Scratch, Scratch, Wheeze, Sniffle, Lick; Is Your Cat Allergic?

It is important to note that allergies develop over time.  Typically it’s repeated exposure to a substance that triggers an allergic response…

Summertime finds many cat companions suffering from various allergies but our cats can also have allergies to many substances, including foods, pollens, molds and fleas.

Clinical signs of allergies in cats can be different than those in other species (including dogs and humans), so it’s important to learn to recognize these symptoms in order to keep your kitty comfortable year-round.

It is important to note that allergies develop over time.  Typically it’s repeated exposure to a substance that triggers an allergic response from the immune system.  We’ll talk about allergy testing and treatments a bit later in this column.

Food Allergies
Cats with food allergies typically have waxy, itchy ears (often confused with an ear mite infestation) and also are itchy (pruritic) over the face, ears, neck and upper third of the body.  Gastrointestinal signs, including vomiting and diarrhea, also can be seen.  An individual cat can be allergic to any food or combination of foods.  Some of the more allergenic foods for cats include:  Beef, lamb, seafood/fish, corn, soy, milk and wheat gluten.  Cats with signs of otitis (ear infection or inflammation) should have a few simple tests performed, including the following:
• An examination for ear mites (a small amount of ear debris is placed under the microscope and the slide is examined for the presence of adult mites, as well as their eggs; many times ear mites can be seen with the use of an otoscope by the veterinarian)
• Ear cytology (another specimen of ear debris is stained and checked for the presence of yeast, white blood cells and bacteria)
• Skin scrapings (to check for mites) and a flea combing (to find fleas or flea “dirt").
Depending on the extent of the skin disease, your kitty’s veterinarian may choose to perform a test to check for ringworm (dermatophytosis) or even skin biopsies.

If food allergies are suspected, a diet trial is generally recommended.  This involves feeding a food with a protein source and a carbohydrate that your cat has not eaten previously.  This often can be a challenge, since many cats eat a variety of foods and brands.  Generally, rabbit, venison or duck-based diets are used with the addition of green peas, barley or millet.  There are several prescription diets that are available for use and the selected hypoallergenic one is fed exclusively (no treats or table food) for at least six weeks, while the appearance of the skin is monitored.  Most cats with food allergies respond well to these hypoallergenic diets and are maintained on them.

It’s important to know that cats generally do not get “ear infections” as commonly as dogs do.  If your kitty has a history of ear infections, consider discussing with your veterinarian the possibility of food allergies, as well as the presence of polyps (seen in younger cats) or cancer of the ear canal (typically seen in older cats).

Feline Asthma
In a previous Vet Chat, I wrote about feline asthma as an allergic disease of the small airways.  Last month, we learned that asthma in cats can be caused by heartworm disease as well.  If your kitty had been coughing and was diagnosed with asthma, in addition to proper medications (generally a steroid inhaler and a bronchodilator), environmental control can be an important part of disease management.  Using air filters, changing furnace filters, changing pillows (to reduce dust mites), avoiding indoor cigarette smoking and the use of candles and incense and keeping the home as dust-free as possible (including using a dust-free cat box filler, like Feline Pine) are all changes that can positively impact asthma management in cats.

Inhalant Allergies
Like their human companions, cats can be allergic to pollens, molds, grasses, weeds and indoor air contaminants.  Cats with inhalant allergies ("atopy") often lick the insides of their forelimbs.  Some cats also over-groom the outsides of their front limbs as well.  Occasionally, cats with allergies can have watery eyes and a clear discharge from their nostrils (conjunctivitis and rhinitis), but these are uncommon signs.  Most cases of conjunctivitis and rhinitis are due to upper respiratory tract infections.

Allergies tend to start with one season (summer, for example, if the kitty is allergic to outdoor allergens or winter, when the heat comes on).  Allergies can stay confined to one season or may worsen with time, so that allergies become multi-seasonal.

For some cats, anti-histamines can provide relief.  However, anti-histamine usage in cats is often trial-and-error and there is not one reliable anti-histamine that works for all allergic cats.  As always, no medication, including anti-histamines, should be used in cats without the direction of the kitty’s veterinarian.  Some cats require a short course of a glucocorticoid (steroid), in addition to the anti-histamine, for appropriate relief.

Cats presented for possible allergies should have a minimum dermatology work-up by the veterinarian that includes skin scrapings and cytology (to rule out mites), flea combing and a ringworm (DTM) test.  If your kitty has access to the outdoors or you have a dog in the home that spends time outside, your veterinarian may recommend application of a flea control product to rule out fleas as a cause of the clinical signs.  Fleabite dermatitis can be particularly severe and the saliva from only one flea can cause intense itching and misery in affected cats.

Allergy Testing
Cats who do not respond to symptomatic care or those with allergic signs that span multiple seasons are candidates for allergy testing.  Most veterinarians offer a simple blood test that can test for many allergens that are specific to the geographic area in which the kitty lives.  This serum testing is NOT reliable for the diagnosis of food allergies, however.  The allergy test results are sent to the veterinarian and can be used to develop hyposensitization injections that clients can give at home.  While many cats do respond to the allergy injections, it may take a year or more to see improvement.  Lab requirements vary as to whether the kitty must not have received anti-histamines or steroids for a period of time prior to the testing.

The “gold standard” for allergy testing is the intra-dermal skin test (IDST)offered by veterinary dermatologists.  For this test, the kitty is shaved along one of his or her sides and very small doses of various allergens are injected under the skin.  After a short time period, the areas are examined for swelling and are graded.  Those areas with the largest amount of swelling generally indicate substances to which the patient is allergic.  Hyposensitization injections then can be developed from this information.  Generally, cats who are presented for IDST must not have received glucocorticoids (steroids) or anti-histamines for several (six) weeks prior to the testing.

“Rodent Ulcers”
Some cats develop large, red lesions on their lips, down the backs of their legs and on their abdomens.  The medical terms for these lesions are eosinophilic granulomas or plaques.  They are often called “rodent ulcers” since in the past they were erroneously thought to occur when cats fought with mice and rats.  These lesions, which can be very disconcerting to the cat companion, generally do not cause problems and are more of an aesthetic problem for the human, rather than an issue for the cat.
These lesions are hypersensitivity reactions and contain large numbers of eosinophils, normal white blood cells that are seen with hypersensitivity and allergic problems.
Although steroids often provide relief, the use of repository steroids (long-lasting injections) should be avoided.  Cats who have severe eosinophilic plaques or granulomas often can be treated successfully with cyclosporine.  Doxycycline is an antibiotic with anti-inflammatory effects that also can be used for these lesions.  Biopsies of the lesions may be necessary to ensure that the masses are benign and not cancerous.

Allergies to plastic bowls may be responsible for some of these lesions located on the lips of cats.  Using glass or ceramic dishes and thoroughly washing them after each use may reduce the incidence of “rodent ulcers” on the lips of cats.