The Atopic Dog

ATOPY (ALLERGIC INHALANT DERMATITIS) IN THE DOG    

Now that spring has arrived we are starting to see more dogs with allergies, which are one of the most frustrating conditions that we treat as veterinarians.  Skin allergies can be caused by many different substances or ‘allergens’ and include, flea bites, food, contact allergies (eg wandering dew), inhaled substances or even normal skin surface bacteria or yeast.  Atopic dermatitis (atopy) is an allergy to substances that are either inhaled into the lungs and then are absorbed into the body, or they are absorbed through the skin.  The ‘allergen’ is usually to normal harmless substances eg. pollens (grass/trees/weeds) moulds, house dust mites. It is generally owing to a genetic predisposition in certain dogs, where repeated exposure of the allergen leads to an overreaction by the immune system to lead to the symptoms of skin allergy.   Unfortunately the condition is generally life-long with no cure - but often can be managed with time and patience.

Symptoms

The first signs we generally see are licking, scratching or rubbing, with the skin often looking normal at this stage.  Most dogs start developing signs around 1-3 years of age after initially being exposed for a season or two to the allergen. Dogs unfortunately don’t have the will power we generally have, and often scratch/lick and bite until the skin starts to become traumatised.  This leads to red, bumpy, or thickened skin eventually leading to hair loss and an increase in pigmentation (a darkening of the skin). The skin may also become malodorous with an increase in bacteria/yeast on the coat which may worsen the itching. Saliva from constant licking also leads to a rust brown discolouration of the hairs.  Areas affected with atopic dermatitis are usually the paws, face, ears, underarms, groin and front legs. The signs are generally seasonal (often spring/summer), especially if the allergy is to pollens which can be worse in temperate environments with long allergy seasons and high pollen counts  eg Hawkes Bay. Dogs may also have concurrent allergies to fleas and some foods which can increase the severity of the signs.

Diagnosis

As you can imagine it would be pretty miserable feeling continually itchy and uncomfortable, so it’s vital you seek veterinary intervention before the skin becomes too damaged from self trauma.  Diagnosis of the condition may be aided by areas affected, age of onset, or breed of dog (some very prone to atopy).  Your vet will also visually check for evidence of fleas.  One other important condition to rule out is mites, so your vet may take a skin scraping to check and also check for bacteria or yeast on the skin surface.  Biopsies of the skin may be undertaken, which can rule out other diseases and point towards allergies, however, it will not tell us what they are allergic to!  Blood testing (looking for antibodies against allergens) or skin allergy testing, by injecting small amounts of the allergen into the skin and looking for reactions, is a great way to try to determine the offending substance.  Lastly but not least, trial therapy to rule out other allergies may be elicited by monitoring response after removing possible allergens, eg flea control; changing to a low allergen diet (please consult your vet) for at least 6-8 weeks – food allergies generally only make up 10% of allergies but it’s worth ruling out; changing bedding; and avoiding grass.    

Treatment

Allergies can be very hard to treat and no one therapy is effective for them all.  However, in many dogs symptoms can be controlled with a variety of therapies. Often we need to break the itch scratch cycle first before starting on any specific therapy.  This may include antibiotics or anti-fungals to treat secondary bugs on the skin, soothing shampoos containing aloe-vera or colloidal oatmeal, topical creams or sprays especially if the area is small (and inaccessible to the tongue!), cortisone (steroids) or Apoquel a drug that blocks the action of the itch nerve – effectively stopping the scratching but without the associated side effects of cortisone use.

 

Ongoing management can include:

·  Ongoing use of anti-itch medications eg prednisone or Apoquel.  Other options include Atopica, which is a treatment with minimum side effects compared with cortisone but is often cost prohibitive. Antihistamines are less effective in dogs compared with humans but can help prevent signs in some dogs.

· Cytopoint – this is a new monthly injection that contains an antibody that targets a key substance that is involved in itching effectively stopping the itching and the associated skin trauma. It has no side effects and is safe to use with all other medications.

· Diet – Hills have developed a diet call ‘Derm Defense’.  This is a blend of ingredients including Essential Fatty acids that are proven to strengthen the skin barrier, nourish the skin and support the immune system. Essential fatty acids can help to decrease skin inflammation but the correct ones need to be given.

· Desensitisation vaccines can be formulated on the basis of the skin or blood test containing the substance they are allergic to.  By continually exposing the dog to the offending substance the immune system may learn to stop overreacting.  This vaccination generally has to be given lifelong and is effective in improving clinical signs in 60-80% dogs.

· In some cases several allergens can add together to cause an animal to itch, where each individual substance alone would not be enough to cause an itching sensation – all animals should therefore be flea treated as sometimes this alone is enough, even if not suspected to be the cause.

· Washing feet after walks, and avoiding cut grass/high grass paddocks may help with contact/atopic allergies as when walking though grasses dogs noses are low to the ground and act as a vacuum to suck up all the increased number of pollens present. 

 

Overall the take home message is remember allergies cannot be cured and there is no easy fix solution.  Finding effective therapies and working out the allergic substance(s) can be difficult and time consuming – patience is required!  However left untreated, allergic skin conditions, can be very distressing for your beloved pet and leads to unnecessary suffering.