreacts to certain small molecules in the environment. Substances which can cause allergic contact dermatitis include certain antibiotics applied to the skin; metals such as nickel; materials such as rubber, wool, and plastic; and chemicals such as dyes and carpet deodorizers. Irritant contact dermatitis occurs when the skin is exposed to severely irritating chemicals such as the sap in poison ivy and salt on the road.

Allergic contact dermatitis only affects those animals with a hypersensitivity to the molecule. Irritant contact dermatitis would affect every dog that is exposed to the irritant. Allergic dermatitis requires multiple exposures to the molecule before it develops. It rarely occurs in animals less than two years old. Irritant contact dermatitis often occurs in inquisitive young animals who get into things they should not. The first signs include lesions which generally occur on the areas of skin that are sparsely haired and directly exposed to the offending molecules. This often means the back of the paws, abdomen, muzzle and lips. The affected areas are very red, have small bumps or vesicles (blister-like lesions), and itch. In irritant contact dermatitis ulcers may appear.

The history and physical exam can often indicate what is going on. To isolate the allergen (molecule that caused the dermatitis), exclusion trials are often performed. In these trials, the animal is restricted to an uncarpeted room and kept off the grass, for instance. If the animal's condition improves, potential allergens are slowly introduced one by one. A 'patch' test can also be performed. In this test, a small amount of the allergen is rubbed on the skin, or a gauze pad containing the suspected allergen is bandaged on the pet's skin. The skin is monitored for 2-5 days for a reaction.

The key to managing this condition is removing or restricting exposure to the allergen or contact irritant in the pet's environment. If this cannot be done, the pet often needs to receive steroid therapy. Unfortunately, this is not always effective. As a rule, for any pet suspected of having an allergy problem that could include an allergic contact component, we recommend:

  • Glass or stainless steel food and water bowls (to decrease the possibility of contact dermatitis occurring from exposure to plastic or dyes)
  • Hypoallergenic detergents for the pet's bedding
  • Routine hypoallergenic shampoos for the pet to remove any allergens

Veterinarians who limit their practice to dogs and cats see a lot of skin problems. There are numerous conditions that cause problems with a dog or cat's skin, but the most common, by far, is allergies.

Symptoms of allergies

Dogs with allergies may show the following symptoms:

  • Chewing on feet
  • Rubbing the face on the carpet
  • Scratching the body
  • Recurrent ear infections
  • Hair loss
  • Mutilated skin

In addition, allergic dogs will often chew on their feet until they are irritated and red (the feet are the only place dogs have sweat glands and these become inflamed with allergies). They may rub their faces on the carpet or couch, or scratch their sides and belly. Because the wax-producing glands of the ear overproduce as a response to the allergy, they get ear infections. Bacteria and yeast often "over grow" in the excessive wax and debris. The skin lesions seen in an allergic dog are usually the result of him mutilating his skin through chewing and scratching. Sometimes there is hair loss which can be patchy or inconsistent over the body leaving a mottled appearance. The skin itself may be dry and crusty, reddened or oily depending on the dog. It is very common to get secondary bacterial infections of the skin due to these self-inflicted lesions. Such infections may be treated with antibiotics.

Allergens

When a dog is allergic to something, his body is reacting to certain molecules called 'allergens.' These allergens may come from: 7. Trees 8. Grass 9. Weed pollens 10. Fabrics such as wool or nylon 11. Rubber and plastic materials 12. Foods and food additives such as individual meats, grains, or colorings 13. Milk products 14. House dust and dust mites 15. Flea bites The reason that all these allergens cause itchy skin is that, simplistically, when allergens are inhaled, ingested, or come in contact with the dog's body, they cause the immune system to produce a protein referred to as IgE. This protein then fixes itself to cells called 'tissue mast cells' that are located in the skin. When IgE attaches to these mast cells, it causes the release of various irritating chemicals such as histamine. In dogs, these chemical reactions and cell types occur in appreciable amounts only within the skin.

