Flea infestations are the most common ectoparasitic problem of dogs and cats in North America. Here in Southern California, it’s been a particularly bad flea season due in part to the warmer than usual summer and fall. Of the more than 2,000 species of fleas, the most likely culprit your pet will encounter is called the “cat flea” (Ctenocephalides felis). This flea infests both cats and dogs. You should become familiar with this pest because it causes allergic dermatitis (itchy, red possibly infected skin lesions), may carry bacterial pathogens (heard of Cat Scratch Fever?), and can transmit tapeworms to both you and your pet (after swallowing an infected flea).

An important clinical note: dogs and cats may have either flea bite dermatitis (FBD) with mild skin irritation, hot spots or lick granulomas — or they can have flea allergy dermatitis (FAD), a more severe allergic reaction characterized by crusted papules (small bumps) with erythema (redness), hair loss, hyperpigmentation, and other clinical signs. Both patients are frequently infected with tapeworms, so we recommend submitted a fecal sample if your pet has recently been treated for fleas. Furthermore, dogs that are intermittently exposed to fleas are MORE likely to develop FAD than dogs that are chronically exposed to fleas. That is, irregular flea control is more likely to result in FAD. Cats are believed to be similarly affected. IT IS IMPORTANT TO MAINTAIN MONTHLY FLEA CONTROL ALL YEAR ROUND.

Controlling fleas can be very frustrating. A multimodal strategy is most effective. This includes treating both the host and the environment. Vacuuming any carpets, furniture cushions, rugs, even bare floors once a day for at least a week will remove many flea eggs and larvae, and some pupae. The vibration of the vacuum cleaner may stimulate pupae to emerge from their cocoons deep within the carpet. Make sure your vacuum has a rotating “beater bar.” Empty vacuum containers and dispose of bags immediately. Flea populations also live outside in shaded areas; so consider re-routing your daily walk if necessary. If necessary, chemical treatment of the indoors and outdoors is best done by a licensed professional exterminator.

There are several safe topical and oral flea control products currently on the market. It’s important to avoid excessive bathing if using a topical product — use soap-free products, but do NOT use a follicle-flushing shampoo. The oral products are obviously unaffected by bathing; but, these products only control fleas (so if you also need to fight ticks, you need a topical medication). Before selecting a product, you should know how they work. Some are adulticides; they kill adult fleas. Others contain insect growth regulators or insect development inhibitors to target eggs, larvae or pupae.

Most adulticides have a high affinity for insect nicotinc acetylcholine receptors (nAChRs) [a receptor for a chemical signal to stimulate a muscle or nerve cell] and an extremely low affinity for veterbrate nAChRs… for example, it would take more than 100 X the concentration of dinotefuran (an ingredient in Vectra products) to have the same affect on a dog or cat (or human).

Here’s an overview of common MONTHLY flea control products — and their active ingredients / mechanisms of action.

1. Vecra 3D – topical – for dogs only; contains third ingredient to kill ticks:
a. dinotefuran: binds insect acetylcholine receptor, causing continuous nerve stimulation, eventual paralysis and death of the insect
b. pyriproxyfen: disrupts hormonal signs necessary for developing or molting
c. permethrin: disrupts the sodium channel current in arthropod nerve cell membranes, resulting in paralysis and death
* Labeled for control of adult fleas, flea eggs, flea larvae, flea pupae; four tick species; also sand flies, sucking lice, and mites that cause dandruff and scale (NOT Scabies)

2. Vectra – topical – for dogs and cats (does NOT contain permethrin)
* Labeled for control of adult fleas, flea eggs, flea larvae, flea pupae

3. Comfortis – oral – for dogs only
a. spinosad: causes involuntary muscle contractions and tremors, the hyperexcitation leads to neuromuscular fatigue and death by paralysis
* Labeled for control of adult fleas

4. Capstar – oral – for dogs and cats (lasts only 24 hours)
a. nitenpyram: blocks acetylcholine-mediated neuronal transmission causing paralysis and death of the flea
* Labeled for control of adult fleas

5. Revolution – topical – for dogs and cats
a. selamectin: stimulates the release of neurotransmitter GABA in arthropods, causing paralysis and eventual death
* Labeled for control of adult fleas, flea eggs; one kind of tick (D. variabilis); the most common ear mite; Scabies skin mite; heartworm preventative

6. Sentinel – oral – for dogs and cats
a. luferuron: inhibits chitin synthesis, polymerization, and deposition in fleas, thereby preventing eggs from developing into adults
b. milbemycin: disrupts the transmission of the inhibitory neurotransmitter GABA in invertebrates
* Labeled for control of flea eggs; heartworm prevention; controls hookworm, roundworms and whipworms

In case you were wondering…

Fleas eggs are very tiny, about 1/50 of an inch (0.5 mm); when found in high numbers, the eggs may look like salt… I have yet to witness this. Eggs hatch in about a week, producing slender white larvae (2 – 5 mm in length). Larvae feed on adult flea feces (your pet’s digested blood), organic debris in the environment and on flea eggs. Flea larvae can move deep into carpet fibers where they’ll develop into the pupal stage (in a cocoon). The new adult flea is stimulated to emerge by vibration and heat. In most household environments, fleas complete their life cycle in 3 to 8 weeks.

Flea adults crawl out from under beds or sofas and jump in the direction of a light source that’s been suddenly interrupted by shadow (dog or human walking by). They may survive several days before needing a meal (blood). Their survival is also greatly dependent of warmer temperatures and higher humidity; only 5% can survive as long as two weeks at 22.5 C (72.5 F) and 60% relative humidity. In general, relative humidities are moderate to high along the California coast throughout the year. New adult fleas will often bite humans before parasitizing their preferred host — the dog and cat. Fleas start feeding within minutes and mating within hours. Females lay eggs shortly thereafter in the pet’s fur… about 50 eggs per day! These eggs are not sticky so they slide off the host into the environment — and we begin again. That familiar flea dirt you may see in your dog or cats coat is their own digested blood excreted by fleas. While C. felis adults are much more likely to stay on their original host, it is possible for them to transfer to another pet in close contact. More typically, a new infestation on a pet comes from its environment (eggs, larvae, pupae).

Please call to schedule an appointment to discuss which flea product is best for your pet. Remember, once you’ve started flea control medication, you still need to treat the environment as discussed: vacuum carpets, floors, furniture and wash pet bedding (your bedding too if necessary).


Blagburn BL, Dryden MW. “Biology, treatment, and control of flea and tick infestations.” Vet Clin North Am Small Anim Pract. 2009 Nov; 39(6): 1173-200, viii.

Plumb DC. Plumb’s Veterinary Drug Handbook, 6th Edition. Ames, Iowa: Blackwell Publishing, 2008.