Canine environmental allergy and allergen specific immunotherapy (ASIT)

by Nicole A. Boynosky BVMS, MS, DACVD.

Atopic dermatitis (AD) or environmental allergy is a complicated disease which may often include a combination of genetic factors, environmental factors, skin immune dysfunction, diet and skin barrier dysfunction. AD is an over-reaction to typically innocuous environmental allergens such as pollens, molds, etc. Dogs absorb allergens across their skin. In dogs with concurrent skin barrier deficiencies, allergens penetrate deeper into the skin and are taken up by specialized immune cells. Allergy manifests itself in different ways, the most common being pruritus (itching). Signs of pruritus are scratching, licking, chewing, biting, and rubbing.

AD is considered a diagnosis of exclusion since there is no one definitive test, and there are a multitude of causes of itching. Extensive client discussion and an extensive dermatologic workup is important prior to testing to diligently work through other causes of pruritus and types of allergy. Diagnosis involves ruling out infectious causes (i.e. bacterial) as well as ectoparasites (i.e. fleas). Year-round flea prevention is paramount. A prescription based novel or hydrolyzed prescription diet elimination trial to rule out any role the diet may play is also essential. The range for the diet trial is 8-12 weeks so it can take months to appropriately diagnose AD.

Allergy testing is used as a diagnostic aide to help decide which allergens should be included in the serum, it does not provide a diagnosis for AD. Dogs without AD can show multiple positive reactions on skin and serum testing. The process of desensitization is geared toward gradually exposing our patients to increasing concentrations of the allergens they had positive reactions to, with the hope that their immune system will stop recognizing these allergens as foreign invaders. Successful therapy is customized to the individual dog while taking client and patient needs into account. Most literature supports 60-75% success rate when used in the correct context. It can take few months or even a few years to reap the full benefits of ASIT. Overall success rate is often higher when started earlier in life. There is an art to managing these patients, and treatment often requires more than ASIT alone.

For more information: www.vshsd.com

Itchy Dog-1836
Skin test in a 4 year old pit bull terrier. Note the multiple positive erythematous red raised reactions.-1837