Fleas Persist, But Reason Isn’t Resistance

Keeping clients informed about how to manage fleas and ticks on pets is the best way to prevent the return of the parasites.

Veterinarians are in a tough spot when a client challenges the efficacy of spot-on insecticides. They can’t force the client to follow product directions, nor can they administer the flea control every month.

Asking a client about product application, the home environment and untreated pets can reveal a potentially resolvable situation. However, more often than not, the owner projects a sterling report of by-the-book compliance and a bewilderment of continued flea propagation.

Attempting to resolve the infestation, veterinarians often switch to a different product and the resistance tale grows.

“What clients are likely seeing are new fleas from the environment as opposed to fleas surviving after a proper spot-on application,” says Michael Dryden, DVM, Ph.D., a professor of veterinary parasitology in Kansas State University’s Department of Diagnostic Medicine and Pathobiology. “I have investigated homes that by owner description sound like there could be a resistance problem but found, when I looked closer, there was always a reason for the failure. None was ever resistance.”

Without an investigation, experts say, it’s difficult to know why fleas persist on a client’s pet after treatment. One thing researchers agree on is it’s not a resistance issue.

“Resistance to spot-on products has never been documented,” Dr. Dryden says, noting that resistance is likely to happen eventually with commonly used products. But he says it hasn’t happened yet.

“Human error is found to be the cause for lack of control time and time again. Veterinarians can’t just be a Wal-Mart or Kmart; we have to educate clients about what they can expect from the product and show them how to apply it.

“A lot of us aren’t taking the time to do this, but if we did we could improve control and more accurately know if resistance occurs.”

Certain parasites, even within the same species, can be harder to eradicate than others, according to the professionals.

“Some organisms are more susceptible than others,” Dryden says. “Natural variation in the population happens with everything. This means that even if you heard of someone else’s flea problem ending with one application, yours may not. In these cases, owners must be diligent with washing pets’ bedding and using a spray on the yard.”

The products available today are the fastest acting and most efficient ever presented for a pet owner’s use.

“Today’s flea control is like comparing an iPhone or BlackBerry to a 1980s cell phone. Both can get the job done, but the newest technology does it better,” says Sebastien Gray, DVM, product manager with Summit VetPharm of Fort Lee, N.J. “We can assume the technology will continue to make our lives easier and fleas’ lives worse.”

Take Time to Educate

Some clients have unrealistic expectations of spot-on products, experts say. Print and television advertising plays to a flea phobia and simply promises to rid a pet of parasites.

“From the corporate standpoint, advertising can sometimes overpromise results,” Dryden says. “But it gets the word out about product availability. It is up to the veterinary profession to educate clients about what to expect and how to use the product. If we don’t show or tell clients this information, how can we expect them to know anything or have realistic expectations?”

Experts advise veterinarians to tell the client what fleas are capable of and what the products can do. Explain that one flea can lay 40 to 50 eggs a day, that treating all household pets is necessary and that skipping a month’s application after the infestation appears to be over can lead to repopulation and potential resistance.

“A practitioner is asking for a resistance problem if clients aren’t treating regularly,” says Jay Stewart, DVM, of the Companion Animal Parasite Council and the owner of Aumsville Animal Clinic in Aumsville, Ore.

“Sometimes clients are simply mistaken about their compliance. One client swore she was doing everything as instructed, but when we asked her to come to the clinic to demonstrate her application technique, we found that she hadn’t opened the pipette.”

What Is Resistance?

The term “resistance” might mean different things to different people. A general practitioner may say any decrease in efficacy shows resistance. A parasitologist’s definition may allow for a little leniency.

“When parasitologists talk about resistance they do not necessarily mean a total lack of efficacy,” says Patrick Meeus, DVM, Ph.D., Dipl. EVPC, the vice president of the American Association of Veterinary Parasitologists. “Resistance [occurs] only if efficacy is less than when the product was first launched or below the 90 percent efficacy levels typically required by government agencies to get a claim in the first place.”

Disease Concern

While owners’ complaints are largely propelled by their disgust at the thought of parasites crawling in their home and on their pet, there’s a lot more to be concerned about from an epidemiologic standpoint.

Dryden, who performs ongoing flea and tick biologic research, says North American flea species number more than 400. The cat flea accounts for 99.9 percent of what is found on dogs and cats. Ticks, which also are fought with spot-on treatments, carry a plethora of disease.

