McCune Animal Hospital
One of the most common conditions affecting cats is allergy. In the allergic state, the cat's immune system "overreacts" to foreign substances (allergens or antigens) to which it is exposed. Those overreactions are manifested in three ways. The most common is itching of the skin, either localized (one area) or generalized (all over the cat). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea.
Types of Allergy
There are four known types of allergies in the cat: contact, flea, food, and inhalant. Each of these has some common expressions in cats, and each has some unique features.
Contact allergies are the least common of the four types of allergies. They result in a local reaction to the skin. Examples of contact allergy include reactions to flea collars or to types of bedding, such as wool. If the cat is allergic to those, 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 require some detective work.
Flea allergy is common in cats. A normal cat experiences only minor irritation in response to flea bites, often without any itching. 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 bite causes 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, allowing a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail). In addition, the cat may have numerous, small scabs around the head and neck. These scabs are called miliary lesions, a term which was coined because the scabs look like millet seeds.
The most important treatment for flea allergy is to get the cat away from all fleas. Therefore, strict flea control is the backbone of successful treatment. Unfortunately, this is not always possible in warm and humid climates, where a new population of fleas can hatch out every 14-21 days. When strict flea control is not possible, injections of corticosteroids (or "cortisone" or "steroids") can be used to block the allergic reaction and give relief. This is often a necessary part of dealing with flea allergies. Fortunately, cats appear relatively more resistant to the side effects of steroids than other species. If a secondary bacterial infection occurs, appropriate antibiotics must be used.
The most common type of allergy is the inhalant type, or atopy. Cats may be allergic to all of the same inhaled allergens that affect us. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda), weed pollens (ragweed, etc.), molds, mildew, and the 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; it is sometimes called "hay fever." The cat's reaction, however, usually produces severe, generalized itching. In fact, the most common cause of itching in the cat is inhalant allergy.
Most cats that have an inhalant allergy are allergic to several allergens. If the number is small and they are the seasonal type, 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 they are present year-round, the cat may itch constantly.
Treatment depends largely on the length of the cat's allergy season. It involves two approaches. Steroids will dramatically block the allergic reaction in most cases. These may be given orally or by injection, depending on the circumstances. As stated previously, the side effects of steroids are much less common in cats than in people. If steroids are appropriate for your cat, you will be instructed in their proper use.
Some cats are helped considerably by a hypoallergenic shampoo. It has been demonstrated that some allergens may be absorbed through the skin. Frequent bathing is thought to reduce the amount of antigen exposure through this route. In addition to removing surface antigen, bathing alone will provide some temporary relief from itching and may allow the use of a lower dose of steroids. Antihistamines are usually of little value in the cat, but can be tried.
The second major form of allergy treatment is desensitization with specific antigen injections (or "allergy shots"). Once the specific sources of allergy are identified, very small amounts of the antigen are injected weekly. This is all in an attempt to reprogram the body's immune system. 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 continue for several years. For most cats, a realistic goal is for the itching to be significantly reduced in severity; in some cats, itching may completely resolve. Steroids are not used with this treatment protocol, except on an intermittent basis. This therapeutic approach is 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.
1. Cost: This is the most expensive form of treatment.
2. Age of Patient: Because many cats develop additional allergies as they get older, young cats may need to be re-tested 1-3 years later.
3. 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 people undergoing desensitization.
4. Food Allergies: Although tests for food allergy are available, the reliability of the test is so low that it is not recommended at this time. A food trial remains the best diagnostic test for food allergy.
5. Time of Response: The time until apparent response may be 2-5 months, or longer.
6. Interference of steroids: Cats must not receive oral steroids for 2 weeks or injectable steroids for 6 weeks prior to testing; these drugs will interfere with the test results.
Cats are not likely to be born with food allergies. More commonly, they develop allergies to food products they have eaten for a long time. The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey. Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress. We recommend testing for food allergy 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 done with a special hypoallergenic diet. Because it takes at least 8 weeks for all other food products to get out of the system, the cat must eat the special diet exclusively for 8-12 weeks (or more). If 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. We cannot overemphasize this. If any type of table food, treats or vitamins are given, these must be discontinued during the testing period.
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 and antigen preparation are occurring.