It’s not always easy to re-educate clients who think they have all the answers. In practice, veterinarians hear a lot of misinformation from pet owners every day, especially about internal parasites and parasite protection.
Here are seven common myths about worms in dogs—and how to set the record straight.
7 Myths About Worms in Dogs
Myth 1: My pet only needs heartworm prevention if I live in a certain area.
Although it’s more prevalent in some areas like the American South, heartworm has been identified in all 50 U.S. states (1) and several warmer parts of Canada, including southern Ontario and southern Quebec (2).
“Even if the risk of transmission is low in your area, that doesn’t mean no risk,” says Dr. Christine Heinz-Loomer, DVM, MBA, of Elanco Animal Health. “It only takes one bite from an infected mosquito to transmit heartworm. This disease is so much easier, less costly and better for the health of the pet to prevent than to try to treat after an infection has already set up.”
Pet owner Ashling Grigorian and her family know firsthand that low risk doesn’t mean no risk. When the family moved from Chicago to Southern California with their dog Ulysses, they promptly scheduled an appointment with a new veterinarian to discuss the dog’s environmental allergies, which seemed to worsen shortly after the move.
“During the appointment, the veterinarian discussed heartworm and how it was uncommon in Southern California,” Grigorian says. “The doctor made it seem like heartworm preventive was not needed. Since Ulysses was on tons of other medicines for allergies, we thought something so uncommon was not worth adding more medicines to his daily life.”
One year later, Ulysses had a positive heartworm test. He had been in Southern California the entire time. “The treatment is so long and hard on the dog,” Ashling says. “Ulysses had a few hospital stays, plus he couldn’t move around much. He also gained a lot of weight during this time, which we’re still working to get off. It probably cost about $7,000 total. We now are huge advocates of all dogs going on heartworm prevention no matter where you live. The monthly [preventive medication] is better than the treatment.”
And while heartworm is a parasite we certainly want to prevent, broad-spectrum parasite control is about more than just preventing heartworm disease.
“By treating dogs for nematodes and tapeworms every month with broad-spectrum internal parasite control products, we are protecting dogs from many internal parasites, not just heartworm,” says Dr. Susan Little, DVM, Ph.D., DACVM (Parasitology), a Regents Professor and Krull-Ewing Professor in Veterinary Parasitology at the Center for Veterinary Health Sciences at Oklahoma State University. “In fact, in areas of the world where heartworm has not been shown to be locally transmitted, products like milbemycin oxime/praziquantel are frequently used as intestinal dewormers.”
Myth 2: My dog only needs parasite protection in the spring and summer.
Although many pet owners only administer endo- and ectoparasite control products in the warmer months, year-round protection is far more effective. Intermittent use of parasite protection often backfires, especially since many clients forget to re-start their pet’s medication when warmer weather arrives.
To encourage year-round protective measures against a wide variety of parasites, make sure clients are aware that the risk of contracting parasites does not disappear in fall and winter. For instance, while hookworm infections in dogs in the U.S. are more prevalent in late summer and early fall, prevalence of whipworm and roundworm infections peak in winter, a recent study reveals (3).
Changes in climate may also be affecting parasite survival and transmission. As ticks, fleas, and mosquitoes become more prevalent in certain regions or for longer periods of the year, they can bring tapeworm, heartworm, and other vector-borne diseases with them.
Additionally, clients may not know that heartworm preventives can eradicate parasites that a dog contracted in the previous month. So if an infected mosquito bites a dog in September, and the pet owner stops treating every October, that dog can develop heartworm disease. Since some heartworm preventives also cover intestinal parasites, the dog would also potentially lose protection against hookworms, whipworms, roundworms, and tapeworms, depending on the product used. For instance, Interceptor® Plus (milbemycin oxime/praziquantel) protects against five major types of worms in one monthly chew.
See important safety information for Interceptor® Plus below.
“We know these parasites can cause disease in dogs (and in some cases are zoonotic) and that they are a common risk for dogs to encounter, especially if they live a social lifestyle,” Heinz-Loomer says. “Thinking beyond just the risk of heartworm to providing more broad-spectrum parasite protection, including intestinal parasite protection, is an important concept for clients to understand when looking to protect their dogs.”
