What causes an anaphylactic reaction?
Before an anaphylactic reaction can occur, the pet must have a previous exposure to the offending substance. A common example is a dog that is stung by a bee and later develops a hypersensitivity to bee stings. The first time the dog is stung, a short-term localized reaction called a humoral response occurs. This causes the immune system to produce a substance called Immunoglobulin E (IgE) that binds to the surface of mast cells. Mast cells are responsible for the redness and swelling (hives) that you observe. At this point, the patient is said to be sensitized to the bee’s toxin. The second time the dog is stung, the sensitized cells will recognize the foreign protein (bee toxin) and release their contents in a process known as degranulation and activation. In severe reactions, this causes further release of the contents of mast cells throughout the body, resulting in systemic anaphylaxis. Localized hypersensitivity reactions such as extreme swelling at the site of the bee sting are c
