Practice Tips for a Successful Outcomes in allergic Pets

 Common reasons for dietary trial failure and lack of response to antipruritic medication such as steroids, Janus Kinase Inhibitors and Cyclosporine: 

- Ectoparasites e.g Sarcoptes, Demodex, Ringworm ( Microsporum canis, Trichophyton)

- Cutaneous T-cell lymphoma

When above possibilities have been ruled out, the most common in household pets is Malassezia dermatitis +/- hypersensitivity: skin condition caused by the overgrowth of Malassezia pachydermatis, a yeast that normally resides on canine skin in low numbers. When the skin barrier or immune system is compromised, the yeast multiplies and causes inflammation.

It often occurs alone or together with underlying hypersensitivity disorders such as:

• Food allergies- Owner self control of table foods and ruling out diet triggers

• Atopic dermatitis (environmental allergies)- Goes in hand with food allergies also requires nutrition management and ingredient elimination. 

• Flea allergy dermatitis - Ruled out if on preventative care, Veterinary skin exam, flea comb test 

• Endocrine diseases (hypothyroidism, Cushing’s)- Ruled out with bloodwork but still requires nutritional management.

Clinical Signs

• Pruritus (mild to severe itching)

• Erythema and skin inflammation

• Greasy, flaky, or waxy skin (seborrhea)

• Musty, yeasty odor

• Hyperpigmentation (darkened skin)

• Lichenification (thick, elephant-like skin)

• Red, irritated paws, interdigital spaces

• Ear canal inflammation with brown wax (otitis due to Malassezia)

Pathophysiology With Hypersensitivity

When hypersensitivity is present:

• The skin barrier becomes compromised

• Immune dysregulation promotes yeast overgrowth

• Inflammation increases pruritus → scratching → more yeast proliferation

• It becomes a cycle of allergy + yeast infection

Diagnosis

• Rule out or identify underlying allergies or endocrine disease

• Cytology (tape prep or skin scrape): presence of Malassezia (footprint-shaped yeast)

Demodex and Malassezia are different organisms, but they often appear together because they both flare when the skin’s normal defenses are weakened.

Demodex canis is considered a normal resident of a dog’s skin and ear canals. It lives primarily within hair follicles and sometimes in sebaceous glands. Under normal immune function, the mite population remains low and causes no issues. However, when the dog’s immune resistance decreases, the mites can multiply excessively and lead to Clinical Demodicosis.

A dog with allergies since 10 months of age with an entire body region effected mainly head demodicosis is classified as Juvenile- Onset Generalized Demodicosis

A negative result with Wood's lamp cannot rule  out dematophytes (Ringworm ) also known as Microsporum canis. In dogs and cats. It has a 5% chance of becoming fluorescent under the lump, leaving a considerable percentage undetected. Pets can be infected with other dermatophyte strains that the lamp cannot detect such as Trichophyton

To rule out dermatophytes (ringworm), a PCR sample collected from the dog/cats hair and crusts has to be sent to the lab to search for dermatophyte DNA  if tested negative. However if your pet is also not behaving as usual - eating less or being less active do bloodwork.

Why: 

Differentiation between juvenile and adult on set may sometimes be difficult. More important to find and correct predisposing factors regardless of age to achieve the best possible outcome.

Canine Demodicosis is a Slow Progression Symptoms

When Demodex mites increase gradually, signs often start subtle and worsen over time:

Early/Subtle Signs - Most of the time ruled as environmental, or genetic related issues or "normal age pigmentation". 

- Small patches of hair loss (especially on face, around eyes, muzzle, forelimbs)

- Dry, scaly skin or mild dandruff

- Slight redness of the skin

- Thinning coat without obvious discomfort

Progressive Signs - Most of the time ruled as breed related or age especially when undetected throughout their lifetime. 

- Expanding areas of alopecia (localized patches become generalized)

- Darkening of the skin (hyperpigmentation)

- Skin thickening or a “wrinkled” appearance

- Comedones (blackheads) due to clogged follicles

Mild to moderate itching - Most of the time ruled as behavioural, environmental related, self trauma

** Usually low at first, increases if secondary infection develops

- Foul odor from the skin if bacteria/yeast overgrow

- Advanced or Chronic Signs

- Large areas of hair loss across the body

- Oozing, crusting, or moist lesions from secondary bacterial infection

- Pustules or papules

- Lethargy or discomfort if infections become severe

- Swelling of the feet (pododemodicosis) – thick, reddened, swollen paws

Localized demodicosis 

Occurs as one to several small, circumscribed, scaly areas of alopecia. Most cases occurs at 3-6 months of age and heal spontaneously without treatment

Generalized demodicosis 

Covers large areas of the body (whole head is a large area). A dog with many localised lesions involvement of an entire body region or has complete involvement of more than 2 feet is considered to have generalized demodicosis usually starts before 18 months and between 30 - 50% of the heal spontaneously 

Juvenile - Onset demodicosis 

First - clinical signs of juvenile demodicosis in dogs typically occurs in the first 18 months of life . In young dogs, generalized demodicosis has a genetic basis. Breeding of these dogs should be discouraged!!

