COMMON SKIN
DISEASES OF THE DOG ALLERGIES
Dog Owners and Breeders Symposium
University of Florida
College of Veterinary Medicine
July 29, 2000
Gail Kunkle, D.V.M., Dip A.C.V.D.
Professor, SACS, CVM, UF |
INTRODUCTION
Allergic diseases of the dog most often involve
the skin rather than the respiratory system as
is seen in man. Allergies are caused by a
complex chain of events in the immune system,
and even today, we do not understand all of the
trigger factors. Genetics, as in man, appear to
play a role in certain types of allergies. The
immune system in allergies over-reacts to
exposure to allergens in the environment. These
allergens can be proteins from pollens, plants,
insects, or foods.
TYPES OF ALLERGIES
It is perhaps easiest to consider that an
allergic animal may have one or more types of
allergies and that, in the broad sense, there
are four different types:
1. Atopic dermatitis or Atopy
We used to believe that in atopy the allergens
were breathed into the respiratory system, such
as in hay fever in man. Now, there are many
veterinary dermatologists who believe that there
may be a combination of allergen exposure both
by inhalation and by contact of the pollens or
dust mites with the skin. This is a common
problem in dogs, especially certain breeds like
terriers and retrievers. We will discuss this in
more depth.
2. Flea allergy dermatitis
This is common and occurs when a dog is
exquisitely sensitive to the bite of one flea.
Dogs with flea allergy usually chew the back
half of their bodies often almost hairless. They
have a higher incidence of hot spots and usually
it is very difficult to find fleas on these pets
because, they immediately ingest the flea that
bites them because they are so sensitive to
their bite. We now have many good medical
management techniques for canine flea allergy.
It is important to remember that a high
percentage of dogs with atopy also have flea
allergy.
3. Food allergy and/or food intolerance
We do not know what percentage of dogs truly
have immune reactions to foods. There are other
types of adverse reactions to foods that are not
allergy but still result in skin signs. We do
not have a good way to separate these and at
this point, it is just
important to identify which dogs have adverse
food reactions and to get them on the right
diets to prevent signs. Dogs with adverse food
reactions may have dermatologic signs or
gastrointestinal signs or both. There is no good
diagnostic test for this condition. No blood or
skin test is especially helpful. The best test
is to place the dog on a very special
hypoallergenic diet and watch for improvement.
The numbers of cases are likely not high, and
thus we will not discuss this type of allergy in
detail.
4. Contact allergy
The best way to understand this is to think
about poison ivy in people. Poison ivy is a type
of allergy to the plant and most of the human
population becomes allergic to poison ivy if
they are exposed in their lifetime. It is the
result of a different kind of immune reaction.
Another example of human contact allergy is that
which occurs to metals, and the reason that many
people cannot wear certain kinds of jewelry
without getting a rash. For a long time,
dermatologist believed that contact allergy was
rare in the dog because they were covered with
hair and protected. We know that dogs do not get
poison ivy, even though they can transfer it
from their hair coat to the owners who then may
get it. However, dogs do have reactions to other
plants in their environments. Some of these can
be very troublesome to the pet.
MAJOR COMPLICATIONS OF ALLERGIES
In addition to the primary symptoms noted with
allergic diseases in the dog, often times the
signs are made worse by secondary infection.
There seems to be a strong association of
allergic skin disease in dogs with
predisposition to two types of skin infections.
These infections will often be recurrent and can
cause symptoms as bad or worse than the
allergies alone. It is imperative that the
veterinarian and owner work to sort out the
signs of these secondary infections and deal
with them as well as addressing the allergies.
1. Staphylococcal infections
These are among the most common infections seen
with allergies. These staphylococcal infections
are not contagious between dogs or between owner
and dog. Signs include pustules and rashes, hot
spots, spotty areas of hair loss and often
worsening itch. Common anatomic locations
include the belly or groin region, the dorsal
trunk and feet and ears. Before trying to treat
the allergy or better characterize it, it is
important to see how much of the clinical signs
are due to secondary bacterial infection. To
diagnose staphylococcal infection it is not
usually necessary to do a culture, but rather
some simple cytology from the skin (scraping,
tape prep or impression) and see if the animal
responds to oral antibiotics. Topical therapy
alone is not usually sufficient for treatment
and the duration of oral antibiotics must be a
minimum of three weeks before re-evaluation.
