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Your dog is suffering from "flea allergy dermatitis".
Flea allergy dermatitis (FAD) is a very common cause of allergic dermatitis. There are convenient and very effective treatments available. I recommend Capstar, Revolution, Advantage, or Frontline. We also use a very effective product called Buhach powder http://www.buhach.com/ since we have a variety of animals (dogs, cats, birds, etc.). We also sprinkle the powder under the bedding of animals and around our premises. Since Buhach powder kills invertebrate parasites, it's important not to get the powder near fish.
Dogs that have flea allergy dermatitis are hypersensitive to the saliva a flea passes into the dog’s skin when it bites. The bite from a single flea will have a minimal affect on a normal animal, but dogs with flea allergy will experience immediate itching, redness and swelling. It is the dogs themselves, and not the fleas, that typically do the worst damage. When a dog scratches its fleabites excessively, hair loss and skin abrasions can result. Some dogs will develop circular, red, painful sores called hot spots that can occur anywhere on the skin, but commonly are seen along the back and tail base.
Supportive medical therapy must be instituted to control pruritus (itching) and secondary skin disease in hypersensitive animals. The efficacy of antihistamines for the treatment of pruritus is variable. The most commonly used antihistamines include Atarax (hydroxyzine hydrochloride) 2.2 mg/kg, by mouth three times daily or Benadryl (diphenhydramine) 2.2 mg/kg, by mouth twice a day. A 7 to 10 day therapeutic trial of any one antihistamine is required to see maximum benefit. Glucocorticoids are the most effective drugs in the management of pruritius. Systemic glucocorticoids (are often needed to control inflammation and associated pruritus. Short-acting prednisone or prednisolone can be administered initially at a dosage of 0.5-1.0 mg/kg, once a day, tapering the dosage and using alternate-day therapy until the lowest dose possible that still controls the pruritus is given. As soon as flea control is accomplished, the glucocorticoid can be discontinued. Anti-inflammatory therapy should never be used as a substitute for flea control.
Secondary bacterial skin infection can be associated with flea allergic dermatitis. Systemic antibiotics are commonly used to control the pyoderma and thus reduce the associated inflammation and pruritus. Selection of an appropriate antibiotic should be based on bacterial cultures and results of antibiotic sensitivity tests.
Hyposensitization consists of administering allergens to a hypersensitive animal on a regular basis in an attempt to obtain a state of clinical nonreactivity to flea bites. The effectiveness of currently available whole flea extracts is controversial.
When a flea bites a dog it is looking for a meal of blood in which to nourish itself. In order to suck this blood it inserts an anticoagulant into its saliva to prevent the blood from clotting while it sucks it through its small proboscis. It is the allergens in this saliva that cause an allergic reaction to occur.
The most common canine allergic skin disorder, flea allergy only can be resolved by preventing the dog from being bitten by the flea and removing all the fleas from the dog’s environment. There are medications available, however, that will alleviate the itching and discomfort until complete flea control is achieved.
The most prevalent flea on dogs is Ctenocephalides felis. Flea allergy dermatitis or flea bite hypersensitivity is the most common dermatologic disease of domestic dogs in the USA. When feeding, fleas inject saliva that contains a variety of histamine-like compounds, enzymes, polypeptides, and amino acids that span a wide range of sizes (40-60 kD) and induce Type I, Type IV, and basophil hypersensitivity. Flea-naive dogs (dogs who have not been previously exposed to fleas) exposed intermittently to flea bites develop either immediate (15 min) or delayed (24-48 hr) reactions, or both, and detectable levels of both circulating IgE and IgG antiflea antibodies.
The goals of flea control are elimination of fleas on pet(s), elimination of existing environmental infestation, and prevention of subsequent reinfestation. The first step is still the elimination of existing pet flea infestations. Elimination of those fleas currently established on the dog is necessary to eliminate pet discomfort. When treating a dog with a topically applied formulation, it could take several hours (12-36 hrs) until the compound has spread sufficiently or reached sufficient systemic concentrations to eliminate all existing fleas. If a more rapid rate of kill is needed, a flea spray or nitenpyram may be desirable. Capstar (nitenpyram) is an oral treatment that effectively kills adult fleas.