Genetic factors and time influence allergies

Remember that pets must be exposed to the allergen for some time before the allergy develops. Exceptions may occur such as an allergy to insect bites which may develop after only a few exposures. The pet's body must learn to react to the allergen. It is a learned phenomenon of the immune system that is genetically programmed and passed from generation to generation in several breeds. Allergies are especially common in certain terriers such as the Scottish, West Highland White, Cairn, and Wire Haired Fox; Lhasa Apsos; and larger breeds such as the English and Irish Setter, Retrievers, and the Dalmatian. Allergies are also well documented in the Pug, Miniature Schnauzer, and English Bulldog. In pets, allergies usually start to develop between one and three years of age. They may start as late as age 6 or 8, but over 80% start earlier. To make matters worse, as the animal ages, it usually develops allergies to additional things and the response to any one allergen becomes more severe.

Diagnosing allergies

Confronted with a scratching pet and frustrated owner, it is too easy for a veterinarian to miss a diagnosis or at least fail to make the owner fully understand the problem. Sometimes veterinarians take the easy way out and "shotgun" the pet with several different medications hoping that at least one will hit the target and make the signs go away. If the pet stops scratching, the hair starts to grow back and the owner can sleep nights -- all may look well but the allergy is not necessarily cured. Most allergies are the inhalant type and are seasonal (at least at first). The dog may be allergic to a certain tree pollen that is only present in the environment for three weeks out of the year. This case is easy to handle. No matter what you treat the animal with, she will start getting better in four weeks. In cases in which the allergy is mild but the irritated skin has become infected with bacteria, a broad-spectrum antibiotic will eliminate the infecting organism and the skin may return to near normal appearance even though the treatment has in no way been directed toward the allergy. A definitive diagnosis of an allergy and determination of exactly what the animal is allergic to can only come in one of three ways. They are: 16. Allergy testing (intradermal or blood testing) 17. Eiminating things individually from the animal's environment until the culprit is isolated The latter is not as exact, but usually shows the quickest improvement for the pet and is easiest on the owner's pocketbook. An excellent example of this would be the dog that is allergic only to tree pollen. Every year, in the same month, the dog starts chewing his feet, scratching his sides, and rubbing his face on furniture. The veterinarian chooses either a tablet and/or single injection that will suppress the allergy for the 3-4 weeks necessary. In two days, the animal is back to normal and only has to wait until the following year when he or she will be returned with the same problem. The veterinarian will glance at the file and probably repeat the same treatment. The veterinarian is now two for two, and in the owner's eyes, has reached the level of genius. Unfortunately, things just do not always go that well. A more common scenario in a dog, for instance, would be that the dog is now five years of age. When he was 18 months old he started scratching and has not stopped since. There are large areas of his skin that are 2 to 3 times their normal thickness, it is cracked open and bleeds intermittently and is completely void of hair. The ear canals are painful, infected, and swollen to the point of limiting the dog's ability to hear. The dog is uncomfortable, rarely able to sleep through a night, waking frequently to scratch and chew on himself. He may even have intermittent fevers from reoccurring bacterial skin infections. He still enjoys being a dog, however, chasing squirrels, eating treats, and looking forward to the bus bringing the children home. The owner and dog have by now been in every veterinary clinic within a 100-mile radius and that circle will probably soon grow larger. And to make matters worse, the dog is getting worse. This is an isolated but not rare case and we wanted to tell you about it here so you could appreciate the true difficulty of the diagnosis and treatment of canine allergies. It is extremely important that we find out what allergen(s) the dog is reacting to in order to really help such a dog. So now you know the basics of canine allergies. If you have more specific questions about the different types of allergies, how to diagnose them or treat them, I encourage you to read the other articles in this section. They provide the newest and most up-to-date information on this very common problem.

Allergy testing is a way to get a positive diagnosis for atopy (inhalant dermatitis) and to a lesser extent for contact allergies. Scratching, licking the feet, chewing, and red irritated skin are all symptoms of atopy in the dog. Atopy is the name given to allergies that result from breathing in pollen, dust, or mold. Other than flea bite allergies , atopy is by far the most common cause of allergies in dogs. When an allergy to a specific substance can be identified, the dog can receive immunotherapy (hyposensitization injections).

Types of allergy testing

There are two basic types of allergy testing. The most common is a blood test that checks for antigen-induced antibodies in the dog's blood. There are two standard tests that are used to test the blood. The first is called a RAST test (radioallergosorbent). The other is an ELISA test (enzyme-linked immunosorbent assay). Both of these tests are very similar but many practitioners feel that the ELISA test gives more accurate results than the RAST test.