2. Yeast infections
These are also common secondarily to allergic
skin disease. They are especially prevalent in
the southeast where the high humidity and high
temperatures are optimum for yeast infections.
The yeast infections that affect dogs are not
the same as those that affect people and they
are not the result of chronic antibiotic
administration, like that which can occur in
man. Yeast likes to grow where the skin is
greasy and especially moist like areas which we
call intertiginous areas where the skin falls in
folds or rubs together. Therefore, yeast
infections occur most often in the neck fold,
the axilla, the area around the lips, the ears,
and between the toes. Yeast can cause severe
itch in allergic dogs, even when the infection
is not severe. Some dermatologist treat this
with topical therapy first and then if it does
not respond and can still be found on cytology,
they will use oral drugs like ketoconazole or
itraconazole. Many shampoos will kill yeast, but
the skin may become repopulated; hence the need
for two to three weeks of oral therapy to help
everyone to decide how much of the itch and
other signs in the dog are due to secondary
yeast infection.
3. Combination infections
When these occur, we may treat both or we may
treat the one that is present in highest
quantity first and then re-evaluate the patient.
TWO MAJOR CANINE ALLERGIES FOR DISCUSSION:
1. Atopy or Atopic Dermatitis
Clinical Signs and Patient Descriptions
Most cases of atopy begin when the dog is
between one and three years of age. This is
highly variable, but when we see itching in dogs
less than one year of age, we put other
possibilities higher on the list. There are
breeds that are predisposed, and this varies
throughout the country as it appears that
genetics play a role. The exact genetics are
unknown, and when an atopic dog is bred to an
atopic dog, not all of the puppies develop
allergy. There are many factors that likely
complicate the exact initiation and continuation
of allergy in all species. Some breeds that are
over-represented include the terriers, the
Chinese Shar-Pei, Retrievers, Bulldogs and other
brachiocephalic breeds. But remember that any
breed of dog can develop atopy, even mixed
breeds. The clinical signs are highly variable
but involve itching (pruritus). The itching may
be generalized or it may be especially common in
the axilla, the face, ears, and foot chewing.
Licking may be present as well as scratching and
self-trauma. There has been a long debate
amongst dermatologists as to whether there is a
primary eruption, like a rash, in this kind of
allergy or whether the rash is due to secondary
self-trauma or infection. So you will hear
dermatologists talk about the “itch that rashes”
or the “rash that itches”. Initially the signs
are responsive usually to corticosteroids, but
as the dog gets older and more drug therapy is
used, and as secondary infections occur,
steroids become less effective. At best they are
symptomatic treatment, and do not eliminate the
allergy.
Diagnosis of Atopy
Most initial diagnoses are made by the
appearance of the clinical signs. Further
identification of the substances to which the
dog is allergic (allergens) can be determined by
two methods of allergy testing. One is the
intradermal skin test in which many needles are
pricked very superficially into the skin and the
area examined 15 minutes later for hive-like
reactions. This is considered the Gold Standard
for diagnosis. An easier way, but argued by some
to be less accurate, to test for allergy is with
a serum (blood) test which is sent away for a
RAST or ELISA blood allergy testing. Then
therapy options can be considered. There are
some problems with the blood testing for
allergies. It is CRITICAL that the veterinarian
rule out other problems and be very certain of
the diagnosis of atopy before doing the blood
tests. They are positive in many normal dogs and
only mean that the dog has been exposed to the
antigen (allergen) and has developed circulating
antibodies against it. It does not mean that
these antibodies are causing the signs one sees.
Also, the levels of antibodies in the blood may
not be proportional to those in the skin, so a
blood test may not be as accurate. We also know
that blood testing does not seem to be an
effective test for food allergy.
