One Health at the Dog Park: canine intestinal parasites common across USA

Whether travelling with their owners or moving long distances to be adopted, pet dogs are integrated into our modern mobile lifestyle, often moving freely between cities, states, and nations. This movement of dogs can also spread parasites, including some with zoonotic implications, increasing the risk of infection and raising questions about the prevalence of parasites in public parks.

In the USA, dog parks — fenced areas where dogs and their owners can enjoy off-leash exercise and play — are incredibly popular, constituting the fastest growing segment of the urban park landscape. Although dog parks provide wonderful opportunities for positive social interaction for dogs and owners alike, they also encourage dogs of many different backgrounds to congregate, often without any requirement for prior veterinary wellness care.

In a first-of-its-kind study, fecal samples were collected from over 3000 dogs attending hundreds of dog parks in 30 major metropolitan regions across the USA. Samples were analyzed using both centrifugal flotation and coproantigen immunoassay. We also asked owners about their parasite control practices and their dog’s history of intestinal parasites. While we confirmed parasites are common in dogs at dog parks, we also found that veterinary care and routine preventive use can mitigate the risk.

Parasite infections widespread

Intestinal parasites were detected in one in five dogs and at 85% of dog parks, with Giardia most common followed by hookworm (Ancylostoma caninum) and whipworm (Trichuris vulpis). In Florida, almost one-third of dogs were infected with hookworms. Prevalence of common parasites in dogs attending USA dog parks is presented in the following table:

Parasites found Canine prevalence Park prevalence
All 20.7% 85.1%
Giardia 13.0% 74.0%
Hookworms 7.1% 43.4%
Whipworms 1.9% 18.1%

Nematodes were common in all ages, with 8% of all adult dogs and almost 6% of dogs 7 years or older harboring nematodes, confirming that age does not eliminate the risk of infection. Ascarids (Toxocara canis) were uncommon (<1%), not detected in any dog older than 3 years, a finding likely influenced by the small proportion (~12%) under 12 months of age.

These results confirm that parasites are present at the vast majority of USA dog parks. Fortunately, parasites present a risk that can be controlled. The Companion Animal Parasite Council advises that all pet dogs be maintained year-round on broad spectrum intestinal parasite control products and regularly tested for parasites. This advice is particularly important for dogs exposed to areas frequented by other dogs – dog parks, on leash walks, or other common pet-relief areas outside apartment complexes or while traveling.

Test and protect is an effective strategy

Owners who indicated their dog had been previously diagnosed with intestinal parasites were more likely to report administering a preventive than owners without that history, underscoring the power of diagnostic testing to motivate action. Most importantly, dogs reportedly receiving a preventive were significantly less likely to be infected with intestinal nematodes, confirming preventives are effective at reducing prevalence.

(Image by Guidy Willekens from Pixabay)

Nonetheless, some dogs whose owners reported using preventives were still infected with nematodes. While we can’t eliminate compliance as a possible confounder, for hookworms, post-treatment exposure to infection with patency developing before the next scheduled treatment is possible. For whipworms, the finding could reflect efficacy limitation of some preventives. Veterinarians should carefully select appropriate, broad-spectrum preventives considering lifestyle and risk of infection. While most are approved against hookworm and ascarids, few are effective against whipworm.

Fecal tests have their limits

Veterinary vigilance in detecting intestinal nematodes in pet dogs is critically important. In the DoGPaRCS study, combining centrifugal flotation with coproantigen immunoassays resulted in the detection of 78% more infections than centrifugal flotation alone. Other studies have shown that passive flotation, as is commonly done in veterinary practices, is an inferior method that fails to identify many parasite infections.

In addition, fecal flotation is poorly suited to identify cestode infections. The absence of a reliable test precludes accurate estimation of cestode prevalence. One recent study found that fecal flotation failed to identify Dipylidium caninum and Taenia sp. in most infected dogs. Recent reports of Echinococcus multilocularis in pet dogs in North America suggest infection risk may be increasing in this region. Given current limitations of fecal tests, both nematode and cestode infections are likely underdiagnosed in veterinary practices and surveys.

(Courtesy of Dr. Kathryn Duncan, Oklahoma State University)

Zoonoses remain a concern

Considering the high prevalence of parasites, particularly hookworm, we were dismayed to see dog park attendees walking in open-toed sandals, flip-flops, or even bare feet. In some cases young children were playing with toys directly on dog park soil. Our findings that at least 43% of dog parks harbor hookworm larvae and that 6% or more have ascarid eggs indicate a major need for education about the inherent public health risks.

While most owners picked up after their dog, deposited feces were still evident at the parks. Public education about dog and human health risks arising from canine fecal contamination is needed. Prompt collection and disposal of canine feces in dog parks and in any public area remains a key responsibility all dog owners must practice.

Funding and competing interests declaration: The study was funded by Elanco Animal Health and IDEXX Laboratories, Inc. Susan E. Little has received honoraria, expense reimbursement, or research support from companies that manufacture parasite control and diagnostic products. William G Ryan has received payments for clinical research and consulting fees from Elanco.

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