The other type of testing is intradermal skin testing. In this test a small amount of antigen is injected into the skin of the animal and after a short period of time the area around the injection is observed to determine if the animal is allergic to the agent. The pros and cons of both tests will be discussed in greater detail later in this article.

Blood testing by RAST and ELISA

To perform either of these two tests to determine what substances an animal may be allergic to, a blood sample is drawn from a suspected atopic dog and sent into the lab. The blood is screened for a reaction to a broad range of allergens including pollens, dust and molds that are common to the geographical area in which the dog lives. Tests for reactions against different foods and contact allergies such as cotton or nylon can also be done, although the tests perform less accurately for these allergens. The testing generally takes several weeks.

Unfortunately the RAST and ELISA tests have some inherent problems in their design. They were initially developed for humans and the circulating antibodies that they test for are different in dogs and cats than in people. The result is that there are a lot of false positives. In other words, the test results indicate that your animal is allergic to things that he is really not. For this reason veterinary dermatologists may opt for intradermal skin testing. The RAST and ELISA, however, are used in special circumstances in which intradermal skin testing cannot be performed, such as:

  • The skin is too unhealthy to test either due to infection or severe inflammation.
  • Prolonged drug withdrawal for antihistamines and corticosteroids cannot be tolerated.
  • The dog is very young.
  • dog is a show dog whose hair cannot be clipped.
  • Intradermal skin testing is unavailable.
  • The intradermal skin test (IDST) is negative yet atopy is still suspected.
  • As a screening test to limit the number of allergens tested for in intradermal skin testing.
  • Of all of the blood test performed the ELISA is the most accurate and if a blood test must be used than this is the one the author recommends performing.

Intradermal skin testing

Intradermal skin testing is the gold standard of allergy testing for atopy. The animal is sedated and an area on his side is shaved down to the skin. On this shaved area a small amount of antigen is injected into the dog's skin. This is done in a specific pattern and order so that if the dog shows a small raised reaction the offending antigen can be identified. After a period of time (hours), the shaved area is examined to detect which antigens, if any, created a reaction. Reading the reactions and determining if they are large enough to create an allergic reaction in the dog is somewhat of an art. This is where having a veterinary dermatologist really pays off. Successful identification and treatment of atopic dogs by this method is listed to be as high as 75%. This test works best if performed during the season when the allergies are at their worst and isn't necessarily more expensive than blood testing.

The basics of all allergy tests

The blood and intradermal skin tests have some similarities: Animals to be tested must not have been treated with steroids or anithistamines for several weeks to months before testing. The exact time differs with the drug used and type of test performed, however, the length of drug withdrawal for the intradermal skin test if usually longer. These tests work best if performed during the season when the allergies are at their worst. Once the allergens for the dog are identified, an appropriate immunotherapy is manufactured for that specific dog, and treatment can begin. After the offending antigens are identified then a mixture of these antigens can be formulated into a hyposensitizing injection. Depending on the type of agents used these injections will be given over a period of weeks to months until the dog or cat develops immunity to the agents. After initial protection an occasional booster may have to be given. Before any animal is tested for allergies, a complete diagnostic workup ruling out other potential causes of skin problems should be performed. Ectoparasites such as fleas or mites, fungal or yeast infections on the skin such as Malassezia, and chronic bacterial infections must be eliminated. In addition the possibility of concurrent hypothyroidism must be ruled out. It is often recommended that animals be placed on a homemade or hypoallergenic diet for 12 weeks before undergoing testing to insure that a food allergy is not the cause. After the cause of the skin problem has been identified as atopy than it is time to do the test. I will take this time to warn pet owners that if they are not committed to the necessary follow-up treatment which involves numerous injections over a long period of time, or if the veterinarian does not offer immunotherapy (hyposensitization) as a treatment option, then all of these test may be a waste of time and money.

