Fleas in Dogs and Cats

Fleas are probably the most prevalent ectoparasites that affect dogs and cats! These tiny dark brown insects prefer temperatures of 65-80 degrees and humidity levels of 75-85%, so for some areas of the country they are considerably more than just a problem of the summer months. For example, here in Florida, fleas on dogs and cats persist year round unrelentingly. In fact, when the weather drops occasionally into the 50s and 60s (degrees F), flea infestations become considerably more prevalent, as the fleas become more aggressive, desperate to latch onto a warm body. Dogs and cats often get infested with fleas through contact with other animals or from the environment. The strong, spring-like back legs of this flea, enable it to jump from host to host or from the environment onto the host. If a flea was the same size proportions as a human being, the flea would have the ability to jump the height of the Statue of Liberty, and the length of the Brooklyn Bridge. The flea’s bite can cause itching and irritation for the host but for a dog or cat that is hypersensitive to the bite of the flea, this itching can be quite severe and leads to hair-loss, inflammation and secondary skin infections; a condition called flea allergy dermatitis. Some dogs and cats are so hypersensitive to the flea’s saliva, that they will itch all over from the bite of a single flea. The flea information detailed here will outline techniques and medications for treatment and prevention of fleas in dogs and cats.

There are other conditions that have the potential to cause severe pruritis (itching) in dogs and cats, which is why it is important to know if fleas are causing all that itching. Generally, unlike the burrowing, microscopic Demodex or Sarcoptic (Scabies) Mites (organisms that cause the condition called mange), fleas can be readily seen scurrying along the surface of the skin. Dark brown colored and about the size of the head of a pin, fleas are photophobic (dislike light) so it is best to look for them within thickly haired regions and on the pet’s belly. inner thighs, and armpits will give you the best odds of spotting them. Also, be sure to look for the presence of flea dirt, the feces of the feces that looks like black pepper sprinkled in the fur.

To better understand how and why various treatment options work, it is important to first understand the flea’s life cycle since the different dog and cat flea treatment protocols and prevention products work on different parts of this life cycle. The different stages of the flea life cycle are: egg, larva, pupa (coccoon)-like state, and adult. The length of time it takes to complete the flea life cycle varies depending upon the environmental conditions (temperature, humidity), and the availability of a good, nourishing host. Yes… the various flea stages are quite resistant to freezing temperatures. The flea’s that attach and thrive on dogs and cats are specific to these species and although they may bite people, it is not believed that they can use humans to successfully complete thier life cycle.

The adult female flea typically lives for several weeks on the pet, during which time she will feed on the pet’s blood two to three times and lay twenty to thirty eggs each day. She has the ability to lay several hundred eggs throughout her life span. These eggs fall off of the pet onto the grass of the backyard, bedding, carpet, and wherever else the animal spends time.

These eggs then proceed to develop where they have landed. Approximately 1/12 to 1/8 the size of the adult flea, they proceed to develop in quite inconspicuously. The egg then hatches into the next stage, which is the larvae. These tiny worm-like larvae also develop in the environment inconspicuously, feeding on organic matter, shedded skin scales, and blood protein rich adult flea feces. The larvae grow, undergo two moltings, and then form into a cocoon or pupa, where they undergo thier final transformation before hatching into a an adult flea. These pupae are very resilient in the environment, since they are protected by their cocoon. Pupae can persists for long periods, until environmental conditions and host availability are optimal. They emerge from their cocoons when they detect heat, vibrations, moisture and carbon dioxide, all of which indicate that a host is nearby. The newly emerged adult flea has the ability to jump onto a readily accessible host virtually immediately. Under ideal conditions and with readily available host, the flea can complete its entire life cycle in just two weeks. Consider the numbers of eggs that each adult female flea produces, the number of fleas that can be produced in just one two weeks life cycle is staggering!

Having insight in the flea life cycle allows us to understand why it has always been important to treat both the host pet as well as the indoor and outdoor environments in order to successfully control flea numbers. Simply sprinkling some flea powder on your pet will not work; nor will merely vacuuming the home even vigorously. Most flea collars are virtually useless There is a large variety of dog and cat flea products on the market today, but it is only a select number of newer prescription products that are finally making flea control a realistic concept. In some cases, using the appropriate product, it is now even possible to effectively control fleas by treating only the pet.

One of these fleas preventative products is called Program, given orally monthly for dogs and cats, or by injection once every six months for cats. The adult flea is not killed by Program, but the hatching of the eggs is inhibited, thus breaking the life cycle of the flea; with no reproduction the flea population eventually dissipates. The limitation of this product is that it only effectively works if the pet is not constantly coming into contact with novel flea populations. In warm climates, this treatment is must be used year round, but in other climates treatment should begin in early spring before the flea season starts. This may not be the product of choice for animals that are allergic to flea saliva (have flea bite hypersensitivity) since the adult fleas are not killed and are still able to bite the animal.

