Understanding Dog Allergies – From Allergic Dermatitis to Malassezia

Understanding Dog Allergies by Dr. Joel Murphy

The G.I. (Gastrointestinal) System

The GI system is overloaded every day with external stimuli.

On a daily basis, beneficial substances (like food) and unthreatening microbes in the environment enter your dog’s body. Additionally, your dog’s intestinal tract is regularly confronted with potentially dangerous pathogenic microbes (bacteria, protozoa, fungi, viruses) and/or various toxic substances.

The crucial position of the gastrointestinal system is testified by the huge number of immune cells that reside within it. Indeed, gut-associated lymphoid tissue (GALT) is the prominent part of mucosal-associated lymphoid tissue (MALT) and represents almost 70% of the entire immune system; moreover, about 80% of plasma cells [mainly immunoglobulin A (IgA)-bearing cells] reside in GALT. The immune mechanisms functioning in the GI tract are extremely complex and beyond the scope of this post. Suffice it to say, since the stomach, intestines, and colon come in direct contact with the external environment, the GI system must protect your dog from dangerous substances potentially entering the bloodstream of his body through the mucosal lining.

Understanding Dog Allergies

An important thing to understand is that health in the digestive tract is maintained by the constant sensing and scanning performed by the cells of the immune system. It is an active function and not just a situation of the immune cells ignoring certain things. The immune system is actually a tricky balance between a pro-inflammatory response and an anti-inflammatory one.

If this balance is not maintained, the immune system can become over-reactive to harmless substances (as in the case of allergies and sensitivities) and lead to inflammatory disease. On the other hand, if the immune system becomes overly anti-inflammatory, dangerous pathogens would not be kept under control.

Allergic Dermatitis

Different from human, dog allergies manifest most commonly on their skin in allergic dermatitis. Allergic dermatitis causes immense suffering in dogs, prompting them to itch and scratch excessively. The more dogs itch and scratch themselves, the worse the dermatitis. This creates a cycle of pain and trauma. Secondary to the inflammation in the skin and self-induced injury, surface bacteria invade the skin, in turn causing more itching, scratching and self-induced trauma.

Allergic dermatitis can be the result of an inappropriate reaction to:

• Fleas
• Atopy (caused by inhaling pollen, mold, etc.)
• Contact allergies
• Food allergies
• Unusual response to medications
• Secondary yeast infections

Allergic otitis and Malassezia

In humans, we use the catch-all phrase “candida” which is an overgrowth of a specific yeast in the digestive system in humans. While candida infections are rare in dogs, other yeast infections are rampant. The primary yeast infection in dogs is Malassezia.

When dogs have allergies, commonly the external ear is almost always affected. The inflammation in the ear from allergy creates a perfect condition for bacteria and Malassezia to grow. The Malassezia creates even more inflammation resulting in chronic progressive otitis (inflammation of the ear).

Allergic otitis with secondary Malassezia and bacterial infections is one of the most common dog maladies treated by veterinarians. If detected early and treated effectively – which includes maintenance treatment for the underlying allergy – atopic/allergic otitis is easily , and the ear returns to normal. Left untreated severe inflammation and changes in the cartilage and can be a very painful disease that is difficult and expensive to treat. In severe cases, sometimes surgery is necessary to remove the entire ear, solving the infection and pain but resulting in deafness.

Itchy skin diseases such as allergies to pollens and molds cause inflammation. Yeast infections invade the dog’s skin, especially when the surface is compromised by allergies and another dermatitis. It is essential to treat both the allergy and the yeast infection to make your dog comfortable again.