Who should be allergy tested

Allergy testing should be considered for any animal that is suffering from allergies that occur for more than four months out of the year and, or do not respond to traditional treatment. Due to the increased time and cost necessary to do skin testing most mild cases of allergies are treated with a combination of avoidance, fatty acids, and antihistamines. Unfortunately, there are many animals that suffer from moderate or severe allergies that should be tested and treated but are not. One of the biggest impediments to animal testing is not the owner but the veterinarian. To become proficient at allergy testing, a veterinarian must do it frequently. Many veterinarians aren't comfortable with testing and hyposensitizing treatments and therefore fail to recommend it as an option for their patients. Many times owners must search out a veterinary dermatologist or travel to a larger metropolitan area to find a veterinarian that will correctly perform the testing and then follow up with the hyposensitization. Allergy testing is rarely done to diagnose food allergies.

Allergy testing is the best diagnostic tool and the best road to treatment for dogs that are suffering from moderate and severe allergies. There are several different testing methods available and the intradermal skin testing is the one that is most recommended and performed by veterinary dermatologists, however the blood testing available now is much more accurate than it was in the past. The hyposensitization injections have had good results in reducing the symptoms of allergies in many dogs.

Anaphylaxis is a rare, life-threatening, immediate allergic reaction to something ingested or injected. If untreated, it results in shock, respiratory and cardiac failure, and death. What types of agents can cause anaphylaxis?

Stinging insects, antibiotics, vaccines, certain hormones and medications, and foods can cause anaphylaxis in susceptible animals.

What are the symptoms of anaphylaxis?

The most common symptoms are the sudden onset of diarrhea, vomiting, shock, seizures, coma, and death. The animal's gums will be very pale, and the limbs will feel cold. The heart rate is generally very fast but the pulse is weak. There is no facial swelling.

How is anaphylaxis treated?

Anaphylaxis is an extreme emergency. If you think your dog is having an anaphylactic reaction, seek emergency veterinary assistance immediately. Epinephrine should be given as soon as possible - we are talking within a few minutes. IV fluids, oxygen, and other medications are given as needed.

Can anaphylaxis be prevented?

In general, there is no way to predict which animals may have an anaphylactic reaction to which substances. If a dog has already had a reaction, such as anaphylaxis, angioedema, or hives, to a substance, the substance should be avoided. If your dog has ever had a reaction to a vaccine or medication, be sure your veterinarian knows and the information is placed in your pet's medical record.

If your dog has ever had a reaction to a vaccine, subsequent vaccinations should be given by your veterinarian. In some cases, certain vaccines may be excluded from your dog's vaccination regimen, or a different type of vaccine will be used.

If you vaccinate your own pets, you should have epinephrine available and know how to use it in case a reaction occurs. If your dog has an anaphylactic reaction after a vaccination, inject the proper dose of epinephrine and seek emergency veterinary assistance immediately. Many vaccines contain antibiotics as preservatives. If your dog is allergic to an antibiotic, be sure to check all vaccines for the presence of that antibiotic before use. For animals that are allergic to insect bites, such as bees, ask your veterinarian about getting a prescription for an 'epi-pen' and be sure to take the 'epi-pen' with you on any trips or hikes. An 'epi-pen' is a special syringe and needle filled with a single dose of epinephrine. If your pet has an anaphylactic reaction, inject the epinephrine using the 'epi-pen' and seek emergency veterinary assistance immediately.

Bacterial hypersensitivity is a rare disease in dogs and occurs when a dog's immune system overreacts to Staphylococcus (Staph) bacteria on its skin. When this occurs, the skin reacts dramatically to the presence of Staph.

What are the symptoms of bacterial hypersensitivity?

Bacterial hypersensitivity causes the skin to become very red. Pustules and large vesicles filled with fluid develop on the skin. There is severe itching, and many dogs will cause further damage to their skin through scratching and biting.

It appears that bacterial hypersensitivity in the dog is more likely to occur if other conditions such as hypothyroidism, atopy (allergy to inhaled substances like pollen), or flea allergy dermatitis are present.

How is bacterial hypersensitivity diagnosed?

Bacterial hypersensitivity is diagnosed through bacterial culture and examination of a biopsy sample. Microscopically, there are certain unique changes in the blood vessels of the skin in bacterial hypersensitivity. An intradermal allergy test may also be helpful. In this procedure, a small amount of extract made from the Staph bacteria is injected in the skin. The area is examined for a reaction 15 minutes, 24 hours, and 48 hours after the injection. This method is not as accurate as the biopsy.

