Flea Control in Cats

By Ryan Llera, BSc, DVM; Catherine Barnette, DVM; Ernest Ward, DVM

How can my cat get fleas?

Adult fleas live, feed, and mate on our pets; the female flea lays eggs that fall off into the environment where they hatch into larvae. The larvae eat organic debris until they mature into pupae. The pupae may lie dormant for weeks to months, awaiting the ideal environmental conditions before hatching into adults. Newly hatched adult fleas jump onto a host animal to complete their life cycle.

Two days after eating a blood meal from the host, the female flea begins to lay eggs. Under ideal conditions, the flea can complete its entire life cycle in as little as two weeks; in adverse conditions, the cycle can take as much as a year.

The most important source of cat fleas is newly emerged adult fleas from flea pupae in your house or yard. Homes with carpets and central heating provide ideal conditions for the year-round development of fleas. The highest numbers of flea eggs, larvae, and pupae will be found in areas of the house where pets spend the most time, such as their beds and furniture.

"Even though fleas may be in your house, you probably will not see them."

Even though fleas may be in your house, you probably will not see them. The eggs are tiny white specks the size of dust particles, while the larvae, which are somewhat larger, with dark heads and lighter bodies, migrate deep down in carpets, furniture, or cracks in floors away from the light.

How do fleas affect my cat?

Many cats live with fleas but show minimal signs. However, problems can occur. Some cats develop an allergy to flea bites, especially if they are repeatedly bitten. Flea allergic cats groom or scratch excessively after being bitten by even a single flea, and often develop skin infections secondary to this self-trauma. Lesions most often appear at the base of the tail. Excessive grooming may also result in removing all evidence of a flea infestation on your cat. To eliminate this possibility, your veterinarian may advise rigorous flea control even though no fleas can be found.

Adult fleas live on animals and feed on blood. A single adult flea consumes many times its weight in blood over its lifetime. If a kitten, or a debilitated or older cat, has a lot of fleas, the blood loss can be severe, resulting in anemia.

The flea acts as the intermediate host for one species of tapeworm. This means that the tapeworm must complete part of its life cycle within a flea. Flea larvae become infected by eating tapeworm eggs, and if a cat swallows an infected flea while grooming, the tapeworm larva will develop into an adult tapeworm. Any cat with fleas is likely to also have a tapeworm infestation (see handout "Tapeworm Infection in Cats" for more information).

What products are available to treat my cat?

Shampoos, sprays, powders, and topical or oral preparations are all available. Although most topical insecticides kill adult fleas, many have limited effectiveness because they only work for a few hours after application. This is particularly true of flea shampoos and powders; they kill fleas present on your cat at the time of application but have little lasting effect; the following day, your cat may have fleas again.

In general, cats strongly dislike being sprayed so many cat owners prefer to use topical flea products. Flea collars may seem convenient, but most do not work well (the exception is flea collars that contain an IGR) and are not generally recommended. Flea collars, especially ones with a strong pesticide smell, may be harmful to some cats or may cause a skin reaction or rash.

"Flea collars, especially ones with a strong pesticide smell, may be harmful to some cats or may cause a skin reaction or rash."

There are very effective products made to be administered once per month or every three months. Some of these products are conveniently combined with medications to prevent heartworm and intestinal worms. Some products contain adulticide ingredients (kills adult fleas) that remain effective between scheduled doses, while others contain insect growth regulators (IGRs) that prevent the larval stages from maturing. For best results in a flea infestation, use flea control products that contain an IGR.

Newer products that have the combined advantages of adulticides and IGRs are available through your veterinarian.

ALWAYS READ THE LABEL CAREFULLY. Apply the product as instructed and repeat at the intervals stated. Ensure that the product is labeled for use in cats, as some dog products may be poisonous to cats.

How can I treat my home environment?

A number of products are available to kill the adult and larval stages of fleas and stop the flea life cycle, such as:

• adulticide sprays for use in the house
• sprays containing IGR for use in the house
• insecticides applied by professional pest control companies

Sprays inside the house should be used in places where the flea eggs, larvae, and pupae are likely to be. Treat the entire household first and then concentrate on the hot spots - your cat's favorite napping spots - such as soft furniture, beds, and carpets. Once they hatch from the egg, flea larvae move away from the light and burrow deep into carpets and into other nooks and crannies where they are difficult to reach. Be sure to move cushions, furniture, and beds to spray under them. Larvae are also likely to live in baseboards and the cracks and crevices between floor seams or floorboards.

Flea eggs and pupae are extremely tough and resistant to the effects of insecticides. To remove the eggs along with the dead fleas, your pet's bedding should be washed in hot water or replaced. Regular and thorough vacuuming of your carpets, floors, and soft furnishings can remove numerous flea eggs, larvae, and pupae. You will need to throw away the vacuum bag to prevent eggs and larvae from developing inside the vacuum cleaner. Vacuuming prior to using a spray for the house is helpful because the vibrations will encourage newly developed fleas to emerge from pupae, which will then be killed by the insecticide.

Are insecticides safe for my cat and my family?

Insecticides for flea control should be safe both for pet dogs, cats, and humans, as long as the manufacturer's instructions are followed. Avoid combining insecticides with similar modes of action. Always seek your veterinarian's advice if you are unsure and always tell your veterinarian about any flea control products you may be using other than those that have been prescribed. When properly used, side effects are quite rare and do not affect all cats. Certain types of pets (e.g., birds, fish, amphibians, reptiles, and invertebrates) may be susceptible to some products. Do not use any flea control products in the room in which these pets are kept without first consulting your veterinarian for advice.

I noticed my cat had fleas after her return from boarding. Did she get fleas there?

Not necessarily! Pre-adult fleas can survive for up to 140 days within their protective pupa. When you or your pets are absent from home for extended periods of time these adult fleas remain in the pupae because no host is available. As soon as you or your pet returns home, these fleas will emerge in large numbers and jump onto cats, dogs, and even people in the search for a blood meal. Vibrations (from walking) and/or increased carbon dioxide (from breathing) will trigger the emergence of fleas from their pupae.

Why does my cat still have fleas after treating her and the environment?

The apparent failure of treatment almost always results from improper application of the preventive, inadequate treatment of the home, or exposure to other infested pets or environments. There is no evidence of fleas developing resistance to insecticides, especially once-a-month topical flea preventives that contain a sterilizing agent or IGR in addition to the adulticide. Consider treating storage sheds, cars, and any outdoor sleeping spots. Bear in mind that your cat may be going into other people's houses if allowed to roam outdoors. Most of these problems can be overcome by using an effective flea preventive product on your cat in addition to treating your home.

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