Intestinal parasites: screening & prevention best practices

Ectoparasites, such as fleas, ticks, and mosquitoes, often dominate our discussions about parasite control with both colleagues and clients. While these external parasites can cause a host of conditions in companion animals—and controlling them is certainly important—a deeper problem hiding within is often overlooked: gastrointestinal endoparasites.

These parasites, including hookworms, roundworms, whipworms, and tapeworms, not only cause gastrointestinal signs of vomiting, diarrhea, and anorexia in our canine patients,^1,2 they can also lead to severe medical conditions in their owners when they serve as an aberrant host.¹ For many pet owners, the mere sight of a roundworm in the pet’s stool or tapeworm proglottids on the pet’s rear end can lead to panicked phone calls to the veterinarian, isolation of the pet from family members, and a decrease in the overall quality of the human animal bond in that household until the matter is resolved. Considering these factors, it becomes clear that the need for proper detection of intestinal parasites—and treatment of the diseases they cause—are as important as ever.

ENDOPARASITE PREVALENCE

The prevalence of endoparasites varies significantly both across the country and from study to study. A review of recently published studies shows a nematode prevalence ranging from about 6% to almost 30%._^3,4 Despite current veterinary protocols, a study analyzing data from the Companion Animal Parasite Council (CAPC) website even shows an increasing trend in positive fecal samples for hookworms and roundworms across the country.⁵ One recent study analyzing over 3000 fecal samples from dogs at nearly 300 dog parks across the United States found parasites in over 85% of locations and in 20% of samples tested.⁶ Keep in mind that all prevalence studies are affected by a wide range of factors. Data will vary quite a bit based on seasonality, testing methods, age of the patient, sample size, and geographic region.^5,7

WHAT ARE THE DIAGNOSTIC OPTIONS?

The most common tool in the veterinary arsenal to detect intestinal parasites is fecal flotation. Although this simple test can be found in most veterinary practices, it is easy to miss key steps in the testing process that ensure accurate results. A wide variety of flotation solutions are available, but the most common and useful are zinc sulfate and Sheather’s sugar solution. Both offer pros and cons that should be considered for individual veterinary practices.

The Kansas State Veterinary Diagnostic Laboratory offers a succinct and useful summary of these options as well as tips on how to perform the best flotation possible.⁸ The summary’s authors, Kansas State University parasitologists Mike Dryden, DVM, MS, PhD, and Brian Herrin, DVM, PhD, also explain the benefits of centrifugation in fecal flotation, which significantly increases the accuracy of these tests.

Passive fecal floats are no longer considered appropriate tests.⁸ Many national veterinary laboratories now offer antigen testing in combination with fecal flotation. Detecting small traces of proteins enables diagnosis of infections during the prepatent period—before eggs are being shed—in parasites with intermittent shedding as well as in cases with low worm burden.⁹

Given the variation in both parasite prevalence and the availability and methods of testing for them, we must consider occult infections and false-negative results when making recommendations for our patients. Although most veterinarians feel comfortable diagnosing and treating common intestinal parasites, research suggests that these parasites are actually underdiagnosed in veterinary medicine.

In fact, a recent study showed that fecal flotations have missed up to 96% of Dipylidium caninum and over 30% of Trichuris vulpis.¹⁰ The rate of false-negative results is less dramatic for other parasites that shed eggs more reliably, but even with centrifugation and antigen testing Toxocara canis was missed in over 20% of cases in this study.¹⁰ That our best testing methods have been shown to leave us with a significant level of undiagnosed parasites, we must consider other options to protect our patients.

BEST PRACTICES FOR OUR PATIENTS

There are several steps veterinarians can take to reduce the number of undiagnosed cases of intestinal parasitism in our patients and to protect those that do fall through the cracks. All fecal samples should be run as a combination of both microscopic examination by flotation and fecal antigen testing in order to reduce false-negative results on these samples.⁴ CAPC recommends a testing frequency of every 6 months.² This allows us to catch these infections and treat them sooner and increases the likelihood of finding occult infection.