Myth 3: My pet cannot have worms because I haven’t seen any.
Many pet owners mistakenly believe that if their dog has internal parasites, they will see signs like worms in the stool. What they don’t realize is that many pets don’t show signs of internal parasites, even if they are infected.
“Surprisingly, most dogs with internal parasites do not show any clinical signs, especially at first,” says Dr. Kathryn Duncan, DVM, a resident in veterinary parasitology at Oklahoma State University College of Veterinary Medicine. “Over time, as the parasites go untreated, pathology can worsen and intensity of infections may increase as the dog re-infects himself from the environment. The best approach is early detection through routine—at least annual—testing and regular preventive treatment to limit the length of time dogs are infected.”
Myth 4: My community is clean. We don’t have a parasite problem here.
Internal parasites are more prevalent than most clients (and even some veterinarians) might think. As an increasing number of pet owners travel with their dogs and socialize them at community dog parks, parasitic risks continue to shift. In fact, a national survey of dog parks across the U.S. showed that 1 in 5 dogs are positive for internal parasites (4).
“One of the biggest hurdles for veterinary staff to overcome is the owner’s misconception that their own dog could not possibly have internal parasites because they are taking good care of their pet,” Duncan says. “Whether at the dog park, on their daily walk, at dog day care, or even inadvertently carried in on our clothing or shoes, dogs and parasites find each other and infections result.”
Parasite threats are also changing as the animal rescue movement continues to grow and more dogs are being transported across state lines (and even from other countries). For example, the ASPCA reports transporting more than 40,000 dogs in 2018 in the U.S. (5). While relocation efforts should be applauded for helping reduce problems associated with pet overpopulation, one of the potential risks of this phenomenon is the introduction of parasites to new areas.
“Dogs recently rescued from another area of the country where heartworm is hyperendemic are very likely to be infected,” Little says. “When infected dogs are brought to an area where fewer resident dogs are on heartworm prevention…tragedy can ensue because nothing is stopping the few mosquitoes that are there from transmitting the infection to unprotected dogs.”
With the risks for each patient more dynamic than ever before, it’s especially important for veterinarians to always be evaluating broad-spectrum parasite protection recommendations.
Myth 5: Worms are not a big deal.
Many clients not only underestimate the risk that parasites pose to the health of their dog, but they also do not always appreciate the risk that zoonotic disease presents to their human family members. Although it seems like these things should be common knowledge, in reality, much of the pet-owning population remains uneducated.
“Owners often think NIMD (Not in My Dog),” Little says. “But zoonotic parasites like hookworms are very common in dogs, with almost 1 in 10 pet dogs visiting dog parks across the U.S. infected with hookworms.” (4)
Hookworm larvae develop in the soil in recreational areas like dog parks and other outdoor places where people and pets congregate, where they readily infect dogs and humans. “Ascarids are also common in dogs, especially young puppies, and the eggs, once in the soil, will survive and remain infective for years,” Duncan says.
In fact, 1 in 20 people in the U.S. have been infected with ascarids from dogs and cats at some point in their life, the CDC has shown (6). “Although most of us don’t go on to develop severe disease from these infections, treating dogs for internal parasites helps protect public health as well as canine health,” Duncan says.
Myth 6: A negative fecal test means the dog does not have worms.
Although passive fecal flotation is one of the most common tests performed in veterinary clinics, it isn’t definitive by any means. “Performing a centrifugal flotation, either in-house or by sending samples to a reference laboratory, greatly increases the likelihood of detecting infections, but some are still missed,” Little says.
According to Little, whipworms are the second most commonly diagnosed nematode in adult dogs, with some surveys showing that nearly 40 percent of dogs in animal shelters in some areas are infected with whipworms (7). “[However], of the nematodes, fecal float is least likely to detect whipworms because the eggs are heavy and shed in lower numbers than hookworm or ascarid eggs,” she says.
