Pet Allergies - An Overview of Dog and Cat Allergies

When your dog pumps its leg frantically to scratch its ear, or your cat bites its tail furiously until the fur falls out, it's clear that your pet is itching for relief.

Occasional scratching is normal, but if a pet scratches or bites itself relentlessly, a health problem may be the cause. Itching can be triggered by a variety of conditions, ranging from liver disease to lice, from fungus to fleas, from mange to anxiety.

But the leading cause of itching and scratching in dogs and cats is allergies, says Linda Messinger, D.V.M., a board-certified veterinary dermatologist at the Veterinary Referral Center of Colorado in Englewood. "Allergies are also the most common underlying cause of ear problems in dogs," she adds.

Unlike people with allergies, animals don't usually get stuffy or runny noses or watery eyes. Their main symptom is itchy skin, which can turn raw and red from scratching, licking, and chewing. This condition is called allergic skin disease, or allergic dermatitis. With enough scratching and biting, open sores can form, creating a haven for bacteria or yeast that can lead to infection.

"Just about every mammal can get allergies," says Lisa Troutman, D.V.M., a veterinarian with the Food and Drug Administration. "So can hamsters, rabbits, birds, and some other pets." But dog allergies and cat allergies are most frequently seen.

To relieve the itch, dogs may scratch and bite at themselves and rub their face with their paws or against the floor and furniture. "Cats tend to pull out their hair and get patchy hair loss on their ears, legs, and around their eyes," says Troutman. "They'll make themselves bald."

There is no cure for dog allergies or cat allergies. "They are a lifelong problem," says Messinger, "and oftentimes they get worse as a pet gets older."

But there are treatments to relieve itchiness, clear up infections that arise from constant scratching, and even "desensitize" a pet to substances that cause allergies. In addition to regulating drugs for people, the FDA regulates drugs for animals, and the agency's Center for Veterinary Medicine has approved medications to treat itchy pets and their infections.

The key to making your pet comfortable is to find out the cause of the itchiness. If the pet is allergic, determining the source of the allergies will help with treatment, says Messinger.

Types of Dog Allergies and Cat Allergies

The four most common dog allergies & cat allergies are: flea, food, atopic, and contact.

The most common type of dog allergy and cat allergy is flea allergy. The offending allergen is actually the protein in flea saliva left in the skin after a fleabite.

Atopic, or inhalant, allergy is the second most common dog allergy and the third most common cat allergy. Breathing in or directly contacting airborne particles in the environment, such as mold spores, dust, tobacco smoke, and pollens, will activate atopic allergies.

If a pet is allergic to pollens, it will show symptoms even if you keep it indoors, says James Jeffers, V.M.D., a board-certified veterinary dermatologist at the Animal Allergy and Dermatology Clinic in Gaithersburg, Md. Outside airborne substances waft their way into the house, and air filters don't tend to bring relief to pets with these types of allergies, he says.

Although pets with atopic allergies sometimes have respiratory problems, such as coughing and sneezing, they more typically develop itchy skin. Certain dog breeds are more likely to develop atopic allergies, including terriers, Dalmatians, and golden and Labrador retrievers.

Food allergies are the second most common type of cat allergy and the third most common dog allergy. Food ingredients most likely to trigger cat allergies are fish, milk, beef, and eggs. Ingredients most likely to cause a reaction in dogs are beef, soy, chicken, milk, corn, wheat, and eggs. Some pets with food allergies may have vomiting and diarrhea.

A reaction to physically touching a substance is called contact allergy, the least common type of dog allergy and cat allergy. Contact allergens include grass, wool, and plastic. Jeffers occasionally sees dogs in his clinic with "plastic dish dermatitis," an irritation to the skin on the nose caused by a reaction to an antioxidant found in a plastic food or water dish. The condition clears up when the pet is switched to a metal or ceramic dish. And although uncommon, some cats become allergic to kitty litter, says Jeffers. But allergies caused by contact with chemicals, uch as those contained in cleaning fluids, waxes, carpet cleaners, and lawn fertilizers, are "about 1 in a million," he says. Nevertheless, these products are potentially toxic, and pets should be restricted temporarily from areas treated with them.

Seasonal Dog Allergies and Cat Allergies

Some dog allergies and cat allergie are set off by seasonal changes. Springtime, with its tree pollens, brings on the animal form of hay fever, which is primarily itchy skin. Mosquitoes and flies, which may trigger allergies, are rampant in summer. Grasses and flowers often release pollen in summer and late-blooming plants produce pollen in early fall, creating airborne irritants. Fleas and the allergies they activate persist in spring through fall in most parts of the country, but are found year-round in some areas.

Geography also plays a role in allergic reactions. Regional changes mean different varieties of grasses, trees, insects, and other environmental elements, which can affect allergies. Jeffers says when he took his dog camping in Maine, the pup was healthy, but when he brought him back home to Maryland, he started itching.

