External Parasites of Cats--Fleas

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The most common flea affecting both dogs and cats in North America is the cat flea, Ctenocephalides felis.

Flea infestation is most common in the summer months (or when the temperature is between 60-80°F, and humid). Eggs are usually found in dark, humid areas such as deep in carpet pile. Flea eggs and pupae are more resistant to pesticides than are adult fleas. Fleas are about 1 mm long, thin, brown and shiny, and can jump long distances. Sometimes, a flea may not be seen (they scurry under the fur pretty quickly!), but the telltale flea dirt which appears as small dark clumps or coils may be seen in the fur when it is parted. A flea comb can be very helpful to screen for flea infestation as it will pick up both dirt and fleas!

Fleas like to live on their warm host, and the flea dirt you see is the digested blood that the flea passes out. Eggs fall out and develop in the rugs and furniture. Within a week if environmental conditions are right, first stage larvae are crawling around and feeding. These larvae molt twice then form a little pupa in a cocoon. Three to four weeks later, an adult emerges. In some environments, immature forms can survive up to one year before developing into an adult flea.

Fleas can cause a variety of diseases, from allergy to zoonoses. Flea infestation can cause blood loss anemia in young or debilitated animals. When animals ingest fleas, parasites such as Dipylidium tapeworms may be transmitted. In these instances, not only do fleas need to be treated, but the tapeworms as well. Some cats have hypersensitivity reactions to flea saliva resulting in flea allergy dermatitis. Flea allergy dermatitis can cause intense pruritis (itchiness) and alopecia (hair loss), especially around the head and neck, over the topline near the tail, and in the inner thighs. Sometimes eosinophilic skin lesions develop. See our article Eosinophilic Granuloma Complex to learn more. Just a single flea or only a very small number of fleas can result in allergic reactions.

Your veterinarian can treat fleas with a variety of products. Topical monthly pesticides such as selamectin (Revolution ®), fipronil (Frontline ® Spray), and imidacloprid (Advantage ®) are available. Lufenuron (Program ®), an insect growth regulator is available as an injection or oral medication. In addition to appropriate treatment of all animals in the household, the environment needs to be treated with proper chemicals. All bedding should be washed, carpets thoroughly vacuumed, and every crack and crevice of the home needs to be treated. The environment needs to be treated twice, two weeks apart, so as to kill the newly hatched eggs that may have been missed the first time. It is easiest to hire a professional exterminator to get rid of fleas. If the cat goes out in the yard, family car, cat carrier or in the garage, these areas should also be treated. If there are dogs in the house, or other cats in contact with the infested cat, they should all be treated. Flea collars are no longer considered a control method of choice. They tend to just keep the fleas away from the neck area. Many insecticide products found at your local pet store are dangerous, especially in cats. Cats should not be given permethrin, organophosphate, or piperonyl butoxide containing products. They should never be given dog flea products. Many sprays and powders that were in use 20 years ago are no longer first choice options for cats so consult your veterinarian for the modern treatment that is best for your cat.

If your pet has flea allergy dermatitis, your veterinarian will likely prescribe anti-inflammatory medication such as corticosteroids for symptomatic relief while flea control gets underway. Flea problems can be frustrating to clear, so work with your veterinary health care team to get a comprehensive control program in place!