Allergies are common, but complex. Determining if your pet has an allergy, and to what, requires a thorough history, clinical exam and multiple tests.
- Flea Allergy Dermatitis (FAD) results from an allergy to a protein in flea saliva, which comes into contact with the pet when the flea bites. Dogs and cats with FAD may not have a large flea burden – even a few fleas can cause itching in these animals. In dogs, red, irritated skin and hair loss over the rump, tail base and thighs may be seen. Cats may also be affected on the head. A diagnosis of FAD is usually made based on the location of the lesions and the itch resolving after flea treatment. Evidence of fleas or flea “dirt” (faeces) can help the diagnosis, but they are not always easy to find, particularly in cats who groom themselves so well. FAD can be managed by ensuring the pet is on a regular flea preventative, and that the pet’s environment has been treated for fleas, to minimise exposure.
- Canine Atopic Dermatitis (AD) is a genetically predisposed allergic skin disease. These dogs are allergic to environmental allergens such as dust mites and tree pollens. While the location of the itch can vary slightly depending on the breed of dog, generally the muzzle, axillae (armpits), elbows, ears, and the skin around the eyes and between the toes are affected. Diagnosis is made by ruling out other causes of itch, such as the allergies listed on this page, as well as bacterial and fungal infections and mites. The history of the pet’s itching and the sites of itchiness are assessed to ensure they fit with AD. Then an allergy test can be performed, which is usually either a blood test, or intradermal injections. The allergy test helps determine which environmental allergens the dog is allergic to, so that the allergens can be avoided (not always possible) or desensitising vaccines can be prepared.
- Allergic Contact Dermatitis occurs when the pet comes directly into contact with something they are allergic to. Red, raised bumps can be seen on the sparsely haired areas of the underside of the body and feet – where skin can touch the allergen. The most common allergens are plants such as Wandering Jew, but other things such as carpet deodorisers and cement have been shown to cause symptoms. A diagnosis of contact dermatitis is made by looking at the location of the clinical signs, and demonstrating that the clinical signs resolve when the dog is isolated from possible allergens. “Patch testing”, where possible allergens are applied to the skin to see if the reaction occurs, can help determine which plants or other materials are the likely cause.
- Cutaneous Adverse Food Reaction (CAFR) is caused by an allergy to a component of the pet’s food. In dogs the most common allergy is to beef, followed by soy, chicken, milk, corn, wheat and eggs. In cats, allergies to beef, dairy and fish are most common. An allergy to a certain food develops over time, so it will likely be something that has been in your pet’s diet for a while. CAFR should be considered if the animal is itchy all year round. The range of sites affected can be from just the ears to the whole body. Some pets may have concurrent gastrointestinal signs, such as vomiting, diarrhoea and flatulence. To determine whether a food allergy is present, and to which food, an elimination diet trial needs to be performed. This consists of feeding your pet either a hydrolysed diet from your vet, or a home cooked diet that contains ingredients your pet has never eaten before. If the itching stops, then beef, chicken and other food can individually be introduced to see what the pet reacts to. A diet that avoids the specific allergen can then be chosen for long term use.