Derm's Dirty Dozen: These six diabolical diseases are bound to plague your patients and your patience - DVM
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Derm's Dirty Dozen: These six diabolical diseases are bound to plague your patients and your patience


Flea allergy dermatitis

Ctenocephalides felis (C. felis) is the common flea found on most domesticated animals. This cat flea is found on cats, dogs, raccoons, opossums, domesticated rabbits, ferrets, cattle, foxes, coyotes, bobcats, koalas and some avian and rodent species. It is also found to infest the mongoose population in Hawaii. They are rarely found on squirrels or wild rabbits. C. felis stay permanently on these hosts where they feed, breed and eventually die. They do not survive for extended periods of time off the host, however, survival rates of 12 days or more were reported under moist conditions in homes. In addition, adult fleas can on occasion, leap onto clothing of humans and be carried away to a new location.

Fleas are obligate parasites and are a permanent parasite on the host until it dies, usually in about 100 days. The average pet has twice as many female fleas as male fleas. The female flea begins feeding on the pet and starts to lay eggs within 24 hours of hatching and can lay up to 40 to 50 eggs per day. The eggs are not sticky and fall off the pet into the environment. It has been clearly shown that many eggs do not survive and undergo desiccation in dry environments. However, due to the massive reproductive capabilities of the adult flea, a substantial infestation can still occur in the home as well as the outdoors.

The ova of C. felis begin hatching within a few days after they enter the environment (home and outdoors). The proper conditions for survival include adequate temperature (probably the most important factor) and humidity. The ideal temperature is 40 to 85 degrees F and humidity above 50 percent. Dry conditions with humidity below 50 percent can be lethal to ova. Ova and larvae simply desiccate when exposed to hot and dry conditions with inadequate moisture. The surviving eggs hatch into larvae within a few days or weeks. The larvae also undergo several moltings. Larvae survival is also dependent upon similar temperature and humidity values as the ova but are also reliant on a food source such as adult flea feces and dried host blood. The larvae enter the pupal stage by spinning a loosely packed silk cocoon. This sticky cocoon often is coated with environmental particles and is much more resistance to extreme environmental conditions and insecticides. Pupae will hatch in 13 days or less under ideal conditions but can survive for five months or more without an adequate host. The time for pupal development and hatching is termed the pupal window. The time from deposition of eggs to adult flea emergence is called the developmental window and can be up to three months in duration. These pre-adults are found in the carpeting fibers, pet bedding, under furniture, cracks in hardwood floors, under sofa cushions, soil, grass, sand and in animal burrows.

When encountering a flea infestation on a pet, especially a pet with symptoms of flea allergy dermatitis (FAD), a three-step program is recommended to eliminate or reduce flea bites on the pet. Initially, the proper application of adulticides, such as fipronil, imidocloprid or selemectin, on all pets is advised. Some of these products demonstrate larvicidal properties. Cats tend to lick the non-dried product after application, so these products are applied to the base of the head in an area that cannot be groomed. Most animals that have adult active fleas on the coat are most likely exposed to an infested environment thus overwhelming the adulticide product. Frequent shampoo therapy (especially in dogs) with strong soaps or stripping ingredients can remove some of the product as well. It is recommended to apply adulticides on a dry coat and delaying shampoo several days after application.

The second objective is to apply treatment to the home environment. There are at least two insect growth regulators (methoprene and pyriproxyfen) available on the market in the Unites States and are designed to interfere with egg hatchability and larval development. These two stages can comprise greater than 50 percent of the pre-adult population. Most house sprays are water-based and contain an accompanying adulticide, such as permethrin or tetramethrin. The spray should be applied to pet bedding, all carpets, hardwood floors, under furniture, under sofa cushions, closets, carpeted-based cat condominiums, doormats and carpeted areas in the automobile. These insecticides also demonstrated some ovicidal and larvicidal properties but may not persist in the environment for long periods of time. It is therefore recommended to treat the home with a second application two weeks later (pupal-window) thus achieving a quick knockdown of newly emerging adult fleas. A third application is also advised three months to six months later. Finally, sodium polyborate powder has been shown to be effective in controlled indoor pre-adult stages. The powder acts as a desiccant, and when ingested by larvae, it acts as a toxin.


Source: DVM360 MAGAZINE,
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