PULLMAN, Wash. - A parasite commonly carried by foxes that can be passed to domestic dogs and cause severe illness in humans on rare occasions appears to have established itself in the Pacific Northwest.
Commonly known as the fox tapeworm, Echinococcus multilocularis is carried by foxes and coyotes and can spread to humans through contact with feces or feces-contaminated soil. When humans are infected, they can develop a disease known as alveolar echinococcosis. Symptoms may take years to appear and often do not emerge until significant liver damage has occurred. The disease can mimic liver cancer and spread to other organs if left untreated.
While common in parts of Europe, Asia and northern North America, the parasite was not believed to be present in the Pacific Northwest until recently. In May, pathologists at Washington State University's Washington Animal Disease Diagnostic Laboratory detected the tapeworm during a necropsy of a fox kit found on the WSU Pullman campus. The diagnosis followed a study published in March in the journal PLOS Neglected Tropical Diseases that found the parasite is widespread in coyotes in the Puget Sound area.
Foxes and coyotes are common in and around Pullman and throughout the Pacific Northwest, increasing the potential for environmental contamination. Experts recommend avoiding contact with wild animal feces, wearing gloves when cleaning areas where feces may be present and washing hands thoroughly afterward. Pet owners should also prevent dogs from eating rodents or scavenging wildlife.
"There's likely more of it in the environment than people realize," said Dr. Kyle Taylor ('08 DVM), a veterinarian and pathologist at WADDL. "Awareness and basic precautions are the best prevention."
The infected fox kit in Pullman was estimated to be about 9 weeks old. After being found sick, it was taken to WSU's Veterinary Teaching Hospital, where its case was overseen by exotics and wildlife veterinarian Dr. Marcie Logsdon. The fox did not survive, and its body was submitted to WADDL for further examination. A necropsy found it had a heavy infestation of E. multilocularis, which was confirmed through PCR testing and genetic sequencing.
"What was surprising was the sheer number of small tapeworms in the intestine," Taylor said. "For an animal that young, that kind of burden can take a significant nutritional toll and likely contributed to its decline."
The parasite requires two mammalian hosts to complete its life cycle. Adult tapeworms most frequently live in the intestines of foxes and coyotes, with infected animals typically showing no signs of illness. Those animals, however, shed microscopic eggs in their feces, contaminating soil, water and other surfaces.
Rodents such as mice and squirrels ingest the eggs and develop the larval form of the parasite in their livers. Foxes and coyotes are then infected when they consume those animals, continuing the cycle.
Dogs and other mammals, including humans, can become accidental hosts and develop the larval form of the parasite, or alveolar echinococcosis. These infections are difficult to treat and require extensive medical management or surgery, with outcomes that can be poor even with treatment. Dogs can also develop adult or intestinal infections, which are typically treatable with standard anti-parasitic medications. Monthly parasite prevention can help protect against the adult tapeworm stage, reducing environmental contamination and the risk of human exposure. Pet owners concerned about E. multilocularis should contact their veterinarian for guidance.
"Humans get infected the same way rodents do, through fecal-oral contamination," Taylor said. "If you're handling soil or anything contaminated with fox or coyote feces and then inadvertently ingest those microscopic eggs, that's how infection can occur."
In 2024, WADDL's Parasitology section, headed by Dr. Laura Williams, also detected the parasite in a squirrel in Pullman and dogs lin Idaho Falls, Idaho; Milton-Freewater, Oregon; Missoula, Montana; and Winthrop, Washington. All the cases involved the larval form of the parasite, or alveolar echinococcosis. The detections indicate the parasite may already be established across the region and that some intestinal infections in dogs may be going unnoticed.
WADDL serves as the state's primary veterinary diagnostic lab, providing testing and expertise for veterinarians, producers and public health agencies across the region. Located on the WSU campus, WADDL plays a key role in detecting emerging diseases, including zoonotic threats like E. multilocularis.
