Next
to fleas, allergies are the most common cause of itching and scratching
in your pet. Fleas are dealt with in another article in this series.
Once you are certain that no fleas are present, it is likely that
allergies are the cause of your pet’s scratching. In human
beings, allergies are often expressed through the respiratory
system. If you yourself have allergies, you are likely to have
a stuffy nose, sneezing and watery eyes. This is because the histamines
that humans produce are released primarily in the membranes of
the respiratory system and eyes. In dogs, histamines are released
primarily in the skin.
How
Allergies Occur:
All chronic allergies are based on the body recognizing protein
substances as foreign and trying to rid itself of them. Mold,
dander, bacteria, pollen, flea saliva along with a host of other
substances are allergens made up of proteins foreign to the body.
We will talk about pollen allergies for an example because they
are so common. In this case pollen is called an allergen –
something the body recognizes as foreign. When a pet’s immune
system is exposed to pollen for the first time, some pollen attaches
to the linings of the nose and lungs . The body’s immune
system recognizes that pollen is not supposed to be there and,
in response, produces antibodies against the pollen called immunoglobulins
of the E class (IgE) and G class (allergen-specific IgG). This
process is called sensitization. The IgE attaches to cells in
the body called mast cells. These cells then leak and release
histamines, bradykinins, and proteolytic enzymes, which cause
the symptoms of allergy. In people large numbers of mast cells
are located in the respiratory system. That is why our allergies
usually have respiratory system symptoms. In dogs and cats, more
mast cells are present in the skin. That is why dog and cat allergies
usually cause signs associated with the skin and ears such as
itching, hives and inflammation. This allergic disease is called
atopy. Only 15% of pollen allergies in dogs and cats cause respiratory
system signs, such as nasal stuffiness and sneezing.
Types of Allergies:
There are two types of allergies that cause dogs and cats to itch.
Because susceptibility to allergies is inherited, it is quite
common for pets to have both types.
Canine Inhalant Atopy
This is the type of allergy for which we used pollen as an example.
It is the most common form of allergy in dogs and cats, making
up over ninety percent of the cases I see. About nine percent
of the canine population has this disease. Certain breeds are
more susceptible to than others. Among the most susceptible are
Shar-peis, Fox Terriers, Golden Retrievers, West Highland White
Terriers, Scottish Terriers, Shih Tzus, Dalmatians, Lhasa Apsos,
Boston Terriers and Labrador Retrievers. Cats of any breed can
be affected. Dogs usually show their first signs of itching between
10 months and 4 years. If a dog does not have this condition by
the time it is four years of age it is unlikely that it will ever
have atopic skin disease. The disease often begins as a seasonal
problem but after a number of years (or moving to a southern climate)
the itching occurs year round. Some common allergens are flea
saliva, tree, grass and shrub pollens, house dust, mold, dust
mites, and feathers.
Flea saliva allergy is a special form of Atopy. Fleas survive
by sucking blood from your pets. To get this blood they drill
their mouthparts into the dog or cat’s skin and inject special
anticoagulant saliva into the site to keep blood flowing while
they engorge. This saliva is highly irritating to some dogs and
cats. These pets do not only itch at the site of the flea bites,
they itch all over. The pads of their feet are often itchy, puffy
and inflamed. Areas between the toe pads as well as the ears often
become infected with bacteria due to the pets constant licking
and chewing. Because of the availability of excellent flea-control
products such as Advantage and Frontline, I see less flea allergy
than I used to.
Food
Allergies:
Food allergy cases are less than fifteen percent as common as
canine atopy but occur with about the same frequency as atopy
in cats. The itching food allergies produce is constant throughout
the year. Cocker Spaniels, West Highland White Terriers and Labrador
Retrievers are particularly susceptible to food allergies. However,
the majority of these breeds that have itching problems do not
have food allergies. Dogs and cats can be any age older that a
few months when signs first begin. Some common food allergies
in dogs are to beef and pork, fish, dairy, eggs, corn, soy, wheat
and preservatives and dyes in food and treats. But almost any
diet ingredient can be involved. The most common allergens in
cats are to fish, beef and chicken.
