Fleas of Dogs

The short version

Fleas are small wingless insects that feed on animal blood. In addition to 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 and the typhus-like rickettsiae.

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 (and even up to a year) 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.

Flea Allergy Dermatitis

When feeding, fleas inject saliva into the host on which they are living. Many dogs and cats are allergic to flea saliva. Even nonallergic animals will scratch due to the annoyance of flea bites. Allergic dogs itch intensely in some or all areas of the body. They are likely to be restless and uncomfortable, spending much time scratching, licking, rubbing, chewing, and even nibbling at their skin. The classic clinical signs include crusted, itchy skin over the hips, base of the tail, and thighs. This often leads to hair loss, scabbing, and secondary infections. As the disease becomes chronic, hair loss, thickened skin, and darkening of skin color are seen. In heavy infestations (or in young puppies), anemia may develop due to the loss of blood.

Flea Control Methods

Flea control measures have changed dramatically in recent years. Flea control previously required repeated application of insecticides on the animal 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. Insect growth regulators prevent fleas from reproducing. Flea treatments include topically applied liquids, oral and injected medications, and “fogger” sprays. You should discuss flea control products with your veterinarian and select one that works well for your individual pet and the environment in which it lives.

The goals of flea control are elimination of fleas on pet(s), elimination of existing populations in the environment, and prevention of later infestations of the dog. The first step is to eliminate the existing fleas on the pet. This is necessary to reduce immediate pet discomfort. One common consideration is termed rate or speed of flea kill on a pet. However, it is important to differentiate between speed of elimination of fleas already on the pet and elimination of newly acquired fleas after a product has been applied. When treating a dog with a product applied to the skin externally, it can take up to 36 hours until the medication has spread sufficiently or reached sufficient concentrations to eliminate all existing fleas. If a more rapid rate of kill is needed, a flea spray or one of the new fast-acting oral products may be desirable.

If your dog spends time outside regularly, also treat the outside areas it frequents. Spraying flea control products over the whole yard is not worthwhile. Instead, concentrate outdoor treatments on shaded areas, including dog houses, garages, under porches, and in animal lounging areas beneath shrubs or other shaded areas. Other outdoor spaces where fleas can be found include cracks in shaded or moist brick walks and patios and areas under decks and steps.

Frequently asked questions

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