Dog and Cat Reactions to Allergies

Pets, like people, have allergic responses when their immune system overreacts to certain substances. When they enter the body, the offending substances, called antigens or allergens, set off an alarm. This alarm stimulates the body to produce antibodies to defend itself against what it perceives as a threat--the allergen invaders. The antibodies attach themselves to immune cells, called "mast cells," within the skin and other body tissues. When the allergens penetrate these tissues' surfaces, they are captured by the antibodies, which then stimulate the mast cells to release powerful chemicals into the surrounding tissues. It is these chemicals, called histamines, that cause inflammation and itching.

The body's immune system is meant to protect against harmful substances, so why do some animals have a severe reaction to non-threatening substances? "We think it's very similar to the situation in human beings," says Daniel O. Morris, D.V.M., a board-certified veterinary dermatologist and chief of staff of the veterinary hospital at the University of Pennsylvania in Philadelphia. Some animals, like some individuals, "may carry genes that put them at risk for developing allergic reactions," he says.

Another explanation is the hygiene theory, says Morris, which suggests that if you allow children to be exposed to infectious organisms early in life, their immune response may better control infections and make them less likely to develop allergies. In societies that stress cleanliness and try to protect children from dirt and disease, a child's body may overreact when confronted with a foreign substance, even a harmless one. The hygiene theory may explain why allergies in children are on the rise in the developed world, and the same explanation could apply to allergies in pets, says Morris.

Diagnosing Dog Allergies and Cat Allergies

There are many conditions that can make a pet itch or have hair loss, including endocrine, autoimmune, infectious, and parasitic skin diseases. It takes some detective work to identify the cause. A veterinarian may be able to diagnose the problem or may refer your pet to a veterinary dermatologist, a specialist in treating skin conditions in animals.

If dog allergies or cat allergies are suspected, the first thing a veterinarian will usually ask is if the pet is on a flea-control product, says Troutman. Flea allergies are the most common type of allergies and the easiest to control, she says. And just because a pet is kept indoors doesn't mean it can't have fleas. An owner might bring fleas into the house on a piece of clothing, and the fleas can jump onto the pet. Just a single fleabite can cause an allergic animal to itch severely for more than five days, according to the American Animal Hospital sociation.

Pet owners have many options for flea control on pets and in their environment. Veterinarians can recommend an appropriate product.

Once flea allergies are ruled out and if the itch is non-seasonal, food allergies are checked next. Food allergies are not related to a season, while many atopic allergies start out as a seasonal problem, says Morris. Dogs and cats that develop atopic allergies usually show symptoms between 1 and 5 years of age, he says, but food allergies can crop up at any time. They are high on the list of suspects when a dog or cat first exhibits itchy skin at an age less than 6 months or over 5 years.

To test for food allergies, the pet is put on an "elimination diet" for at least 10 weeks, which means it is fed food that consists of a protein and carbohydrate that the pet has not eaten before, such as duck, venison, and potatoes. Veterinarians offer these special foods, and some may be found in retail stores. Or the owner may choose to feed the pet a homemade diet of foods recommended by the vet.

If the animal's itching subsides by at least half, the allergen is considered to be one or more food ingredients, says Jeffers. To confirm this, the owner can reintroduce the old food to see if the symptoms return. To find the specific ingredients that trigger the allergy, the owner should feed the special diet again and add one ingredient at a time from the old diet for at least a week until the itching increases, indicating that the last added ingredient is an allergen. Or the owner may choose to stay with the special food to avoid causing the pet discomfort each time an allergic ingredient is fed.

While the pet is being tested for food allergies, it should not be given treats, chewable medications, table scraps, or rawhide toys that may contain an allergen.

To check for atopic and contact allergies, veterinary dermatologists use an intradermal allergy test, or skin reaction test. The pet is mildly sedated, a postcard-sized area on the side of the pet is shaved, and small amounts of potential allergens are injected into the skin on the shaved area. If the pet is allergic to a particular substance, the skin will become inflamed at the area of the injection.

Jeffers tested Nora, a wire fox terrier, for 58 different allergens. The dog had been "scratching and biting herself all over, 24 hours a day," since it was 3 months old, says owner Katie Mathews of Bethesda, Md. "The scratching kept Nora up all night and kept the family up all night," she says. Before she was referred to Jeffers, Mathews had taken Nora to several veterinarians, who prescribed various antihistamines, shampoos, sprays, and a food elimination diet--none of which worked. "Steroids were successful," says Mathews, "but I didn't want to keep her on them because of the long-term side effects." Mathews also "wanted to get to the root of the problem" so that the allergic substances could be avoided if possible.