Perhaps the biggest difference we can make is to reinforce our recommendations for monthly ectoparasite and endoparasite prevention for our patients. Even at relatively high-risk locations, such as dog parks, samples from dogs that are on monthly prevention are significantly less likely to test positive for parasites.⁶ CAPC states it perfectly: “To help protect the unique relationship of dogs and cats and their human family, our recently announced guidelines lead with the recommendation that all family pets be treated year-round with broad-spectrum heartworm anthelmintics that also protect against intestinal nematodes.”¹¹

Many readily available products protect against a range of intestinal parasites seen in our patients. Products containing milbemycin, as opposed to ivermectin with pyrantel, will provide the best whipworm prevention, and those that contain praziquantel have the added benefit of protecting against tapeworms, which are among the most commonly underdiagnosed parasites. By recommending year-round monthly protection with products that include protection and treatment for common intestinal parasites, including tapeworms and whipworms, we can ensure that all of our patients maintain optimal health and a close bond with their human caretakers

Dr. Calabro practices small animal medicine at Brick Town Veterinary Hospital in Brick, New Jersey. His special interests include endocrine pathologies and feline medicine.

References

1. One Health: Zoonotic diseases. Centers for Disease Control and Prevention. Updated July 14, 2017. Accessed August 19, 2020. www.cdc.gov/ onehealth/basics/zoonotic-diseases.html.
2. CAPC guidelines: Intestinal parasites. Companion Animal Parasite Council. https://capcvet.org/ guidelines/. Accessed August 19, 2020.
3. Little ES, Johnson EM, Lewis D, et al. Prevalence of intestinal parasites in pet dogs in the United States. Vet Parasitol. 2009;166(1-2):144-152.
4. Savadelis MD, Evans CC, Mabry KH, et al. Canine gastrointestinal nematode transmission potential in municipal dog parks in the southeast United States. Vet Parasitol Reg Stud Rep. 2019;18:100324.
5. Drake J, Carey T. Seasonality and changing prevalence of common canine gastrointestinal nematodes in the USA. Parasit. Vectors. 2019;12:430. doi: 10.1186/s13071-019-3701-7
6. Stafford K, Kollasch, TM, Duncan, KT, et al. Detection of gastrointestinal parasitism at recreational canine sites in the USA: the DOGPARCS study. Parasit Vectors. 2020;13:275. doi:10.1186/ s13071-020-04147-6
7. Understanding the maps: Key factors that influence the results. Companion Animal Parasite Council. Accessed August 29, 2020. https://capcvet.org/ articles/understanding-the-maps-key-factors-thatinfluence-the-results/
8. Herrin B, Dryden M. Steps to Increase the value of fecal diagnostics. Kansas State Veterinary Diagnostic Laboratory. www.ksvdl.org/resources/ news/diagnostic_insights_for_technicians/ december2017/fecal_diagnostics.html. Accessed August 19, 2020.
9. Fecal Dx antigen testing—find parasite infections the microscope misses. Idexx Laboratories. Published March 2017. Accessed August 19, 2020. www.idexx.com/en/veterinary/reference-laboratories/ fecal-dx-antigen-test/fecal-study/
10. Adolph C, Barnett S, Beall M, et al. Diagnostic strategies to reveal covert infections with intestinal helminths in dogs. Vet Parasitol. 2017;247:108- 121. doi: 10.1016/j.vetpar.2017.10.002 11. The bond cats, dogs and their owners shouldn’t share. Companion Animal Parasite Council. Accessed September 10, 2020. https://capcvet.org/articles/thebond-casts-dogs-and-their-owners-shouldnt-share/
11. The bond cats, dogs and their owners shouldn’t share. Companion Animal Parasite Council. Accessed September 10, 2020. https://capcvet.org/articles/thebond-casts-dogs-and-their-owners-shouldnt-share/