How is bacterial hypersensitivity treated?

It is extremely important to treat the underlying disease such as hypothyroidism or flea allergy dermatitis. A test is run in the laboratory to determine which antibiotics are most likely to kill the Staph and the animal is started on one of those antibiotics. Some animals may need to be on antibiotics or immune stimulants long-term to prevent the Staph from multiplying on the skin and causing the hypersensitivity.

Studies have shown that there are over 15 different antigens in the saliva of the flea. Each one of these is capable of causing an allergic response in a sensitive dog or cat. Despite recent advances in flea control, flea bite allergies still continue to be a common problem.

Dogs and cats rarely become desensitized to flea bites once they develop an allergy. Dogs and cats that are not sensitive to flea bites rarely develop lesions from the bites but may bite or scratch at the flea when it bites them. Some studies have shown that up to 40% of dogs in any given area will test positive for flea bite allergies. Other studies show, that many dogs with flea allergies also have inhalant allergies compounding the problem. There does not appear to be a breed or sex predilection for this allergy.

Symptoms

Flea bite allergy is characterized by being a seasonal allergy that is worse during peak flea times in the summer and fall. Even in temperate areas or in cases with home infestations, the symptoms of flea bite allergies appear to worsen in the summer and fall. Dogs that have flea allergies will bite at the base of their tail and scratch frequently. The bite of a single flea can cause hours and days of intense itching. Many dogs have a characteristic loss or thinning of hair above the base of the tail. In addition, fleas or flea dirt (feces) can be found on the dog the majority of the time. The feces, or flea dirt will dissolve into a red color when moistened; this is because it is primarily digested blood. However, if the dog is bathed or treated regularly, very little evidence of fleas may be found. Severely affected dogs may itch over their entire bodies, have generalized hair loss, and red inflamed skin. Hot spots are often a result of flea bite allergies.

Cats with flea allergy dermatitis can have a wide spectrum of symptoms including miliary dermatitis which is characterized by crusty papules (small, red, raised skin lesions), symmetrical hair loss (alopecia), and eosinophilic plaques and linear granulomas.

Diagnosis

Diagnosis can be made by visual signs in combination with the presence of fleas or through intradermal skin testing. Intradermal skin testing is a very effective diagnostic tool for this particular allergy, although some false negative results can occur. Since many affected dogs also suffer from other allergies, many times the flea bite antigen is incorporated into a broader intradermal skin testing program. Some cats with flea allergy dermatitis do not have a positive intradermal test.

Treatment

Treatment primarily involves preventing the flea from coming into contact with the dog or cat.

Topical Treatment of Pets: With the advent of topical flea and tick control products, it has become much easier to have effective flea control. When choosing a topical powder, spray, or once-a-month flea control product, be sure to choose a product that not only kills fleas, but repels them. Such products contain pyrethrin or permethrin. NOTE: Products containing permethrin should NOT be used on cats. Pyrethrins, on the other hand, are safe for cats. If a dog or cat is sensitive to flea saliva, just one bite can set off an allergic reaction. If a product does not repel fleas, then all of the fleas must bite the animal before they die. Remember, the once-a-month pills that act as growth regulators do not stop fleas from biting pets. They just make the fleas unable to reproduce. Since a flea can live for months, a pet with flea bite allergies can suffer throughout an entire flea season with just occasional flea contact. Controlling the contact of fleas with the pet appears to be the most successful route. If a pet is on a good flea control program but occasionally still gets bitten and has a flair up, antihistamines, or in severe cases oral steroids, can be used to get the itching under control.

Treatment of Environment: Remember that good environmental treatment for fleas involves treating the house, yard, and sleeping area of the pet with a product that kills the adults (adulticide) and with an insect growth regulator as well. Other pets in the home should also be treated, as they could continue to bring fleas into the environment. While injudicious use of pesticides and growth regulators is never recommended, an effective flea prevention program is much safer and easier than dealing with a full blown flea infestation.

Hyposensitization: Hyposensitization of dogs with a series of injections does not appear to be very effective. There are several of these commercially available products available for veterinary use, but most dermatologists do not use them.

