A dangerous tapeworm that has spread across North America has been discovered in the Pacific Northwest, according to a new study. Scientists have discovered a parasite known as. Echinococcus multilocularisa local coyote, and the first time it has been confirmed in a wild host along the contiguous U.S. West Coast.
This parasite typically infects coyotes, foxes, and other canids. These animals often show no signs of illness, but tapeworm transmission can cause serious illness in domestic dogs and humans.
For decades, E. multilocularis It is recognized as a major public health concern in Europe and some parts of Asia. However, it was once considered extremely rare in North America. This situation changed about 15 years ago when infections began to appear in dogs and humans in Canada and the Midwest, indicating that the parasite was expanding its range.
Tapeworms found in coyotes in the Pacific Northwest
Researchers at the University of Washington surveyed 100 coyotes in the Puget Sound region and found 37 were carrying the parasite. Their discovery is Tropical diseases ignored by PLOS.
“It’s concerning because this parasite is widespread across North America. There are many cases of dogs getting sick and a small number of people getting infected with tapeworms,” said lead author Yasmin Hentati, who just graduated from the University of California with a PhD in environmental and forest science. “The fact that we found this species in a third of the coyotes here was surprising, as this species had not been found anywhere else in the Pacific Northwest until earlier this year.”
when E. multilocularis When infected in humans or animals, it can cause cancerous cysts in the liver and sometimes other organs. If untreated, the infection can be fatal.
how do parasites spread
Despite the risks, many infected animals never become ill. This parasite relies on a complex life cycle involving multiple different hosts.
Coyotes and other canids serve as primary hosts for adult tapeworms. These animals can carry thousands of worms in their intestines without getting sick. The worms release eggs, which are passed into the environment through feces.
Rodents are also an important part of this cycle. Ingestion of food contaminated with coyote feces can lead to infection. The parasite’s eggs travel to the rodent’s liver and grow into cysts, eventually debilitating or killing the rodent. When coyotes eat those rodents, they become infected and the cycle continues.
Humans and domestic dogs are considered incidental hosts. You can become infected by swallowing tapeworm eggs, such as through food contaminated with coyote or dog feces. Infection can cause alveolar echinococcosis, which is characterized by slowly growing metastatic cysts. Symptoms may not appear until 5 to 15 years after exposure, making diagnosis and treatment particularly difficult.
Alveolar echinococcosis is considered the third most important foodborne illness in the world and is listed among the top 20 neglected tropical diseases by the World Health Organization. Many countries have established extensive surveillance programs to track the disease.
Risks for dogs and people
exposed dog E. multilocularis It doesn’t necessarily mean you’ll get sick. Results vary greatly depending on which stage of the parasite is encountered. Dogs often carry the parasite and lay eggs without developing symptoms. However, dogs exposed to parasite eggs can develop the same cancer-like cysts seen in other infected animals.
“To minimize the risk of your dog becoming infected, E. multilocularisPet owners should not allow their rats to prey on rodents or scavenge their carcasses,” said co-author Guilherme Berocai, associate professor in the Texas A&M University College of Veterinary Medicine and Biomedical Sciences and director of the Diagnostic Parasitology Laboratory.
Berokai also recommends regular veterinary care, including parasite testing and insect and tick preventatives.
More than a third of the coyotes examined in the study carried the parasite, but the researchers found little evidence that the parasite was spreading to other hosts. One study recorded seven dog infections in Washington, Oregon and Idaho since 2023, five of which occurred in Washington. Human infection remains rare in the United States, with no cases reported on the West Coast.
“The reason there are so many coyotes is because coyotes regularly eat raw rodents, which is their main transmission route. Most domestic dogs don’t eat raw livers from wild rodents,” Hentaty said.
More infectious variants
report of E. multilocularis It has appeared before in North America. Before cases rose in the 2010s, the parasite was recorded on a remote island in northwestern Alaska.
Researchers say these early incidents involved a different strain than the one causing the current outbreak. Genetic analysis shows that while older infections are associated with the Tundra variant, today’s outbreak is associated with a more contagious strain of European origin. The coyotes examined in this study carried the newer variant, which is now believed to be the predominant type circulating in both the United States and Canada.
Scientists still don’t know how this parasite became established in North America. One possibility is that infected dogs entering the United States and Canada did not need to be dewormed. Another theory proposed in early research suggests that the parasite may have entered red foxes imported for hunting about a century ago.
“The main point is that Echinococcus multilocularis “They are quite prevalent in local coyote populations and people need to be aware of the potential risks,” Hentaty said.
Co-authors include Ellie Reese, a laboratory manager at the University of California; Samantha Crelling, California State University doctoral graduate in environmental and forest sciences; Laura Proulx, University of California professor of environmental and forest sciences; Chelsea Wood is an associate professor of fisheries and fisheries science at the University of California. Claire Curran of the College of William and Mary; Erica Miller of Sound Data Management. Dakeishla M. Diaz Morales of DePaul University; Christopher J. Schell of the University of California, Berkeley.
This research was funded by the National Science Foundation and the University of Washington Hall Conservation Genetics Fund.
