PCR Testing Detects Echinococcus Tapeworm in Pennsylvania

A survey of more than 27,000 canine fecal samples in Pennsylvania has detected the zoonotic Echinococcus tapeworm exclusively in wild canids. The findings point to a significant diagnostic gap, as the routine fecal flotation test used by most veterinary clinics is unlikely to identify the parasite.

Justin Brown, DVM, PhD, an associate teaching professor at Penn State College of Agricultural Sciences, explained the risk. Echinococcus can pass from wild or pet dogs to humans, where it can cause infections, typically in the lungs or liver, that are complicated to diagnose or treat, he said in a university news release. The parasite frequently shows no clinical signs in its canine hosts but can cause serious disease in people.

The Scope of the Survey

Investigators analyzed 27,293 fecal samples using a gastrointestinal parasite PCR assay called KeyScreen. This DNA-based test panel detects and differentiates 20 gastrointestinal parasites in dogs and cats. The sample set broke down into three distinct groups.

The research team hypothesized that parasite levels would be highest in wildlife and lowest in pets. This pattern held true, with wild canids showing higher levels of multiple parasites compared to pet dogs. Hunting dogs also had higher levels of parasites like hookworms and whipworms than household pets did.

Where the Parasite Was Found

The PCR testing identified Echinococcus multilocularis in two gray foxes and two coyotes. One additional coyote tested positive for Echinococcus canadensis (G8). Crucially, no samples from pet dogs or hunting dogs were positive for either Echinococcus species.

Although the prevalence of infection in wild canids appears to be low in Pennsylvania, we think it is important that veterinarians, pet owners, and hunters and trappers know that this parasite is present in the commonwealth, Brown stated.

The Limits of Traditional Testing

The detection challenge is largely diagnostic. Brown noted that Echinococcus eggs in feces look identical to those of other common tapeworms under a microscope. The parasite is also very small, measuring only 2 to 7 mm, making it easy to miss visually. "But when we started using this PCR test, which is very sensitive and identifies parasites by analyzing DNA, we started detecting Echinococcus more frequently," he said.

A companion project led by then-undergraduate scholar Noelle Kuhn directly compared fecal flotation to the PCR panel in wild canid samples. Kuhn performed the flotations and submitted parallel samples for PCR testing. Her statistical analysis confirmed the PCR assay was more sensitive for the parasites on the panel and could distinguish between visually identical eggs.

Brown cautioned that the molecular panel is not a complete replacement for traditional methods, especially in wildlife which can carry parasites not covered by the assay. He said Kuhn's research helped highlight the value of this new diagnostic tool for surveying wildlife for these gastrointestinal parasites, but also emphasized that the best surveillance approach for wildlife likely involves a combination of contemporary and traditional diagnostic approaches.

Implications for Pet Owners and Vets

For veterinary practitioners, the absence of positives in owned dogs is reassuring but does not eliminate concern. The parasite is established in local wildlife, and canine hosts are typically asymptomatic. The diagnostic method most clinics rely on-fecal flotation-is poorly suited to detecting it. Dogs with access to wildlife habitat, rodent prey, or hunting activity remain a potential bridge for human exposure.

Brown framed the entire project as a One Health exercise, focusing on the interconnectedness of human, animal, and environmental health. The success of the survey depended on collaboration across industry, multiple academic institutions, state and federal agencies, hunters, and pet owners.