Symptoms:
Canine Atopy and food allergies are not visually distinguishable
because the signs of both diseases are the same. The most common
sign of the conditions is constant itching, scratching and licking.
Dogs will often rub on objects. The degree of discomfort the pet
undergoes is partly dependent on its temperament. High strung
breeds and very active pets do severe damage to their skin. The
face, lumbar area at the base of the tail (particularly if fleas
are the cause) ears and paws show the most damage. In severe cases
the skin of the whole body is inflamed and covered in crusts while
the hair coat is thin and broken. In mild cases the pets only
lick these areas, discoloring light hair coats with salivary stain.
When fleas are the problem, small pepper-like granules are present
over the neck or in the dorsolumbar area. These specks of digested
blood or flea dirt will “bleed” a rust-colored trail
if moved to white tissue paper and wetted with water.
As the dog or cat scratches, it destroys the outer waxy layer
of the skin. This allows bacteria and mold to enter the skin and
causes a musty, oily skin condition called seborrhea. Because
ears are covered with skin, ear canal redness, odor and inflammation
are common in canine atopy. Sometimes ear problems are the only
sign present. When this is the case, we treat the ears with specific
antibiotic, antifungal, corticosteroid preparations but must treat
the whole dog with medications as well.
Cats develop a condition called milliary dermatitis in which the
surface of the back and scruff of the neck are covered with bumps
and scabs. Allergic cats sometimes develop another condition called
eosinophilic granuloma complex in which ulcers form on the lips,
tongue and surface of the body. After months and years of scratching,
the skin of the inner thighs and flank often becomes thickened
and blackish. This condition is called acanthosis nigricans.
Damaged skin due to the pets scratching often leads to superficial
staphylococcus bacterial infections (pyoderma) and infection with
the yeast, Malassezia. Mild bacterial conjunctivitis or eye infections
with greenish matter at the inner corner of the eye are common.
It is important to realize that although a bacterial or fungus
condition is present and may need treatment, the root of the problem
is allergic dermatitis. In very severe cases of skin allergy,
the superficial lymph nodes of the body enlarge due to secondary
skin infections.
Diagnosis
of Allergic Skin Problems:
The clinical diagnosis of allergic dermatitis is one of exclusion
of other causes of skin disease. I usually do skin scrapings when
pets with this condition are presented to me for the first time.
Through skin scrapings, I try to rule out mange as a cause of
the pet’s problems and locate bacteria and fungi. If I cannot
rule out mange, if the dog’s history suggests it might be
mange, or other members of the household are itching, I may put
the pet on a test dose of a safe anti mange medicine called ivermectin.
I next try to rule out fleas as the source of the problem. Some
dogs are so good at grooming that no fleas remain on them when
they are examined. Even when I cannot locate fleas on the pet
I can often locate flea dirt. In some of these pets the presence
of tapeworms is the only indication of fleas or I may find fleas
on another household pet, which does not have skin problems.
There
are other signs that the problem may be allergic. Typically atopy
occurs in dogs between one and three years of age. This makes the
diagnosis of allergies in puppies and older dogs less likely. The
first two or three years that the condition exists it is often seasonal
occurring only in the spring and summer months. Flea-related allergies
tend to subside after the first few freezes of the winter. Golden
retrievers and arctic breeds with thick oily hair are susceptible
to a special form of dermatitis called hot spots or acute pyotraumatic
dermatitis. In these cases the dogs suddenly become extremely itchy
over a small area. They are so troubled that they pull out the fur
of this area and infect it through chewing in a matter of hours.
The itching sensation departs rapidly thereafter -with or without
treatment. It is not known if they represent a true form of allergy.
Another form of the disease is called acral lick dermatitis. In
these cases a small area of skin itches over an extended period.
Licking leads to a well-defined small area of raw skin, scarring
and bacterial infection.
I
try to learn if the parents of the dog or cat or its brothers and
sisters also have itchy skin disease. Canine atopy as well as food
allergies runs in families.
