INHALANT ALLERGY
What are allergies, and how do they affect 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.
What are the several types of allergies?
There are five common types of allergies in the dog: contact, flea, food,
bacterial, and inhalant. Each of these has some common occurrence in the dog,
and each also has some features unique to the particular type of allergy.
What is inhalant allergy?
The most common type of allergy is the inhalant type, also known as atopy.
Dogs may be allergic to all of the same inhaled allergens that affect humans.
These include tree pollens (cedar, ash, oak, etc.), grass and weed pollens,
molds, mildew, and the house dust mite. Many of these allergies occur seasonally,
such as the grass pollens. However, others are with us all the time, such as
molds, mildew, and house dust mites.
What happens when a dog inhales something to which it is allergic?
When humans inhale allergens, we express the allergy as respiratory problems.
These include coughing, sneezing, a runny nose, and watery eyes. The dog's reaction,
however, usually produces severe, generalized itching. It will chew, lick, or
scratch almost any area of the body, including the feet. Chewing and scratching
produce hair loss and inflamed areas of the skin. Saliva will stain light colored
hair, so dogs that lick excessively will have orange or reddish brown hair.
This is often seen on the feet. Although most people think that itching is related
to fleas, the most common cause of itching in the dog is inhalant allergy.
What is causing my dog's allergy?
That is not a question that can be answered easily. The itching produced by
grass pollen is the same as that produced by oak pollen allergy. In other words,
an individual animal can be allergic to many different things with the end result
(itching) being the same. In some cases, allergy testing can make specific determinations,
and sometimes an educated guess can be accurate if the itching corresponds with
the blooming season of certain plants. However, it is not always necessary to
know the specific allergen for treatment to be successful.
What is meant by "seasonal allergy" and "year round allergy"?
As the names imply, some dogs only have allergic reactions during specific
periods of the year. Others will itch year round. A year round allergy occurs
for two reasons. First, the allergen is present year round. This is the case
for indoor dogs that are allergic to house dust mites, also known as "house
dust". Second, the dog is allergic to so many things that at least one of those
allergens is present at all times.
My dog seemed to have a seasonal allergy for several years, and now it seems
year round. Is that possible?
Not only is that possible, it is almost expected. As the dog ages, it usually
becomes allergic to more and more things. After several years of acquiring new
allergies, it reaches the point that it is constantly exposed to something to
which it is allergic.
My dog seems to have a grass allergy. Does that mean it should not walk
on grass?
No. Dogs that are allergic to "grass", for example, are really allergic to
grass pollen. The blades of grass will cause no harm to your dog. Some grasses
are more allergenic than others, depending on the amount of pollen they release
into the air. Keeping it mowed so it does not pollinate seems logical, but your
neighbors must do the same because the pollen is airborne. The same principle
applies to trees. Dogs are not allergic to the wood of a certain tree, only
to its pollen.
How is inhalant allergy treated?
Treatment depends largely on the length of the dog's allergy season and involves
four approaches:
1. Anti-inflammatory drugs. Anti-inflammatory therapy will dramatically
block the allergic reaction in most cases. Corticosteroids ("cortisone")
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 antihistamines. When the three of them are
combined, most allergic dogs are significantly improved. This is a nonspecific
approach which does not treat the allergy, only the result 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. Some of the hypoallergenic
shampoos incorporate fatty acids; these may be absorbed through the skin and
offer a localized anti-inflammatory action. The role of the fatty acids in allergy
treatment is an area of active research interest in veterinary medicine.
3. Hyposensitization. The third major form of allergy treatment is
hyposensitization with specific antigen injections . Once testing identifies
the specific allergens, 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.
4. Antibiotics. Dogs that damage their skin by licking, chewing and
scratching are quite susceptible to bacterial infections in the skin. If this
occurs, antibiotics should be given until the infection is controlled. The skin
infection itself can be quite irritating and cause a dog to itch even more.
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:
(a) Cost: This is the most expensive form of treatment.
(b) Age of Patient: Because many dogs develop additional allergies as
they get older, young dogs may need to be retested 1-3 years later.
(c) Success Rate: About 50% of dogs will have an excellent response, about
25% get partial to good response, and the remaining 25% get little or no response.
The same statistics are true for people undergoing hyposensitization
(d) Food Allergies: Although tests for food allergy are available, the reliability
of these tests is so low that it is not recommended at this time. A food trial
remains the best diagnostic test for food allergy.
(e) Time of Response: The time until apparent response may be 2-5 months,
or longer.
(f) 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.
My dog has fleas. Are these responsible for the itching?
A dog with inhalant allergy will itch even if fleas are not present. However,
if your dog has fleas, the itching will increase. Although getting rid of all
of your dog's fleas will not stop the itching, it will make it much easier to
control the itching successfully.
My dog has a terrible odor. Is that related?
There are two possible causes of odor associated with inhalant allergy. These
dogs are very prone to ear infections because the ear canal is an extension
of the skin. When it becomes inflamed, it is easily infected and this will smell
it is likely to have seborrhea.
Sebum is the oily material normally produced in the skin. When a dog scratches,
sebum production increases dramatically. This produces a musty odor A bath will
remove the odor, but it is gone for only a few hours. The key to controlling
seborrhea. is to stop the itching and scratching. In addition the sebum is a
good medium in which bacteria can grow. This again results in an unpleasant
smell.
Is there another disease that can be part of my dog's problem?
Yes. Hypothyroidism is a disease in which the thyroid gland does not produce
enough thyroid hormone. This has many effects on the body because it controls
the rate of metabolism. Hyporthyroid dogs frequently have abnormalities of the
skin and haircoat. Skin infections (which themselves may increase itching) are
common with this hormonal disorder and may aggravate allergic conditions.
How is hypothyroidism diagnosed and treated?
A simple blood test will make the diagnosis in most dogs. However, with dogs,
the thyroid value may be questionable and further testing of the thyroid gland
is necessary to confirm a diagnosis. Sometimes, illness will cause a dog to
have low thyroid values when hypothyroidism is not really present.
Hypothyroidism can be treated with thyroid hormone replacement tablets. Without
treatment for this disease, treatment for inhalant allergy is more difficult.
The itching did not stop as expected. What does that mean?
There are two areas in which there will be disappointing results.
1. The first is when tablets are given and the response is poor. A few dogs
will respond better to injectable steroids than to the oral form. Fortunately,
this only occurs about 5% of the time. However, successful management of itching
in those dogs will require periodic injections of steroids, if the itching cannot
be controlled with other drugs or other forms of treatment.
2. The other problem is when there is a total failure to respond to injectable
or oral steroids or the response to an injection is short-lived, lasting only
a few days instead of a few weeks. This can occur because if the dose is too
low; however, it may also mean that the dog has food allergy. Food allergy causes
itching and scratching identical to inhalant allergy, but it responds very poorly
to steroids. Food allergy is diagnosed with a food trial using a hypoallergenic
diet.
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