Third Street
Veterinary Hospital, PC
McMinnville, Oregon 97128
Office phone: (503) 472-9418
Allergy in
Dogs
One
of the most common conditions affecting dogs is allergy. In the allergic state, the dog's immune
system "overreacts" to foreign substances (allergens or antigens) to
which it is exposed. These
overreactions are manifested in three ways.
The most common is itching of the skin, either localized (one area) or
generalized (all over the dog). 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 Allergies
There
are five known types of allergies in the dog: contact, flea, food, bacterial,
and inhalant. Each of these has some
common expressions in dogs, and each has some unique features.
Contact Allergy
Contact
allergy is the least common of the five types of allergy. They result in a local reaction of the
skin. Examples of contact allergy
include reactions to flea collars or to types of bedding, such as wool. If the dog 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 dogs. A normal dog
experiences only minor irritation in response to flea bites, often without any
itching. On the other hand, the flea
allergic dog 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 dog 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).
The
most important treatment for flea allergy is to get the dog 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,
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, dogs are more
resistant to the side effects of steroids than humans, so much of what you know
about the side effects in people do not apply to dogs. If a secondary bacterial infection occurs,
appropriate antibiotics must be used.
Bacterial Allergy
Staphylococcus (Staph) is a bacterium found on normal dog skin. If the skin is normal and the dog's immune
system is normal, Staph causes no
problems to its host. However, some
dogs develop an allergy to this bacterium.
When this happens, the dog develops areas of hair loss that look much
like ringworm. They are often round and
1/2 to 2 inches in diameter. These same
lesions develop in true Staph
infection; they are easily treated with certain antibiotics, but the Staph-allergic dog has recurrent "Staph infections." The lesions will usually clear with
appropriate antibiotics but return as soon as antibiotics are
discontinued. After a while, some dogs
become resistant to antibiotic treatment.
Treatment
of Staph allergy involves antibiotics
to control the immediate problem and desensitization with Staph antigen for long-term relief.
Inhalant Allergy
The
most common type of allergy is the inhalant type, or atopy. Dogs 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), 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 dog's reaction, however, usually
produces severe, generalized itching.
In fact, the most common cause of itching in the dog is inhalant allergy.
Most
dogs that have inhalant allergy react 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 dog may itch
constantly.
Treatment
depends largely on the length of the dog's allergy season. It involves three approaches:
1.
Anti-inflammatory. Anti-inflammatory
therapy will dramatically block the allergic reaction in most cases. Steroids may be given orally or by
injection, depending on the circumstances.
If steroids are appropriate for your dog, you will be instructed in
their proper use. Antihistamines can be
of value in treating the allergic dog when they are combined with
steroids. In some dogs, antihistamines
can significantly decrease the amount of steroid needed to provide relief. Fatty acid supplementation can also be
implemented with steroids and antihistamine.
When the three of them are combined, most allergic dogs are
significantly improved. This is a
non-specific approach, which does not treat the allergy, only the complications
of the allergic state (itching).
2.
Shampoo therapy. Many dogs are helped
considerably by frequent bathing with 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 dog but can be tried.
3.
Hyposensitization. The third major form
of allergy treatment is hyposensitization with specific antigen injections (or
"allergy shots"). Once the
specific sources of allergy are identified, very small amounts of the antigen
are injected weekly. The purpose of
this therapy is 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 hyposensitization appears to help the
dog, injections will continue for several years. For most dogs, a realistic goal is for the itching to be
significantly reduced in severity; in some dogs, itching may completely
resolve. Generally, steroids are only
used on a brief and intermittent basis.
This therapeutic approach is recommended for the middle-aged or older
dog that has year round itching caused by inhalant allergy. This approach is not successful with food
allergy.
Although
hyposensitization is the ideal way to treat inhalant allergy, it does have some
drawbacks and may not be the best choice in certain circumstances and for these
reasons:
1. Cost: This is the most expensive form of
treatment.
2. Age of Patient: Because many dogs develop
additional allergies as they get older, young dogs may need to be retested 1-3
years later.
3. Success Rate: About 50% of dogs 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: Dogs 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.
Food Allergy
Dogs
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 dog has a poor
response to steroids, or when a very young dog 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 dog 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 types of
table food, treats or vitamins are given, these must be discontinued during the
testing period. There may be problems
with certain types of chewable heartworm preventative, as well. Your veterinarian will discuss this with
you.
Because
dogs 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 is occurring.
INSTRUCTIONS: Those instructions, which
are specific for your dog, have been checked:
___
1) An injection of steroids was
given. Relief should be apparent within
12-24 hours. If not, please call. The dog should feel better and itch less for
about one month. If an increase in
water consumption or urination occurs, please report this to us for future
reference. These side effects are
common with steroid administration and will go away in a few days without
treatment. Return for further
evaluation when the first signs of itching recur.
___
2) Begin oral steroids when the first
signs of itching return. Give ____
tablets every other morning. Adjust the
dosage upward or downward to the lowest effective dose, with a maximum dose of
__________ permitted. Stop giving the medication
every 4-6 months to see if there are times of the year when therapy is not
needed. Report any increase in water
consumption to us at once.
___
3) We have dispensed oral steroid
tablets. Prednisone is most commonly
used. The specific drug being dispensed
for your dog is labeled on the bottle.
Give ____ of the ____ mg tablets every other day for 3 doses (6 days),
then ____ tablets every other day for 3 more doses (6 more days). Continue this downward progression
(___________________) until the first signs of itching recur. At that time, go back to the next higher
level and report that level to us (so we can be sure it is a safe level). Stop giving the tablets every 4-6 months to
see if there are periods of the year when they are not necessary. When itching returns, begin immediately at
the maintenance dose. If that does not
stop the itching, increase the dosage slightly (to a maximum of ___ tablets)
for a few doses, then return to the lower dose. Report any increase in water consumption to us at once. (This may occur at the initial dose but
should stop on the maintenance dose.)
___
4) Your dog is to exclusively eat a
hypoallergenic diet. If it will not do
so readily, mix it 25:75 with the current diet for several days, then gradually
increase the special diet to 100%. If
this does not work, contact us for an alternative plan. Discontinue any chewable treats or vitamins,
including heartworm preventatives.
(There is a heartworm prevention product available in a non-chewable
tablet than should be substituted.)
Table food is not allowed. Offer
only distilled water to drink, if that is possible.
___
5) Your dog has a flea allergy or has
enough fleas to make the other allergy problem worse. Flea control is very important and should include treating the
dog and its environment. Bear in mind
that flea allergies often accompany other types of allergies, especially
inhalant allergy.
___
6) Your dog has a bacterial skin
infection secondary to allergy. The
following are recommended:
a)
Antibiotics are to be used for the next _____ days. If the infection is not gone by the time the
medication is completed, call for a refill or for a change in
medication.
b)
The medicated shampoo,_____________________, is to be used every _____
days. Allow the
shampoo to stay in the haircoat for a few minutes before thoroughly
rinsing the dog.
c)
The topical medication,_____________________, is to be used ______ times daily
for __________
days.
___
7) Your dog has a Staph allergy. The following are recommended:
a)
Antibiotics are to be used for the next _____ days.
b)
The medicated shampoo, ______________, is to be used every _____ days.
c)
Staph antigen injections will be
given daily for 5 consecutive days beginning __________ then once
weekly for 3 weeks. Thereafter,
weekly injections will be given by you, depending on need and
response.