What are allergies and
how do they affect cats?
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.
Are there several
types of allergies?
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
Allergy
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 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 require some detective
work.
Flea
Allergy
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. However, the new topically applied monthly flea products may kill
fleas before they have a chance to bite your cat. 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.
Inhalant
Allergy
The most common type of allergy is the
inhalant type. 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 "hayfever." 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 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.
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 retested 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 two weeks or injectable steroids for six weeks prior to
testing; these drugs will interfere with the test results.
Food Allergy
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 eight 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.