Treatment of Atopy
There are many methods from avoidance (which is
almost impossible) to antihistamines, fatty
acids, topicals, corticosteroids, and
immunotherapy. Immunotherapy is when the owner
or veterinarian gives the dog shots of the
substances to which he is allergic. This is
similar to people taking allergy shots. This is
effective in approximately half of the cases of
well-characterized allergic disease. In the near
future, it is likely that there will be new ways
to alter the immune system in the management of
this condition.
2. Contact Allergy
Clinical Signs
Although for a long time, we considered this an
uncommon condition in the dog, we now know that
in the southeastern US, there are cases of
contact allergy that go undiagnosed. This is
partly because it can be very difficult to
diagnose. Most dogs have foot chewing,
especially the bottom of their feet, with
redness, and even ulcerations as a major
clinical sign. This is because they get
sensitized while walking on some substance. They
may also have problems around the rump, ventral
abdomen and many dogs transfer the allergen to
the region around the mouth as they chew their
feet. They then develop a rash there. This
disease does indeed have a rash as the primary
clinical sign and it usually affects the lightly
haired areas first, unless it is a reaction of a
shampoo or spray of some kind that is spread
over the animal.
One of the more common contact allergy reactions
we see in Florida is to plants which are from
the Commelinaceae family. These go by the name
of doveweed and dayflower and have little white
or purple flowers. They are commonly seen
growing intermixed in St. Augustine sod from sod
farms; hence we see it often from new suburban
development areas with professional landscaping.
It may require a diligent examination to find it
as it tends to grow under the wider leaves of
the grass. These two plants as well as the
Wandering Jew plant (Tradescantia) seem to
affect dogs like poison ivy affects man. These
plants do not cause problems in people, and
usually will not affect all of the dogs in the
household.
Diagnosis
This is one of the reasons that this condition
is uncommonly diagnosed. There is no easy test
for it. There are two major methods used to
prove contact allergy. One is to remove the dog
from the suspected allergen for two weeks. This
should be preceded by a hypoallergenic shampoo
to remove any residual contactant. This may mean
kenneling the dog for two weeks which results in
many other changes. The second method is what is
known as a patch test. This is easier to do even
in young children than in dogs. Patches with
suspect plants or chemicals are placed on
clipped skin and must be held in place for 48
hrs. This is the difficult part because dogs
chew or scratch the patches off and the skin of
the dog is so loose that the bandaged areas may
easily slide forward or backward or if they
really stick, an irritant reaction to the tape
may be noted. The sites are examined shortly
after patch removal and then again at 24 hrs.
but the dog cannot be allowed to traumatize the
region. For those of you who have had poison ivy
yourselves, you know how hard it is to keep from
scratching and a dog can’t understand this.
Treatment
The management of contact allergy is best done
by avoidance of the allergen, as with poison ivy
in people. Every time the dog comes in contact
with the substance, the reaction is likely to
worsen. There are steroids which are used in
severe cases to relieve the inflammation but
these are not good long term solutions. There
are some types of mechanical coverings which may
be helpful (booties, etc). Pre-exposure
treatment with the drug, pentoxifyline (Trental®)
can be helpful in some dogs if it is known that
they are going to an area where they will be
exposed. The most difficult part of managing
contact allergy is that it is a lifetime
commitment from the owners, as it is unlikely
the dog will “outgrow” the reaction or improve
over time. Some owners have resorted to making
concrete or rock kennels in their yards or even
using Astroturf if the problem is a grass or
weed. The common plants that cause this
reactivity in the dog are very difficult to
eliminate from your yard, and in some cases,
clients have literally killed the grass and the
weed has thrived.
SUMMARY
I have only briefly discussed allergic disease
in the dog, secondary complications and
elaborated on two of the four kinds of allergic
diseases that we see. Although many new
antihistamines have been developed for allergy
treatment in man, especially for hay fever
signs, it appears that the chemical mediators
that cause the symptoms we see in the dog are
not histamines, and this explains why
antihistamines are not that effective. It is
exciting to see that there are many
investigators of human allergy looking at other
ways to alter the allergic response in man, not
just with antihistamines. We can be hopeful that
one of these means may be beneficial in the
future management of canine allergic diseases.
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