In diagnosing food allergies I look for uniform involvement of the
skin over the entire body. I rarely find that diarrhea accompanies
food allergies. Often the best way to rule out food allergies is
to put the pet on a sixty to ninety day trial eating a hypoallergenic
diet exclusively. Many hypoallergenic diets are available. Until
recently these diets relied on novel protein sources such as lamb,
venison duck or fish. The problem is that with time, pets eventually
became allergic to these diets too. Now two brands of hypoallergenic
diets are available that use heat and hydrolysis to break food proteins
into a size too small to cause allergies (less than 10,000 daltons).
The biggest problem with these diets is that some pets won’t
eat them.
I will usually examine pets with skin disease in a darkened room
with an ultraviolet lamp. Hairs that glow are diagnostic for ringworm.
Ringworm is almost never itchy and glowing hairs are not found in
cases of allergic skin disease.
Il often encounter Malassezia yeast in skin scrapings of dogs with
itchy skin. This fungus is a normal inhabits the skin of dogs. It
only becomes a problem when the pet has an underlying problem such
as allergic skin disease. Antifungal shampoos are quite helpful
in controlling it.
Allergy
Tests
Rast Test (In-vitro (laboratory) test, performed
on your pet's blood)
As
in humans, allergy testing can be helpful in diagnosing allergic
skin disease. Two forms of allergy testing are available. The easiest
and most commonly performed test in animal hospitals is called the
RAST test. This test, which is performed on a blood sample from
your pet, stands for radioallergosorbent test. In the test, the
presence of IgE antibodies to specific antigens is determined by
a central laboratory. Pets must not have had corticosteroids or
antihistamines administered for thirty days prior to testing. The
problem with this test is its high number of false positives. If
the test determines that a pet is not allergic to an antigen - that
is probably correct. But positive reactions often turn out to be
wrong. If the RAST test is used, the central laboratory will prepare
an antigen extract, which can be injected into the pet’s skin
periodically to decrease the effects of allergies. The most current
research indicates that this test extremely inaccurate
in pets and humans.
Go with skin tests if at all possible.
Skin
Test
A more reliable test is an intradermal skin test. Before the test
is administered, the pet is taken off all corticosteroid, tranquilizing
or antihistamine medications for 30-60 days. In this test, small
amounts of various allergens are injected into the skin. The entire
side of the pet must be shaven to perform this test. Then the injection
sites are monitored over an hour’s period to judge the degree
of redness and swelling at each site. A list of offending antigens
is used to prepare an allergen extract, which is injected periodically
into the pet. With time and success, these injections lessen the
pet’s allergies to these allergens. Because a high degree
of skill is necessary in giving and interpreting the results of
this test, veterinary dermatologists usually perform it.
Occasionally, when I am uncertain if the problem is a routine case
of allergy, I will take a biopsy specimen of the skin involved and
send it to a pathologist for evaluation and diagnosis. This can
rule out the presence of other disease such as lupus. Blood tests
may detect elevated levels of eosinophiles, which occasionally also
occur in allergic skin disease.
Treatment
of Allergic Skin Disease:
It is next to impossible to avoid all the environmental allergens
that plague allergy-prone dogs and cats. The exceptions are pets
that are chiefly bothered by fleas. I enforce strict flea control
– even if I am uncertain that fleas are present. Many dogs
and cats are cured by this simple task alone.
Approximately one in twenty of my clients elect to undergo skin
testing and desensitization of their pets. This figure differs from
practice to practice. The procedure takes a bit over a year to show
results. Dermatologists argue for the procedure pointing out, correctly
so, that even if desensitization does not cure the pets, it may
lower the dose of corticosteroids they require later in the disease.
Skin testing also identifies the allergens and perhaps some of them
can be avoided or eliminated from the pet’s environment. The
procedure is extensive, expensive, and requires a life-long commitment
to frequent injections. Most owners learn to give these injections
themselves.
Medicines of the cortisone class are effective and dramatic in controlling
the symptoms of allergic skin disease. The problem is that this
class of drugs has substantial and serious side effects when given
in high doses or over extended periods of time. My challenge is
to treat these pets as long as I can without the use of these steroids.
To do so, I use medications that are effective but less dramatically
so.
