Dogs can have respiratory or digestive problems caused by allergies, but most likely they will itch. Allergic reactions are rarely fatal for dogs, though they are a persistent nuisance and, for some especially sensitive dogs, a source of ongoing misery. A severely allergic dog may itch constantly, damaging its skin and coat with continual scratching, biting and rubbing. The skin damage may result in secondary bacterial and yeast infections. An allergic dog may also have chronic and occasionally severe respiratory or digestive problems. Or, in the worst-case scenario, succumb to anaphylactic shock. However, with proper diagnosis and treatment, most dogs can live in relative comfort.
Allergies are the physical expression of the immune system’s over-reaction to substances, called allergins, that are not actually threats. These things can range from pollens and molds to common food items. Flea bite dermatitis is the most common canine allergy; the dog reacts to the saliva of fleas. An allergy does not develop unless there has been prior exposure which allowed the immune system to recognize the allergen and “decide” that it needed to be attacked if encountered again. Exposure can occur through breathing or eating the allergen or getting it on the skin.
Environmental factors that contribute to allergies include not only exposure to allergens, but parasite load and the administration of vaccines. If a dog has parasites, the immune system will react to their presence. This can lead to severe allergic reactions if the dog is also exposed to allergens. Fleas are the most problematic parasites where allergies are concerned, but heartworm and intestinal parasites can also set the dog up for allergy attacks.
Both killed and modified live vaccines are potentially allergenic, though for very different reasons. Dogs may react to chemicals called adjuvants found in killed vaccines that enhance efficacy without exposing the dog to the pathogen. In modified live vaccines the toxins produced by the pathogen are what cause the reaction. The vaccines are not the cause of the allergy, but the trigger. A dog must be genetically predisposed to allergies for the reaction to take place.
Atopic dermatitis, a hypersensitivity reaction of the skin, is the second most common form of allergic reaction in dogs. When a dog is exposed to an allergen, usually by inhaling it, the immune system reacts causing itching, inflammation and swelling, often around the feet, ears, or anus. If the skin within the ear is affected, the dog may also develop secondary ear infections. Dogs may also experience allergic respiratory problems, digestive problems and eye irritation, but these are much less frequent than the skin reactions.
Food allergies can manifest as digestive problems or skin reactions. In humans, food allergy is over-diagnosed and this is probably also the case in dogs. A number of foods contain substances that can cause mast cells to release histamine, leading to an allergy-like reaction even in a normal individual. Any food can cause reactions in an allergy-prone dog, but some are more likely culprits than others.
Severely allergic dogs should not be bred. The crosses that produce them should not be repeated. The parents and other near relatives may be bred to dogs that do not have a recent family history of allergies.