🟢 Strong Evidence
A lethal tapeworm that causes cancer-like disease in humans has been detected in wild coyotes across the Pacific Northwest for the first time, according to new research published in Parasitology International. The study found Echinococcus multilocularis in 37% of tested coyotes around Puget Sound, representing the parasite’s first confirmed presence in West Coast wildlife populations.
Key takeaways
- 37% of tested coyotes in Puget Sound carry the deadly Echinococcus multilocularis tapeworm
- This marks the parasite’s first detection in Pacific Northwest wild animal populations
- Human infections cause alveolar echinococcosis, which has 95% mortality if untreated
- The disease can remain asymptomatic for 10-15 years before becoming fatal
Study at a Glance
| Source | Parasitology International |
| Study type | Wildlife surveillance study |
| Sample size | N = 187 coyotes |
| Population | Wild coyotes in Pacific Northwest |
| Country | United States |
Echinococcus multilocularis Detection Rates Across U.S. Regions
Percentage of tested wild canids infected, by geographic region
Source: University of Washington, 2026 | Georgian Medical Journal News
First West Coast Detection Signals Geographic Expansion
The University of Washington research team conducted extensive surveillance of coyote populations around Seattle and Tacoma between 2022 and 2025. Lead researcher Dr. Sarah Mitchell, professor of veterinary epidemiology at the University of Washington School of Veterinary Medicine, stated that the 37% infection rate exceeded all expectations for a newly introduced parasite.
“This represents a significant geographic expansion of E. multilocularis from its traditional range in Alaska and the northern Great Lakes region,” according to the Centers for Disease Control and Prevention surveillance data. The parasite had previously been confined to arctic and sub-arctic regions of North America.
Climate change may be facilitating the parasite’s southward spread, as warming temperatures allow intermediate hosts like small mammals to survive in previously inhospitable regions. The Global Health implications extend beyond wildlife, as domestic dogs and cats can serve as definitive hosts for human transmission.
Human Disease Carries Near-Fatal Prognosis
Echinococcus multilocularis causes alveolar echinococcosis in humans, a condition that mimics liver cancer in its growth pattern and clinical presentation. The World Health Organization classifies it as one of the most dangerous parasitic diseases worldwide, with mortality rates exceeding 95% in untreated cases.
The disease’s insidious nature compounds its lethality—infected individuals typically remain asymptomatic for 10 to 15 years while parasitic cysts slowly invade liver tissue. By the time symptoms appear, including abdominal pain, weight loss, and jaundice, the disease has often progressed beyond surgical intervention.
Dr. Peter Kern, professor of infectious diseases at Ulm University and leading echinococcosis researcher, noted in his landmark Lancet review that early detection through serological screening remains the only reliable method for improving patient outcomes. Treatment requires prolonged chemotherapy with benzimidazoles, often lasting several years.
Transmission Pathways Raise Public Health Concerns
Human infection occurs through ingestion of parasite eggs shed in the feces of infected carnivores, particularly foxes, coyotes, and domestic dogs. The eggs remain viable in the environment for months, contaminating soil, water sources, and vegetation in endemic areas.
The clinical implications for Pacific Northwest residents are still being assessed, but public health officials recommend avoiding direct contact with wild canid feces and ensuring pets are regularly dewormed. Hunters and outdoor enthusiasts face elevated risk through handling of infected animals or consumption of contaminated water sources.
The 37% infection rate in Pacific Northwest coyotes represents the highest documented prevalence for a newly established E. multilocularis population outside its historic range
— Dr. Sarah Mitchell, University of Washington School of Veterinary Medicine (Parasitology International, 2026)
Surveillance Expansion Needed Across Western States
The discovery prompted immediate calls for expanded surveillance programs across western North America. The research team recommends systematic screening of wild canid populations in California, Oregon, and British Columbia to determine the parasite’s full geographic distribution.
Veterinary diagnostic laboratories in the region are implementing new testing protocols for domestic animals, particularly dogs with suspected echinococcosis. The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service is coordinating with state wildlife agencies to establish standardized surveillance methods.
What this means
Frequently asked questions
How do humans become infected with this tapeworm?
Humans become infected by accidentally ingesting parasite eggs through contaminated food, water, or direct contact with infected animal feces. The eggs can survive in the environment for months, making indirect transmission possible through contaminated soil or vegetation.
What are the early symptoms of alveolar echinococcosis?
The disease typically remains asymptomatic for 10-15 years after initial infection. Early symptoms, when they appear, include vague abdominal discomfort, fatigue, and weight loss—often mistaken for other conditions until advanced liver involvement develops.
Can this disease be prevented or treated?
Prevention involves avoiding contact with wild animal feces and ensuring pets are regularly dewormed by veterinarians. Treatment requires prolonged chemotherapy with benzimidazole drugs, often for several years, with surgical removal of cysts when feasible.
The westward expansion of Echinococcus multilocularis represents a significant shift in North American parasitic disease epidemiology, requiring coordinated public health responses across multiple jurisdictions. Enhanced surveillance, public education, and clinical awareness will be essential for preventing human cases as this deadly parasite establishes itself in new geographic regions.
Source: The deadly tapeworm spreading across America has reached the Pacific Northwest
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Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD. Spotted an error? Contact the editorial team.
