17 – Adverse Reactions to Food

Question 1

What are the 2 main types of adverse reactions?

Answer 1

1. True food allergy
2. Food intolerance

Question 2

What are some examples of food intolerance?

Answer 2

• Food idiosyncrasy
• Pharmacologic reaction
• Metabolic reaction
• Food poisoning
• Dietary indiscretion

Question 3

What do you need for a definitive diagnosis of a true food allergy?

Answer 3

• Show immunologic basis of the reaction
  o More common to see skin than GI manifestations
  o Usually diagnosed with elimination diet/challenge

Question 4

What are the most common allergens for a true food allergy?

Answer 4

• Proteins
• Glycoproteins
• *might be influenced by food processing
• *can be one or multiple components

Question 5

What are some common true food allergies in dogs?

Answer 5

• Milk
• Beef
• Soy
• Wheat
• Oats
• Eggs
• Chicken
• Corn meal
• Pork
• Yeast

Question 6

What are some common true food allergies in cats?

Answer 6

• Milk
• Fish

Question 7

How does a food allergy develop?

Answer 7

• GI tract is bombarded with antigens daily
• Intestinal barrier prevents MOST antigens from being absorbed
• About 0.002% of protein is absorbed intact
  o Stimulates gut associated lymphoid tissue (GALT)
  o GALT produces secretory antibodies and systemic hypo-responsiveness (tolerance)
• Processed by enterocytes or macrophages
• B-lymphocytes become plasma cells producing secretory antibodies to the antigen
• *T suppressor cells result in tolerance

Question 8

Breakdown in normal antigen processing

Answer 8

• Increased mucosal antigen uptake can occur that bypasses normal processing
  o Ex. increased permeability secondary to GI disease
• Can induce an allergy by oral challenge with a DAMAGED gut or by direct injection of antigen into the Peyer’s patch
  o IgA deficiency can also lead to it (German shepherds)
• Increased permeability would lead to allergy
• *once allergy is established permeability increases with challenge
  o Causes further damage and excess antigen bypassing normal immune function
  o *may be genetic (Irish Setters and gluten sensitive enteropathy)

Question 9

Type I reaction

Answer 9

• IgE mediated mast cell degranulation
  o Released mediators increases permeability, change motility and stimulate mucus production and chloride secretion

Question 10

Type 3 immune complex deposition and Type 4 delayed hypersensitivity

Answer 10

• Suspected to be most common
• Delay in signs makes it harder to ‘spot’ the problem as being allergic in origin

Question 11

Clinical signs of a food allergy

Answer 11

• More common in young animals (immature immune function)
• Can be dermatologic (non-seasonal pruritus, miliary dermatitis in cats)
• GI signs: vomiting, diarrhea, changes in appetite, weight loss
• Rare: asthma, behavioural changes and seizures

Question 12

How do you approach a chronic enteropathy case?(3-4 weeks)

Answer 12

• Establish a baseline if possible
  o Factors were more likely related to negative outcomes with treatment
• *more severe the score=less likely to respond or poorer response
  o If itchiness=do less well
• Ex. going from 9 to 5 = success, but only going 8 to 9=not great

Question 13

How do you diagnose a food allergy?

Answer 13

1. Skin test
2. Measurement of food specific IgE
3. Gastroscopic food sensitivity testing
4. Elimination/challenge diet

Question 14

Skin test

Answer 14

• Detects IgE directed against an antigen in the skin
• IgE on skin does NOT have anything to do with IgE in bowel
• Wont spot other delayed responses
• Antigens are ingested may not be allergens; it may be that protein as altered by the gut

Question 15

Measurement of food specific IgE

Answer 15

• Measured by RAST or ELISA
• In vitro test
• Probably good negative predictor
• If positive and elimination/challenge test incriminate same allergen it is strong case for true food allergy
• *problem is that there is a high rate of asymptomatic sensitization

Question 16

Gastroscopic food sensitivity testing

Answer 16

• Perform gastric endoscopy
• Drip some of antigen on stomach and monitor reaction (blanching, erythema)
• Limited to mast cell mediated immediate responses

Question 17

Elimination/challenge diet

Answer 17

• Cannot differentiate between allergy and food intolerance (but does not matter)
• Feed antigens that have not been fed for at least 6 months prior to testing
• Mostly novel antigen diets in regard to protein (elk, fish, rabbit, kangaroo, pinto beans)
• Novel CHO (potato, barley, oat)

Question 18

Treatment of food sensitivity

Answer 18

• Maintain novel diet
• Hydrolysates
  o Proteins broken down to a form no longer allergenic
  o If haven’t responded in 4 weeks, change it and try another
• Avoid offending antigens
• Corticosteroids

Question 19

Food idiosyncrasy (food intolerance)

Answer 19

• Probably most common source of GI related food problems
• Do NOT require sensitization or immunological response

Question 20

Pharmacologic reactions (food intolerance)

Answer 20

• Histamine in spoiled fish
• Chocolate

Question 21

Food poisoning (food intolerance)

Answer 21

• Can be from spoiling
• Can be an integral part of food ingested if not properly prepared

Question 22

Dietary indiscretion (food intolerance)

Answer 22

• Too much food

Question 23

What are the 4 types of enteropathies?

Answer 23

1. Food responsive
2. Antibiotic responsive
3. Immune responsive (“IBD”)
4. Non-responsive