‘Deadly tapeworm’ outbreak – humans and dogs accidental hosts | World | News
A dangerous parasitic tapeworm that can cause life-threatening diseases in humans and dogs has been confirmed for the first time in wild animals on the US West Coast, researchers reported. According to a study published March 24, 2026 in the journal PLOS Neglected Tropical Diseases, scientists detected Echinococcus multilocularis in 37% of coyotes sampled in the Puget Sound region of Washington state.
The findings point to the parasite’s westernmost established presence in wild hosts in the contiguous United States and point to its continued expansion across North America. The parasite, which produces cancer-like cysts in the liver and other organs, has long been a major public health problem in parts of Europe and Asia. In North America, it was historically rare and largely confined to remote Arctic regions where it had a less virulent strain.
Since the 2010s, a more pathogenic European-derived haplotype has spread rapidly throughout Canada, the Southern Midwest, and the East, infecting coyotes, foxes, dogs, and occasionally humans.
The high prevalence in local coyotes — more than a third of 100 samples — was surprising, said lead author Yasmine Hentati, a recent doctoral graduate from the University of Washington.
Ms. Hentati noted: “This parasite is concerning because it is spreading throughout North America.
“It was surprising that we found this here in a third of our coyotes, because it had never been found anywhere in the Pacific Northwest until earlier this year.”
Coyotes and other canids serve as definitive hosts, harboring adult worms in their intestines and shedding eggs in their feces, often without symptoms. Rodents eat the eggs and cysts develop in their livers. Coyotes then eat these rodents, becoming reinfected and completing the cycle.
Humans and domestic dogs are incidental hosts. Infection occurs through contact with contaminated feces, soil, water or food. In humans, it causes alveolar echinococcosis (AE), a slowly progressive disease with cysts that can spread like cancer. It can take 5-15 years for symptoms to appear, making diagnosis and treatment difficult. The World Health Organization classifies AE as one of the top 20 neglected tropical diseases.
No human cases have yet been reported on the West Coast, but seven canine infections have emerged since 2023, seven in Washington, Oregon and Idaho, and five in Washington. Dogs can develop serious disease or act as carriers.
Genetic analysis linked Washington coyote infections to the European strain already circulating in British Columbia, Canada, and suggested movement north and west, possibly aided by animal movement and urbanization.
Experts recommend caution. Pet owners should prevent their dogs from hunting rodents or scavenging, maintain routine deworming, and consult veterinarians. People should practice good hygiene in wildlife areas, wash produce, and avoid contact with wild canid feces.
The study highlights limitations in current surveillance. Non-invasive fecal sampling may underestimate prevalence, highlighting the need for broader wildlife monitoring to monitor and reduce spread.
As coyotes thrive in suburban and urban interfaces, the risk of spread increases. Researchers call for increased awareness and proactive measures before the parasite becomes established in the Pacific Northwest.
“This is quite common here in the local coyote population and people should be aware of the potential risks,” Ms Hentati said.