Through skin testing, Jeffers determined that Nora had atopic and contact allergies and was allergic to dozens of substances, including pollens, molds, dust mites, grass, cotton, and wool.

Treating Dog Allergies and Cat Allergies

Although pet allergies can't be cured, they can be controlled by avoiding the allergens, treating the symptoms, or desensitizing the pet. In Nora's case, all three methods are used.

Fleas, food ingredients, and some substances that trigger contact allergies may be avoidable, but "with atopic allergies, avoidance is virtually impossible," says Jeffers.

Drug products are available to relieve the symptoms of itchiness and inflammation in pets. Like any drugs designed for animals, these products must obtain FDA approval before they can be marketed by meeting rigorous scientific standards similar to those for human drugs.

The FDA approved two itch-relieving drugs in 2003: Atopica (cyclosporine) for controlling atopic dermatitis in dogs weighing at least four pounds, and Genesis Topical Spray (triamcinolone) for controlling itching related to allergic dermatitis in dogs. Atopica, a product of Novartis Animal Health US Inc. of Greensboro, N.C., is a capsule given orally. It works by inhibiting specific immune cells from reacting to allergens, and can be given as a lifelong treatment. Genesis, made by RMS Laboratories Inc. of Vidalia, Ga., is a steroid spray that is applied to a dog's skin for up to 28 days. Both of these drugs must be prescribed by a veterinarian.

The FDA has approved other steroid products for short-term use in dogs and cats to relieve inflammation and itching. Long-term steroid use is discouraged because these drugs work by suppressing the immune system; this suppressant action over time can leave an animal vulnerable to infection, diabetes, and other conditions.

Veterinarians often prescribe antihistamines approved by the FDA for humans to relieve itchiness in pets. Under the Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA), veterinarians may legally treat dogs and cats with drugs that have been approved for people but not for animals. Pet owners should check with their veterinarians before giving a pet any human medications, including over-the-counter antihistamines.

"If we can control the allergies through medication for occasional flare-ups, antihistamines and steroids are useful," says Troutman. But if these medications are needed continuously to provide relief, Troutman recommends seeking other options, such as immunotherapy.

Immunotherapy is a treatment that stimulates the immune system to decrease the body's reaction to allergens. Similar to people with allergies, animals can be given immunotherapy, or desensitization injections. These "allergy shots" contain small amounts, or extracts, of the substances that the animal is allergic to, based on the results of skin testing. The owner gives the shots to the pet at home, usually in the scruff of the neck. The extracts used for allergy testing and treatment in veterinary practices are licensed by the U.S. Department of Agriculture's Center for Veterinary Biologics.

Somewhere between 50 percent and 70 percent of dogs and 75 percent to 80 percent of cats respond to immunotherapy, depending upon the study reported, says Morris. "Occasionally, it is so effective that the animal is normal without other treatments," he says, but the majority require medications in addition to the injections. The injections are usually given every 7 to 21 days, depending on the pet's response, says Morris. And rarely does an animal become permanently desensitized so that the injections can be stopped.

Nora gets a weekly injection. Mathews also gives her Atopica and, when the pollen count is up, an over-the-counter antihistamine. Mathews has placed synthetic blankets around the house for Nora to lie on, since the dog is allergic to cotton and wool in the furniture and carpeting. Nora also has a vinyl bed to lie on in the yard, since she's allergic to grass. This allergy management program helps keep the 18-month-old dog comfortable. "She still has periods of scratching," says Mathews, but "she's not biting herself as much and she's sleeping at night." Mathews reports that her other dog, Nora's littermate Nick, is allergy-free.

Allergies in pets are neither preventable nor foreseeable, says Morris. "You can have one puppy out of a litter of 10 with allergic skin disease, or it can skip generations. We can't possibly predict it," he says, even if you have a pet examined by a vet at a very young age.

Pet Food and How it Impacts Dog and Cat Allergies

Most experts agree that changing foods periodically will not keep a pet from becoming allergic to certain ingredients.

"If you're genetically predisposed to develop an allergy to something you eat, it will occur," regardless of switching foods periodically, says Daniel O. Morris, D.V.M., chief of staff of the veterinary hospital at the University of Pennsylvania in Philadelphia.

Morris advises against changing food ingredients at least for the first year or two of a pet's life. "I see dogs, especially, developing food allergies at very early ages," he says, adding that it's not a good idea to expose young animals to many different ingredients.

"The gut lining in the intestinal tract is not fully formed," says Morris. "The theory is that it allows food proteins larger than appropriate to be absorbed." These food proteins react with the immune system, causing an allergic response.

If you know your pet has allergies to certain food ingredients, read the food label carefully to avoid those ingredients, Morris says. The front of a can or bag of food may state one or two main ingredients, but the label will list a number of others as well. "Changing brands does not necessarily mean you're changing ingredients," he adds.

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