In a Type I reaction, the animal has been previously exposed to an antigen and produces an excess of antibodies. If this antigen appears in the blood, the result can be either anaphylactic shock or more localized reactions (such as itchy patches on the skin). If the antigen enters through the skin, the more localized reaction is typical.
Anaphylactic shock is a rare, life-threatening, immediate allergic reaction to food, an injection, or an insect sting. The most common signs occur within seconds to minutes after exposure to the antigen. Dogs differ from other domestic animals in that the major organ affected by anaphylactic shock is the liver, rather than the lungs. Therefore, gastrointestinal signs are the major signs of anaphylactic shock rather than respiratory signs. These signs include sudden onset of diarrhea, excessive drooling, vomiting, shock, seizures, coma, and death. The dog's gums may be pale, and the limbs may feel cold. The heart rate is generally very fast, but the pulse is weak. There is no facial swelling.
Anaphylaxis is an extreme emergency. If you think that your dog is having an anaphylactic reaction, seek emergency veterinary assistance immediately. A veterinarian can give intravenous injections of epinephrine (adrenalin) to counteract the reaction. Treatment for other associated problems, such as difficulty breathing, may also be needed.
Hives and Swelling
Hives (urticaria) and areas of swelling are caused by allergic reactions to drugs, chemicals, something eaten, insect bites, or even sunlight. They generally develop within 20 minutes of exposure to the allergen (antigen). Hives are the least severe type of anaphylactic reaction. Small bumps occur on the skin. Often, the hair stands up over these swellings and sometimes they itch. Swelling is most often noticed on the face, especially on the lips, the muzzle, and around the eyes. The swelling can be so severe that the dog cannot open its eyes.
Hives and swelling are usually not life threatening and typically go away by them-selves if the source of the allergic reaction is removed or passes through the body. Veterinarians treat these reactions by giving appropriate antihistamines.
Allergic Rhinitis (Nasal Allergies)
Like humans, dogs can suffer from seasonal allergies (usually caused by pollen exposure) that can cause a watery nasal discharge and sneezing called allergic rhinitis. Nonseasonal rhinitis may be due to exposure to such allergens as molds, dander, bedding, or feeds. The condition is diagnosed by a favorable response after treatment with antihistamines and the disappearance of signs when the offending antigen is removed. Although skin tests can diagnose the allergic reaction in people, skin testing is not presently an accurate means to diagnose nasal allergies in animals.
Chronic Allergic Bronchitis
Chronic allergic bronchitis is characterized by a dry, harsh, hacking cough that is easily brought on by physical activity. The disease may be seasonal or may occur year-round. The condition is treated with expectorants, which aid in the removal of thick, sticky mucus. Your veterinarian may prescribe additional medication to help control this type of immune-mediated bronchitis. It is usually not possible to determine the antigen causing the reaction.
PIE Syndrome (Pulmonary Infiltration with Eosinophilia)
Infiltration of the lungs with a thick fluid and white blood cells, called PIE syndrome, is caused by allergens, viruses, and parasites in dogs. Pets with PIE syndrome generally become lethargic and have difficulty breathing with normal exercise. It is usually not possible to determine the antigen causing the reaction. Medications can help control the signs of the disorder.
Food allergies occur in pets as well as people. They can lead to inflammation of the lining of the stomach and intestines. In dogs, the first sign is vomiting that occurs within 1 to 2 hours of eating. The dog is usually healthy except for vomiting, although there can be weight loss, diarrhea or soft feces, and poor coat condition in severe cases. Food allergies often develop following an intestinal infection.
Both the diagnosis and treatment of food allergies are done by strictly controlling the diet at the direction of a veterinarian. Dogs should be fed low-protein diets that contain as few ingredients as possible. A basic diet of rice, cottage cheese (or tofu), and mutton, supplemented with vitamins and minerals, is a good way to begin. When the signs have disappeared, additional foods can be introduced one at a time. Commercial prescription diets are also available. In case the signs do not disappear after the dietary changes, prescription medications can provide excellent relief for dogs.
Skin Allergies (Atopy)
Skin allergy, also called atopy, occurs when a dog's skin overreacts to certain allergens in the environment. It has been estimated that 10% of all dogs suffer from these allergies, which are commonly due to inhaled substances such as dust mites, pollen, mold, or dander. Certain breeds of dogs, including terriers, Dalmatians, and retrievers, are predisposed to developing skin allergies. The most common signs of skin allergy occur in the area of the skin that is sparsely haired and directly exposed to the allergens, such as the back of the paws, abdomen, muzzle, and lips. The affected areas are very red, have small bumps, and itch.
The condition is diagnosed by history and physical examination. To determine the source of the allergy, tests may be performed. In one such test, the dog is injected with small amounts of the possible allergen into the shin. If the dog is allergic to the injected substance, a swelling will occur immediately at the injection site.
The key to managing this condition is removing or restricting exposure to the allergen or irritant in the dog's environment. Treatment consists of an extended series of injections of the offending allergen under the skin until improvement is noted. This type of treatment is effective in 60% of dogs. If the treatment fails, or is not used, treatment with prescription corticosteroids or antihistamines is often helpful. If your veterinarian prescribes a medication to control your pet's allergic reactions, be sure to follow the directions carefully and fully, including any restrictions regarding exposure to carpets, chemicals, or other potential hazards.
Last full review/revision July 2011 by Christine Andreoni; Kevin T. Schultz, DVM, PhD