Medicated
Shampoos.
Medicated shampoos are quite soothing to inflamed skin and lessen
itching. I begin using clear tar preparations such as lye tar shampoos.
If these are not adequate, I dispense selenium sulfide or benzyl
peroxide shampoos. Benzyl peroxide is quite effective in eliminating
secondary bacterial infections in these cases. Some pets are helped
by oatmeal and antihistamine shampoos. With all these products,
the skin should first be cleansed with soapless soaps and then the
medicated product massaged in and allowed a long contact period
with the skin – the longer the better. Weekly shampooing along
with flea control is often sufficient for a number of years. Some
pets cannot tolerate weekly bathing as it dries out their skin too
much. Use of a skin conditioning rinse helps in some cases. Also,
use temperate, not hot water, when you bath your pets.
Antihistamines
and tranquilizers
Antihistamines block the release of histamines by mast cells. They
are quite helpful to some pets. Unfortunately, the effects are not
as dramatic as in humans. Ciproheptadine given twice a day, hydroxyzine
or even OTC Chlorpheniramine maleate are effective in lessening
symptoms in some dogs and cats. Many antihistamines have a calming
effect in dogs. I have had cat owners discontinue their use because
they did not like personality changes in their cats while on these
medications. Some antihistamines can be applied in shampoo form.
Some dogs do well when given mild tranquilizers such as acepromazine
at 0.25mg/ pound.
Corticosteroids
.
Many owners are worried when we suggest that their pets receive
measured doses of corticosteroids to treat stubborn allergy cases.
They should not be. These drugs have nearly miraculous powers in
both human and animal medicine. They just should not be over used.
Some drugs of the cortisone class are prednisolone, prednisone,
triamcinolone, dexamethasone, beclomethasone, and betamethasone.
Often I use so little of these drugs that a bit of itching persists
but at a tolerable level. I usually give prednisolone or prednisone
two or three times a week. At a low dose I do not encounter noticeable
side effects. There will often be a point, many years into the disease,
when higher cortisone doses are required. Combining topical medications,
antihistamines, desensitization and cortisone let us keep the cortisone
dose as low as possible. I do not feel that I have ever used cortisone
to an extent that an allergic pets life was shortened although some
have suffered weight gain. I do know that the use of these drugs
has greatly improved the quality of many pets’ lives. Whenever
possible, the use of long acting corticosteroids such as methylprednisolone
acetate should be limited to a single yearly injection or oral forms
of corticosteroids used instead. You may notice that your pet drinks
more and urinates more on these medications. If they are over used
a disease called Cushings Syndrome or hyperadrenocorticism can result
(see article on that subject).
Antibiotics
.
Dogs that are presented to me with severe bacterial skin infections
subsequent to self- trauma (scratching) need a two-week course of
antibiotics to clear up the infection. I like to use a broad-spectrum
antibiotic such as one of the fluroquinolones (Batryl) or a potentiated
cephalosporin such as Clavamox (Augmentin). I begin antihistamines
and medicated shampoos in these cases immediately but I delay any
corticosteroids until the skin has healed. If yeasts are an important
component of the problem I treat them with ketaconazole shampoos.
Food Supplements
There are a very large number of “neutraceutical” products
marketed for allergic skin disease. Many of them have never been
scientifically tested. The best that can be said of many of these
products is that they can do no harm. When I recommend these products,
I usually suggest one that combines omega-3 and omega-6 fatty acids.
Many of these products also contain zinc. Some clients find them
beneficial.
Your
Pet’s Future:
Allergic dermatitis is a life long condition. Unless the problem
is solely fleas there are no cures. Luckily it is not a life threatening
or a life shortening condition and it can be managed with a minimum
of inconvenience. Often, there will be periods of a year or more
when the disease is not as severe and needs less or no medications.
When a family moves the disease is often left behind. Unfortunately
not too much time passes at their new location before the pet becomes
allergic to new allergens. Because this is an inherited trait, dogs
with this disease should never be bred. The fact that so many dogs
suffer from allergic skin disease shows that many AKC and novice
breeders disregard this.
