Author: Isabelle Remy
Definitions
Food reactions
- food allergy
immunological mechanism
sensitization phase
- food intolerance
non-immunological mechanisms
- metabolic
- toxic
- pharmacological
- idiosyncratic
Etiopathogenesis
trophallers or food allergens
- any food is potentially allergenic
variations depending on countries and eating habits
- beef, chicken, dairy products, cereals, fish, egg, soy, lamb…
quantity?
- (glyco)proteins with molecular weights ranging from 10 to 60 kda (hô)
from what size can a protein induce an allergic reaction in animals?
antigenic fraction (epitope) responsible?
- in humans: cross-reactions between foods and pollens
Pathogenesis
genetic predisposition (race)
atopic state
- in children: relationship between atopic dermatitis and food allergy in approximately 30-40% of cases
- in dogs: no scientific evidence
intestinal parasitism
immaturity/loss of integrity of the intestinal barrier
- increased intestinal permeability allowing increased passage of trophallers
Clinical signs
Digestive symptoms: 10-15%
Skin symptoms in dogs
- non-seasonal pruritus
- variable response to corticosteroid therapy
- age: 30% of cases < 1 year according to some authors
- lesion distribution = atopic dermatitis (AD)
face, ears, extremities, belly…
- recurrent otitis externa
- urticaria, facial edema
- pyotraumatic dermatitis, vasculitis, anal fistula?
Skin symptoms in cats
- facial/neck pruritus
- feline eosinophilic complex lesions
- extensive alopecia
- miliary dermatitis
- mural folliculitis
- urticaria
Other symptoms: rare (human)
- asthma, rhinitis, conjunctivitis, headaches, seizures
Diagnosis
In humans
- in vivo (prick-test) and in vitro (Ig E) tests
In dogs and cats
- in vivo and in vitro tests absolutely unreliable
- elimination diet followed by a provocation test = only method for diagnosing a “food reaction”
Elimination diet
- 3 types of diet
- novel proteins
- homemade diet
- commercial foods
- hydrolyzed proteins
Elimination diet: novel proteins
- Homemade diet
- choice of ingredients based on eating habits: survey
- 1 protein source (1 part) and 1 carbohydrate source (2 to 4 parts)
- horse, rabbit, turkey, fish, ostrich…
- potatoes, lentils, turnips, sweet potatoes…
- preparation: grilled, boiled or microwave-cooked foods without spices or fats
- Advantages
- strict control of food intake
- Disadvantages
- unbalanced ratio (growth)
- digestive problems: gradual introduction
- time-consuming for the owner
- expensive for a large dog
- Commercial diets
- limited and selected protein sources
- attention to the composition!
- many “pseudo” hypoallergenic foods
- proteins too often used in most commercial or homemade foods (lamb, chicken)
- hidden allergens: vegetable oils, animal fats, additives…
- Leistra et al. JAVMA, 2001, 219 (10): 1411-1414.
- Leistra and Willemse Journal of Feline Medicine and Surgery 2002, 4: 185-188
- proteins split into small fragments potentially less or non-allergenic
- average molecular weight
- possible exposure of previously hidden epitopes
- small peptides that can act as haptens
- check the composition: addition of whole grains, vegetable fats…
- Advantages
- highly digestible proteins in adequate quantity
- well-balanced ratio (young animals)
- practical to use
- Disadvantages
- wide variation in “hypoallergenic” quality
- hidden allergens
When to propose an elimination diet?
- immediately in moderate forms of AD (young dogs)
- systematically in classic or chronic forms of AD
- long-term control element
- treat before complications of bacterial pyoderma, Malassezia pachyd. dermatitis, or extend the diet sufficiently after stopping all medication
Conduct of the elimination diet
- hyper-strict diet: no extras, no deviation
- prohibit treats, chew bones, bread for birds, garbage, toys, toothpaste, flavored medications…
- avoid plastic and metal bowls
- owner’s collaboration essential
- duration of the diet
- 6 to 8 – 10 weeks
- regular check-ups, encourage the owner
Response to diet and provocation test
- Provocation test essential for diagnosis
- successive reintroduction of old ingredients for periods of 8 to 15 days or massive reintroduction of the old diet: recurrence within 0 to 8 days
- laborious approach often refused
- % of animals improved by an elimination diet do not relapse during food challenge
- spontaneous improvement of AD symptoms
- balanced, highly digestible food
Response to elimination diet
- Partial improvement: 2 to 4 weeks more
- concurrent allergies
- recurrence of infections (bacteria, yeasts)
- Failure
- diet not followed
- reaction to a protein in the elimination diet
- other hypersensitivity: aeroallergens
- review the diagnosis
Conclusions
- elimination diet
- only valid diagnostic method
- essential step in the management of AD
- difficult food choice
- difficult to perform and interpret
- beware of commercial abuses and media hype
- future:
- more rigorous and reliable biological tests (experimental models)
- identification of major antigens
