Dog - Allergy, Anaphylaxis, Urticaria, Hypersensitivity & Atopy Definitions

Allergy

An allergy, or allergic reaction is an exaggerated response by the body to a particular substance.  This substance is the allergen.  It is usually protein and can be a part of food such as milk, eggs, wheat, etc.  Pollens and also bacteria or moulds can be responsible and sometimes the allergen can be an antigen which is a substance produced by bacteria that stimulates the production of antibodies by the animal but in this case the reaction by the animal can be thought of as excessive.

There are at least five common types of allergy in the dog.  These include flea, food, contact, bacteria (bacterial hypersensitivity) and atopy.

What are the common allergens?

Almost any environmental substance can act as an allergen including many food preservatives, dyes, drugs and vaccines.  Allergens can enter the body by being breathed in, swallowed, touched or injected.  Some dogs appear to be particularly sensitive to some of these substances.

Anaphylaxis

For practical purposes consider anaphylaxis as a very sudden (acute) exaggerated allergic reaction by an animal to a particular substance.  It is always very rapid in onset and frequently results in swelling of the face, head, ears and other parts of the body.

The allergens are broadly the same as those causing allergic reactions.  Bee and wasp stings are frequently responsible in the case of anaphylaxis.  Certain drugs, e.g. antibiotics, vaccines and local anaesthetics can be frequently implicated as can certain moulds and pollens but these tend to be less common causes of anaphylaxis and are more likely to cause a more slowly developing allergic reaction, i.e. a rash, etc.

Urticaria

Urticaria is another name for an acute allergic (anaphylactic) reaction.  Food, drugs, vaccines, insect bites and stings can all be responsible.  Other common names are nettle rash or hives.

Nettle rash

This was originally a term confined to the reaction following contact with stinging nettles or other plants to which the subject was sensitive.  Today however it is often used to describe the skin lesions caused by other allergic or hypersensitivity reactions.

Hypersensitivity

Following the primary (first) exposure to the allergen which may have resulted in an anaphylactic or allergic response, subsequent exposure to the same substance can result in hypersensitivity.  This allergic reaction may be an immediate, anaphylactic type reaction, or delayed as with many allergic responses, resulting in eczematous lesions.  In some cases, e.g. food allergy  (hypersensitivity) it can be described as systemic in that the whole dog is involved, whereas contact dermatitis is an example of a local hypersensitivity since it only affects the skin that has been in contact with the allergen and may just involve the face, abdomen, paws, etc.

To complicate matters contact dermatitis may be immediate, i.e. itchiness, swelling or rash developing as soon as the dog has come in contact with the allergen (e.g. grass pollen, stinging nettles) or it may be delayed and only occur some time after contact as occurs with many food allergies.

Atopy

Atopy is also known as atopic disease, atopic dermatitis and allergic dermatitis.

Atopy is a predisposition by the dog to develop allergies (hypersensitivity mediated skin disease) against environmental allergens.  These may be inhaled, absorbed through the skin, swallowed or injected.