Dog - Atopy

What are allergies and how do they affect dogs?

Allergic reactions are very common in dogs and are fully described in a separate handout on Allergies and Hypersensitivities.

Is there more than one type of allergy?

Yes, there are at least five common types of allergy in the dog:

• flea
• food
• contact
• atopy
• bacterial hypersensitivity

I have been told that my dog is atopic. Is this the same as inhalant allergy?

Yes and no. After flea allergy dermatitis (FAD) which is also known as flea hypersensitivity, atopy is the most common type of allergy in the dog. It was once thought to be caused by an inhaled allergen (substance which causes an allergic reaction) to which the dog’s immune system overreacts and so the terms are often used interchangeably. The cause of atopy is still unknown, it is probably due to contact of the allergic particles directly on the skin or mucous membranes (eg gums).

What sort of things cause it?

There are a whole variety of allergens which can produce atopy. These are very similar to some of the things causing hay fever or asthma in humans.

When the affected individual is exposed to dust mites, pollens or moulds, for example, an allergic response can occur.

What happens to the dog when this occurs?

Atopy in the dog is usually seen as severe generalised itching. The dog chews, licks and scratches almost every area of the body, including the feet. Saliva will stain light coloured hairs so that dogs that lick their feet excessively will have orange or reddish brown hair. The dog may also scratch and rub the face, particularly around the eyes and ears. The axillae (armpits), groin and the inside of the thighs may also be affected.

In humans these environmental allergens are usually inhaled and cause respiratory (breathing) problems, hay fever or asthma. Occasionally in the dog there will also be respiratory signs, usually in addition to the pruritus (itching).

How do you diagnose this condition?

Diagnosis is not easy. It is based on the presence of the signs discussed above, ruling out other causes of pruritus, e.g. fleas. The itching produced by grass pollen is similar to that produced by house dust mites. Therefore your dog may be allergic to several different things with the same end result, i.e. continuous scratching.

Careful history taking will narrow down the causes. For example, if it only occurs in the spring when certain pollen is prevalent this narrows the field of investigation.

I understand my dog will have to have skin tests to make a diagnosis. Is this true?

In around 80% of cases diagnosis can be confirmed by intradermal allergy testing. This is a complicated procedure and you may have to be referred to a veterinary dermatologist. Once the diagnosis has been made it is often possible to desensitise the dog. This involves the use of specific antigen injections (injections containing the specific protein/s that the pet is allergic to) which are made up according to the results of the skin tests. The theory is that the controlled injections of increasing amounts of the allergen reprogramme the dog’s immune system to reduce the response. For most dogs this can result in significantly reduced severity of itching and in some it may be completely curative.

If this does not work, are there other forms of treatment that can be used?

Yes, frequently hyposensitisation (as described above) is one of the last lines of treatment. Anti-inflammatory drugs including corticosteroids and antihistamines will often bring the acute phase under control. In addition, the use of certain fatty acids, e.g. evening primrose oil or fish oil does help. However this is a non-specific approach that doesn’t treat the allergy, only the result, i.e. the pruritus.

My friend’s dog has an atopy and seems to be helped by regular shampooing. Can I try this?

Many dogs are helped considerably by frequent bathing with special hypo-allergenic shampoos. It has been demonstrated that some allergens are absorbed through the skin and the theory is that frequent bathing reduces the amount of antigen that the patient is exposed to by this route.

Some of the special shampoos incorporate fatty acids which may also be absorbed through the skin and so help to reduce itching, i.e. act in the same way as capsules of evening primrose oil.

Antibiotics may also help particularly if the dog has scratched to such an extent that there is a secondary bacterial infection.

My dog only seems to itch in the spring and I have been told she has a seasonal allergy. What does this mean?

Probably she is allergic to a particular type of pollen that is only produced during a specific period of the year, e.g. in spring. Some atopic dogs will have an all year problem, in other words it is not seasonal. This means the allergen is present throughout the year. With dogs the cause is often house dust mites.

Another explanation may be that the dog has developed separate hypersensitivities to so many different allergens that at least one is present at any one time.

My dog has a grass allergy each year. Does that mean it should not walk on grass?

No. So-called grass allergies are more correctly grass pollen allergies. Closely cut grass with no seeding heads will not cause problems. However, do remember the pollen is airborne and cutting your own grass will have little effect if you live next door to a flowering meadow.

Are there any other conditions connected with atopy that I should know about?

Yes. Some dogs with atopy often are hypothyroid, in other words the thyroid gland is not producing sufficient thyroid hormone. This in turn affects the skin and may aggravate allergic conditions.

Blood tests are available to check this.

When my dog is badly affected with her atopy she seems to have a terrible smell.

When dogs scratch, sebum which is an oily material produced by the skin, often increases dramatically and is responsible for a musty odour. Once the itching and scratching has been controlled usually the seborrhoea (the increased sebum) also clears up.

Another cause can be bacterial or fungal (yeast) infection. This is due to the damage caused to the dog’s skin. The ear canals are extensions of the skin. These become badly infected and can be overlooked when the more obvious skin lesions are being treated.