Little goes on to say that tapeworms are almost always overlooked. In one study, passive flotation missed approximately 96 percent of Dipylidium caninum infections and 86 percent of Taenia spp. infections in dogs (7). In another study on tapeworm prevalence in western European dogs, 10.4 percent of dogs tested positive for cestodes when traditional methods were combined with coproantigen testing, whereas fecal flotation or centrifugation identified only 0.2 percent of the dogs as positive (8).
“We just don’t have good diagnostic tests for them,” Little says. “In fact, veterinarians often don’t realize their patients are infected with tapeworms even though recent surveys show that cestodes can be more common in dogs than…hookworms or whipworms.”
To ensure dogs are protected from common parasites that they will frequently encounter in the environment, Little, Duncan and Heinz-Loomer recommend treatment every month. “We just can’t leave dogs infected until the next physical exam and hope we are able to diagnose the infection then,” Duncan says. “Instead, we have to treat proactively given how common these infections are.”
Myth 7: My dog is protected—I give him medicine every month.
Pet owners don’t always understand what type of parasite protection products they are giving their dogs, including what they do and do not provide coverage against.
“Our clients have so much information they are trying to understand and apply to be good ‘pet parents’ that the details of their dog’s preventive care can be very confusing,” Heinz-Loomer says.
For example, the client might be using an oral tick and flea control medication and assume that it also covers internal parasites, even if it doesn’t (or only covers some).
“Even though we as veterinarians and veterinary staff feel like we talk about this kind of stuff all the time,” Heinz-Loomer says, “our clients may only hear this once or maybe twice a year, and may need the ‘refresher’ and reinforcement so they continue to understand and see the value in consistently using parasite protection.”
Interceptor Plus is indicated for the prevention of heartworm disease caused by Dirofilaria immitis and for the treatment and control of adult roundworm (Toxocara canis, Toxascaris leonina), adult hookworm (Ancylostoma caninum), adult whipworm (Trichuris vulpis), and adult tapeworm (Taenia pisiformis, Echinococcus multilocularis, Echinococcus granulosus and Dipylidium caninum) infections in dogs and puppies six weeks of age and older and two pounds of body weight or greater.
Interceptor Plus Important Safety Information
Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Interceptor Plus, dogs should be tested for existing heartworm infections. The safety of Interceptor Plus has not been evaluated in dogs used for breeding or in lactating females. The following adverse reactions have been reported in dogs after administration of milbemycin oxime or praziquantel: vomiting, diarrhea, depression/lethargy, ataxia, anorexia, convulsions, weakness, and salivation. For full prescribing information see Interceptor Plus package insert.
Disclaimer: The author received compensation from Elanco US Inc., the maker of Interceptor Plus, for her services in writing this article.
- Parasite Prevalence Maps. Companion Animal Parasite Council. Retrieved from https://capcvet.org/maps/#2019/all/heartworm-canine/dog/united-states/
- Heartworm. Canadian Parasitology Expert Panel Guidelines. Retrieved from https://research-groups.usask.ca/cpep/parasites/heartworm-supplementary.php
- Drake, J., Carey, T. Seasonality and changing prevalence of common canine gastrointestinal nematodes in the USA. Parasites Vectors 12, 430 (2019) doi:10.1186/s13071-019-3701-7
- Elanco. Data on File.
- Animal Relocation. ASPCA. Retrieved from https://www.aspca.org/animal-placement/animal-relocation
- Parasites – Toxocariasis (also known as Roundworm Infection). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/parasites/toxocariasis/epi.html
- Adolph, Chris & Barnett, Sharon & Beall, Melissa & Drake, Jason & Elsemore, David & Thomas, Jennifer & Little, Susan. (2017). Diagnostic strategies to reveal covert infections with intestinal helminths in dogs. Veterinary Parasitology. 247. 10.1016/j.vetpar.2017.10.002.
- Drake J et al SEVC 2018. Innovative Multicenter Analyses of Tapeworm Prevalence in Western European Dogs.
Interceptor is a trademark of Elanco or its affiliates.
© 2020 Elanco. PM-US-20-0723