Pruritus 2- Food Allergic Derm And Contact Dermaitits Flashcards by Corinne Perra

What is the difference between food allergy, dietary intolerance, and food anaphylaxis?

Food allergy — immune response

Dietary intolerance — no immune response

Food anaphylaxis — systemic involvement

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What are the types of dietary intolerance ?

Food idiosyncrasy - resembles allergy but no immune response

Food poisoning - non immune reponse to food or toxin

Pharmacological rxn — drug like effect of food on host

Food indiscretion — gluttony, pica or indigestible material

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T/f: food intolerance occurs following the first exposure to food/additive/toxin

True

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What is food anaphylaxis?.

Acute food allergy

systemic consequence
resp distress
vascular collapse
urticaria

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T/F: food allergies are relatively rare

True

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What are the most common food allergens

Protein (most commonly beef protein in cats and dogs)

Glycoproteins - water soluble (10,000-70,000 Da)

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Food allergy is a type __ hypersensitivity rxn

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What is part of the normal innate immune response to food antigens?

Anatomical - mucosa of intestine

Physiological

pH
mucous protective layer
peristalsis
body temp

Cellular

neutrophil
macrophage
NK cells

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What is part of the normal adaptive immunity response to food antigens

Cell mediated - T lymphocyte

Humoral : B lymphocyte , plasma cell, and immunoglobulins

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Normally food allergens are prevented by passing through the intestinal wall barrier by.. ?

Innate immune system and IgA antibodies in mucous layer

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What cells of the intestine are capable of capturing food antigens?

Macrophages
Dendritic cells
M-cell (associated with GALT)
Enterocytes

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T1 helper cells activate what repsonse ?

Cell mediated response —> T lymphocyte proliferation and macrophage activation

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T2 helper cells activate what response?

Humoral response —> B lymphocyte proliferation and immunoglobulin production

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What are all the possible hypersensitivity rxns that a food allergy can cause, most common to least common?

Type 1 > type 4 > type 3

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What is the pathogenesis of food allergy in a type 1 hypersensitivity rxn?

Allergen -> activate TH2 —> activated B lymphocyte –> plasma cell —> produced IgE —> bind mast cells

Mast cells release
-histamine, protease, chemotatic factors, prostaglandins, leukotrienes, and cytokines

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Clinical signs associated with type 1 hypersensitivity from food allergy?

Vasoactive amines cause
—>Pruritus
—>Hyperemia
—>Angioedema

Local rxn in GIT
—> diarrhea
—> abdominal discomfort
—> vomiting

Severe rxn causes
—> anaphylaxis, angioedema, hypotension, respiratory distress

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Pathogenesis of type 4 hypersensitivity cause by food allergy?

Food allergen —> activate TH1 —> T lymphocyte proliferation —> release of chemotaxic factors (attracts macrophages) —> degranulation

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What are the 3 most common hypersensitivity skin diseases in adult dogs from most to least?

Flea > atopy > food

What are the 3 most common hypersensitivity skin diseases in dogs less than 6months, from most to least?

Flea > food > atopy

Breeds predisposed to food allergy?

Labrador retriever 
Collies 
Miniature schauzers 
Spaniel 
Chinese shar-pei 
Boxer
Dashunds
GSD 
West highland white terrier

T/F: food allergies are non-seasonal

True

Although they can flare up more in summer when wet and humid —> predispose to secondary bacterial infection

Types of lesions seen with food allergy?

Primary

papule
erythema
wheal
plaques

Secondary

excoriation
crusting
hyperpigmentation/lichenification
ulcer due to deep scratches

Where are food allergy lesions usually localized in dog?

Muzzle, ear, distal limb/ paw, axillary, groin

Where are food allergy lesions usually localized in cats?

Head, face
Pinnae
Neck

What is the ONLY way to diagnose food allergy dermatitis?

Positive response to an elimination diet —> 95% of dogs improve within 3 weeks **biggest limitation - owner compliance**

T/F: intradermal skin testing is useful in determining food allergy

False Very inaccurate - low sensitivity

T/F: ELISA serology shows good correlation between positive serology result and the antigen causing reaction

False —> often false positive -high sensitivity and low specificity

What is colonoscopy allergen provocation?

Allergens are injected into the mucosa of the colon Observation made of wheal or flare reaction ** more sensitive than interdermal or ELISA serology testing** Technically challenging Cost is thigh

What are the three dietary options available for dogs with food allergies?

Low allergy commercial diet (novel proteins and carbohydrate sources) Homemade hypoallergenic diet (novel proteins, carbohydrate, and free of additives) Hydrolyzed protein diet (eg z/d)

For homemade hypoallergenic diets, which carbohydrates appear to be least allergenic?

Tofu and brown rice

What is a hydrolyzed protein diet?

Proteins hydrolyzed into small particles The smaller the particle the less antigenic they become —> should be less than 10,000Da These small particles cannot bind to IgE on mast cells => degranulation is prevented

How are hydrolyzed protein diets made?

Antigenicity of protein is determined by structure —> disrupt 3D structure —> alter amino acid side chains —> cleave peptide bond Done with —heat or pH —enzymatic hydrolysis —ultrafiltration

What is the difference between hills z/d ultra allergen free and hills z/d low allergen ?

Z/d ultra —> only have proteins under 3000Da Z/d low allergen —> average 3000Da but can have more of a range

What is the disadvantage of hydrolyzed protein diets?

Low palatability

How do you treat secondary skin infections due to food allergy?

Antibiotics for bacterial dermatitis - cephalexin - pyostat/pyoderm Antifungals prep for Malassezia spp - Niz shampoo - pyostat/pyoderm - imaverol dips

How will you treat secondary pruritus due to food allergy?

Only if unresponsive to topical washes - prednisolone - topical steroid preps —> hydrocortisone

A minimum of ___ antihistamines should be tried before before a failure of response to antihistamines can be determined for pruritus?

3 ``` Chlorphenamine Diphenhydramine hydrochloride Clemastine Hydroxyzine Terfendine ```

What is the prognosis for food allergy dermatitis?

Excellent if dog responds to diet Cannot exclude food allergy if does not respond - reaction to additive/protein - owner compliance - try another diet

Urticaria and angioedema is an allergic/ non-allergic response to....?

``` Drugs Insect stings/bites Food Vaccine Plant Heat/cold Sunlight Stress ```

Clinical signs of urticaria and angioedema ??

Sudden onset of local or generalized wheals, oedematous swelling Dyspnea Anaphylaxis Pruritus

Treatment for urticaria and angioedema ?

Remove antigen Injectable antihistamine (mepyramine maleate, diphenhydramine) Injectable steroids - corticosteroids Dyspnea may require Adrenalin

What is contact dermatitis

Prolonged exposure to a offending surface —> type 4 hypersensitivity rxn *extremely rare*

Clinical signs of contact dermatitis?

Intensely pruritic Papule, erythema, macule, alopecia, plaques, vesicles, excoriation Hyperpigmentation and lichenification Secondary infection Lips if food bowl is caused Neck if collar

Treatment for contact dermatitis

Identify allergen Treat secondary infections Mechanical barriers Poorly steroid responsive