Allergy - General in Cats
What are allergies and how do they affect cats?
One of the most common conditions affecting cats is allergies. An allergy occurs when the cat's immune system overreacts to foreign substances called allergens or antigens. Allergens and antigens are simply foreign proteins that the body's immune system tries to remove, much like fighting an infection. These overreactions are manifested in one of three ways:
1. The most common manifestation is itching of the skin, either localized in one area or a generalized reaction all over the cat's body.
2. Another manifestation involves the respiratory system and may result in coughing, sneezing, and wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge.
3. The third manifestation involves the digestive system, resulting in vomiting, flatulence or diarrhea.
How many types of allergies are there?
There are four common types of allergies in the cat: flea, food, inhalant, and contact. Each has common clinical signs and unique characteristics.
What is flea allergy and how is it treated?
Flea allergy is the most common allergy in cats.
"The flea allergic cat has a severe, itch-producing reaction when the flea's saliva is deposited in the skin."
A normal cat experiences only minor skin irritation at the site of flea bites. The flea allergic cat, on the other hand, has a severe, itch-producing reaction when the flea's saliva is deposited in the skin. Just one flea bite may cause such intense itching that the cat may severely scratch or chew itself, leading to the removal of large amounts of hair. There will often be open sores or scabs on the skin, resulting in a secondary bacterial skin infection (pyoderma). The area most commonly involved is over the rump or base of the tail. In addition, the cat may have numerous small scabs around the head and neck. These scabs are often referred to as miliary dermatitis, a term that was coined because the scabs look like millet seeds.
The most important treatment for flea allergy is to eliminate all fleas. Therefore, strict flea control is the cornerstone of successful treatment. Unfortunately, this may be challenging in warm and humid climates, where a new population of fleas can hatch out every fourteen to twenty-one days. Some monthly flea products may kill fleas before they have a chance to bite your cat (see handout "Flea Control in Cats"). When strict flea control is not possible, injections of corticosteroids, also referred to as cortisone or steroid shots can be used to block the allergic reaction and give immediate relief. This is often a necessary part of the initial treatment of flea allergies. Fortunately, cats appear relatively more resistant to the negative side effects of steroids than other mammals. If a secondary bacterial skin infection occurs from the flea allergy dermatitis, appropriate antibiotics must be used, generally for two to four weeks. See handout "Allergy - Flea Allergy in Cats" for more detailed information about flea allergies in cats.
What is food allergy and how is it treated?
Cats are not likely born with food allergies.
More commonly, they develop allergies to food products they have eaten for a long time. Food allergies are now estimated to be the second leading cause of allergic dermatitis in cats. The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey. Vegetable proteins such as those found in corn or wheat may cause food allergies in some cases. Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress.
"Food allergies are now estimated to be the second leading cause of allergic dermatitis in cats."
Food allergy testing is recommended when the clinical signs have been present for several months, when the cat has a poor response to steroids, or when a very young cat itches without other apparent causes of allergy. Testing is conducted by feeding an elimination or hypoallergenic diet. Because it takes at least eight weeks for all other food products to be removed from the body, the cat must eat the special diet exclusively for a minimum of eight to twelve weeks. If a positive response occurs, you will be instructed on how to proceed. If the diet is not fed exclusively, it will not be a meaningful test. This means absolutely no treats, other foods, people foods, or flavored medications during this period. This cannot be overemphasized. Even accidentally providing a tiny amount of the offending protein can result in invalidating the test.
If your cat’s symptoms improve after the food trial, a presumptive diagnosis of food allergy is made. Exclusively feeding a hypoallergenic diet lifelong is highly successful in treating food allergic skin disease in many cats.
Because cats that are being tested for inhalant allergy generally itch year round, a food allergy dietary test can be performed while the inhalant test results are pending or antigen preparation is occurring. Remember that many cats are allergic to many things – pollens, fleas, and foods – and a combination of therapies is often required to keep your cat as comfortable as possible.
What is inhalant allergy or atopy?
Inhalant allergy or atopy is estimated to be the third most common type of allergy in cats. When itching is the primary clinical sign the term atopic dermatitis is often used to describe the condition. It is also referred to as 'seasonal allergy' when believed to be related to pollens and grasses.
"Most cats that have an inhalant allergy are allergic to several allergens."
Cats may be allergic to all of the same inhaled allergens that affect humans. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda grass), weed pollens (ragweed, etc.), molds, mildew, and the common house dust mite. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others are with us all the time, such as molds, mildew, and house dust mites. When humans inhale these allergens, we express the allergy as a respiratory problem. Atopy is also sometimes called 'hay fever'. The cat's primary reaction to atopy is severe, generalized itching.