The entire process of a pet being sensitized to a particular agent in food and the complicated antibody response that occurs in the intestinal tract in pets with food allergies are not very well understood. Despite our lack of understanding of the actual disease process, there are many things that we do know including the symptoms, how to diagnose food allergies, and also how to treat them.

Food allergies affect both dogs and cats. Unlike atopy, there is no strong link between specific breeds and food allergies. Food allergies affect both males and females and neutered and intact animals equally. They can show up as early as five months and as late as 12 years of age, though the vast majority of cases occur between 2 and 6 years. Many animals with food allergies also have concurrent inhalant or contact allergies.

Food allergy or intolerance?

There is a distinction that needs to be made between food allergies and food intolerances. Food allergies are true allergies and show the characteristic symptoms of itching and skin problems associated with canine and feline allergies. Food intolerances can result in diarrhea or vomiting and do not create a typical allergic response. Food intolerances in pets would be similar to people that get diarrhea or an upset stomach from eating spicy or fried foods. Fortunately, both food intolerances and allergies can be eliminated with a diet free from offending agents.

Common food culprits

Several studies have shown that some ingredients are more likely to cause food allergies than others. In order of the most common offenders in dogs are beef, dairy products, chicken, wheat, chicken eggs, corn, and soy. As you may have noticed, the most common offenders are the most common ingredients in dog foods. This correlation is not a coincidence. While some proteins might be slightly more antigenic than others, many proteins are similar in form and the incidence of allergic reactions are probably associated with the amount of exposure. For example, pet foods have historically been made up of beef, chicken, corn, and wheat. In an effort to combat food allergies, several companies produced a diet made of lamb and rice. There was nothing special about lamb and rice diets except those two ingredients were normally not present in pet foods. Animals had not eaten lamb or rice before, and therefore, had not developed an allergy to it yet. If the main ingredients in pet food become lamb and rice, then it would stand to reason that the most common problem foods could become lamb and rice. The determinant of whether a food is likely to cause a food allergy or not is based on the structure and size of the glycoprotein in the food. In addition, many lamb and rice-based foods contain many other ingredients, and if the animal has a food allergy to any of them, this lamb and rice food will do nothing to treat the food allergy. In addition, while many people criticized and blamed preservatives and flavorings as a source of food allergies, studies have shown that they are not the causes, and while we may not have justifiable health concerns about preservatives, food allergies is not one of them.

Symptoms

The symptoms of food allergies are similar to those of most allergies seen in dogs and cats. The primary symptom is itchy skin. Symptoms may also include chronic or recurrent ear infections, hair loss, excessive scratching, hot spots, and skin infections that respond to antibiotics but reoccur after antibiotics are discontinued. There is evidence that dogs with food allergies may sometimes have an increased incidence of bowel movements. One study showed that non-allergic dogs have around 1.5 bowel movements per day where some dogs with food allergies may have 3 or more per day.

It is difficult to distinguish an animal suffering from food allergies from an animal suffering from atopy or other allergies based on physical signs. However, there are a few signs that always make me suspect food allergies. One of these, is a dog with recurrent ear problems, particularly yeast infections. Another, is a very young dog with moderate or severe skin problems. A third tip off, is if a dog suffers from allergies year-round or if the symptoms begin in the winter. And the final clue, is a dog that has very itchy skin but does not respond to antihistamines or steroid treatment.

