Ectoparasites: The Risk is Present all Year Long

But clients aren’t always willing to accept that reality.


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“So, you’re telling me that fleas, ticks and mosquitoes are going to be in my yard, biting my dog and giving her allergies and heartworms in these freezing temperatures,” Mrs. Client says sardonically, looking at price tags and glaring at you in disbelief. “Really?”

While some clients will always be skeptical about the need to use flea, tick and heartworm prevention products year round, veterinary entomologists and scientific researchers have evidence to prove that most ectoparasites are a continual problem, especially in the southern U.S.

“Frankly, with ectoparasites, we’ve never been able to determine that weather has much effect on their life cycle,” said Nancy C. Hinkle, Ph.D., professor of entomology at the University of Georgia College of Agriculture and Environmental Sciences. “The host maintains its microhabitat and, so long as the host stays warm, the ectoparasites are very comfortable.

“If you are a flea and you live on a squirrel, your habitat is the same temperature as that squirrel,” she said, adding that mammals are always warm and the fleas will survive “unless they make the mistake of getting off the squirrel.”

Ditto for people’s houses, said Susan E. Little, DVM, Ph.D., veterinary parasitologist at Oklahoma State University’s Center for Veterinary Health Sciences.

“In mild winters, we’ll see home infestations with fleas, even in January or February in much of the South. In other years, when winters are cold and dry for longer, the fleas are more likely to be kept in check and the home infestations don’t become severe until late summer or early fall,” she said.

Fleas and some ticks, particularly Rhipicephalus sanguineus, the brown dog tick, prefer to live in the house, so winter weather doesn’t deter them as much, said Dr. Little, regents professor and holder of the Krull-Ewing endowed chair for veterinary parasitology. She is president-elect of the Companion Animal Parasite Council.

Granted, freezing weather puts a damper on outside environmental flea populations, said Michael Dryden, DVM, Ph.D., University Distinguished Professor of veterinary parasitology at Kansas State University College of Veterinary Medicine. “The longer and colder the winter is, the later in the year we see them return,” he said.

“Regardless, flea infestations are at their worst not in the spring or early summer, anyway. In temperate climates, the worst flea infestations occur in the late summer or fall as temperatures moderate.”

The No. 1 thing clients always say is, “We don’t see them, so we don’t have them,” noted Chris Adolph, DVM, who has a master’s of biomedical sciences in parasitology and owns Southpark Veterinary Hospital in Broken Arrow, Okla.

“That is a mindset, a paradigm that we work very hard to shift. We say, ‘Yes, that‘s a common misconception, but the fleas and ticks in Oklahoma are active year round. It never gets cold enough to wipe these guys out.’”

Clearing Up Temperature Myths

At temperatures above 40 degrees Fahrenheit, adult deer ticks (Ixodes scapularis) can be found seeking hosts on vegetation above snow-covered ground, Little said. Deer ticks, the most common species to infest dogs and horses during winter months, are most active from October through February, she said.

“In contrast, adult lone star ticks (Amblyomma americanum) usually don’t start emerging until late March or early April, but in a mild year we will see them come out as early as February. And although a late spring freeze may slow them down, they quickly resume activity as soon as the temperature warms up.”

Indeed, lone star ticks have been spotted on dogs as early as January during thaws, said Dr. Dryden, a founding member of the CAPC.

“The problem is that while sub-freezing temperatures do slow their activity, these cold spells don’t last for weeks on end. We see small periods in December, January and February where the temperature warms sufficiently for these ticks to become active. These are very resilient organisms.”

For practitioners, perhaps the hardest “sell” to clients is the notion that they should be concerned about mosquitoes and heartworm disease during winter months.

“Certainly, tropical species are going to be susceptible to cold weather but native species have, over time, adapted to their environment,” said Dr. Hinkle. “Even on a cold winter day, if you’re out walking around and you break through ice on a standing pool of water, you may see mosquito larvae bumping around in the water under the ice.”

For the larvae, all that’s required for continued development are a thaw and slight warming of the ambient temperature, she said.

“In many areas of the southern U.S., there probably are days in January where the temperature goes above 65 degrees and I wouldn’t be surprised to see mosquitoes flying around. That’s why here in the Southeast, it’s important for animals to be on heartworm prevention year round, because the heartworm-vector mosquitoes are active and potentially biting dogs and cats.”

Bottom line, “The risk is present all year and we can’t predict with certainty when mild winters will occur, elevating risk even further,” said Little. Both the CAPC and the American Heartworm Society recommend year round protection of pets for fleas, ticks and heartworm disease.

A Constant Threat

“We try to be very kind when giving our clients information that they may or may not be interested in,” Dr. Adolph said. “I might say, ‘This is information I sure was glad to hear when I heard it; there was a time that I didn’t know this, either.’ Or, ‘That is what I believed growing up, but now we know. . .’”

Adolph said he tells clients that fleas and ticks are a constant threat that is far better to prevent than to treat, adding, “We never see rabies in your pets, either, but we vaccinate them to prevent that from happening.”

Flea and tick prevention has vastly improved in recent years, he noted.

“Twenty years ago, clients would leave with a grocery sack full of medication to be used both on the pet and in the environment. These methods were labor-intensive and marginally efficacious.”

Today, Adolph tells a client, “I can send you home with a small box of pills and a small container of tick prevention. Use both year round, and your external parasite burden will be greatly reduced, if not totally controlled.”

Zoonotic disease is another compelling reason for tick prevention.

“I remind them that ticks carry Rocky Mountain spotted fever, Lyme disease and ehrlichiosis, and you want to protect your two-legged babies,” Adolph said.

Although some topical flea and tick prevention products are labeled for mosquito repellency, Adolph said he stresses to clients that a monthly topical or oral, or a six-month injectable, heartworm preventive given year round is the base foundation for heartworm prevention.

“Everything else is a limiting factor. Topical mosquito repellent, and limiting pets’ outdoor time at dusk, when mosquitoes are most active, are adjuncts,” he said.

Adolph said he and his staff role play scenarios to enable them to knowledgeably educate clients.

“We use that information to build a case. Then, if the clients decide that’s not what they want to do, it’s on them,” he said. “But we never want to let them walk out the door thinking it’s not necessary.”

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