by Veterinary Practice News Editors | April 17, 2009 4:06 pm
For veterinarians and pet owners alike, few conditions in pets are as frustrating as allergies. But as awareness of the challenges associated with allergies continues to increase—as do the number of treatment options available—veterinarians are finding greater success in diagnosing and managing allergic pets.
The list of allergies most commonly seen in dogs and cats has remained relatively constant over the years.
“These allergies are to things they come in direct contact with, such as pollens, mites, fleas and molds,” says Dena Ware, a marketing manager for Heska Corp. “Additionally, they can have adverse reactions to foods they eat, which causes them to exhibit the same signs as contact allergens.
“Until fairly recently, it was commonly believed that atopic disease is caused by allergens inhaled by the animal, but now it is understood that the allergens are absorbed into the animal’s skin,” Ware says.
Some emerging allergic trends are evident. For example, Ware notes that the incidence of adverse reactions to foods has increased as the number of pet food choices has grown.
Lowell Ackerman, DVM, Dipl. ACVD, a clinical professor in the dermatology and allergy service at Tufts University Cummings School of Veterinary Medicine, notes another trend.
“In years gone by, fleabite hypersensitivity was more common, but with newer flea control regimens, fleabite sensitivity is becoming much less common—at least in my area,” he says.
The most common means of determining the source of an animal’s allergies has been the same for decades. Most veterinarians currently rely on either intradermal testing or serum allergy testing to identify culprit allergens; however, some disagreement remains as to which method is preferred.
“For many years, dermatologists relied on intradermal testing—similar to the allergen prick test used on humans—to determine what the animal was allergic to, but serum IgE testing is now available and is much more convenient for the pet, pet owner and veterinarian,” Ware says.
“Serum IgE testing identifies the IgE antibody in the animal’s serum, which reacts with the test’s reagents. IgE is allergen-specific and is the antibody that is the culprit in the allergic reaction. This means if you can identify significant allergen-specific IgE in an animal’s serum, you can identify what allergen is causing the allergic reaction.
“When researching serum IgE testing companies, a veterinarian needs to ensure that the test identifies IgE and IgE only, and will not cross-react with other antibodies, leading to false positives,” she adds.
Jenise Daigle, DVM, Dipl. ACVD, a practitioner at Austin Veterinary Dermatology & Allergy in Texas, notes that in vitro testing has changed over the years.
“We are seeing more of the labs that do these tests show validation methods in regards to the in vitro airborne panels,” she says. “Most dermatologists still feel intradermal testing is the gold standard since we are testing the skin, which is where the disease process is occurring.
“We know the route of transmission in animals is mainly percutaneous; therefore it makes sense that intradermal testing would correlate more since we are testing the skin, where the antigens are.”
Susan Keesee, Ph.D., president and chief scientific officer of Bio-Medical Services in Austin, Texas, recognizes that some veterinarians prefer intradermal methods of testing.
“There’s an old dogma that skin testing is better than serum testing,” she says. “However, over the years it has been pretty well established that the two are equivalent.”
Founded in 1989, Bio-Medical Services was the first laboratory to develop a commercial application for in vitro allergy diagnostics in the veterinary industry, Keesee says. Over the years, the company has continued to add to its offerings. For example, last year it introduced a new specialty diet food-allergy test.
“We have noticed a trend by pet food companies to include non-traditional ingredients in new food formulas entering the market,” Keesee says. She says the new in vitro allergy test—designed to test for allergic reactions to ingredients such as duck, venison, apple, tomato and green peas—provides an accurate, reproducible means of measuring IgE specific to individual food allergen proteins.
Still, the use of serum food tests is the focus of a good deal of debate among veterinarians.
“Too many veterinarians are still using allergy tests to attempt to diagnose adverse food reactions in dogs and cats,” Ackerman says. “The predictive value of these tests is quite low, and clients would be better advised to perform appropriate elimination diet trials.”
“Food allergy can only be ruled out by an eight- to 10-week food trial with a prescription hypoallergenic diet with either a novel protein diet or a hydrolyzed diet,” Daigle says. “In vitro allergy tests for food are 100 percent unreliable and are often used in general practice. They can be misleading due to the high incidence of false positives.”
Many veterinarians operate under a broad misconception when it comes to allergy testing, Ackerman adds.
