Food Allergy and Contact Allergy

Question 1

What is the definition of food allergy?

Answer 1

non-seasonal pruritic skin disorder associated with the ingestion of a substance found in the animal’s diet

Question 2

What are some typical reactions to food?

Answer 2

• immunologically mediated (or true allergy)
  
  • any type of hypersensitivity
• non immunologically mediated
  
  • food intolerance
  • metabolic effect
  • pharmacologic effect
  • toxic effect

Question 3

What are the characteristics of food allergens?

Answer 3

• proteins (10,000-70,000 Da)
• able to trigger an immune response
• factors that determine the allergenic potential are:
  
  • molecular complexity
  • solubility
  • stability
  • concentration

Question 4

Describe the pathogenesis of food allergy

Answer 4

• typically considered a type I hypersensitivity
  
  • type II, III, IV hypersensitivity

Question 5

Describe the clinical disease of food allergy in the dog

Answer 5

• uncommon!
• no age or sex predilection
• it can start at any age
• no change in diet is necessary
• non seasonal pruritis +/- responsive to steroids
• distribution of pruritus
  
  • face, feet, ears
  • perineal
  • generalized
• recurrent infections (bacteria and yeasts) - skin and ear

Question 6

What are three common food allergens for the dog?

Answer 6

• beef
• eggs
• soybean

Question 7

What are the clinical signs of food allergy?

Answer 7

• recurrent moist dermatitis
• recurrent urticaria
• pauplar, macular eruption
• secondary lesions
  
  • scaling
  • lichenification
  • hyperpigmentation
  • excoriations
  • crusting
• concurrent GI symptoms: > 4 bowel movements/day, vomiting, diarrhea, bloating, cramping

Question 8

Describe feline food allergy

Answer 8

• Signalment: no age and sex predilection
• Pattern of dz:
  
  • may mimic atopy or flea allergy
  • head and face pruritus
  • may be assoc w/ other allergies
• C/S:
  
  • miliary dermatitis
  • self-induced alopecia
  • eosinophilic granuloma complex
    
    • indolent ulcer
    • eosinophilic granuloma
    • eosinophilic plaque
  • Concurrent GI signs: diarrhea and vomiting

Question 9

How do you diagnose food allergy dermatitis?

Answer 9

• food trial = method of choice
• intradermal skin testing
• serology

Question 10

Describe a food trial

Answer 10

• novel source of protein and carbohydrate
• homemade vs. commercial
• no chewable medications, treats
• clear infections before the trial
• control concurrent allergies
• monitor for pruritus and recurrence of infections

Question 11

What are the challenges of a food trial?

Answer 11

• most food allergic dogs have had the same diet for years
• just changing the diet is NOT the equivalent of food trial
• few diets are truly “clean diets”: read the label!
• ensuring complete compliance (no snacks!)

Question 12

What are some home cooked sources for a food trial?

Answer 12

• Protein: pinto beans, fish, horsemeat, turkey, ostrich, venison, rabbit, pork, alligator
• Carbs: potato, corn starch, pasta, rice

Question 13

What are some novel proteins used in commercial diets?

Answer 13

• lamb
• venison
• duck
• rabbit
• kangaroo
• lentils
• salmon

Question 14

What are some concerns for potential food allergens in commercial diets?

Answer 14

• fish
• animal fat
• preservatives

Question 15

Describe hydrolyzed diets

Answer 15

• Rationale:
  
  • minimum molecular weight (7,500) to cause cross-linking of IgE
• Limitations:
  
  • it only applies to Type I hypersensitivity
  • small peptides can still aggregate to reach appropriate size
  • incr risk for Type IV hypersensitivity

Question 16

What are 3 canine hydrolyzed diets?

Answer 16

• Hills Canine z/d
• DVM ExClude
• Purina HA

Question 17

Describe Royal Canin - Anallergenic (Ultamino) diet

Answer 17

• feather hydrolysate with low molecular weight
  
  • source of L amino acids and oligopeptides
• maize starch

Question 18

Why is a rechallenge for a food trial necessary to confirm the diagnosis?

Answer 18

• to determine specific food
  
  • important to allow more dietary options
  • if new allergies develop, will make the approach easier
• recurrence within hours to 7d

Question 19

What is the therapy for food allergy?

Answer 19

• avoidance
• some dogs can be just managed with home-cooked diets
• new allergies to other foods may develop over time

Question 20

Describe contact dermatitis

Answer 20

• Two types:
  
  • irritant
  • allergic - type IV hypersensitivity
• considered uncommon in animals d/t protection from the coat
  
  • common in FL (plants)

Question 21

Describe irritant contact dermatitis

Answer 21

• all animals in contact are affected
• chemical, physical
• C/S develop at first exposure:
  
  • pain +/- pruritus
  • vesicles
• no prior sensitization

Question 22

Describe contact allergic dermatitis

Answer 22

• type IV hypersensitivity
• C/S do not develop at first exposure
  
  • ​pruritus
  • papules
• prior sensitization
  
  • sensitization period: 2-6 mo
• usually only one animal is affected

Question 23

What are features of contact allergens? Give some examples.

Answer 23

• small size molecules that can penetrate skin barrier (haptens)
• antigenicity is accomplished by conjugation with skin proteins
• Examples:
  
  • detergents
  • dyes
  • insecticides
  • shampoos
  • topical antibiotics
  • plants

Question 24

What are the clinical signs of a contact allergy?

Answer 24

• pruritic papular eruption
  
  • face
  • feet
  • groin
  • axillae
• pruritus may be severe

Question 25

How do you diagnose a contact allergy?

Answer 25

• resolution of clinical signs with avoidance (7-10d)
• relapse after re-exposure (1-3d)

Question 26

Describe a patch test

Answer 26

• best way to ID the specific allergen
• shave an area on the thorax 24h before
• apply suspect substance and neg control
• bandage
• read after 48h

Question 27

What is the therapy for contact allergies?

Answer 27

• avoidance
• glucocorticoids
• hyposensitization is not effective
• pentoxifylline
  
  • 48h prior to exposure
  • 15 mg/kg TID w/ food