“Cat fleas are the most resilient,” Dryden says. “They are the toughest to get rid of because of their biology. Since spot-on treatments eliminate these fleas, pets will be protected against other species of fleas if challenged, too. I believe clients are largely unaware of the extent of parasite-transmitted disease risks.”

Resistance to treatment, real or perceived, is important not only in regard to fleas but also to ticks, flies, lice and helminthes, Dr. Meeus says.

“While the AAVP doesn’t carry out research, the issue of resistance is discussed vigorously every year at our annual meeting and will be the topic of a special session at this year’s meeting in Atlanta,” Meeus says. The group meets July 31-Aug. 3, 2010.

Veterinary parasitologists spend a lot of time in the field collecting fleas, monitoring flea environments and examining the animal host to monitor flea evolution and population.

“Students and I go to an animal shelter once a week to see dogs that likely were never treated for fleas,” says Thomas M. Craig, DVM, Ph.D., a professor of veterinary pathobiology at Texas A&M University. “We’re finding all sorts of parasites on these dogs–ones that we’re surprised to see.”

Experts say certain flea and tick species dominate in some geographic regions but that human and animal travel as well as environmental changes have made parasites much more portable and adaptable overall.

“In a few decades all parasites will be found everywhere,” says Dr. Gray, of Summit VetPharm. “We’re already seeing parasites in regions we never thought they would go.”

This article first appeared in the March 2010 issue of Veterinary Practice News

Treating the Environment

After applying a spot-on treatment, an owner can make the mistake of quarantining a pet from its usual indoor activities. This means flea larva living in the carpet and other home environments will seek their first adult blood meal from the closest warm body.

“There are many stories about clients thinking they’re helping to resolve the flea infestation in their home when they are actually making it worse,” says Josh Norsworthy, parasitics product manager at Virbac Animal Health of Fort Worth, Texas.

“One client’s Labrador retriever slept under the baby’s crib, so when they found it had fleas, they treated it with a spot-on treatment and kept it from going in the baby’s room. With no dog to jump on, newly hatched fleas jumped on the baby.

“This is a great example supporting the need to treat the environment along with the pets.”

Carpets and soft surfaces harbor the majority of the flea life cycle, but cracks in hardwood floors can serve as an environment as well. Many spot-on manufacturers market sprays that can be used effectively in the home and outdoors.

“Sometimes owners try to cut corners when they discover their pet has a flea infestation. They purchase the least expensive products they can find at the local convenience store, then find the products weren’t effective,” Norsworthy says. “A huge percentage of people go to their veterinarian to figure out how to treat the problem. These people are the ones who save the most because they purchase products that work better and in less time.”

Treating the indoor and outdoor environments requires a motivated client, experts say. When clients are informed and want to solve the problem, they take all the proper precautions.

“While selling spot-on treatments, veterinarians may want to recommend the owner also use some insecticides around the property,” says Jay Stewart, DVM, of the Companion Animal Parasite Council. “Preventive care can mean we aren’t always stamping out fires.” 

— J.T.


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28 thoughts on “Fleas Persist, But Reason Isn’t Resistance

  1. The m poo st patronizing article on the subject I’ve ever read. I have now spent over £350 on household flea killing products in the past 6 months. Nothing works. Not even professional navigator products. My Chihuahua gets treated by Endocrin monthly without fail…with a cut pipette.

    1. I agree! I have tried so many solutions including topical, and spray….we are going to flea bomb the house this weekend. Hopefully that works!

    2. Agree. There is a huge determination never to admit that flea treatments don’t work. Wonder why? Who funds the studies? A lot of reports of products not working say that they used to, but no longer do. Or that this one doesn’t, but this one does. How do they get round that? Tell you that the times it worked were actually a figment of your imagination and it wasn’t working? I’ve had vets tell me – quoting the manufacturers – that the stuff won’t work if there are fleas in the environment. So get rid of all the fleas everywhere, and the stuff will work. Only problem is, you would then not need it, surely? Don’t you use it because there are – er -fleas around? But you may as well save your breath. You can’t buy brains. I’ve read studies which profess to be scientific, but they start and end with “but the reason the fleas aren’t dying couldn’t possibly be resistance and we refuse to entertain that possibility no matter what. That open “I’m determined before I start that it can’t be true” is unusual for scientific articles, but many must be funded by the huge chemical industry. I’ve found one study which admits that one strain of flea is strongly resistant to a number of chemicals but goes on to insist that it can’t be true elsewhere. does that mean that one study was independent and the others are trying to explain it away? Interesting.

