Tracking the spread of a deadly parasite in North America

Echinococcus multilocularis. (Photo: Dotana/Adobe Stock)

Researchers and veterinarians have been seeing an emerging detection and range expansion of echinococcus multilocularis around the globe. The rise in detection of this parasitic tapeworm poses a concern not only for individual patients, but carries One Health implications as well, presenting an environmental and public health risk. At the 2025 American College of Veterinary Internal Medicine (ACVIM) Forum in Louisville, Kentucky, a group of specialists (Michelle Evason, DVM, BSc, DACVIM, MRCVS, global director of veterinary clinical education, Antech Diagnostics/MARS Petcare Science & Diagnostics in Prince Edward Island, Canada; Christian M. Leutenegger, DrMedVet, BSc, PhD, FVH, vice president of research & development, Antech Diagnostics/MARS Petcare Science & Diagnostics in Fountain Valley, California; Roger Ramirez-Barrios, DVM, MS, PhD, DACVM (Parasitology), professor at Virginia-Maryland College of Veterinary Medicine in Blacksburg, Virginia; Michael R. Lappin, DVM, PhD, DACVIM (SAIM), professor at Colorado State University in Fort Collins, Colorado) led a lecture on “E. multilocularis and other emerging One Health concerns in dogs,” which covered the geographical expansion of the parasite and recent detections.

Domestic dogs and wild canids such as coyotes, foxes, and wolves serve as definitive hosts of E. multilocularis.¹ Meanwhile, rodents act as the typical intermediate hosts of the parasite—during which it will be in its larval, or metacestode stage—while humans and dogs can serve as “dead-end” hosts following accidental ingestion of E. multilocularis from water, food, or the environment.¹ According to the presenters, dogs can also autoinfect, most commonly through grooming.¹

If a dog or wild canid consumes a rodent with E. multilocularis, the adult form of the parasite will develop in its small intestine. The animal will then shed the parasite eggs in their feces.

“A friend of mine and I usually refer to these eggs as little time bombs, right? Ticking time bombs, in part, because not only are they immediately infective, but they are environmentally resistant,” said Evason during the presentation, explaining that eggs can survive harsh weather conditions like Alaskan or Canadian winters.

In humans and dogs, E. multilocularis can cause alveolar echinococcosis (AE), one of the most lethal helminthic infections in humans, dogs, and rodents if left untreated.

According to Ramirez-Barrios, it is not exactly known how long the incubation period of AE is, but it is believed to be as long as 20 or 25 years.¹ He noted that survival is poor without treatment, as by the time many cases are detected, it is too late for effective intervention.

The emergence of E. multilocularis

In the US, Northern Virginia has reported 3 positive cases of E. multilocularis in foxes.¹ Pennsylvania, meanwhile, has seen 13 positive cases in coyotes, with detections in coyotes in Georgia as well.¹ In Canada, the parasite has also been detected in British Columbia and Alberta.¹

“We don't know why, but we have only found [positive] foxes in Virginia and only [positive] coyotes in Pennsylvania. But we already know that [E. multilocularis]—just to give a brief background—has several haplotypes. Historically, in the [US], the haplotypes found [have been] the North American haplotype, and they have been present only in the central states in the United States,” said Ramirez-Barrios.¹

“However, when [a] former parasitologist...found [a] dog with [AE], it was a new European haplotype. And then...all the foxes and coyotes [with AE] that we have found in eastern US [have carried] the European haplotype, which is really more pathogenic...than the North American haplotype,” said Ramirez-Barrios.

According to Ramirez-Barrios, the first human case of AE in Eastern US was reported in 2021 from Vermont, around the same time E. multilocularis was detected in foxes in Northern Virginia.¹

After contacting the authors of the Vermont case, Ramirez-Barrios and his team began a molecular analysis of the parasite and discovered a second human case. Phylogenetic testing from his team revealed that the parasite from both human cases and the infected foxes shared the exact same European haplotype.

According to Ramirez-Barrios, one of the human patients grew up in Maryland hunting foxes, near the counties where foxes positive for E. multilocularis were found. “When we did the phylogenetic [testing] of the 3 different isolates that we found, we discovered that they were exactly the same haplotype, so they were genetically the same organism,” Ramirez-Barrios said. “And that's when we published [a] report of the 2 human cases and their link with wildlife, which demonstrates that the parasite is actively transmitting in Eastern US, especially the upper haplotype, which is emerging.”

How can we prevent spread?

In the session, Evason emphasized the need for an interdisciplinary One Health approach for managing gastrointestinal parasites like E. multilocularis. She highlighted the need for better communication with pet owners.

“The goal is to educate our clients that they need to pick up [their dog’s] feces, especially in their backyards,” stressed Ramirez-Barrios, noting that not picking it up poses a contamination risk to its surrounding environment.

“We need to educate—I am educating new generations of veterinarians to educate their clients,” he said. “Right now, it is one of the best things that we have to control parasites.”

“In [future] years, it's going to be the only thing that we will have. So, if we don't start now, it's going to [cause] a big problem in the future,” he concluded.

References

1. Evason M, Leutenegger C, Ramirez-Barrios R, Lappin M. Echinococcus multilocularis and Other Emerging One Health Concerns in Dogs and Cats. Presented at: American College of Veterinary Internal Medicine Forum; Louisville, KY; June 18, 2025.