Page 603 - Small Animal Clinical Nutrition 5th Edition

Adverse Reactions to Food 625

single-blind food challenge, only the veterinarian is aware of long as seven days, particularly if the responsible allergen was
removed from the food for longer than one month (Guilford et
what food is being given. In a double-blind food challenge, nei-
VetBooks.ir ther the client nor veterinarian is aware of whether a specific al, 2001; Walton, 1967).
food is being given. Double-blind, placebo-controlled food
challenges are considered to be the “gold standard” for the diag- Treatment Phase
nosis of adverse food reactions in people (Sampson, 1993; For most adverse food reactions,avoiding the offending foods or
Bock, 1991). Only half of human patients thought to be aller- food additives is the most effective treatment.Thus,after a diag-
gic to a food react to the food when challenged in controlled, nosis of adverse food reaction has been made through the prop-
blinded conditions (Bock, 1991). Unfortunately, all reports and er use of elimination-challenge trials, the elimination food, if
most food challenge recommendations in the veterinary litera- nutritionally complete and balanced, should be fed for mainte-
ture have been open challenges. Open challenges will continue nance. Ideally, when used for long-term feeding, the food choice
as the most practical method of establishing tentative diagnoses should also have appropriate levels of phosphorus and sodium
of adverse food reaction in dogs and cats, but are subject to false for dogs and cats, and magnesium and the recommended uri-
interpretation by clients and veterinarians. nary pH range for cats (Tables 31-5 and 31-6). An attempt
Provocation involves introducing single ingredients until as should always be made to find an acceptable commercial food
many positive reactions as possible can be documented. Clients that will increase owner compliance with the feeding change.
and veterinarians are often reluctant to pursue challenge and
provocation after clinical signs have improved or have been
eliminated.Provocation may also be difficult to perform in many REASSESSMENT
dogs and cats because commercial pet foods contain large num-
bers of ingredients and feeding the same ingredients often can- How selective or meticulous an avoidance food must be
not be duplicated in challenge studies. As an example, use of depends on the individual patient’s sensitivity. Some dogs and
chicken meat in a provocative food challenge may not duplicate cats may suffer adverse reactions to even trace quantities of an
the types or levels of antigens found in poultry by-product meal. offending food or food additive, whereas others may have a
Elimination trials are often difficult to interpret because of higher tolerance level. Concurrent allergies may influence the
concurrent allergic skin disease. In several studies, up to 30% of threshold level of clinical signs in some patients. Symptomatic
dogs and cats with adverse food reactions had concurrent therapy for pruritic patients may also include corticosteroids
hypersensitivities (White,1986; Carlotti et al,1990; Rosser, and antihistamines. Corticosteroids along with feeding changes
1993, 1993a; Paterson, 1995; Roudebush and Schick, 1995). are often used in cats with IBD. One-third of people fed a strict
These patients may only partially respond to an elimination avoidance food for one to two years have tolerated the reintro-
trial. Flea-allergy and atopic dermatitis triggered by environ- duction of food allergens (Pastorello et al, 1989). Whether this
mental allergens are the most common concurrent diseases and is the case in dogs and cats is not known.
should be eliminated through other diagnostic testing.

PERFORMING AN ELIMINATION TRIAL IN ACKNOWLEDGMENT
PATIENTS WITH GI DISEASE
Elimination-challenge trial designs for patients with GI dis- The authors and editors acknowledge the contribution of Dr.
ease are similar to those for patients with dermatologic prob- Kevin J. Shanley in the previous edition of Small Animal
lems. However, shorter elimination periods are usually satisfac- Clinical Nutrition.
tory (two to four weeks). One study in cats with GI sensitivity
showed that vomiting stopped almost immediately in all affect- ENDNOTES
ed cats and diarrhea resolved within two or three days
(Guilford et al, 2001). In chronic relapsing conditions, the a. Ishida R, Masuda K, Kurata K, et al. Lymphocyte blasto-
elimination period chosen must be longer than the usual symp- genic responses to inciting food antigens in cats with food
tom-free period of the patient to allow reliable assessment of sensitivity. Unpublished data. University of Tokyo, Japan,
how food sensitivity contributes to the patient’s signs. 2002.
As with skin disease, the degree of clinical improvement dur- b. Roudebush P. Unpublished data. May 1992.
ing the elimination trial will be 100% only if food sensitivity is
the sole cause of the patient’s problems. For instance, resolution REFERENCES
of allergies acquired as a result of GI disease will not eliminate
the clinical signs due to the primary GI disease process. A The references for Chapter 31 can be found at
return of GI signs after challenge with the responsible allergen www.markmorris.org.
will usually occur within the first three days, but may take as