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Cornell Feline Health Center

Supporting Cat Health with Information and Health Studies.


Among the more than 2,200 types of fleas identified by entomologists over the years, none is more problematic, at least to cats and their owners, than a minute creature called Ctenocephalides felis felis. These little critters, commonly referred to as “cat fleas,” are almost imperceptibly small, ranging in size from that of a pinhead to about one-eighth of an inch in length.

In order to thrive and propagate, cat fleas need to dwell in a warm, moist, and safe environment, and these will be provided by a cat’s dense, furry coat. The consequences of flea infestation will be terribly uncomfortable for most affected cats and can be the source of deadly disease for some. At the least, flea bites are apt to cause insufferable itching, but a hypersensitive cat’s incessant scratching may open wounds in the skin that are vulnerable to serious infection.

Indeed, these tiny, wingless creatures often carry infectious agents themselves, such as tapeworm eggs and a variety of pernicious bacteria—including the organism that causes feline infectious anemia—which can be passed among cats that are in close physical contact. The risk that cat fleas pose to humans is also consequential, since these tiny insects can harbor such zoonotic agents as those that cause such human diseases as cat-scratch disease (Bartonella henselae), murine typhus, and plague.

A flea’s life cycle typically lasts about a month, but it can go on for longer than that, depending on temperature and humidity. During the cycle, the insect moves through a complete metamorphosis—from egg to larva to pupa to adult—and is most dangerous in the larval and adult stages. “Under ideal conditions,” says William Miller Jr., VMD, a professor of dermatology at Cornell University’s College of Veterinary Medicine, “one mating female will lay at least 20 eggs a day, half of which hatch as females. This can eventually produce about 20,000 new adult fleas in 60 days.”

All cats—regardless of age, breed, or gender—are subject to flea infestation and its consequences. According to Dr. Miller, they tend to be bitten mostly on the back of the neck and the top of the tail head. Cats with flea allergy dermatitis are apt to show especially distressful signs—reddish, crusty bumps, for example—even in areas that have not been obsessively scratched.

Flea infestation can pose a special danger to kittens, Dr. Miller adds. “A flea doesn’t actually bite,” he points out. “It sticks its proboscis into the skin and sucks blood. It doesn’t take too much of this sucking to cause anemia in a kitten that is carrying innumerable fleas.”

To counter flea infestation, Dr. Miller points out, you must, of course, rid the cat of the insects. However, you must also get them out of your home and off of your property—an effort that will certainly entail meticulous vacuuming of all furniture, rugs, and carpeting, a chore that may require the services of a professional exterminator.

“To treat the animal,” says Dr. Miller, “some very effective products have been developed in recent years—a wide variety of powders, topical antiflea products that are applied directly onto an infested animal’s fur and sort of wrap the animal in an insecticide, and medications containing flea preventives that circulate in the blood.” These products—whether sold over-the-counter or by prescription—may contain chemicals that are potentially harmful to an animal or its owner if misapplied or accidentally ingested and should be used only with the advice and guidance of a veterinarian. According to Dr. Miller, if you use one of these products faithfully—beginning in the spring of the year and going into the fall before colder weather sets in, your cat is very likely to remain free of fleas.

At the same time, he points out, owners who treat their animals with an effective antiflea product but neglect to prevent recurring infestation in the environment will never resolve the flea problem. “Skunks, raccoons, and other wildlife will seed your backyard with fleas,” he says. “Your animal brings one or two of them inside, and suddenly you’ll have thousands of fleas.”