Several currently available insecticides provide excellent elimination of established flea infestations; these include Frontline (fipronil), Advantage (imidacloprid)http://www.peteducation.com/article.cfm?cls=0&cat=1463&a rticleid=1370, Capstar (nitenpyram), Revolution (selamectin)http://cal.vet.upenn.edu/dxendopar/drug%20pages/selamectin .htm, and pyrethroids (similar to the natural chemical pyrethrin produced by the flowers of a chrysanthemum). Orally administered Capstar will eliminate fleas within 3-4 hr, while the topically applied residual spot-on formulations containing fipronil, imidacloprid, or selamectin take 12-42 hr.
The second goal is to eliminate existing infestation in the pet’s environment. This can be accomplished in several ways: 1) topical application of residual insecticides that kill newly acquired fleas (within 24 hr) before they can initiate reproduction, 2) administration of topical, injectable, or oral IGR to stop flea reproduction, 3) repeated application of insecticides and/or IGR to the premises, or 4) combinations of the above.
Topical application of residual insecticides and administration of topical, injectable, or oral insect growth regulators (IGR's) have become the preferred methods of eliminating flea infestations. Several of these new insecticides and insect growth regulators have been shown to be extremely effective in controlling fleas on pets living in infested premises. Field studies have shown that Frontline (with or without the addition of (S)-methoprene), imidacloprid, lufenuron (with pyrethroid spray or nitenpyram tablets), and selamectin may be effective in controlling flea infestations, without the need for premise treatment. Flea infestations can be eliminated via chronic use of topical and systemic approaches because most fleas are killed prior to and/or directly inhibited from reproducing.
If residual flea products are applied at the appropriate dose and treatment intervals, there may be adequate residual activity between applications to kill many newly acquired fleas before egg production is initiated. However, flea survival and reproduction may occur prior to the next application for a variety of reasons such as: 1) residual activity <100% within the labeled time frame, 2) rate of flea kill slows during the third or fourth week, 3) delayed or infrequent product reapplication 4) simple under-dosing, and 5) mechanical removal of water-soluble insecticides during bathing or swimming. These problems may result in delays in control or outright treatment failures.
None of the currently available residual flea products is 100% effective against all flea strains between labeled reapplication periods due to genetic variability of different flea populations. Many of the factors that allow flea infestations to persist could possibly lead to genetic selection of resistant flea populations. Surviving fleas may be capable of producing viable eggs. Continued reproduction must be halted to prevent persistent flea infestations and selection for resistant fleas. Reproduction can be prevented by administration of topical or systemic IGR, which provide prolonged residual ovicidal activity, interrupting future flea development even after residual activity of an insecticide is diminished. Application of methoprene or pyriproxyfen to the hair coat of dogs and cats rapidly kills developing flea eggs in addition to residual ovicidal activity. The combination of fipronil/(S)-methoprene or other adulticidal/ovicidal products has demonstrated activity against adult fleas and provides prolonged residual ovicidal activity, thus reducing the potential for genetic selection.
In cases of massive flea infestations or severe pet or human flea allergy, treatment of the premises with adulticides and insect growth regulators IGR may still be necessary. Control may be achieved by using insecticides with residual activity (or by repeated application of short-acting insecticides) in combination with an IGR to prevent the development of flea eggs and larvae. Methoprene and pyriproxyfen are the 2 currently available IGR for premise application. Insecticides and IGR can be applied by broadcast treatment (hand pump sprayers or pressurized aerosols) or with total release aerosols or “foggers.” During application, the surface of all rugs and carpets must be treated adequately. Efforts should be directed to areas where flea eggs and larvae accumulate, such as carpets, cracks, grooves in hardwood floors, behind baseboards, under the edge of rugs, beneath furniture (beds, tables, and sofas), and within closets. In severe infestations, a second treatment may be necessary 7-10 days later due to continued emergence of adult fleas from cocoons hidden deep within carpets.
Pet owners should also conduct mechanical control. Helpful procedures include washing pet blankets, throw rugs, and pet carriers; in addition, pet sleeping and resting areas should be vacuumed thoroughly to help remove flea eggs and larvae. Seat cushions and pillows on sofas and chairs should be removed and vacuumed, and special attention should be given to crevices in sofas and chairs and to areas beneath sofas or beds where flea eggs and feces may drop from the pet and accumulate.
Dr. Hanson, DVM, PhD
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