    3. That insistence that resistance is not the problem – well, I can’t believe he really said that. Even if resistance had not been demonstrated, which is not quite true, it does not prove that it doesn’t exist. that’s extremely unscientific. A number of studies have been funded by Bayer: they have their own labs, surely? Why do they do that? This insistence that the customer is always wrong is funny. When the products were new and everyone said they worked it was because the customers were all compliant in their use, and now increasingly they aren’t, and that’s the sole problem? Have the customers’ genes mutated? What a joke!

  2. @GC I couldn’t agree more. This article is pet pharma propaganda several studies and basic evolution PROVE fleas are developing resistance to these meds and environmental factors only inc this. ” Insecticide/acaricide resistance in fleas and ticks infesting dogs and cats published in US library of Medicine shows what a lie this article is.

  3. Pat Xmas eve 2017
    I despair of ever ridding my cat of fleas.
    She rarely goes out being old but sits on the window ledge.
    Take her to the vets for Advocate flea treatment monthly, but she still rips her neck till it bleeds, and I can still find a dopey flea or two on her being an all white cat….
    Im 80 the cats 12…wish there was a cure…..

    1. Try NexGard it is Euros 10 for one tablet which lasts for a month but it is an extra strong tablet. This tablet was for my dog but they also do one for cats as all animals in the household have to be treated at the same time. Good luck

  4. Not Everyone has 12 hours a day to vacuum up the house, and clean every nook and cranie. It is basically impossible. So basically it is impossible to get rid of the darned things.

  5. i’ve used ‘revolution’ for years. our cat weighs a bit more than the 7.5kg=16.5lb weight limit. i hesitate to use more than one vial/pipette on her. the most effective means to control fleas in my home has been VICTOR THE ULTIMATE FLEA TRAP which i found at HomeDepot for $15. it uses a 7 watt bulb with a sticky pad beneath. the warmth/light attrack insects of all types. in a perfect world i would vacuum daily.

    1. I have used 3 of the traps for years. I do treat cats and vacuum every day, but feel success is due to traps. Every flea caught is a flea not breeding.

  6. This is a straight up lie, frontline does not work anymore, hasn’t for a couple years now, neither does advantix or any other flea treatment. Vacuum every day, bombed the apartment, frontline the cat every 30 days regularly and the cat and house is infested. 50 bucks for a 3 month supply which probably amounts to 1/10 of an ounce. If I sold something for the price of gold that cost me penny’s to make, I’d probably lie and tell you it works great. Don’t bother wasting your money on these things, you’ll just be poisoning your cat

  7. I agree, the fleas this year have a resistance to Everything!!! I used Advantage II plus on all of my cats, I fog bombed the house 3 times in the last 6 weeks, I have used just about every flea killing product since the beginning of Summer. I have used natural products, diamatacious earth, vacuumed every nook and cranny, washed pets bedding… And my poor kitties STILL have fleas!!! Just like in the world of agriculture, the weeds that 50 years ago were small and easily eradicated, today, those same weeds grow bigger, with thicker stalks and are harder to kill because of the strong chemicals i.e.(glyphosphate) and genetically the weeds change to become resistant. I’m believing the fleas are doing the same thing. I have a veterinary nursing degree. I have 17 cats of my own. I do kitty rescue for injured, or abandoned Kitty’s and try to find them good homes.
    Believe me I’m on top of this and they can’t tell me I’m doing something wrong. The fleas this year are totally resistant. And I’m at a loss, as I don’t want to poison all my kitties with chemicals!

    1. Well I’m glad I’m not the only one invaded by invincible cat fleas. I’m resorting to calling in a guy, over the counter stuff from the pet shop is doing diddy squat.

    2. have 2 dogs and a 16 year old cat. Fleas are terrible this year. I’ve tried everything and nothing is working. Washing everything, vacuuming, topical treatments, I even got Nexguard and my chiwinnie had seizures from that and I had to go back to topical treatments for him. All kinds of sprays, everything! I’m going to try flea foggers and after that, I give up. I’m getting flea bites now too.

