Navigating bewildering array of pet antiparasitics

Experts advise against one-size-fits-all approach

Published: August 15, 2013
By Christy Corp-Minamiji, DVM

Photo by Dr. Michael Dryden
Two American dog ticks (Dermacentor variabilis) “quest” on a blade of grass. Questing ticks, hungry for a blood meal, wait for someone to pass close enough to climb aboard.
Dr. Mark Grossman practices veterinary medicine in the heart of flea and tick territory. The climate of Roanoke Island, N.C., provides a perfect breeding ground for legions of arthropod assailants. By necessity, Grossman has become something of an expert in the long and seemingly ever-changing list of flea and tick control products for pets.

On message boards of the Veterinary Information Network (VIN), an online community for the profession, questions and confusion about flea-and-tick-product selection are so common that Grossman, a VIN consultant, has with assistance from colleagues compiled a chart describing the various sprays, topical “spot-ons,” oral medications and collars available.

It’s a chart that must be updated periodically, as products come and go. Lately, more are coming than going. The expiration in 2011 of the patent for fipronil, the active ingredient in the widely used flea-and-tick product Frontline, has generated a spate of generics containing fipronil. A few novel products have come on the market, as well, including a new spot-on parasiticide called Activyl, and a flea-and-tick collar dubbed Seresto.

“The number of products is completely overwhelming,” says Dr. Michael Dryden, a veterinary parasitologist at Kansas State University, also known as “Dr. Flea.”

Grossman’s latest chart has 19 entries, and that’s not everything. Grossman focuses on information important to veterinarians, adding products that contain new chemicals or new chemical combinations. He has chosen to omit the myriad of generic products or products not sold primarily through veterinarians.

Veterinarians’ questions about parasiticides range from wanting to know the most effective products for particular regions or particular pet lifestyles to concerns about human and animal safety.

Dryden, directing his comments to practitioners, says: “In any region, there’s a parasite that’s the foundation of your practice. … Pick a parasiticide that manages your core foundational parasites.”

While there may be an overwhelming array of products to choose from, the choices overall are much improved from those of the past, says Dr. Sharon Gwaltney-Brant, a veterinary toxicologist and consultant for VIN.

A generation ago, the best-known means of flea and tick control killed only adult fleas, leaving eggs and immature parasites unscathed. Some products were highly toxic to mammals, to boot. “Many of the chemicals we were using back then were horrible,” Gwaltney-Brant says.

As pets moved from the kennel and backyard into the bedroom, companies began to take advantage of an increased understanding of insect biology to develop and market products that target various life stages of arthropods, and their unique physiology. Targeting areas specific to insect metabolism such as chemical receptors not possessed by mammals made these new products far safer and more effective than the old shampoos, sprays and dips.

The evolving technologies have unleashed a complicated array of products covering everything from flea “birth control” to broad-spectrum medications designed to prevent heartworm and intestinal parasite infections in addition to flea infestations.

Drugs such as lufenuron inhibit the development of the flea larvae, breaking the life cycle at its root. Topical drugs such as fipronil and imidacloprid paralyze and kill adult fleas. Newer drugs such as indoxacarb are activated by the flea’s own enzymes.

Does a pet owner need the fleas gone now, or are they more concerned with having a product that will continue to kill fleas and ticks long after they have forgotten the problem? Products such as Vectra 3D and Advantage vie for bragging rights over speed of flea kill, while others such as the Scalibor collar may not be effective immediately but may last for up to 6 months.

Contributing to the complicated nature of pet parasite control, regulation and availability of these products is not uniform. Some products are considered insecticides and, in the United States, are regulated by the Environmental Protection Agency, while others count as medications and fall under the jurisdiction of the U.S. Food and Drug Administration. Some flea-and-tick control methods are available to pet owners over the counter from pet and big-box stores. Others are available only from veterinary clinics or from pharmacies presented with a prescription from a veterinarian who has examined the pet.

Given the many products available and the variety of conditions under which pets live, Grossman cautions against adopting a one-size-fits-all approach. “The challenge is the work with each case, to figure out what’s best for the individual animal, those clients and their lifestyle,” he says.

Cooperation between the veterinarian and pet owner is as important to developing a sound flea control protocol as it is in any medical case. Grossman stresses that a thorough history of the pet, its housemates, and environment plays a role in determining product selection. He also says, “A working relationship and good communication with the clients is just as important. Some clients do not like topicals put on their pets. Some are afraid of their cat or child contacting the dog with topicals.”

Grossman suggests veterinarians and pet owners consider regional flea and tick habits and susceptibility, pet species and breed, the pet’s exposure to the outdoors and to water, and what products are available.

Another thing to consider: Not every product seems to work equally well in all areas or for all pets, judging from practitioners’ anecdotal observations.

“It does seem like different vets in different areas have more or less success with different products,” says Grossman. “It does seem like the fleas seem to have different sensitivities in different areas.”

