Fleas Persist, But Reason Isn’t Resistance

March 2, 2010

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.”

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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.”

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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.”

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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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