  8. Fleas tend to hide and lay eggs in places those home treatments can’t reach. Even flea bombs do not get into every nook and cranny. While expensive, exterminators are the only true way to be rid of the fleas in the home. I will say that flea resistance does exist indeed but after having my home professionally exterminated i have yet to see a flea on any of my cats. I continue to use revolution because they are indoor/outdoor cats and my yard has not been treated. I no longer have a flea problem.

  9. I have 2 dogs and a 16 year old cat. Fleas are terrible this year. I’ve tried everything and nothing is working. Washing everything, vacuuming, topical treatments, I even got Nexguard and my chiwinnie had seizures from that and I had to go back to topical treatments for him. All kinds of sprays, everything! I’m going to try flea foggers and after that, I give up. I’m getting flea bitesbow too.

  10. I’m sad but glad to hear I’m not the only one. Tried many products and they all seem to be just water in my book. I’ve seen fleas actively biting on the area where treatments were put within 24 hours and they WERE NOT dying. Use flea bombs and the next morning there is fleas Treat the yard and there is fleas. Starting to think the only solution is just not having a pet. Getting ridiculous spending tons of money for zero results

  11. My personal experience: I used Fipronil for two decades. Owned several dogs and did rescue, dog-sitting, etc., so had lots and lots of dogs come through. I also know about cleaning the entire environment, bedding, flea bombing the house, diatamaceous earth in the garden beds, bathing, etc.
    Frontline Plus was my go-to and always worked beautifully. Two years ago the Fripronil (Frontline Plus) just plain ol’ stopped working. Two other people who had used it for years had told me the same thing. I was skeptical until it happened to me too.

    1. This has been my experience as well…so I switched to the even MORE expensive revolution. It worked great until last year when it STOPPED WORKING!! Now I’m struggling to get relief without poisoning my pets

  12. We have 4 dogs and thus year have been inundated. First time ever owning pets that we gave had fleas….
    I Hoover twice daily, smoke bomb kennel and wash their bedding weekly, spray and bomb house weekly. We even treat the dogs every 2 weeks. No ticks which is brilliant here in South Downs, but we are just fire fighting the fleas. Ironically no humans have been bitten… not sure what else we can do except wait for summer to be over (if that helps??)

  13. Anyway that’s now all dog bedding thrown out, kennel and run hoovered, bombed and sprayed, dogs bathed and treated and house hoovered and resprayed…. let’s see if it lasts longer than 2 weeks this time….

  14. I have done all of the above….I feel like I’m poisoning my pets and my house. I’m about to try diatomaceous earth. It is safe …unless you or your pet breathe it into lungs. YIKES

  15. This summer has broken temperature and drought records here in our part of Appalachia and brought an unprecedented flea infestation. We keep Advantage II on our cat year round, which always kept fleas at bay in the past. This summer Advantage seemed to stop working completely, even after applying every two weeks instead of monthly. I have taken everything off the wood floors except for furniture, vacuumed daily (moved furniture around to get under it), sprayed the floors and baseboards with Precor 2000 premise spray…and still have fleas jumping on my white socks. Two days ago took the cat to the vet for a Capstar flea pill and bought and applied Revolution. Still seeing lots of live fleas on my cat 48 hours after applicaton. Probably will have to wait for cold weather, turn the thermostat down to just above freezing, and hope cold immobilizes or even kills the fleas in the environment, as the poisons seem to have little efficacy.

  16. im more than late but i have used advantage 2 for cats and within a few hours i have seen dead fleas on beading and within 24 hours not a living flea could be found on the cats but with frontline plus for cats its still been two weeks and i cant find a single dead/dying flea and there numbers have only increased. ive used frontline two separate times with the same outcome and with all treatments never being used on anything more than a light to light/moderate infestation. both products are administered the same way so i doubt its user error. i am not endorsing advantage just sharing my experience

    1. Here in 2022, Advantage seems to not work as good as it did in previous years. Frontline was working until 2005, when I had to switch to Advantage. Over the last couple of years, Advantage seems to be becoming less and less effective.

      Considering that I’m experienced with spot on products and the various flea treatments, something has had to changed, and, contrary to what this old patronizing article implies, it is not “user error”. At least not on my end. Maybe it’s on the fleas’ end and they’re not following the directions.