Most cats that have an inhalant allergy are allergic to several allergens. If the number of allergens is small and they are seasonal, itching may last for just a few weeks at a time during one or two periods of the year. If the number of allergens is large or they are present year-round, the cat may itch constantly. Cats with atopic dermatitis may develop skin lesions such as eosinophilic plaques in more serious cases.
"Some allergens may be absorbed through the skin."
How is atopy treated?
Treatment depends largely on the length of the cat's allergy season. It involves one of two approaches:
- The first approach involves the use of corticosteroids (steroids) and medicated shampoos in acute or sudden cases. Steroids will dramatically block the allergic reaction in most cases and bring about rapid improvement in the cat's clinical signs. Steroids may be given orally or by injection, depending on the cat's condition. If steroids are appropriate for your cat, you will be instructed in their proper use. Some cats are also helped considerably by hypoallergenic or medicated shampoos. It has been shown that some allergens may be absorbed through the cat’s skin. Frequent bathing will reduce the amount of antigen exposure through this route. In addition to removing surface antigens, bathing alone will provide some temporary relief from itching and may allow the use of a lower dose of steroids or other treatments.
- Antihistamines are unlikely to help cats during an acute flare of atopic dermatitis. This is because histamine has already been released by the body’s mast cells and administering a histamine receptor agonist (blocker) will not block the effects of histamine. Omega-3 fatty acids (fish oils) are similarly ineffective during acute episodes because they require several weeks to take effect. Cats predisposed to atopic dermatitis should be tried on fatty acid supplements to see if they help lessen future flare-ups and symptoms.
- The second approach to chronic inhalant allergy treatment is desensitization with specific antigen injections or 'allergy shots'. This is not to be confused with injections of corticosteroids. Once the specific sources of allergy are identified through allergy blood tests (most commonly IgE blood tests) or intradermal skin testing, very small amounts of the antigen are injected weekly. The aim is to 'reprogram' the body's immune system response to the allergen. It is hoped that as time passes, the immune system will become less reactive to the problem-causing allergens. If desensitization appears to help the cat, injections will often continue for several years. For most cats, a realistic goal is for the itching to be significantly reduced in severity rather than be completely cured. In some cats, the itching and associated clinical signs may completely resolve while others may experience minimal improvement. Steroids are not used with this treatment protocol, except on an intermittent basis. On average, approximately half of the cats receiving desensitization therapy will experience a significant decrease in their clinical signs. This therapeutic approach is usually recommended for the middle-aged or older cat that has year round itching caused by inhalant allergy. This approach is not used with food allergy.
Although desensitization is the ideal way to treat inhalant allergy, it does have some drawbacks and may not be the best choice in certain circumstances.
Cost: This is the most expensive form of treatment.
Age of Patient: Because many cats develop additional allergies as they get older, young cats may need to be retested one to three years later.
Success Rate: About 50% of cats will have an excellent response. About 25% get partial to good response. About 25% get little or no response. The same statistics are true for humans undergoing desensitization.
Time of Response: The time until apparent response to allergen-specific immunotherapy may be two to five months, or longer.
Interference of steroids: Cats must not receive oral steroids for two weeks or injectable steroids for six to twelve weeks prior to testing. These drugs will interfere with the test results.
Any cat suspected of having atopic dermatitis should also consider a hypoallergenic food trial. Many cats with atopic dermatitis are also allergic to an ingredient in their food, making diagnosis and treatment more challenging. This food trial should last 8 to 12 weeks in most cases. Other treatments to help combat chronic atopic dermatitis include cyclosporine, long-term corticosteroids alternating with anti-histamines, and daily omega-3 fatty acids.
It is important to keep in mind that atopic dermatitis is a lifelong condition and frequent relapses are common. There is no 'cure' for allergic skin disease, only treatments that mitigate symptoms and improve quality of life. While cats certainly appear less likely to develop side effects associated with chronic steroid usage than dogs or humans, their prolonged use must be carefully monitored. Ideally a cat or dog requiring long-term steroids would be placed on them every 48 to 72 hours, using anti-histamines on 'off' days. Cyclosporine has also been used long-term in many cats to help treat allergic skin disease with fewer reported side effects than steroids. It is important to work closely with your veterinarian to provide the best care for your cat’s allergic condition and fully understand the risks and benefits of each treatment.
What is contact allergy and how is it treated?
Contact allergies are the least common of the four types of allergies in cats.
"They result in a local reaction on the skin from contact with an offensive (allergic) substance."
They result in a local reaction on the skin from contact with an offensive (allergic) substance. Examples of contact allergy include reactions to shampoos, flea collars or to types of bedding, such as wool. If the cat is allergic to such substances, there will be skin irritation and itching at the points of contact. Removal of the contact irritant solves the problem. However, identifying the allergen can be challenging in many cases.
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