What to know about an emerging tapeworm risk

Photo: Lars Gieger/Adobe Stock

A red fox, which can be a host for Echinococcus multilocularis.

The Echinococcus multilocularis tapeworm is becoming more prevalent in North America with rapid expansion being seen in the northeastern United States, following its introduction from Europe.^1-3 A study published in 2024 also noted a need for veterinary awareness of endemic risk regions as well as emerging risk of this zoonotic parasite in northwestern US states.⁴

“We're finding a European strain now, and the European strain does seem to be more transmissible to humans and dogs. We think that that might be what we're seeing [with] rapid spread right now,” said Brian Herrin, DVM, PhD, a parasitology expert and clinical professor at the Kansas State University College of Veterinary Medicine in Manhattan, Kansas.¹

E multilocularis largely affects wild and domestic canid species serving as definitive hosts as well as intermediate hosts that include rodents.² The risk to humans increases dramatically when domestic dogs are infected with the parasite, according to Herrin. In a ‘lunch and learn’ session at the 2025 WVC Annual Conference in Las Vegas, Nevada, he also discussed diagnosis of E multilocularis infection and managing this parasitic infection.¹

Tapeworm transmission

E multilocularis definitive hosts such as dogs, red and gray foxes, and coyotes typically become infected by feeding on rodents infested with these parasites. According to the Virginia Department of Wildlife Resources, adult E multilocularis tapeworms in canids live in the small intestines and are transmitted through the hosts’ feces. Feces containing E multilocularis eggs are then consumed by mice and voles, which serve as intermediate hosts for the parasite. Domestic dogs can also be intermediate hosts as well as definitive hosts.²

Once consumed, the larvae of E multilocularis travels to organs that include the liver and lungs of its’ hosts. The larvae become hydatid cysts, forming grape-like clusters in an intermediate host’s gut, which eventually affects organ function.^2,5 “[A cyst] puts a lot of pressure on the surrounding tissues,” Herrin said.

Identifying the parasite

Although wild canids do not typically show signs of E multilocularis infection, symptoms shown in other species depend on the severity and location of the cysts. These signs may include abdominal pain, weakness, weight loss, and liver disease. However, because E multilocularis cysts grow slowly, signs of infection may not be seen for years.²

E multilocularis proglottids are microscopic and cannot be seen, according to Herrin. He noted that annual fecal flotations using centrifugation are important for early identification for this parasitic infection. These eggs are heavy and will not float with a passive flotation, he cautioned. “It’s just not a sensitive technique,” Herrin said. “Sedimentations might be a better option.”

When E multilocularis infection is suspected, Herrin recommended following up a centrifugal fecal float by administering a PCR test designed for Echinococcus spp.³ “It detects 20 parasites and can differentiate Dipylidium, Taenia and echinococcus species,” Herrin said.

In a study published in 2024 that was cited by Herrin in his lecture, 26 of more than 2.3 million PCR surveillance tests were positive for E multilocularis infection between March 2022 and July 2024. Seventeen of the 26 positive tests were sequenced as European haplotypes, and 8 also had eggs identified by centrifugal flotation.⁴

Treating E multilocularis

Treatment of E multilocularis infection often includes praziquantel, which is effective at the adult stage, according to Herrin. The 2024 study found that 25 dogs were administered praziquantel for detected infection, and all were qPCR-negative in 3 to 5 weeks after treatment with the drug.⁵

There is no drug on the market that can prevent dogs from infection at the alveolar stages once eggs are ingested, Herrin said. However, prevention of E multilocularis may be achieved by educating veterinary teams and clients, and having pets avoid the ingestion of canid feces.¹

References

1. Herrin B. Echinococcus multilocularis: a slow-moving trainwreck? Presented at: WVC; Las Vegas, NV. March 2-5, 2025.
2. Echinococcus multilocularis. Virginia Department of Wildlife Resources. Accessed March 4, 2025. https://dwr.virginia.gov/wp-content/uploads/media/E.-multi-factsheet-1.pdf
3. Conlon CL, Brigandi JP, Frair JL, et al. Echinococcus multilocularis in New York wildlife: distribution and genetic diversity of an emerging pathogen. J Parasitol. 2024;110(6):697-708. doi:10.1645/24-54
4. Evason MD, Peregrine AS, Jenkins EJ. Emerging Echinococcus tapeworms: fecal PCR detection of Echinococcus multilocularis in 26 dogs from the United States and Canada (2022-2024). Am J Vet Med Assoc. 2024;263(2). doi:10.2460/javma.24.07.0471
5. Parasites and diseases: alveolar hydatid disease. Alaska Department of Fish and Game. Accessed March 4, 2025. https://www.adfg.alaska.gov/index.cfm?adfg=disease.internal1