There are three popular topically applied prescription therapies available: Advantage, Frontline Plus, and Revolution, and K9Advantix; each had their day of being effective effective, but are progressively dwindling in their effectiveness as fleas are increasingly becoming resistant to them. Each of these products kills the adult fleas which are present on the animal. Unique to K9Advantix, in addition to killing all stages of the flea life cycle, the company that makes it claims that the product repels the fleas to begin with The adult fleas typically do not have a chance to bite the animal with these topical products making them a good choices for flea-allergic pets. They are typically applied once per month, although Frontline Plus is labeled to control fleas on cats for one month and up to three months in dogs. An advantage to Frontline Plus is that is also controls ticks when used monthly. Revolution is labeled not only for use against fleas and ticks but also treat ear mites, sarcoptic mites (Scabies Mites) and prevent Heartworm disease. For more information on these products, consult your veterinarian, as different vets have different opinions about various flea prevention products based on experience with efficacy and safety.

Capstar® is another product that can be a useful tool in the prevention of fleas in dogs and cats. It is approved for use in in both species, and is available through veterinarians as well, however, it is not a prescription product. Capstar is a tablet that kills fleas within 20 minutes of oral dosing. It has no residual action and is useful if you want to quickly eliminate a new flea infestation, while waiting for a long term flea preventative to kick in. There are many other products which will kill fleas on the pet and for which no prescription is needed. However, most of these “other” products do not provide a full flea kill off, nor do they provide protection beyond the immediate area of application or for long term. Also many of the active ingredients have questionable safety for dogs, cats, and people.

Comfortis is an orally administered pill that has been proven very safe for use in all canine patients, with the exception of patients that suffer from seizure disorders. While Comfortis will not cause seizures, it is known to exacerbate patients prone to seizures. As such, for example, it would not be appropriate for a patient that suffers from epilepsy. The company that makes Comfortis also has  a topical equivalent for cats called Assurity®. Being a very new product at the time of this article’s latest update, both efficacy and safety are not well established at this time.  Comfortis is not used commonly anymore, as its chief ingredient, sponosad is now integrated in the combination flea, heartworm and intestinal worm preventative, Trifexis.

The newest generation of flea preventatives are in a category I call the “laners.”  Afoxolaner, sarolaner, and fluralaner.  They are the flea preventatives in the oral products Nextgard (monthly), Simparica (monthly), and Bravecto (every 3 months).  Nextgard now comes in an all in one flea/tick/heartworm/intestinal worm preventative Nextgard Combo, as does Simparica, called Simparica Trio.

If you find yourself in the midst of a severe household, multi-pet flea infestation, you will likely need to treat both pets, as well as indoor/outdoor environments. Treating the indoor environment includes washing all bedding with detergent and hot water (this includes your bedding as well, especially if the pets spend time on your bed). All of the carpeting should be vacuumed thoroughly and the vacuum bag discarded even if it is not full. Steam cleaning the carpet in addition to vacuuming will help kill some of the larvae and eggs as well. Keep in mind, however that vacuuming and steaming a carpet may still leave some of live fleas, larvae, and viable eggs, so some sort of chemical treatment may be necessary.

Once this preliminary treatment has been accomplished, if needed, the next step is chemical treatment of the house. Several choices are available including sprays and foggers. The most effective products are those which contain ingredients that kill all stages of the flea life cycle. Adult flea kii chemicals are common, but ones with added Methoprene give the product a more enhanced ability to kill immature stages in addition to adults. Aerosol foggers may not penetrate well enough, in many cases, to kill all the hiding fleas and larvae. Another option for indoor control is a sodium borate product that is applied directly to the carpeting and vacuumed up. The best option, however, is to call a local exterminating company. The best companies provide a guarantee that their procedure will rid your premises of fleas for a specified period of time. Flea eradication can be quite expensive, but will increase both the quality of life of your family and that of your dogs and cats.

As for outdoor control, sprays and pelleted insecticides are generally used after dog houses and kennels have been washed and cleaned. An insect growth regulator is a good choice here as well. Pyriproxifen, which is sold under the trade name Archer or Nylar, is more stable in sunlight and has better outdoor longevity than Methoprene.

Roger L. Welton, DVM

Founder and Chief Editor, Web-DVM.net

CEO Premier Veterinary Care

Host Space Coast Pet Podcast

Author, The Man in the White Coat

Article updated 3/117/2023