Fleas are small, wingless insects that feed on animal blood. Besides being a nuisance, they can also transmit diseases and cause allergies or anemia. There are more than 2,200 species of fleas recognized worldwide. In North America, only a few species commonly infest house pets. Two common species of flea are the cat flea (Ctenocephalides felis) and the dog flea (Ctenocephalides canis). However, most of the fleas found on both dogs and cats are cat fleas. Fleas cause severe irritation in other animals and humans. They also transmit a wide variety of diseases, including tapeworm infections (see Digestive Disorders of Cats: Tapeworms) and the typhus-like rickettsiae (see Disorders Affecting Multiple Body Systems of Dogs: Ehrlichiosis and Related Infections in Dogs).
Transmission and Life Cycle
Cat fleas begin reproduction about 1 or 2 days after a blood meal from a host. Female fleas lay eggs as they feed and move about on the surface of the skin. A single female flea can produce up to 50 eggs per day and about 2,000 in her lifetime. The eggs are pearly white, oval, and tiny. They readily fall from the fur and drop onto bedding, carpet, or soil, where they hatch in 1 to 6 days. Newly hatched flea larvae are mobile and free-living, feeding on organic debris found in their environment and on adult flea droppings. Flea larvae avoid direct light and actively move deep into carpet fibers or under organic debris (grass, branches, leaves, or soil).
Larvae can easily dry out, and exposure to relative humidity under 50% will kill them. However, they are capable of moving as far as 3 feet (1 meter) to find locations suitable for their survival. Indoors, flea larvae best survive in the protected environment deep within carpet fibers, in cracks between hardwood floor boards, and on unfinished concrete floors in damp basements. Flea development occurs outdoors only where the ground is shaded and moist. The larval stage usually lasts 5 to 11 days but may be prolonged for 2 to 3 weeks, depending on the availability of food and the environmental conditions.
After completing its development, the mature larva produces a silk-like cocoon in which it pupates. The pupa is fully developed in 1 to 2 weeks, but the adult flea may remain in the cocoon for several weeks until a suitable host arrives. When it emerges from the cocoon, it can survive 1 to 2 weeks before finding a host on which to feed. It is the newly emerged, unfed fleas that infest pets and bite people. Fleas generally do not leave their host unless forced off by grooming or insecticides. Cat fleas in any stage of the life cycle cannot survive cold temperatures. They will die if the environmental temperature falls below 37°F (3°C) for several days.
Depending on temperature and humidity, the entire life cycle of the flea can be completed in as little as 12 to 14 days or last up to 350 days. However, under most conditions, fleas complete their life cycle in 3 to 6 weeks. Fleas mate after feeding, and females lay eggs within 1 to 2 days of their first blood meal.
A flea-infested cat or dog can easily introduce fleas into a home where they deposit eggs that develop into newly emerging fleas. These then infest other pets and bite people.
Flea Allergy Dermatitis
When feeding, fleas inject saliva into the host on which they are living. Many cats are allergic to flea saliva. Even non-allergic animals will occasionally scratch due to the annoyance of flea bites. Cats with flea allergy dermatitis will have itching that can range from minimal to severe, depending on how sensitive the cat is to the flea saliva. When fur is parted to inspect for skin irritation, small, solid bumps will be visible. This pattern of irritation is known as feline miliary dermatitis because it resembles tiny, round millet seeds. Bumps are typically spread over the back, neck, and face. They can become crusted over after the cat damages its skin by scratching. These bumps are not flea bites, but a system-wide allergic reaction to having been bitten by fleas. The allergic reaction causes the bumpy rash to develop and the cat's entire body to itch. Itching can be severe, prompting the cat to repeatedly lick, scratch, and chew its skin. Cats with flea allergy dermatitis can also have widespread hair loss.
Most cases of flea allergy dermatitis occur in the late summer, corresponding to the peak of flea populations. Animals younger than 1 year old do not usually have flea allergy dermatitis. Usually, diagnosis is made by visual observation. Slowly parting the hair often reveals flea excrement or rapidly moving fleas. Flea excrement is reddish black, cylindrical, and pellet- or comma-shaped. Placed in water or on a damp paper towel, the excrement dissolves, producing a reddish brown color. Examination of the pet's bedding for eggs, larvae, and excrement is also useful. The presence of fleas does not exclude another disease being at least partially responsible for the cat's itching and skin condition.
Your veterinarian may do skin testing to eliminate other causes for the itching and confirm a diagnosis of flea allergy dermatitis. However, skin testing does not always reliably identify flea allergy dermatitis in cats. Other diseases and conditions that can cause similar signs include infestation with other skin parasites, ringworm infection, sensitivity to medication, food allergy, respiratory allergy, and hair follicle infections.
Flea control measures have changed dramatically in recent years. Flea control previously required repeated application of insecticides on the cat and the premises. Recently, new insecticides and insect growth regulators have been developed that provide residual control and require fewer applications. The most effective of these products are sold by veterinarians. Many are given once a month and effectively control fleas and other parasites. By using these products, it is possible to eliminate a flea infestation in a household; however, the amount of time necessary to achieve flea control will vary because of the flea's life cycle and conditions in the environment. Typically, control of an infestation can take 6 weeks to 3 months.
You should discuss flea control products with your veterinarian and select one that works well for your cat and the environment in which it lives (see Skin Disorders of Dogs: Flea Allergy Dermatitis).
Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; Thomas R. Klei, PhD; David Stiller, MS, PhD; Stephen D. White, DVM, DACVD; Michael W. Dryden, DVM, PhD; Carol S. Foil, DVM, MS, DACVD; Paul Gibbs, BVSc, PhD, FRCVS; John E. Lloyd, BS, PhD; Bernard Mignon, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice Villalobos, DVM, DPNAP; Patricia D. White, DVM, MS, DACVD