Adult - Onset demodicosis

Rare but more serious than the juvenile form. This entity is usually a sign of an immunosuppressive condition and occurs on dogs older than 18 months old. Most adult-onset generalized demodicosis will require treatment to eliminate mites in addition to correction the underlying predisposing cause . 

Relationship Between Demodex canis and Malassezia Dermatitis

Demodex and Malassezia are different organisms, but they often appear together because they both flare when the skin’s normal defenses are weakened.

1st. Underlying Cause: Compromised Immune Function

Demodex canis increases when cell-mediated immunity is low-->Malassezia overgrows when the skin barrier is inflamed, oily, or allergic.

When a dog develops demodicosis, the skin becomes:

- Inflamed

- More oily/seborrheic

- Damaged

This environment is ideal for Malassezia yeast to multiply.

2. Secondary Yeast Infection is Very Common

Up to 30–60% of dogs with generalized demodicosis develop secondary Malassezia dermatitis because:

- Hair follicles rupture → inflammation

- Bacterial infections appear → more moisture/oil

- The skin barrier becomes compromised → yeast flourishes

So the dog ends up with mixed Demodex, bacteria, and yeast infections.

 They Share Overlapping Clinical Signs

Both can cause:

- Redness

- Itching (though Demodex alone may not be very itchy)

- Greasy skin

- Odor

- Hyperpigmentation

- Thickened skin

Due to signs overlapping, cytology and skin scrapings and proper knowledgeable diagnosis is needed  to confirm what’s present.

Yeast Can Make Demodex Worse

In today’s growing pet food industry, new supplements and novel ingredients can be beneficial for many dogs, especially those with healthy skin and resilient immune systems. However, a dog that is yeast-sensitive or develops multiple sensitivities over time and is continually exposed to these allergenic triggers may:

- Experience chronic inflammation of the skin barrier and itching 

- Develop recurring Malassezia overgrowth due to constant irritation (increases pruritus, leads to more scratching, worsens follicular damage) 

- Show increased pruritus, redness, and greasy or flaky skin

- Become more reactive to even small amounts of the allergen

- Struggle with secondary bacterial or yeast infections

-Have delayed skin healing and persistent hot spots

-Experience worsening allergy cycles, making each flare more severe

-Develop nutritional intolerances, reducing the variety of safe foods

-Enter a chronic flare–remission cycle, especially in atopic or immunocompromised dogs

This makes Demodex treatment take longer, because the skin cannot heal while yeast is active.

5. Treatment Often Needs to Address Both

-Allergy management prevents recurrence

-Amitraz, isoxazolines (Bravecto, NexGard, Simparica) treat Demodex

-Antifungals (ketoconazole/miconazole) treat Malassezia

-Antibiotics may be needed for secondary bacterial infections

Reminder 

**Demodex and Malassezia are not directly related, but Demodex causes skin changes that create the perfect environment for Malassezia to overgrow, leading to a combined infection.

Q & A 

Combo of Apoquel and Vanectyl-P  interactions, risks, or considerations for safe administration:  

A:

To treat allergic inflammation extra label (Vanectyl-P) and itch (Apoquel) is a great combination.  There is a long-term Apoquel if use is required short term due to diligent elimination diet trials of food allergens even better. In some cases, where it works well, it may be necessary to control traumatically induced dermatitis in pets. Annual bloodwork is recommended to make certain the pet is not experiencing any adverse effects.

How about if there's a presence of facial and neck pruritus and then the cat starts to lick and lick it's ventral belly area

A:Could be a combination allergy patient…need to address both food and environmental allergies and eliminate fleas if any. 

Are the serologic tests better than they used to be?  

A: "About 10 years ago I took a large blood sample from my dog, split it into 2 samples and sent both samples in under different names to see if the tests would come back the same.  The tests came back TOTALLY different, with allergy responses to all different allergens, on one sample it wouldn't be allergic, but on the other sample it would be very allergic.  So I have no confidence in this test at all."

First step in diagnosing canine atopic dermatitis

A:

- Skin Biopsy --Routine test-->Skin scraping ( Cytology = Neutrophils, Cocci and macrophages activity,  parasite) 

- Presence of macrophages, Nodules, and swelling  indicates deep pyoderma 

- Bleeding in some places indicate lesions have crossed the basement membrane 

Most common clinical sign of Canine Cutaneous Adverse Food Reaction 

A: Chronic ear infections. Gold standard for diagnosing Cutaneous Adverse Food Reactions in dogs. Food Elimination diet followed by owner compliance and social media influence can pose challenging. 

Ingredient commonly used in hypoallergenic diets for dogs suspected of food allergies 

A: Hydrolyzed protein

Purpose of food elimination trials 

A: Identify the specific food allergen causing reaction

Common medication used to manage pruritus in Atopic Dermatitis

A:  Antihistamine and immunity suppressants (e.g. Apoquel)

How long should food elimination trials typically last to be effective

A: 

Old school 8-12 

 Modern time 2-4 weeks  

Which diagnostic test is often used reliable to identify environmental allergens in dogs with Atopic Dermatitis

A: 

Intradermal/ Serologic allergy test 

Resource 

Yu, A. (2023). Practice tips for a successful outcome in your allergic patients [Seminar presentation]. Ontario Association of Veterinary Technicians (OAVT)