Dogs and cats rarely become desensitized to flea bites once they develop an allergy. Dogs and cats that are not sensitive to flea bites rarely develop lesions from the bites, but may bite or scratch at the flea when it bites them. Some studies have shown that up to 40% of dogs in any given area will test positive for flea bite allergies. Other studies show that many dogs with flea allergies also have inhalant allergies compounding the problem. There does not appear to be a breed or sex predilection for this allergy.
Symptoms
Flea bite allergy is characterized by being a seasonal allergy that is worse during peak flea times in the summer and fall. Even in temperate areas or in cases with home infestations, the symptoms of flea bite allergies appear to worsen in the summer and fall. Dogs that have flea allergies will bite at the base of their tail and scratch frequently. The bite of a single flea can cause hours and days of intense itching. Many dogs have a characteristic loss or thinning of hair above the base of the tail. In addition, fleas or flea dirt (feces) can be found on the dog the majority of the time. The feces, or flea dirt will dissolve into a red color when moistened; this is because it is primarily digested blood. However, if the dog is bathed or treated regularly, very little evidence of fleas may be found. Severely affected dogs may itch over their entire bodies, have generalized hair loss, and red inflamed skin. Hot spots are often a result of flea bite allergies.
Cats with flea allergy dermatitis can have a wide spectrum of symptoms including miliary dermatitis, which is characterized by crusty papules (small, red, raised skin lesions), symmetrical hair loss (alopecia), and eosinophilic plaques and linear granulomas.
Diagnosis
Diagnosis can be made by visual signs in combination with the presence of fleas or through intradermal skin testing. Intradermal skin testing is a very effective diagnostic tool for this particular allergy, although some false negative results can occur. Since many affected dogs also suffer from other allergies, many times the flea bite antigen is incorporated into a broader intradermal skin testing program. Some cats with flea allergy dermatitis do not have a positive intradermal test.
Treatment
Treatment primarily involves preventing the flea from coming into contact with the dog or cat.
Topical Treatment of Pets: With the advent of topical flea and tick control products, it has become much easier to have effective flea control. When choosing a topical powder, spray, or once-a-month flea control product, be sure to choose a product that not only kills fleas, but repels them. Such products contain pyrethrin, etofenprox, or permethrin. NOTE: Products containing permethrin should NOT be used on cats. Pyrethrins and etofenprox, on the other hand, are safe for cats. If a dog or cat is sensitive to flea saliva, just one bite can set off an allergic reaction. If a product does not repel fleas, then all of the fleas must bite the animal before they die. Remember, the once-a-month pills that act as growth regulators do not stop fleas from biting pets. They just make the fleas unable to reproduce. Since a flea can live for months, a dog with flea bite allergies can suffer throughout an entire flea season with just occasional flea contact. Controlling the contact of fleas with the dog appears to be the most successful route. If a dog is on a good flea control program but occasionally still gets bitten and has a flair up, antihistamines, or in severe cases oral steroids, can be used to get the itching under control.
Treatment of Environment: Remember that good environmental treatment for fleas involves treating the house, yard, and sleeping area of the dog with a product that kills the adults (adulticide) and with an insect growth regulator as well. Other pets in the home should also be treated, as they could continue to bring fleas into the environment. While injudicious use of pesticides and growth regulators is never recommended, an effective flea prevention program is much safer and easier than dealing with a full blown flea infestation.
Hyposensitization: Hyposensitization of dogs with a series of injections does not appear to be very effective. There are several of these commercially available products available for veterinary use, but most dermatologists do not use them.
