The Deworming Debate

Should veterinarians recommend year-round prevention when geography is not a factor?

December 19, 2018

By Marissa Heflin

Hookworms, tapeworms, whipworms, roundworms, and heartworms. They are intestinal and circulatory parasites no one wishes to encounter. Yet, they’ve squirmed their way into too many pets to continue practicing status quo programs.

Heartworm infections, for example, are forecasted to be above normal across virtually the entire U.S., according to Companion Animal Parasite Council (CAPC). Nationally, prevalence rates have risen each of the past five years and are now up 20 percent from 2013 levels, the group further noted.

Establishing a deworming program is important because parasites, both external and internal, pose a real threat to pets and, in many cases, to the humans around them, according to CAPC board member Rick Marrinson, DVM, of Longwood Veterinary Clinic in Longwood, Fla.

Practice protocol

Depending on where you live in the U.S., one might come across two very different deworming approaches: a year-round program versus risk-based assessment, according to Andrew Peregrine, DVM, BVMS, PhD, Dipl. EVPC, Dipl. ACVM, a professor in the department of pathobiology, Ontario Veterinary College, University of Guelph in Canada. Dr. Peregrine is also the former president of the American Association of Veterinary Parasitologists (AAVP). He noted AAVP does not have an official policy endorsing a specific deworming program.

“Once you go to the northern parts of the U.S. and Canada, the risk of most parasites become very different from that in the southern United States,” he said.

That’s when the philosophical discussion begins: Does it make sense to recommend year-round prevention when the risk is not year-round in a particular geographic region?

Some veterinarians prefer a risk-based assessment due to cost factors (clients save money by not administering the medication every month) and the possible dangers of overmedicating (which could lead to drug-resistant heartworms), Peregrine said.

A risk-based approach also pushes veterinarians into deeper discussions with clients, which take travel and other potential risk factors into account. It takes more time, Peregrine said, but pet owners don’t want oversimplification, such as hearing that all pets, no matter what, should be on a deworming program.

“[Pet owners] are going to wonder why a veterinarian is recommending heartworm medication when it’s not prevalent in the area,” he said.

However, Peregrine noted many veterinary organizations promote a year-round deworming program. The American Heartworm Society (AHS), the American Animal Hospital Association (AAHA), the American Veterinary Medical Association (AVMA), and CAPC are among those.

“While climate differences can make the risks for parasites higher or lower in varying geographies, no one is safe,” Dr. Marrinson said. “The basic premise remains the same for all pets no matter where they are; test, treat, and prevent parasites. With the high mobility of pets (travel, relocation, and movement of rescue animals), as well as the ever-increasing range of parasite vectors, CAPC recommends all pets be tested on schedule, receive year-round monthly preventive medication, and be treated when necessary.”

AHS’s recently released 2018 Canine Heartworm Guidelines notes environmental and climatic changes, along with the relocation of microfilaremic dogs and the expansion of microfilaremic wild canid territories, are all contributing factors to both incidence numbers and the spread of heartworms to areas once considered non-endemic.

“For these reasons, we continue to stress the importance of year-round administration of macrocyclic lactone preventives, along with practical steps to reduce mosquito exposure, such as eliminating standing water on the property and keeping pets indoors during peak mosquito times,” said AHS president Chris Rehm, DVM.

AAHA and AVMA, with their joint preventive health-care guidelines, support year-round broad-spectrum parasite control with efficacy against heartworms, intestinal parasites, and fleas, said Heather Loenser, DVM, AAHA’s senior veterinary officer.

The Centers for Disease Control and Prevention advocates monthly preventatives for fleas, heartworms, and other parasites through its “Healthy Pets, Healthy People” campaign.

Forecasting heartworm infection
  The Companion Animal Parasite Council (CAPC) forecasts heartworm infection prevalence to be above normal across most of the United States. Prevalence rates have risen each of the past five years and are now up
20 percent from 2013 levels.The increase is partially attributed to the hot and wet weather that occurred in 2016, (mosquitoes like these conditions), and in 2017, weather was again hot and wet, according to CAPC. In addition, infected dogs act as “reservoirs of infection,” increasing the number of infected mosquitoes and ultimately spreading the parasite to other dogs, CAPC further noted. This increase in heartworm activity, CAPC says, supports its recommendation that all dogs be given heartworm preventives year-round, and tested annually for both heartworm antigens and microfilariae.

