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Winter Fleas? Pets are Itching for Relief

It may seem strange that I choose to write a flea article just as most of the nation is being hit with winter storms.  However, those snowstorms can lull pet owners into a sense of false security when it comes to fleas.  While those fleas may be effectively killed outside, they are doing just fine in their nice and cozy, warm homes, happily feeding on dogs and cats and making lots of babies.

There is also the reality that here in Florida where I practice veterinary medicine, the flea problem is the worst in the country with no seasonal kill-off to keep flea infestations in check.  Combined with a high feral cat population and abundant wildlife that propagates the presence of fleas in the environment, veterinarians in Florida and other southeast states have a special interest in safe, but aggressive, effective flea control.

Anywhere there is wildlife, stray cats, and a time of year where the temperature rises above 50 degrees; there is a flea threat to dogs and cats.  Fleas are far more than just a nuisance, but are responsible for discomfort, skin infections, and can even transmit a tapeworm parasite.  Although the disease is rare in modern society, fleas are responsible for transmission of Yersinia Pestis, the causative bacterial agent of bubonic plague.  Not to cause mass hysteria – as I stated the disease is very rare in modern society – there recently was a report of an 11-year-old boy in California who contracted plague from fleas that were present on his cat that slept in bed with him.  The bottom line is, fleas are bad, and our pets and families are better off without them around.

With all of the products out there, it is important for veterinarians to help pet owners sift through which products work, which products do not, and which products are safe or toxic.  Let us begin with how flea preventive products work.

The flea lifecycle consists of 4 life stages: (1) eggs, which hatch into (2) larvae, which cocoon themselves into (3) pupa, from which emerges the (4) adult flea.  Some products are geared toward killing the larvae and adult fleas, while others are geared toward flea sterilization, making their eggs unviable.  The former is called an insecticide, while the latter is called an insect growth regulator.  No product currently kills the pupa stage.

Examples of common flea insecticides that kill larvae and adult fleas include imidacloprid, fipronyl, indoxacarb, and spinosad.  Examples of common insect growth regulators that sterilize fleas include methoprene, pyriproxyfen, and lufenuron.  Various retail products have varying elements that provide flea control for your pet, some of which are topical, some of which are taken orally.  For me to discuss every flea preventive product in the industry would take a several page document, the likes of which I – and I assume my readers as well – do not have the patience nor the time for.  Instead, I will discuss my favored approach to flea control in dogs and cats in terms of safety, effectiveness, and cost – observations from my everyday general practice in the flea capital of the United States.

Let me begin by letting you know what I absolutely do not like: any products that have organophosphates.  Organophosphates are not only toxic, but despite being touted by the companies that sell them as being capable of killing larvae and adult fleas, they really do not work.  There are too many brands that have these chemicals in them to list them, but in general, pet store grade flea preventives, most flea collars, flea shampoos, and flea dips are comprised primarily of organophosphates.

The most comprehensive approach to flea control is to break the flea life cycle with veterinary grade products.  While fleas can accidentally bite people, they cannot reproduce with our blood.  In order to reproduce, they need the blood of their definitive hosts, dogs and cats.  As such, if we can effectively prevent fleas from feeding on their definitive hosts, as well as kill as many life stages of the flea as possible, we will create the best scenario in which we can keep these pests out of our homes.

To accomplish this, if you were to use just an insecticide, you will effectively kill the adult fleas and larvae that are on the pet, but with eggs and larvae that are persisting in the carpets, hard wood floor cracks, gaps in tile grout, and in the yard, there will always be a constant persistence of little creepy crawlies in the home and environment.  There would also be a constant infusion of new fleas to battle, making breakage of the flea life cycle challenging.

Click the link below to see a video of larvae embedded deep in carpet fibers where vacuums commonly fail suck them up…it is enough to make anybody’s skin crawl!

On the other hand, treating with just an insect growth regulator effectively sterilizes the fleas making them unable to reproduce.  However, adult fleas may still often be a problem, especially in areas where stray cats and wildlife may move across yards and provide constant new infestations of adult fleas, eggs, and larvae.

In consideration of all of this, I favor a preventive approach that includes both an insecticide and insect growth regulator.  While there are a number of products that include both growth regulator and insecticide, many do not live up to their expectations, the proverbial “jack of all trades, but master of none.” This is especially true in climates like the southeastern United States.  Having practiced veterinary medicine in Florida for the past 9 years, I have come to know very well what the best balance of effectiveness, safety, and cost is when it comes to flea prevention for dogs and cats.


For dogs, the insect growth regulator I like to use in Sentinel.  Sentinel contains the insect growth regulator, lufenuron, but it is also convenient because it is also contains milbemycin oxime, a well-established heartworm and intestinal parasite preventive.  Both insect growth regulator and heartworm/intestinal parasite preventives are compounded into one flavor tablet that is fed to dogs once a month.

The insecticide I favor for dogs for use concurrently with Sentinel is a product called Comfortis, which contains the active ingredient spinosad administered in a monthly flavor tablet.  In my experience, nothing on the market kills adult fleas faster.

Unfortunately, Comfortis has little activity against ticks.  Thus, if you live in a tick prone area, in place of Comfortis to augment Sentinel treatment, I would instead use an insecticide that effectively kills both fleas and ticks.  The monthly topical, Activyl, active ingredient indoxacarb, effectively accomplishes this.  While Activyl does not kill adult fleas as rapidly as Comfortis, it is the next best insecticide option for adult flea control, with the added bonus that it also kills ticks faster than any other product on the market.


For cats, for insect growth regulator, I like the product Revolution with the active ingredient  selamectin.  Revolution is a very nice product, as it prevents heartworm disease (less common, but cats can get heartworm disease too), as well as several intestinal parasites in addition to its effective insect growth regulating activity.

For insecticide, just as for dogs, I like Comfortis for cats.  One major drawback of Comfortis for cats, is that it is a flavor tab that most cats will not readily eat.  Thus, it can be difficult for some feline owners to administer, even monthly.  As an alternative insecticide to use concurrently with Revolution, my recommendation is Activyl for cats.

From skin disease, tapeworms infections in pets, to even posing a health risk to our human family members, comprehensive flea control is one of the most important aspects of responsible, healthy pet guardianship.

Dr. Roger Welton is the President of Maybeck Animal Hospital and CEO/Chief Editor of the veterinary information and blog online community, Web-DVM.

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