Washington coyotes found carrying Echinococcus multilocularis

A newly published University of Washington study has found Echinococcus multilocularis in 37 of 100 coyotes sampled in the Puget Sound region, the first confirmed detection of the parasite in a wild host on the contiguous U.S. West Coast. The paper, published March 24, 2026, in PLOS Neglected Tropical Diseases, suggests the parasite is not an isolated spillover event, but part of an established wildlife transmission cycle in western Washington. (journals.plos.org)

That’s a notable shift for the Pacific Northwest. E. multilocularis has historically been considered a major public health concern in parts of Europe and Asia, and only relatively recently became recognized as an emerging issue in North America. The Washington authors say no prior wildlife survey had documented the parasite on the U.S. West Coast, even as diagnoses in dogs west of the Rockies began to appear. In their paper, they note that since 2023, five Washington dogs had been identified with E. multilocularis, including four definitive-host dogs in western Washington and one dog with alveolar echinococcosis in eastern Washington. (journals.plos.org)

The study drew on coyote carcasses and field-collected scat samples gathered from 2021 through 2024 in the Puget Sound Lowlands, one of the most densely populated regions in the Pacific Northwest. Investigators used both morphological and molecular methods, including next-generation sequencing, to confirm the parasite. Their genetic analysis linked the Washington samples to a haplotype previously reported in British Columbia, supporting the idea that the westward spread seen in dogs and wildlife may be connected rather than random. The authors also argue the high prevalence in coyotes means the parasite was likely established in the region before the first recognized dog cases surfaced. (journals.plos.org)

University of Washington communications around the study framed the result as both a wildlife and companion-animal issue. Lead author Yasmine Hentati said the prevalence in coyotes was surprising, while co-author Guilherme Verocai of Texas A&M emphasized a straightforward prevention message for pet parents: don’t let dogs prey on rodents or scavenge rodent carcasses. The CDC’s prevention guidance aligns with that advice, recommending that dogs be kept away from rodents, wild canids, and potentially contaminated feces or environments. (washington.edu)

For veterinary professionals, the biggest implication may be diagnostic awareness. The PLOS paper notes that classical fecal flotation and sedimentation have limited sensitivity and that Echinococcus eggs are difficult to distinguish morphologically from Taenia species, which creates a real risk of underrecognition. In dogs, exposure can lead either to intestinal carriage with egg shedding or, less commonly, to alveolar echinococcosis with invasive, tumor-like lesions. A 2023 JAVMA report described four dogs with naturally occurring alveolar echinococcosis in the northwestern United States, underscoring that this is not just a theoretical concern for regional practice. (journals.plos.org)

There’s also a public health layer that clinics can’t ignore. CDC materials note that human alveolar echinococcosis is prevented by avoiding contact with feces from infected canids and by limiting dogs’ interaction with rodent populations. Washington State Department of Health guidance lists echinococcosis among reportable conditions and identifies foxes, coyotes, cats, and dogs as definitive hosts for E. multilocularis. Human disease remains rare in the United States, but the long incubation period and severe liver involvement make early awareness important, especially when veterinary and human exposures overlap in shared environments. (cdc.gov)

Why it matters: In practical terms, this finding may change how Pacific Northwest veterinarians think about parasite risk assessments, fecal testing limitations, and client education. Dogs with heavy rodent exposure, off-leash access in coyote-dense areas, scavenging behavior, or unexplained hepatic lesions may warrant a higher index of suspicion than they would have a few years ago. It also reinforces the value of discussing deworming strategy, leash control, rodent predation, hand hygiene, and environmental exposure with pet parents in endemic or newly affected areas. Those conversations are especially relevant because domestic dogs can bridge wildlife and household settings. (journals.plos.org)

What to watch: The next phase will likely center on expanded surveillance in wildlife, more targeted testing in dogs, and whether state and regional veterinary networks begin to formalize guidance for screening, case recognition, and prevention as Washington’s apparent endemic zone becomes better defined. (journals.plos.org)