Allergies

CONTACT ALLERGIES

I have been told that my dog has a contact allergy. Is this common?

Because dogs are covered with hair, contact allergy is a rare disorder compared with people where it is relatively common.

My dog keeps licking himself underneath, particularly around his private parts which are inflamed and sore. Is this likely to be due to his contact allergy?

Symptoms usually involve intense itching (pruritus) and contact sites such as the feet, skin, scrotum, elbows and hocks.

What causes it?

Many substances can induce contact allergy. These include certain plants materials, e.g. pine oil (or even pine needles), disinfectants, wool, nylon, dyes. Sometimes shampoos, ointments and insecticides used in the treatment of skin disease can be implicated.

Does the condition develop rapidly?

This depends on the cause or allergen. Usually contact hypersensitivity develops slowly.

Is there any difference between contact allergic dermatitis and contact irritant dermatitis?

Yes. Contact irritant dermatitis is not uncommon in dogs and should be distinguished from a contact allergy. Only a small percentage of dogs will have an allergic response to a contact allergen whereas all dogs will have a skin reaction on exposure to an irritant.

Common irritants include creosote, concentrated disinfectant or detergent solutions.

Clinical signs of contact irritation are similar to contact allergy but occur very rapidly.

ALLERGIC SKIN DISEASES

Allergic skin diseases are among the most common, difficult and frustrating conditions to diagnose and treat in veterinary practice. In connection with skin disease, four major groups of allergens are identified:-

· Flea saliva

· Food constituents

· Inhaled particles such as dust or pollen

· Contact allergies

Contact allergens include many substances ranging from plant materials to disinfectants, wool, nylon and dyes etc.

Urticaria

Urticaria (hives) is an allergic phenomenon and can result from food, drugs, vaccines, insect bites or stings. Single or multiple weals or swellings of variable size suddenly appear on the skin. Some types of dogs appear to be more susceptible than others.

Flea Allergic Dermatitis

'Hot Spot' eczema.

Many dogs are allergic to proteins in the saliva that the flea injects in order to obtain a meal of blood, which is essential to it for survival. In a sensitive dog this causes itchiness resulting sometimes in very extensive damage to the skin (dermatitis).

Due to the hypersensitivity reaction, often the dog, once sensitised, need only to receive one flea bite to trigger the reaction, which will result in continuous pruritis (itchiness).

FOOD ALLERGY

What is food allergy?

Food allergy is one of at least five specific allergies or hypersensitivities known to affect dogs. We all know of people who are allergic to certain foods, e.g strawberries or nuts. It is only relatively recently that food allergies have come to be recognised in dogs. The signs are usually itchy skin or an upset bowel. Other more subtle changes can also occur including hyperactivity, weight loss, lack of energy or even aggression. In other words, just like children!

What are the signs? My dog just seems to itch and occasionally have diarrhoea.

Many dogs will occasionally react to something they have eaten. This may be a sensitivity to a particular type of food. The symptoms are often not a true allergy, just a mild tummy upset. Once you have associated the upset with that particular food and avoid it in future, the problem is usually solved.

The most common food allergies in dogs are caused by dairy products, beef or gluten.

Food allergy is different. Antibodies are produced against some part of the food. In an allergic animal the immune system over reacts and produces antibodies to substances which normally should be tolerated in the body.

Are some ingredients more likely to cause allergies than others?

The most common food allergies in dogs are dairy products, beef or gluten (from wheat). Every time food containing these products is eaten the antibodies react and symptoms either in the form of a gastro intestinal upset or, more usually, skin irritation occur.

Are these the only food constituents likely to cause food hypersensitivity?

No, virtually any food or food ingredient can produce an allergy. Proteins are the most common cause but other substances and, as with children, additives can also be responsible.

How is the condition diagnosed?

Until relatively recently feeding an elimination diet was the only means of determining the presence of a food allergy. This is a diet chosen which contains none of the ingredients of the previous diet. This had to be fed for a minimum of 3-4 weeks. If the symptoms improved on the new diet, one meal of the old diet is fed to see if the symptoms return. The problem was that since the elimination diet may not be as palatable as the original diet, there was always the possibility that your pet could sabotage your best efforts and even one mouthful of say, beef, could undo weeks of work. If you had other pets in the house eating normal food this could easily happen.

Today there are blood tests available which will give a relatively accurate indication of whether the dog is allergic to constituents in his diet.

How is the condition treated?

Once the offending constituents have been identified a diet is organised that does not contain these particular substances. Originally one had to make one’s own diet, for example chicken and rice was always popular for dogs with beef protein allergies. Today there are a number of commercially available, palatable, hypo allergenic diets on which the dog can be fed for the rest of his life.

Occasionally commercial diets containing the right constituents may not be available or alternatively your pet does not consider them palatable, in which case you may be forced to prepare a home cooked diet.

Can the problem be cured?

Unfortunately at present it is not possible to cure the dog with an allergy to food and thus as outlined above the problematic constituents just have to be avoided.

Is it likely that my dog could develop other food allergies?

It is not uncommon for dogs that have developed an allergy to one particular food to subsequently develop other food related allergies so if signs start to re-appear do not immediately jump to the conclusion that your dog has eaten some of the forbidden food. It may be that unfortunately other food related allergies are appearing.

INHALANT ALLERGY

What are allergies and how do they affect dogs?

Allergic reactions are very common in dogs and are fully described in a separate fact sheet 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:

a) flea

b) food

c) contact

d) inhalant

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

Yes. After flea allergy dermatitis (FAD) or flea hypersenitivity, atopy is the most common type of allergy in the dog. It is caused by an inhaled allergen to which the dog’s immune system over reacts.

What sort of things are inhaled that 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 human asthma.

When the affected individual inhales dust, pollens or moulds, for example, the allergic response occurs.

What happens to the dog when this occurs?

Atopy in the dog is usually seen as severe generalised itching. Your 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 inhaled allergens cause respiratory problems, hay fever or asthma. Occasionally in the dog there will also be respiratory signs, usually in addition to the pruritis.

How do you find the cause of my dog’s inhalant allergy?

Diagnosis is not easy. It is based on the presence of the signs discussed above and ruling out other causes of pruritis, e.g. fleas. However the itching produced by grass pollen is the same as that produced by house dust mites. In other words your dog may be allergic to several different things with the end result being the same, i.e. he is scratching himself to pieces.

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 intra dermal 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 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 hypersensitisation results 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 hyporsensitisation 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, does help. However this is a non-specific approach that doesn’t treat the allergy, only the result, i.e. the pruritis.

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.

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 and in the case of indoor dogs a very common cause is the house dust mite.

Another explanation may be that the dog has developed separate hypersensitivities allergies to so many different things that at least one of those 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 also appear to be hypothyroid, in other words the thyroid gland is not producing sufficient thyroid hormone. This in turn affects the skin and may aggravate allergic conditions.

If you have any concerns in this direction, there are blood tests which will be undertaken.

When my dog is worst 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, due to the increased sebum, also clears up.

Another cause can be bacterial infection due to the damage caused to the dog’s skin and also sometimes, since the ears and ear canals are extensions of the skin, these become badly infected and are overlooked while the more obvious skin lesions are being treated.

This client information sheet is based on material written by Trevor Turner, BVetMed, MRCVS, FRSH, MCIArb, MAE.

Used with permission under license.