One of the most common conditions we see at the Animal Clinic at Thorndale affecting dogs is allergy. In the allergic state, the dog’s immune system “overreacts” to foreign substances (allergens or antigens) to which it is exposed. These overreactions are manifested in three ways. The most common is itching of the skin, either localized (one area) or generalized (all over the dog). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea. The specific response that occurs is related to the type of allergy present.
Types of Allergy
There are five known types of allergies in the dog: contact, flea, food, bacterial, and atopic. Each of these has some common expressions in dogs, and each has some unique features.
Flea Allergy Dermatitis
In spite of common belief, a normal dog experiences only minor skin irritation in response to flea bites. Even in the presence of dozens of fleas, there will be very little itching. On the other hand, the flea allergic dog has a severe, itch-producing reaction to flea bites. This occurs because the dog develops an allergic response to the flea’s saliva. When the dog is bitten, flea saliva is deposited in the skin. Just one bite causes intense itching.
Clinical Signs
The dog’s response to the intense itching is to chew, lick, or scratch. This causes hair loss and can lead to open sores or scabs on the skin, allowing a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail). This is probably because fleas find this part of the dog more desirable. Many flea-allergic dogs also chew or lick the hair off of their legs.
Diagnosis
The characteristic distribution of scratching, licking, and chewing, the presence of fleas or flea dirt confirm the diagnosis. In a true flea allergic dog, fleas do not need to be present in large numbers to cause serious problems. One flea bite can cause intense itching and the flea may no longer be present (similar to a bee sting and the bee is gone). Flea dirt can be identified by combing over the dog’s rump and depositing the debris on a white paper. Flea dirt looks like small black pepper spots. Adding a few drops of water and streaking the dirt with a finger tip will result in a red smear. Flea dirt is partially digested blood.
Treatment
The most important treatment for flea allergy is to get the dog away from all fleas. Therefore, strict flea control is the backbone of successful treatment. There are many products available for flea control, and many work in entirely different manners. In some cases, multiple products may be needed. There are spot on topical medications, such as Frontline Plus and Revolution. FrontlinePlus has a growth regulator that prevents the hatching of eggs from fleas which bite your dog. It has the advantage of not being absorbed into your dog’s body. Alternating Frontline Plus and Revolution (offset by two weeks) has been effective where flea resistance to Frontline Plus alone has occurred. Nexgard is a long acting oral flea preventative. Often the house and yard will also need to be treated. Unfortunately, complete flea control is not always possible for dogs that live outdoors in warm and humid climates, where a new population of fleas can hatch out every 14-21 days. Our flea control article can provide additional information.
Although there are dog fleas and cat fleas, the two flea species do cross between cats and dogs and bite. The cat flea saliva seems to be especially allergenic in dogs.
Some dogs can be desensitized to the adverse effects of fleabites. Flea saliva extract (flea antigen) is injected into the dog in tiny amounts over a prolonged period of time. This is an attempt to reprogram the dog’s immune system so it no longer over-reacts to fleabites. If successful, itching no longer occurs or is less intense when the dog is bitten. However, this approach is only successful 50-75% of the time.
When strict flea control is not possible, antihistamines and corticosteroids (or “cortisone” or “steroids”) can be used to block the allergic reaction and give relief. Newer medications to treat allergy are becoming available. Keep in mind that you cannot cure the allergy, but by removing fleas you reduce exposure to the allergen. Steroids are often a necessary part of dealing with a flea allergy. Dogs are more resistant to the side-effects of steroids than humans, but significant side-effects can occur. For this reason, the goal is to administer the smallest amount of steroid needed to keep the dog comfortable. The advantage to oral medication is that it can be stopped if significant side effects occur.
Some dogs develop a secondary bacterial or yeast infection in the skin. When this occurs, appropriate antibiotics and shampoos must be used.
Bear in mind that flea allergy often accompanies other types of allergy, especially atopic allergy. If your dog itches when fleas have been eliminated, notify us so that we can modify the treatment approach.