Definition

A hypersensitivity or adverse reaction of body tissue to a food substance.

Clinical Signs

Signs same as for dermatitis:

• Pruritus (itching)
• Inflammation
• Lesions from scratching
• May have patchy hair loss

Etiology

Food sensitivities can include any type of adverse reaction to a food or food additive and can be divided into categories such as:

1. A Food Allergy or Hypersensitivity where the reaction may be immediate or delayed.

2. A Food Intolerance of unknown or known immunological mechanisms, such as, lactose intolerance.

In food allergies, proteins within the food may be responsible for a reaginic immune mediated antibody-antigen (IgE) response, when there is an immediate reaction. With IgE mediated reactions inflammatory mediators are released when a food antigen binds to a specific IgE antibody. In general, IgE mediated reactions typically show with rapid development of symptoms, whereas, in food hypersensitivity non-IgE mediated reactions being cell mediated tend to develop over hours to days; although combined IgE and non-IgE reactions may occur. Reactions takes place after the food is digested, and the allergens cross the gastrointestinal lining to enter the bloodstream. As they reach the level of the skin the allergic response is seen as an atopic or an eczematous dermatitis.

Most food allergies in rats are often of a delayed hypersensitivity response. In delayed hypersensitivity the allergic response occurs only after there has been repeated exposure to a food, or product, or antigen, that has been previously encountered. Signs and symptoms are similar to that of eczematous dermatitis, and are like that seen with ectoparasite infestation, or fungal infections. This can sometimes make it hard to discern if food allergies, or another one of these causes is actually responsible for the dermatitis, unless one can identify that parasites are present or knows that an offending food has been given.

With food intolerance, the immune system is not involved. This can be seen where lactase deficiency is present. Lactase is an enzyme that is in the lining of the gut. It is this enzyme that degrades lactose, which is found in most milk products. If lactase is not present in sufficient quantity, the body cannot digest the lactose, and instead is used by bacteria, causing gas formation, bloating, and diarrhea.

Other types of food intolerance produce an adverse reaction to certain products that are added to food to enhance taste, color, or protect against growths of microorganisms. Some of those compounds involved are yellow dye number 5, monosodium glutamate, and sulfites which can occur naturally in food or be an additive to prepared foods.

Still other intolerances (not mentioned here) are associated with ingestion of toxic food and plants.

Those diets containing processed food proteins, fillers, and colorings may trigger skin allergies in rats.

Diagnostics

Obtain history, include type of diet being fed.

Examine for signs of eczema/dermatitis.

Esinophilia and increased serum IgE levels may be present, though not always.

Rule out other causes such as parasites, fungal infections, or other disease process such as tumor growth, or metabolic conditions.

Treatment

If foods known to cause allergenic responses are found to be part of the rat’s diet, exclude these substances.

If no new foods have been added to the diet or the specific food agent is unable to be identified readily, then proceed with an elimination diet. A true elimination diet involves giving one novel protein source and one novel carbohydrate source. This type of controlled diet can be very strict. Listed below is a modified version of an elimination diet (Ducommun 2000):

Give a base diet of cooked brown rice, raw millet, and include 1 teaspoon of Nutri-Cal (purchased at your local Pet Store or through your Veterinarian). Give over 7 to 10 days. If improvement is seen, then begin adding a food to this base diet. Keep a record of when each food is added and the response. If symptoms return following the addition of a particular food, then you have identified the culprit food and can remove it from the diet.

If skin irritation and lesions are present from itching see Dermatitis for treatment options.

Nursing Care

• Assess the skin daily for signs of improvement.
• When beginning an elimination diet, keep a record of which foods have been removed or added, and the response.
• Treat skin lesions, skin irritation, or lesions.
• Keep nails clipped to prevent injury or chance of infection to skin from scratching.
• If condition worsens see a veterinarian for further treatment modality.

Outcome

• Culprit foods identified and removed from diet.
• Any skin irritation, itching or lesions resolved.

Prevention

• Provide recommended balanced diets for rats as listed in the Diet page.
• Avoid known foods to be causative agents of allergic response (e.g., peanuts, dairy products, eggs, and processed foods containing dyes).