A parasitic tapeworm known as Echinococcus multilocularis, or the “fox tapeworm,” has been identified for the first time in wildlife on the West Coast.

Researchers at the University of Washington found the parasite in 37 of 100 coyotes sampled around the Puget Sound region of Washington State.

The study, published earlier this year in PLOS Neglected Tropical Diseases, warns that while the discovery is significant, the overall risk to humans remains low.

Lead author Yasmine Hentati explained that infection rates among coyotes are high because they frequently eat raw rodents, which serve as the main carriers.

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Genetic testing revealed that these animals carried a newer European variant of the parasite that has become the dominant strain across the U.S. and Canada.

Prior to the 2010s, the fox tapeworm was rarely seen in North America, limited mostly to isolated parts of Alaska.

Over the past 15 years, researchers have documented its spread across the Midwest, where infections among dogs and humans have grown in both the U.S. and Canada.

Dr. Linda Yancey, an infectious disease specialist at Memorial Hermann in Texas, said the parasite has been creeping westward, with new cases appearing along the West Coast.

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She noted that although there are scattered infections in Eastern Europe, the disease remains very uncommon in the United States.

Most human cases are recorded in people who have lived in or traveled through Central and East Asia, the Middle East or North Africa, Yancey said.

“The area with the highest prevalence of human infections with the fox tapeworm is western China,” she added.

According to Yancey, the parasite circulates among canids such as foxes and coyotes and passes between them and rodents.

Humans can become infected by accidentally swallowing eggs from contaminated soil, food, or by handling infected pets and touching their mouths, according to the Cleveland Clinic.

Once inside the body, the parasite forms fluid-filled sacs known as cysts, typically in the liver but potentially in other organs.

Because these cysts develop slowly, infections can remain unnoticed for years or even decades.

The Centers for Disease Control and Prevention recognizes two main forms of the disease: cystic echinococcosis and alveolar echinococcosis.

Cystic echinococcosis tends to affect the liver and lungs, where symptoms may include abdominal discomfort, swelling, coughing, or shortness of breath as cysts expand.

Severe complications can occur if a cyst ruptures, sometimes leading to death if the fluid spreads through the body.

Alveolar echinococcosis, the rarer form, grows like a tumor, invading and destroying organ tissue and potentially causing liver failure.

“Symptoms of liver failure include fatigue, yellowing of the skin and eyeballs, and abdominal pain,” Yancey said.

She cautioned that this form can resemble cancer and urged people with concerning symptoms to seek medical care.

While the chance of infection remains small, Yancey emphasized the importance of simple preventive steps.

“The most important way to protect yourself from the fox tapeworm is also the simplest: good hand hygiene,” she advised.

She recommended washing hands thoroughly before meals and after outdoor activities or soil contact in affected regions.

Dog owners should prevent pets from eating rodents and ensure they receive regular veterinary checkups and deworming.

The CDC similarly advises avoiding direct contact with wild animals such as foxes, coyotes, and stray dogs that may carry the tapeworm.

“Routine testing and treatment for worms of all kinds keeps your pups healthy and you safe,” Yancey said.