“The main misconception is that allergy tests are used to diagnose allergies,” Ackerman says. “In fact, the diagnosis of environmental allergies—atopy—is made on the basis of history and clinical signs. Allergy testing is really only indicated if we want to attempt to manage the allergies with immunotherapy—allergy shots—or avoidance.
“The presence of positive scores on either an intradermal or in vitro allergy test does not confirm allergy as a diagnosis, and the absence of positive scores does not mean that the patient is not allergic,” Ackerman adds.
“There are many animals that score negative on allergy tests but are clinically atopic.”
When a pet has been diagnosed as allergic, veterinarians have a wide array of treatment options. Still, managing allergies can be difficult and frustrating.
“Steroids are often relied upon because they can provide immediate relief to the allergic animal,” Ware says. However, steroids can result in long-term negative conditions affecting the internal organs.
“Antihistamines, topical creams, sprays and shampoos can help, but are only temporary relief methods. Other treatments that are being researched are sublingual—under the tongue—or treatment in tablet form. These are not available for animals at this time, but have shown success in humans.
“Currently, the safest long-term solution to non-seasonal or long-season allergies is immunotherapy,” Ware says.
Although immunotherapy isn’t a new treatment, veterinarians have been experimenting with the therapy’s protocol in recent years.
“In the past year and a half to two years, there has been movement toward rush immunotherapy with dogs,” says Sola Alaba, Ph.D., president and chief executive officer of Veterinary Allergy Reference Laboratory in Pasadena, Calif.
“Instead of an induction period of several months, it’s basically a one-day thing. A patient is admitted and injected about every half-hour throughout the day. Then this is followed up with injections every three weeks or so.
“As far as I know, this method hasn’t been tested in cats yet,” Alaba says.
Beyond immunotherapy, veterinarians have a growing range of pharmaceutical options.
“Atopica—cyclosporine by Novartis—is a newer drug that has been developed for atopic dermatitis in dogs only,” Daigle says. “It is a drug that treats the symptoms so dogs will need to stay on the medication for the rest of their lives.
“Atopica has its place and is another tool in our toolbox in managing allergies. I save it more for my patients that do not respond to immunotherapy since we do not know long-term side effects of this drug. Only a 30-month study has looked at side effects with this drug,” Daigle says.
Paul Bloom, DVM, Dipl. ABVP, ACVD, of the Allergy & Dermatology Clinic for Animals in Livonia, Mich., agrees that Atopica enhances veterinarians’ efforts in managing allergic dogs. However, he notes that many veterinarians aren’t patient enough in their treatment of allergic pets.
“You don’t want to use a steroid or Atopica until you first clear up an animal’s skin infection,” he says. “Many veterinarians aren’t being aggressive enough in doing that.”
Dr. Bloom says there are new shampoos on the market that can aid in the treatment of allergic patients. These shampoos include a formula manufactured by Sogeval Laboratories that employs a patented molecule called phytosphingosine in treating seborrheic conditions, he says.
Veterinarians should not discount the importance of prevention, experts say.
“One of the common issues in dogs and cats is flea allergic dermatitis,” says Cristiano von Simson, DVM, a director and veterinary science liaison for Merial.
“It is particularly troublesome in atopic dogs, which will react strongly to mild flea infestations. In these dogs and cats, it is very important to control the causing agent—the flea—constantly. The ideal approach is integrated flea control, using a fast-acting and long-lasting insecticide and a growth inhibitor that would sterilize the eggs laid by adult fleas.
“Educating clients on the need for periodic application to prevent reinfestations is an important part of the treatment,” he adds.
Above all, Ackerman says, an integrated approach to allergy management is key.
“The newest development of most importance is that owners and referring veterinarians are more responsive to an integrated allergy management program, rather than relying on one drug or even one modality, such as topical therapy, pharmaceuticals, environmental management, nutraceuticals, immunotherapy, etc.,” says Ackerman.
“Successful treatment of allergies is all about patient management,” he adds. “We are dealing with pet owners who have a good grasp of medical concepts and who understand that therapies need to be individualized for each particular pet.
“This is a very encouraging development because owners are no longer asking for a shot, a magic pill or a cure. They understand the need for integrated, long-term management options.”
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