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Inhallant Allergies - 'Atopy'

Dr Mark Lewis BVSC

Inhalant allergy, also known as atopy is a common, type of allergy occurring in dogs. Dogs may be allergic to many inhaled allergens including tree pollens (cedar, ash, oak, etc.), grass and weed pollens, moulds, mildew, and the house dust mite. Some of these allergies occur seasonally, such as the grass pollens however others, such as moulds, mildew, and house dust mites, are with us all the time.

When humans inhale allergens, we express the allergy as respiratory problems. The dog's reaction however usually produces severe generalised itching. Affected dogs will chew, lick, or scratch almost any area of the body, in particular the feet. In these dogs saliva discolours the light coloured hair, so that they often have orange or reddish brown hair particularly on the feet.

It is not easy to determine the cause of an atopy. The itching produced by grass pollen allergy 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. Fortunately it is not always necessary to know the specific allergen for treatment to be successful.

As the names imply, some dogs only have allergic reactions during specific periods of the year while others will itch all year round. A year round allergy occurs if the allergen is present all year round or if the dog is allergic to so many things that at least one of those allergens is present at all times.

Unfortunately as the dogs age they usually become allergic to more and more things so that dogs that once had seasonal allergies become year round allergies.

Sebum is the oily material normally produced in the skin. When a dog scratches, sebum production increases dramatically. This produces a musty odour and is a good medium in which bacteria can grow. If bacterial infections occur they will aggravate the itch.

A bath will remove the odour, but it is gone for only a few hours. The key to controlling seborrhoea is to stop the itching and scratching.

Also these dogs often have smelly ears because the ear canal also becomes inflamed and has increased production of waxes.

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 and/or antihistamines can be of great value in treating the allergic dog but they must be used with great care as they can have serious side effects. Fatty acid supplementation can also be implemented with steroids and antihistamines. When the three of these are combined, most allergic dogs are significantly improved. This is a non-specific 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. Some of the hypoallergenic shampoos incorporate fatty acids; these may be absorbed through the skin and offer a localised anti-inflammatory action. The role of the fatty acids in allergy treatment is an area of active research interest in veterinary medicine.

3. 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.

4. Flea control

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.

5. Desensitisation.

The other major form of allergy treatment is desensitisation with specific antigen injections .

Testing is done to identify the specific allergens and then very small amounts of the allergen are injected weekly. The purpose of this therapy is to reprogram the body's immune system.

If desensitisation 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 but, in some dogs, itching may completely resolve.

Although desensitisation is the ideal way to treat inhalant allergy, it does have some drawbacks, these are:

Cost: This is the most expensive form of treatment.

Age : Many dogs develop additional allergies as they get older, so that young dogs may need to be retested 1-3 years later.

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.

Food allergy: Tests for food allergy are available but 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.

Time of Response: The time until apparent response may be 2-5 months, or longer.

Interference of steroids: Dogs must not receive oral steroids for 4 weeks prior to testing because these drugs will interfere with the test results.

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Last modified: November 21, 2006