UW-led study captures the arrival of a parasitic tapeworm in the Puget Sound region
A little-known parasite is circulating in local wildlife.
A parasite is spreading across the Puget Sound region, carried by coyotes and capable of causing a slow, devastating disease in both dogs and humans. It is circulating more widely than expected.
A recent UW-led study found Echinococcus multilocularis—known as the fox tapeworm—in 37 of 100 coyotes tested around Puget Sound. The findings, published in PLOS Neglected Tropical Diseases, mark the first confirmed detection of the parasite in a wild host on the contiguous U.S. West Coast.
Long considered rare in North America, E. multilocularis has become an increasing public-health concern over the past 15 years as infections in humans and dogs have appeared in Canada and the Midwest.
“This parasite is concerning because it has been spreading across North America,” says lead author Yasmine Hentati, ’25, a wildlife ecologist and the lead author of the study. But “that we found it here in one-third of our coyotes was surprising.”
The parasite’s complex life cycle can involve coyotes, rodents and occasionally dogs and humans. Coyotes can carry thousands of worms in their intestines without becoming ill, shedding eggs through feces. Rodents ingest the eggs, developing cysts in their livers. Humans and their dogs become accidental hosts through exposure to contaminated food, soil or feces. In severe cases, the parasite causes alveolar echinococcosis, a disease marked by slow-growing, cancer-like cysts that can spread through the liver and other organs. Symptoms may take five to 15 years to appear, making diagnosis difficult. Untreated infections can be fatal. The World Health Organization considers this one of the world’s top neglected tropical diseases.
Despite the high infection rate in coyotes, researchers say transmission to humans and pets appears limited. Since 2023, only seven canine cases and no human cases have been documented in the region.
Researchers recommend preventing dogs from hunting rodents, maintaining routine veterinary care and using parasite-prevention medications. “The main takeaway,” Hentati says, “is that Echinococcus multilocularis is here, it’s prevalent in local coyotes, and people should be aware of the potential risks.”