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Flea season for Fido

Scratch, scratch, scratch . . . it's flea season for Fido

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• Introduction
• Signs of infestation
• Flea bite dermatitis
• Treatment

Introduction

'Tis spring.

'Tis the season of renewal, of warmer weather, longer days, flowering trees and shrubs, and bright-colored pansies . . . and fleas.

By late spring, fleas begin to emerge from their pupae as adults and migrate to the nearest dog or cat for blood meals. An adult flea mates shortly after emergence and begins laying eggs within 36 hours. In her brief 50-day lifespan, a single female flea can lay more than 2000 eggs.

Fleas are marvelously adapted for survival. The female lays eggs on the host animal, but the eggs fall to the ground, carpet, sofa, dog bed, owner's bed, or easy chair where they hatch in two-to-five days. The flea larva feeds on organic debris in the environment. Within a week or two, depending on temperature and humidity, the larva spins a pupa (or cocoon) to protect it during metamorphosis to the adulthood.

In the hard-shelled pupa, the larva transforms from a tiny maggot-like creature into a six-legged blood-thirsty super-jumper able to leap 150 times its own body length, and the cycle begins anew.

In the Midwest, the flea life cycle (adult flea à egg à larva à pupa à adult flea) takes about 35-40 days in early spring and 17-21 days in mid-summer. By late summer, cycles slow to two months or more, and they virtually shut down between November and March. In southern and Gulf Coast states, however, fleas complete their cycles in 20 days or less for most of the year and only slow down a bit in mid-winter.

Humidity is critical to flea survival. Eggs need relative humidity of 70-75 percent to hatch, and larvae need at least 50 percent humidity to survive. In humid areas, about 20 percent of the eggs survive to adulthood; in arid areas, less than five percent complete the cycle.

All bets are off when Fido brings fleas in for the winter. Household warmth can keep the cocooned larvae alive until conditions are ripe for emergence of the adults and may even allow life cycles to continue at a snail's pace.

Signs of infestation

Fleas are masters of their universe. They can hide in a forest of pet hairs, especially on long-coated or double-coated dogs, and can zig-zag among and between hair shafts faster than an Olympic skier on a slalom course. And then there's the leap. Now you see a black speck with legs, and now you don't.

So, don't depend on seeing the flea to know if he's there. Instead, look for clues.

If Fido scratches, he may have been bitten, but he may also have dry skin, an allergy, or mange mites. If he bites at his rear end especially around his tail or the inside or outside of his thighs, fleas are a possibility. If you find tiny black particles that turn red when dropped on a damp paper towel, voila! — flea feces, the damning evidence.

While Fido may be slightly bothered by a flea or two or may play host to a dozen or more without serious consequences, Rocky may be the unlucky recipient of a tapeworm infestation courtesy of mama flea and Sassy may be allergic to flea saliva and develop mild to severe skin reactions to even a single bite. The tapeworm or the skin bumps may be the only signs that the fleas are present.

Flea bite dermatitis

When flea bites dog, proteins (antigens) in the insect's saliva can cause an immune system reaction — the release of immunoglobulin that in turn causes itching. Depending on the type of cell involved (mast cells, basophils, or T-lymphocytes in the blood) and the type of chemicals released, the irritation can begin immediately, in five-to-six hours or in 24-48 hours or a combination of the three — all from a single bite.

Small red raised bumps on the base of the tail and along the outside of the back legs, self-induced scratches, and thickened skin on the base of the tail are all signs of chronic flea allergy. The diagnosis can be confirmed with an intradermal skin allergy test.

Writing in the AKC Gazette, veterinary dermatologist Dr. John Gordon describes the intradermal test: “With intradermal (skin) allergy tests, a small amount of a specific concentration of flea antigen is injected into the surface layers of the skin. The flea antigen binds to immunoglobulin or is absorbed by T-lymphocytes to create an immediate, late phase, or delayed reaction. Unfortunately, late phase and delayed skin test reactions are often considered negative skin tests because the reaction is not documented. Careful observation will help avoid this problem.”

Gordon described two other allergy tests that rely on drawing blood from the dog, but said that they are not as reliable as the intradermal test.

Treatment

Dog owners have access to a plethora of flea control products from herbs and electronics to biological controls. Powerful chemicals such as Dursban and diazinon and systemic insecticides such as the ingredients in Proban, Prospot, and Spotton seem to be on the way out. The systemic insecticides can build to toxic levels in the dog if not used extremely carefully. Some products repel fleas, some kill adult fleas, some kill larva or eggs, and some prevent fleas from growing and reproducing.

Garlic and brewer's yeast are popular flea repellents with the natural crowd, but there are no tests that indicate these diet supplements are effective. Many dog owners believe they work, however.

Electronic flea traps are sometimes used to attract and kill the pests before they attack the dog, but they do nothing about fleas in the yard or flea eggs or larvae in the house.

Flea collars have mixed results depending on the chemical involved, the size of the dog, and the density of the dog's coat.

The new generation of controls includes natural or genetically engineered pyrethrum, a daisy; flea-specific growth inhibitors (products containing fenoxycarb and methoprene); an environmental control that desiccates fleas and larvae; a once-a-month pill (Program) that prevents the formation of chitin, the flea's external body covering; and new surface products applied to the dog's skin or coat (Advantage and Frontline). Unlike the toxic insecticides in products such as Spotton, Proban, and Prospot, the ingredients in Frontline and Advantage are not absorbed into the bloodstream and are toxic only to fleas, not to dogs or their owners. Program, Frontline, and Advantage are available only through veterinarians; all other flea controls can be purchased over-the-counter in pet supply stores or catalogs.

The type of control depends on the extent of the dog's problem and the preferences of the dog's owner. The pill or topical application take less effort, but they should not be used alone in a heavy infestation because they do not treat the environment. The pill works when flea bites dog, so may not be suitable for an allergic dog. The topical solutions kill adult fleas and have some residual action as long as they remain on the pet's hair — even hair that has been shed on carpets and furniture.

Pyrethrums kill adult fleas but are short-lived. Permethrins, the genetically altered form pyrethrum, lasts for 10 days or so. Pyrethrum and permethrin are often found in shampoos and in pet and premise sprays containing growth inhibitors.

With mild flea infestations, an occasional bath with a permethrin shampoo or a Program prescription may do the trick, especially when combined with a premise spray that contains a growth inhibitor or with application of sodium polyborate, an insecticide that kills fleas by lethal constipation and desiccation. More serious infestations may call for the big guns, especially if the dog is allergic. But whatever combination platter of flea treatments you choose, make sure you have something on hand for the hot, humid days of summer when fleas can invade in hordes.

Norma Bennett Woolf

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