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Flea Allergy in Cats

One of the most common conditions affecting cats is allergy.  In the allergic state, the cat'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 cat).  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 four known types of allergies in the cat: contact, flea, food, and inhalant.  Each of these has some common expressions in cats, and each has some unique features.

In spite of common belief, a normal cat 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 cat has a severe, itch-producing reaction to flea bites.  This occurs because the cat develops an allergic response to the flea's saliva.  When the cat is bitten, flea saliva is deposited in the skin.  Just one bite causes intense itching. 

Clinical Signs

The cat’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 cat more desirable.  Many flea-allergic cats also chew or lick the hair off of their legs. 

Treatment

The most important treatment for flea allergy is to get the cat 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.  Some are used on the cat and some in the cat’s environment.  Unfortunately, complete flea control is not always possible for cats that live outdoors in warm and humid climates, where a new population of fleas can hatch out every 14-21 days. 

Some cats can be desensitized to the adverse effects of fleabites.  Flea saliva extract (flea antigen) is injected into the cat in tiny amounts over a prolonged period of time.  This is an attempt to reprogram the cat’s immune system so it no longer over-reacts to flea bites.  If successful, itching no long occurs or is less intense when the cat is bitten.  However, this approach is only successful about 50-75% of the time.

When strict flea control is not possible, corticosteroids (or "cortisone" or "steroids") can be used to block the allergic reaction and give relief.  This is often a necessary part of dealing flea allergy.  Some cats respond best to long-acting injections and other to oral medication.  Cats 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 cat comfortable.

Some cats develop a secondary bacterial infection in the skin.  When this occurs, appropriate antibiotics must be used.