Diagnosis

The diagnosis for food allergies is very straightforward. But due to the fact that many other problems can cause similar symptoms and that many times animals are suffering from more problems than just food allergies, it is very important that all other problems are properly identified and treated prior to undergoing diagnosis for food allergies. Atopy, flea bite allergies, intestinal parasite hypersensitivities, sarcoptic mange, and yeast or bacterial infections can all cause similar symptoms as food allergies. Once all other causes have been ruled out or treated, then it is time to perform a food trial. Elimination diets and provocative testing: A food trial consists of feeding an animal a novel food source of protein and carbohydrate for 12 weeks. A novel food source would be a protein and carbohydrate that the animal had never eaten before. An example would be rabbit and rice, or venison and potato, or duck and rutabagas. These are homemade diets but there are several commercial diets available on the market. Special Foods produced by Hill's and Purina, and a food named EXclude are used by many dermatologists. Regardless of the diet used, it must be the only thing the animal eats for 12 weeks. This means no treats; absolutely nothing but the special food and water. Young growing pets have special dietary needs and a homemade diet that only contains one protein and one carbohydrate with no multivitamin or fatty acid may not be suitable even for only twelve weeks. For puppies undergoing a food trial, a balanced commercial diet like the ones listed above is recommended. Veterinarians used to recommend that a pet only needed to be placed on a special diet for 3 weeks but new studies show that in dogs, only 26% of those with food allergies responded by day 21. However, the vast majority of pets responded by 12 weeks. Therefore, it is very important to keep the pet on the diet for the entire 12 weeks. If the dog shows a marked reduction or elimination of the symptoms, then the animal is placed back on the original food. This is called 'provocative testing' and is essential to confirm the diagnosis. If the symptoms return after going back on the original diet, the diagnosis of a food allergy is confirmed. If there has been no change in symptoms but a food allergy is still strongly suspected, then another food trial using a different novel food source could be tried. I must reiterate that placing a dog on a commercial lamb and rice formula dog food is not an acceptable way to diagnose or treat food allergies. Lamb and rice are no longer considered novel food sources and most commercial lamb and rice diets also contain wheat, egg, corn, or other ingredients that can be the cause of the food allergy. Despite the implication by dog food companies to the contrary, these foods do not prevent food allergies nor are they considered adequate for diagnosis. While these diets may provide adequate nutrition, they are not a substitute for a true, novel protein source diet.

Blood Testing: Many owners and veterinarians attempt to look to other tests to diagnose food allergies. Blood tests such as the RAST test or the ELISA test can be performed to screen for food allergies. In addition, intradermal skin testing could also be performed. Despite the fact that these tests are routinely performed and used as a diagnostic aid, there is no evidence that blood tests are accurate for the diagnosis of food allergies. Veterinary dermatologists insist that there is no merit in these tests whatsoever in the diagnosis of food allergies. The only way to accurately diagnose food allergies is with a food trial as detailed above. While the intradermal skin testing is excellent for diagnosing atopy (inhalant allergies) it is ineffective for food allergies. While the ELISA and to a lesser extent the RAST test can be used to help in the diagnosis of atopy, they have no benefit in diagnosing food allergies. In my review of all the current books and articles on veterinary dermatology and allergies, I could not find a single dermatologist that endorsed anything other than the food trial as an effective diagnostic aid. If you want to diagnose and treat food allergies you must do a food trial.

Treatment

Once we determine a positive diagnosis, then the treatment is very straightforward. The owner of the animal has two choices. They can choose to feed the animal a special commercially prepared diet or a homemade diet. If the owner chooses to feed the homemade diet, then they can periodically challenge the pet with new ingredients and determine which ingredients are causing the food allergy. For example, if the animal's symptoms subsided on a diet of rabbit and potatoes, then the owner could add beef to the diet for two weeks. If the animal showed no symptoms, then they could then add chicken for two weeks. If the animal began to show symptoms, then it could be assumed that chicken was one of the things the pet was allergic to. The chicken could be withdrawn and after the symptoms cleared up, a different ingredient could be added and so on until all of the offending ingredients were identified. A diet could then be formulated that was free of the offending food sources. If homemade diets are used, it is essential that they be balanced, with correct amount of ingredients, vitamins, and minerals.

A hypersensitive immune system is one which overreacts to a stimulus. A normal immune system reacts when the body identifies a foreign protein such as proteins on the outside of bacteria. This foreign material which invokes the immune response is called an antigen. The body can react to the antigen by producing protein molecules (antibodies) which bind the antigen. The combination of the antibody bound or attached to the antigen is called an immune complex.

In addition to antibodies, various cells can also be activated which produce chemicals such as histamines which can affect multiple parts of the body. In hypersensitivity, the body produces way too much antibody, the wrong kind of antibody, a large number of antigen-antibody complexes, or antibody to proteins which are not really foreign. In addition, an excessive number of cells may be activated to produce histamine and other chemicals. There are four major types of hypersensitivity.