At his own practice in eastern North Carolina, Grossman has noticed different results from those experienced by colleagues in the western part of the state. In fact, within his practice, some clients may swear by a particular product while, he says, “we see other clients who say it doesn’t do much for them.”

Dryden has heard similar comments from practitioners about varying or diminished efficacy of products in certain parts of the country. However, he says that so far there is no evidence of a true shift in fleas’ susceptibility to these chemicals. “Before someone can state the ‘R’ word (resistance), we have to be able to prove it,” he says.

While Dryden credits the importance of practitioner observations, he stresses that it is important to recognize that multiple factors — such as proper administration, the number of animals in the household and the overall flea burden — contribute to the success of flea control.

For example, he says, “In Florida, we’ve seen a continual increase in flea numbers. ... The numbers are astronomical. In the face of that, I don’t care what the product is, they don’t fare well.”

The primary flea-control failure Dryden has seen is not one of chemicals but of communications. “If any recommendation is difficult, time-consuming or expensive, why do we think (clients) are going to comply if we don’t tell them why they have to comply?” he says.

Photo by Dr. Michael Dryden
On the back of this severely infested dog, fleas are visible as small dark specks. The white dusting is flakes of skin caused by inflammation.
Dryden points out that due to the nature of the flea life cycle, depending on the number of eggs laid by fleas on a pet prior to treatment, “in some of these (infested) homes, you’re going to have an upward population trajectory” following initial treatment.

“They have to treat every animal in the home for at least three months if they’re going to break that cycle. It gets expensive,” he explains. He believes that much client frustration could be alleviated through better communication in the veterinary hospital. “Somebody in that practice has to get a life-cycle chart out and explain that to the pet owner,” Dryden says.

For Grossman, island living comes with challenges beyond communication. Many of his canine patients give their flea and tick treatments a run for the money. “For dogs, if they’re swimming a lot, I just don’t think the topicals handle it,” says Grossman. For water-loving dogs, he recommends oral spinosad products.

At the opposite end of the spectrum, for the “little Maltese in a condo,” Grossman may recommend an oral insect development inhibitor to prevent the occasional flea from laying eggs that infest the household, or a topical spot-on, since there is less of a chance that the product will become less effective due to the dog’s swimming habits.

Species and breed also factor into product selection. With a few exceptions, such as Seresto, the newest collar on the market to combat fleas and ticks, Grossman says: “We don’t have the tick control for cats that we do for dogs. Certain tick-fighting chemicals such as amitraz found in the Preventic collar, while harmless to dogs with appropriate use, can be toxic to cats even just with skin contact.”

If a product is dosed appropriately based upon the pet’s weight, breed should not matter; however, practitioners including Grossman report an increase in product reactions with smaller breeds.

Toxicologist Gwaltney-Brant, who previously worked for the Animal Poison Control Center operated by the American Society for the Prevention of Cruelty to Animals, states that “most cases (of suspected poisoning due to flea and tick products) are not actual toxicities; they are skin reactions.”

Like Grossman, she has an impression that owners of small dogs more frequently report product reactions in their pets. Gwaltney-Brant wonders if that has to do with the habits of people who tend to own small dogs.

“Do we see it more in small white dogs?” she asks rhetorically. “It certainly seems that way. I don’t have any data to back that up. Maybe their skin is a little more sensitive, but that doesn’t mean we don’t get it in big, black German shepherds.

“Is it owner perception?” she goes on, pointing out that a small indoor dog may be monitored more closely than the rambunctious Labrador retriever who receives his flea/tick treatment, then is sent into the yard to run off his energy.

Gwaltney-Brant stresses that modern flea-and-tick preventatives are far safer than those of decades past, although occasionally she encounters practitioner reports of true poisonings from the amitraz collars, which can cause profound sedation in an animal that eats the collar.

However, since the advent of reversal drugs, this effect is more easily treatable than in the past. “Lately, we can just reverse the signs with Antisedan and have them try to get the collar out via emesis (vomiting), depending on the time of ingestion,” she says. “Before, we often had to recommend surgery in a dog that was already sedated.” Anesthesia is more risky in an already sedated patient.

She is less concerned about other collars, saying, “Most of what’s in there isn’t something terribly toxic.” In the new Seresto collar, for example, Gwaltney-Brant believes that the low concentration in the collar of pyrethroids, a different ingredient from amitraz, is not likely to pose a toxicity concern.

Overall, says Gwaltney-Brant, most modern products have a wide margin of safety. “You have to measure what you want,” she says. “Is the flea protection more valuable than the pretty low risk of adverse effects?”

In the war against fleas and ticks, the battlefield best determines the weapon of choice. Exposure, degree of infestation, the presence or absence of other animals, animal and owner lifestyles and cost all have a bearing on flea-and-tick-control decisions.

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