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
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
T/f: food intolerance occurs following the first exposure to food/additive/toxin
True
What is food anaphylaxis?.
Acute food allergy
- systemic consequence
- resp distress
- vascular collapse
- urticaria
T/F: food allergies are relatively rare
True
What are the most common food allergens
Protein (most commonly beef protein in cats and dogs)
Glycoproteins - water soluble (10,000-70,000 Da)
Food allergy is a type __ hypersensitivity rxn
1
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
What is part of the normal adaptive immunity response to food antigens
Cell mediated - T lymphocyte
Humoral : B lymphocyte , plasma cell, and immunoglobulins
Normally food allergens are prevented by passing through the intestinal wall barrier by.. ?
Innate immune system and IgA antibodies in mucous layer
What cells of the intestine are capable of capturing food antigens?
Macrophages
Dendritic cells
M-cell (associated with GALT)
Enterocytes
T1 helper cells activate what repsonse ?
Cell mediated response —> T lymphocyte proliferation and macrophage activation
T2 helper cells activate what response?
Humoral response —> B lymphocyte proliferation and immunoglobulin production
What are all the possible hypersensitivity rxns that a food allergy can cause, most common to least common?
Type 1 > type 4 > type 3
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
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
Pathogenesis of type 4 hypersensitivity cause by food allergy?
Food allergen —> activate TH1 —> T lymphocyte proliferation —> release of chemotaxic factors (attracts macrophages) —> degranulation
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