A potentially deadly parasite, Echinococcus multilocularis, has been confirmed to be spreading across the United States, researchers report. This tapeworm can infect humans and dogs, remaining dormant for years and causing severe, cancer-like tumors in organs such as the liver.
Recent findings by a team from the University of Washington detected the tapeworm in dozens of coyotes near Seattle, marking its first appearance in wildlife along the West Coast. Previously, the parasite was a known issue in Northern Plains states like Iowa, Minnesota, Nebraska, and the Dakotas since the 1960s. However, it has now been observed spreading eastward into New York, Pennsylvania, and Vermont in the 2020s, and also appearing in animals in Missouri, Kansas, Colorado, and Nevada.
Wildlife, including coyotes and foxes, can carry thousands of these tapeworms without showing symptoms. The parasites produce eggs shed in feces, which can lead to accidental infections in humans and pets if ingested through contaminated soil, water, or food. Once inside a host, the tapeworm can cause alveolar echinococcosis. This disease is characterized by the growth of cysts that mimic cancerous tumors, primarily in the liver, but potentially spreading to other organs.
Symptoms of the infection can take up to 15 years to manifest, making early diagnosis challenging. Initial signs may include upper abdominal pain, particularly on the right side near the liver, unexplained weight loss, weakness, fatigue, and jaundice if liver function is significantly impacted. If the parasite spreads to the brain, neurological issues and headaches can occur. Lung involvement may lead to coughing, chest pain, and shortness of breath. The cyst growth can resemble liver cancer or cirrhosis, damaging organ tissue.
Experts suggest that increased urbanization, deforestation, and climate change are contributing factors to the parasite's spread, pushing wildlife carrying the tapeworm closer to populated areas. The life cycle of Echinococcus multilocularis involves rodents ingesting contaminated eggs, developing cysts in their livers, and then being preyed upon by canids like coyotes and foxes. These wild animals then spread the parasite's eggs through their feces.
Humans and pets can become infected by coming into contact with contaminated soil or water. For instance, a dog playing in or eating from contaminated dirt, or consuming an infected rodent during outdoor activities, can then transmit the parasite to its owner. A study published in PLOS Neglected Tropical Diseases provided the first concrete evidence of E. multilocularis presence in wild coyotes on the West Coast, with researchers finding the tapeworm in 37 out of 100 examined animals. This suggests the parasite may be more widespread in the U.S. than previously understood.
While the spread is a cause for concern, experts note that widespread epidemics in humans remain unlikely due to the rarity of human infections in the U.S. Nevertheless, researchers emphasize the need for increased wildlife surveillance and public awareness, particularly for pet owners in affected regions. They recommend careful monitoring of zoonotic infections, which are becoming more common.