University of Washington researchers report finding the parasitic tapeworm Echinococcus multilocularis in more than one-third of coyotes tested around Puget Sound, the first confirmed detection of the parasite in a wild host on the contiguous U.S. West Coast.
Researchers at the University of Washington say a parasitic tapeworm that can infect domestic dogs and, more rarely, people has been detected in wild coyotes in western Washington.
In a study published March 24, 2026, in PLOS Neglected Tropical Diseases, the team tested 100 coyotes in the Puget Sound region and found Echinococcus multilocularis in 37 of them.
“This parasite is concerning because it has been spreading across North America. There have been numerous cases of dogs getting sick, and a handful of people have also picked up the tapeworm,” said lead author Yasmine Hentati in the university’s summary of the research. “The fact that we found it here in one-third of our coyotes was surprising, because it wasn’t found anywhere in the Pacific Northwest until earlier this year.”
The parasite can cause a disease known as alveolar echinococcosis when its eggs are accidentally ingested. The illness is marked by slow-growing, tumor-like ("cancer-like") cysts that typically affect the liver and can take years to produce symptoms, according to the U.S. Centers for Disease Control and Prevention.
The UW researchers said there have been few human cases reported in the United States and none reported on the U.S. West Coast in their account of the findings.
Co-author Guilherme Verocai urged dog owners to reduce risk by preventing pets from hunting rodents or scavenging rodent carcasses and by keeping up routine veterinary care, including diagnostic testing for parasites and preventive deworming medications when appropriate.
