Affected Animals:
Any breed or sex of cat. Dogs also can be allergic to fleas.

Overview: The bite from a single flea will have a minimal effect on a normal cat, but a cat with flea allergy will experience immediate itching and swelling.  Flea allergy is the feline allergic skin disorder most commonly found.  Cats that have it are hypersensitive to fleabites; their skin becomes inflamed, irritated and itchy in reaction to allergen in the saliva that fleas pass into the skin when they bite.  The skin reaction and intense itching can lead to hair loss and skin lesions.

Treating flea allergy requires eliminating all fleas from a cat's environment.  Until complete flea control is achieved, however, there are medications that alleviate the itchiness and discomfort.

Clinical Signs:
The clinical signs of flea allergy in the cat are less consistent than in the dog.  Pruritus, excessive grooming, alopecia, barbered hairs, eruptive skin lesions with hemorrhagic crusts called miliary dermatitis are noted commonly.  Miliary dermatitis is a nonspecific skin lesion with different possible causes, but fleabite hypersensitivity is the most common cause.  The distribution of lesions can be generalized, confined to the head and neck, or involve the caudal legs and dorsal trunk region.  Eosinophilic plaques (elevated skin lesion containing eosinophils) and ulcerations of the skin sometimes are noted in cats with flea allergy. 

Symptoms:
Common symptoms include increased grooming, rubbing, or scratching; loss of hair; crusts or erosions of the skin; and red scab-like bumps.  Red, raised skin lesions also can be noted.  Fleas or flea feces may be found in the fur.

Description: Flea allergy is the most common feline allergic skin disorder, affecting cats with an abnormal sensitivity to saliva fleas inject into the skin when they bite.  In reaction to fleabites, allergic cats will have inflammation and irritation of their skin -- not to mention intense itchiness.  Hair loss and skin lesions can result when a cat scratches or bites its irritated skin.  Several different skin lesions can result from the allergic reaction, but miliary dermatitis, which consists of raised bumps with a dried blood scab, is the most common lesion noted.

The problem may occur year-round in warm climates or in flea-infested indoor environments.  In regions with cold winters the allergy will appear seasonally during the warm months of the year.  Treatment of flea allergy requires eliminating the fleas from the cat, other pets, and the surroundings.  Temporary relief of itching, using medications, is provided for severely affected cats until flea control is achieved.

It may be difficult to detect fleas on a cat, but brushing it over a white sheet may help: flea feces, a dark, black material, falling from the cat's fur onto the sheet would suggest the presence of fleas.  A flea comb can also be used to look for the feces or the fleas themselves.  Cats that are itching excessively should be examined often.

Diagnosis:
The symptoms of flea allergy can mimic other disorders of the skin.  Before concluding that a cat is allergic to fleas, the examining veterinarian first will have to rule out allergies to food and inhalants, internal parasites, drug reactions, hair follicle inflammation or folliculitis, fungal infection, and other topical parasites -- all of which have similar signs as an allergic reaction to fleas.  A thorough history and physical exam will be required, during which the veterinarian will analyze the type and size of the skin lesions.  Follow-up examination allows assessment of the cat's response to therapies for flea allergy.  Skin tests and allergy testing by intradermal injection may be advised.  It is possible for a cat to have coexisting allergies, making management of the symptoms more difficult.

Prognosis:
Removing fleas from the environment usually will put an end to the cat's allergic reactions.  However, a cat with flea allergy dermatitis always will remain allergic to fleas.  The severity of this allergy typically worsens with age.  In addition, a cat with concurrent allergies will have an incomplete recovery and should be reevaluated by your veterinarian after flea control is achieved.

Transmission or Cause:
When a flea bites a cat, it passes its saliva into the cat's skin.  Cats that are allergic to flea allergen in the saliva will experience swelling, irritation, and itchiness.  When the cat scratches the bites, further trauma to the skin -- lesions, hair loss, and even worse itchiness -- will result.  A single fleabite can cause these symptoms in an allergic cat; felines without this allergy must be bitten many more times before their skin becomes irritated. 

Treatment:
The goals of treatment are to eliminate the fleas and to alleviate the cat's allergic reaction to them.  The most important step is to remove fleas completely from the cat and its environment.  There are many commercially available products that kill fleas both indoors and outdoors as well as those designed for use on the cat.  Professional pest extermination companies, which usually carry a satisfaction guarantee, are also an option.  Note that other household animals also must be treated for fleas to prevent the allergic cat from becoming reinfested.  A veterinarian can customize a flea control program to meet an allergic cat's individual needs.

Therapy for the allergic reaction is based on the severity and history of the symptoms.  Following an evaluation of the cat, the veterinarian may prescribe any of the following medications: corticosteroids, antihistamines, antibiotics, fatty acid supplements such as skin oil replacement, and topical ointments.  In addition, he or she may recommend a commercially available product that kills fleas before they have the chance to bite the cat; such products are ideal for preventing further allergic stimulus.

The effectiveness of allergy shots, or hyposensitization, for treating fleabite hypersensitivity remains controversial.  They have not been proven to benefit flea allergic cats.  This method of treatment, prescribed by a veterinary dermatologist, usually is reserved as a final therapeutic step for severely afflicted animals.

Prevention:
Prevent fleas from entering the household.  If evidence of fleas is noted on the cat or any other pets in the household, early intervention can stop the problem before the symptoms become severe.