Training and education

A deworming program is only effective if it’s universally understood and implemented within the practice

“Repetitive education with the goal of a unified, consistent message is critical,” Dr. Marrinson said. “All veterinary team members should be well versed in how to test, treat, and prevent parasites.”

CAPC has a variety of resources to help train support personnel at, including prevalence and forecast maps, and guidelines, Marrinson noted. CAPC even has an app that helps teach veterinary teams how to identify the most common parasites.

“It all starts with educating the practice team first, whether it is through weekly team meetings, lunch and learns, or other continuing education,” Dr. Loenser said.

Since the whole team interacts with clients, it’s very important to have everyone on board in whatever program the clinic has decided on, Peregrine said. You can’t have one person advocating a year-round program with another promoting risk-based assessment.

As for client education, exam room conversations still go a long way.

What does age have to do with it?
Parasite protocols can be divided into puppies/kittens and adult animals, according to Rick Marrinson, DVM, of Longwood Veterinary Clinic in Longwood, Fla., and board member of the Companion Animal Parasite Council (CAPC). “Due to their high rates of infection, all puppies and kittens are assumed to have worms,” Dr. Marrinson said. “Not only can they become infected shortly after birth from their mother and/or from their environment, they can be born already infected with certain types of worms. Due to their fragile state and immature immune system, juvenile animals are particularly at risk for parasitic disease. Therefore, the protocol for puppies and kittens is to receive multiple parasite treatments and multiple parasite tests during their first months of life.” Adult dogs and cats should be tested once or twice a year for internal parasites, depending on lifestyle and risk factors, according to Marrinson. Regardless of lifestyle, though, all dogs and cats should receive “continuous, year-round, monthly parasite preventives to eliminate worms to which the pet may have been exposed during the preceding 30 days,” he added. 

“Each month, CAPC releases a ‘Top Ten Cities’ ranking for the highest percentage of change in heartworm diagnoses month-over-month,” Marrinson said. “This can be a great conversation starter when emphasizing the importance of regular parasite prevention.”

Veterinarians can also tap into social media. For example, clinics can incorporate CAPC updates, which, via a direct posting to the clinic’s Facebook page, show clients the number of recent positive parasite tests in their county, according to Marrinson.

While zoonotic risk shouldn’t be used as a scare tactic, it is important for pet owners to understand the increased transmission possibility if their pet gets infected with a parasite, Peregrine explained.

He said he has noticed pet owners have a hard time buying into a parasite control program when they can’t see the parasite. He compares ticks and heartworms.

“The amount of tick products used in North America has gone up dramatically in the past few years, largely because people are seeing ticks in areas where they weren’t before,” Peregrine said. “People, at least around here, are dropping the amount of heartworm prevention. They were using heartworm preventives, but now they see ticks… unfortunately they can’t see heartworms… and so they are switching their financial resources to tick products.
I think the fact this is happening indicates we aren’t doing a good enough job telling people about the risks of heartworm and what it can do to a dog.”

Tools for the toolbox
Need additional resources? The American Animal Hospital Association (AAHA), American Veterinary Medical Association (AVMA), American Heartworm Society (AHS), Companion Animal Parasite Council (CAPC), and the Centers for Disease Control and Prevention (CDC) have you covered. CAPC for veterinarians CAPC for pet owners CDC Healthy Pets, Healthy People CDC on controlling mosquitoes, ticks and fleas inside and outside the home AAHA Parasite Counselor Program AAHA-AVMA Preventive Healthcare Guidelines

For other unseen parasites, conducting regular fecals may help compliance. Showing the infection, if there is one, personalizes deworming efforts, Peregrine said. Incorporating fecals into a wellness program eliminates the likelihood of a client opting out due to cost, he noted.

“Pet owners always look to veterinarians as the trusted source of accurate information,” Marrinson said. “Clients want to be told exactly what to do to maximize their pets’ health. Veterinarians should make firm recommendations based on established protocols, and then place a high level of importance on spreading that information to every client for every pet.”