Atopy Flea Allergy Food Allergy Notes

4. Atopy, Flea Allergy, Food Allergy

ATOPY :

= Canine atopic dermatitis; Canine allergic inhalant dermatitis; Canine atopic disease.

• Atopy is a genetically predisposed inflammatory and pruritic allergic skin disease

• Characteristic clinical features

• Associated with IgE ab to environmental allergens

• Dogs skin disease with orcasional organ involvement

• Cats also devp. Dermatitis also but may also have asthma like respiratory problems

• Atopy is reported to account for 8-30% of canine skin diseases.

  • The prevalence in the cat population is much lower.

Etiology

IgE mediated Type 1 Hypersensitivity

Contributing factors:

• Environmental Allergens

• Staph. Pyoderma

• Malassezia dermatitis

• Concurrent flea or food allergy

• Temperature and humidity

Age and sex predeliction

• First seen between 6mths-3yrs (rarely develops in dogs 7yrs

• No sex predeliction but females reported to be more commonly affected

Breed Predeliction

• Dogs : Boxer, Boston terriers, Cairn terrier,Sharpei, English bulldogs, English/Irish setters, golden retrievers/labradors, WHWT, fox terriers, yorkies

• Cats not been reported

Seasonal Incidence initially seasonal but progresses to non-seasonal

Clinical Signs in Dogs

AD should be considered as a dif. Dig. in any dog with:

• Pruritis

• Recurrent staph or malassezia dermatitis

• Otitis externa

Pruritis Initial and most outstanding C.S. in dogs and cats

• Pruritus may be the only sign in some dogs.

• Most of the lesions observed are secondary to self-trauma.

• Pruritis on one or more of the following: Face, ears, ventrum and distal limbs (can become generalized)

Skin Lesions

• Currently a lot of debate on pathognomic lesions for AD. (assuming 2⁰ lesions aren’t present)

• Some dogs have no primary lesions

• Others Rash (macular/popular dermatitis)

• Chronic self trauma leads to 2⁰ lesions alopecia, lichenification, hyperpigmentation, seborrhea

• Secondary pyoderma common staphylococcus intermedius or Yeast dermatitis Malassezia pachydermatis.

• Otitis externa common in dogs with Ad

• Concurrent signs of fleas and flea allergy dermatitis are present in many patients.

Clinical Signs in Cats

• Pruritis Hallmark

• Other symptoms in cats are not like dogs

• Pruritis in cats may manifest as symmetric alopecia, military dermatitis or part of the eosinophilic comples lesions

• 2⁰ bacterial or yeast infections or otitis less common

Diagnosis :

Diagnosis based on:

• Typical historical features

• Characteristic C.S.

• Exclusion of differential diagnoses

Diagnostic Approach

Step 1

• Dx. And Tx. 2⁰ infections

• Dx. And TX concurrent flea allergy

• Dx. And tx scabies

Step 2

• Confirm that the 2⁰ infection, flea allergies and scabies are ruled out

• Determine that residual pruritis remains

• If pruritis is seasonal and flea allergy has been ruled out = AD

• If pruritis is non-seasonal, carry out a food trial to rule out food allergy

Step 3

• If food trial eliminates the issue = food allergy

• Partial response with food trial Food allergy and AD likely

• No response to food trial = AD

Allergy Testing

Intradermal skin tests (IDT) and serum allergy tests (SAT)

A rapid screening test available for use in clinic Allercet E-Screen

CBC/Biochemistry/Urinalysys :

Eosinophilia is rare in the dog without concurrent flea infestation, but common in the cat.

Differential diagnosis :

Seasonal

• Flea Allergy Dermatitis

• Insect bit hypersensitivity

Non Seasonal

• Food allergy

• Scabies

• Contact dermatitis

Other laboratory tests :

Serum allergy testing to detect allergen-specific IgE is commercially available, with the same indications as intradermal skin testing (IDST).

Treatment :

1. Allergen avoidance

2. ATB therapy

3. Anti-inflammatory therapy

4. Allergen-Specific Immunotherapy (ASIT)

Choice depends on:

• Nature and intensity of signs

• Presence of flare factors pyoderma, yeast dermatitis, otitis etc

• Patient acceptance of repeat treatment

• Owners willingness to accept time effort and expense of therapy

No one formula for treatment but is generally a combination of:

• ATB active infections and prophylaxis

• Flea control whether animal is flea allergic or not

• ASIT

• Crisis management Prednisonefor “crisis busting”

1. Initial therapy (best for those with mild symptoms)

• ASIT

• Hypoallergenic or moisturizing shampoo

• Antihistamine trial Diphenhydramine, Hydroxyzine

• Topical lotion or spray for localized areas

2. Poor response to initial therapy of moderate C.S.

• Reconsider ASIT

• Topical triamcinolone spray 3wks

• CCS Prednisone loading then taper (urinalysis every 6mths)

3. Still poor response or sever disease

• Cyclosporine, collars, t-shirts, body suits

FLEA ALLERGY DERMATITIS (FAD):

(Flea bite allergy; Flea bite hypersensitivity)

= A hypersensitivity reaction to antigens in flea saliva with or without evidence of fleas or flea dirt.

A flea infestation is the presence of a large amount of flea dirt with or without a flea allergy dermatitis.

Several types of hypersensitivities

• Cutaneous basophil hypersensitivity

• IgE mediated hypersensitivity

• Late onset IgE reactions

• Delayed type hypersensitivity

Atopic dermatitis or food allergies can occur in combination with FAD

Etiology

• Ctenocephalides felis cats and dogs; most common

• Ctenocephalides canis

• Pulex irritans

Important Flea Life Stages

• Adult fleas on animal eggs fall into environment hatch in 2-10days larvae pupate and then adults emerge find new host

• Cycle = 3-4weeks

• Pupal stage most troublesome most resistant to environmental changes and insecticides

Clinical Signs

• Pruritis is 1⁰ clinical sign see pic below for areas mostly involved

• Primary lesions = Papules and erythematous macules in dogs; focal crusted erosions or papules in cats

• Secondary lesions Result of chronic inflammation and pruritis induced trauma

• Include alopecia, excoriations, dry hair, sparse hair, hyperpirmentation,...

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