Food Hypersensitivity

Chapter 47 Food Hypersensitivity



Stephen D. White


Adverse reactions to foods have been well documented in small animals. The terms food allergy and food hypersensitivity have been used interchangeably in the human and veterinary medical literature to describe clinical signs induced by food ingestion in which there are demonstrable or highly suspected immunologic reactions. The terms food intolerance and occasionally food sensitivity have been used when an immunologic etiology is unlikely or has not been established. Although the causes of abnormal reactions to ingested foods have not been well established in small animals, food hypersensitivity and food allergy are the terms commonly used. I prefer the former as being more accurate in describing an abnormal response of the immune system. Allergies to inhalant aeroallergens cause atopic dermatitis (see Chapter 46).



ETIOLOGY



• The exact mechanisms of food hypersensitivity have not been delineated in dogs and cats. Reactions to food have been noted in dogs and cats that could be termed immediate (i.e., hypersensitivity type I, occurring within minutes to hours after ingestion) or delayed (i.e., type IV, occurring within hours to days of ingestion). Recent reports (Ishida et al., 2003 and 2004) lend credence to both IgE- and cell-mediated mechanisms. A spontaneous canine model of IgE-mediated food hypersensitivity has been developed (Jackson and Hammerberg, 2002). However, documentation of the mechanisms involved in the development of food hypersensitivity in pet animals is still lacking.

• In dogs, the most common confirmed dietary allergens are beef, soy, dairy products, and cereal. Other allergens reported include cheese, chicken, chicken eggs, lamb, and chocolate.

• In cats, beef, milk, and fish are the most common dietary allergens. I have identified fish as an offending allergen in 50% of cats with food hypersensitivity.

• The vast array of foodstuffs used in commercial pet foods, as well as variable processing methods, probably accounts for the large numbers of allergens reported. Any dietary protein, even in small (mg) quantities may be the cause of food hypersensitivity.

• Food contaminants such as pathogenic bacteria and toxins, food additives such as tartrazines, and vasoactive amines such as tyramine in cheese have all been implicated or suspected as mimicking food hypersensitivity in humans. Their importance in small animals is unknown and is likely to be low.


CLINICAL SIGNS




Key Point


Although the age of onset is variable, predisposition is noted for young dogs (≤1 year of age). Owners seldom relate the onset of clinical signs to any change in diet.



• No sex predilections have been noted in dogs or cats with food hypersensitivity. Terriers and Siamese cats may be predisposed. Clinical signs are variable.

• Pruritus is the most common sign in dogs; rarely, non-pruritic animals are reported. The pruritus is often distributed similar to that for atopic dermatitis (i.e., feet, ears, face, and axillae) and these two diseases are clinically virtually indistinguishable if the pruritus is non-seasonal (year-round). The pruritus may be severe from very early in the disease. Animals with food hypersensitivity have been described as having glucocorticoid-resistant pruritus; however, this should not be regarded as a feature of food hypersensitivity as some animals are responsive to glucocorticoid administration.

• Cutaneous lesions noted in dogs include papules, erythema, epidermal collarettes, pododermatitis, seborrhea, and otitis externa. Rarely, sloughed or cracking claws may be caused by food hypersensitivity.

• In cats with food hypersensitivity, clinical signs include generalized pruritus, miliary dermatitis, facial and head pruritus, pruritic angioedema-urticaria, eosinophilic plaque, eosinophilic ulcer, mural folliculitis, and erythema.

• Gastrointestinal signs (vomiting, diarrhea) have also been noted (see Chapters 67 and 69). These may be more common than previously thought. Dogs in particular may show signs suggestive of colitis. In cats, food hypersensitivity has been manifested as lymphocytic-plasmacytic enteritis or colitis.

• Neurologic signs (epileptiform seizures, malaise) and respiratory distress (asthma-like syndromes) occasionally have been reported.

• Multiple organ involvement is uncommon.


DIAGNOSIS


Suspect food hypersensitivity in the following situations:


• Non-seasonal occurrence of pruritic skin lesions

• Recurrent pyoderma and yeast infection and recurrent otitis

• Lack of response to steroidal or other anti-inflammatory drugs in dogs and cats, although efficacy of corticosteroids in controlling pruritus does not rule out a diagnosis of food hypersensitivity

• Lack of response to progestational drugs in cats


Laboratory Findings


There are no consistent laboratory findings in small animals with food hypersensitivity. Peripheral eosinophilia may or may not be present.



Histopathologic Findings


Histopathologic findings are nonspecific and non-diagnostic, usually characterized by perivascular dermatitis with neutrophils or mononuclear cells predominating and variable secondary suppurative changes. Tissue eosinophilia is uncommon but has been reported. Histopathology is rarely needed as part of the diagnostic workup in cases of suspected food hypersensitivity.



Intradermal Testing


Intradermal skin testing with food extracts usually has been unrewarding in humans and small animals, possibly owing to changes in composition of the allergen with digestion or to improper dilution of the test allergen.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Food Hypersensitivity

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