Type I (Immediate) Hypersensitivity

In Type I hypersensitivity, the reaction of the immune system is immediate and severe. The symptoms are mostly due to cells over-reacting and releasing very large amounts of histamine and other chemicals. This is the type of reaction that occurs when a person or animal is allergic to bee stings or penicillin and is called anaphylaxis. Type I hypersensitivities also include allergies to things inhaled (atopy) such as pollens and dog or cat dander, flea allergy dermatitis, and other antigens which evoke symptoms of an allergy within minutes of when the person or animal was exposed. Urticaria (hives) is another Type I hypersensitivity.

Type II (Antibody mediated) Hypersensitivity

Type II hypersensitivities occur when the body produces antibodies to proteins on its own cells. This is called autoimmunity. In autoimmune hemolytic anemia, the body produces antibodies against its own red blood cells, destroying them, and producing an anemia (lower than normal number of red blood cells). Transfusion reactions are another example of this type of hypersensitivity.

Type III (Immune complex mediated) Hypersensitivity

The over-reaction of the immune system in Type III hypersensitivities causes large numbers of immune (antibody-antigen) complexes to form in the body and lodge in certain organs. A certain type of kidney disease called glomerulonephritis occurs when these complexes lodge in the kidney and block its ability to filter the blood. Lupus erythematosus and rheumatoid arthritis are other examples of this type of hypersensitivity.

Type IV (Delayed) Hypersensitivity

Type IV or delayed hypersensitivity occurs more than 24 hours after the body was exposed to the antigen. Allergic contact dermatitis is one kind of Type IV hypersensitivity. This is the type of reaction that occurs in animals and people exposed to various dyes, chemicals, or metals. It is also the reaction we test for when a tuberculin test is performed.

Genetics and hypersensitivity

All cases of allergies, whether they are severe or mild, are genetic in nature. A dog or cat that becomes allergic to vaccines, drugs, food, pollens, fleas, etc., is genetically programmed to have an immune system capable of mounting the allergic response. An allergic reaction is not the fault of the medication, vaccine, food, or environment; it is a genetic trait inherited from the parents. It is unwise to use individuals with abnormal immune systems in a breeding program.

Urticaria and angioedema are hypersensitivity (or allergic) reactions to drugs, chemicals, something eaten, or even sunlight.

What are the symptoms of urticaria and angioedema?

In urticaria, small bumps occur within the skin. Often, the hair will stand up over these swellings. Sometimes, they itch. In angioedema, we see swelling of the face, especially the muzzle and around the eyes. Sometimes, the swelling is so severe, the animal cannot open its eyes. Angioedema often results in itching. Angioedema and urticaria generally develop within 20 minutes of being exposed to the allergen (substance to which the animal is allergic).

In general, both urticaria and angioedema are not life-threatening and will go away by themselves. Rarely, the swelling in angioedema can affect the throat and make breathing difficult.

How are urticaria and angioedema treated?

Antihistamines are generally the best treatment for angioedema and urticaria. If severe, steroids are sometimes given. If respiration is affected, epinephrine is administered.

Can urticaria and angioedema be prevented?

In general, there is no way to predict which animals may develop urticaria or angioedema as a result of exposure to a certain substance. If a pet has already had a reaction, such as anaphylaxis, angioedema, or hives, to a substance, the substance should be avoided. If your dog has ever had a reaction to a vaccine or medication, be sure your veterinarian knows and the information is placed in your pet's medical record.

If your dog has ever had a reaction to a vaccine, subsequent vaccinations should be given by your veterinarian. Your veterinarian will probably administer an antihistamine prior to vaccination and have you remain in the office for 20-30 minutes after the vaccination, so you are right there if your pet has a reaction. In some cases, certain vaccines may be excluded from your dog's vaccination regimen, or a different type of vaccine will be used.

Many vaccines contain antibiotics as preservatives. If your dog is allergic to an antibiotic, be sure to check all vaccines for the presence of that antibiotic before use.

If your pet has developed urticaria or angioedema from an insect bite, you may want to discuss various options with your veterinarian. Your veterinarian may give you a prescription for an 'epi-pen.' An 'epi-pen' is a special syringe and needle filled with a single dose of epinephrine. If your pet has an anaphylactic reaction or severe angioedema, inject the epinephrine using the 'epi-pen' and seek emergency veterinary assistance immediately. Be sure to take the 'epi-pen' with you on any trips or hikes.

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