Ask a Vet: Do Some Flea Preventatives No Longer Work?


Editor’s Note: The opinions herein are those of Dr. Barchas and not of Catster at large. We routinely invite our experts to share their professional opinions about subjects like these. If you’ve had a different experience with any of these products, we invite you to share them in the comments below.


Anyone who reads my columns regularly knows that I have no love for the manufacturer of Frontline Plus. It wouldn’t bother me if the CEO and entire board of directors of Merial drowned in a vat of counterfeit Frontline. Why the animosity? Merial has a history of shamelessly exploiting veterinarians for our reputations, and then stabbing us in the back once we have served our purpose — in my opinion, at least.

The origin of most vets’ loathing for Merial and the equally noxious Bayer (manufacturer of Advantage) is well documented. I have no loyalty to either (or, for that matter, any) company. But over the past few months I have begun to feel skepticism when people complain about the efficacy — or rather the lack of efficacy — of Frontline Plus or Advantage.

First, let me say that I, too, have complained about the efficacy of Frontline Plus. For years I used it on my pal Buster. Eventually I became dissatisfied with its efficacy, so I switched to Comfortis. (Buster is a dog, but both products are available for cats.) Buster had developed seasonal allergies while on Frontline Plus. When I switched to Comfortis, the itching and red skin went away.

My dissatisfaction with the efficacy of Frontline Plus was based upon my pet’s itchy skin. Buster may have been uncomfortable, but he never had fleas. Never while he was on Frontline Plus did I see a flea on my pet or in my house. Never did I encounter even a fleck of flea feces (colloquially called “flea dirt”) anywhere in my personal life. The only trace of fleas was my pal’s hypersensitivity reaction to their saliva. Frontline Plus was killing the fleas, but it wasn’t killing them fast enough for Buster. An actual flea infestation never occurred.

Over the last few months I have encountered legions of people who are complaining about fleas. They seem to bask in the attention they receive as a result of their tales of woe, and they rarely appreciate the value of succinctness. Their stories go something like this:

“My brother’s friend’s cousin has a cat and I think he brought fleas into the house when he visited. We never had any problems before then. At first it wasn’t too bad — I just saw a few fleas now and then, and I combed them off and gave both my cats a bath. The fleas seemed to go away for a while after that, but then I noticed a few more fleas, so I bathed and combed my cats again and I bombed the house and vacuumed and applied diatomaceous earth to the carpet. But after that they came right back, and now I’m seeing lots of fleas on my cats, and I’ve noticed little things that look like rice grains or sesame seeds on my pillow. I asked my sister’s friend about holistic remedies, and . . .”

I take time during such stories to meditate and practice not rolling my eyes. Everyone thinks their story is unique, special, and worthy of sharing all the details. But I’ve heard it a million times before. When I can take no more, I gently interrupt and ask a question.

“Have you been using a flea preventative?”

Lately, the answer I’ve been hearing most of the time is, “I tried Frontline, but it doesn’t seem to work.”

Again, to be clear, I do not like the manufacturer of Frontline Plus. I do not support them or their product. But when I hear this statement I don’t buy it. And to this day I know of no person who suffered a flea infestation while using Frontline Plus, Advantage, or any decent flea preventative properly.

What is the proper way to use a flea preventative? Apply it to every pet in the house at the regular interval (generally monthly) recommended by the manufacturer.

So why did Frontline seem to fail in the case of my hypothetical client above? Let me translate his version of the story into what really happened.

His brother’s friend’s cousin nothing to do with it. Sure, infested animals can carry fleas into a house, but no such contact is necessary to cook up an infestation in your home. Fleas are famous for being able to jump a distance that is over 100 times their body length. They move around on their own, and they are ubiquitous. They live on squirrels and other omnipresent creatures that pass through your yard. They hop under your door and onto your cat.

Next, there is no such thing only a flea or two. If you are seeing a flea “now and then”, you haven’t grasped the enormity of the problem. Fleas are hard to see; for every flea you see, dozens more go undetected. And adult fleas make up only 5 percent of the total flea population in an infestation situation. 95 percent exist as eggs, larvae, and pupae that dwell in carpet, fabric, and upholstery.

So my hypothetical client thought there were only a few fleas in his home, but in fact there was a significant population of adults that were wildly reproducing. He bathed and combed the cats, which washed off the visible adults. But 19 juveniles were waiting to take the place of every adult removed in this way.

At this point things blew out of control in Malthusian fashion for my hypothetical client. Exponential growth led to an undeniably out of control flea infestation. The cats contracted tapeworms from swallowing fleas, and the tapeworms released small segments that looked like rice grains or sesame seeds on the client’s pillow (and that had, incidentally, passed out of the cats’ anuses to get there). The fleas were multiplying like only insects can.

At this point my hypothetical client was screwed. Here is why: one of the juvenile stages of fleas, the pupa, cannot be killed by anything. No pesticide, no flea bomb, no shampoo, no earthy-crunchy product (Diatomaceous earth?! If you think that stuff works, then please contact me regarding a bridge I have for sale.), no magic potion, and no amount of prayer will kill a flea pupa. Unless you plan to disinfect your home with a hydrogen bomb, then the pupae cannot be eliminated.

So eventually my hypothetical client was cohabitating with millions of indestructible flea pupae. And then he finally tried Frontline Plus. Of course it didn’t seem like it worked. It may have killed all of the visible fleas, but millions more hatched to take their places.

But if he had used the Frontline Plus properly in the first place — if he had applied it to every pet in the house every month — the fleas that entered the house under their own steam would have died before they could produce a viable population of pupae. Frontline Plus is not a perfect product, but it still works well enough to prevent catastrophes when it’s used as directed.

Once you have a serious flea infestation, which is to say once you have a large number of pupae in your house, you will need to reconcile yourself to months of battle.

Fortunately, the winning battle plan is simple. Apply a high quality flea preventative to every pet every month. Be patient for 5 – 8 months, since pupae will be hatching during this time. After a year, you should be in the clear. And once you’re in the clear, keep using the flea preventative. As the saying goes, fool me once, shame on you. Fool me twice …

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Got a question for Dr. Barchas? Ask our vet in the comments below and your topic might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)

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