A rare parasitic disease long documented in Europe appears to have taken root in the United States.
Vermont researchers report two human cases of a disease called alveolar echinococcosis (AE) that was caused by a European strain of the parasite. E. multilocularis.
They also found evidence of the strain in two red foxes in Virginia.
Until now, human cases of the disease in the United States had been reported – many years ago – only in Alaska and Minnesota. And those were caused by North American tribes E. multilocularis parasites that are considered less virulent than European strains.
Thus, the two patients from Vermont represent the first cases of AE in the eastern United States and the first cases caused by a more virulent European strain.
“We haven’t seen that in the US before,” he said Dr. Louis Polandinfectious disease specialist at the University of Vermont College of Medicine.
He emphasized that no one should be concerned about their personal risk. “This disease is extremely rare,” Polish said. “But we wanted to report it so doctors would have it on their radar.”
He and his colleagues describe the cases in a research letter published Nov. 17 in New England Journal of Medicine.
E. multilocularis is a small tapeworm that infects canines, often coyotes and foxes, and is apparently quite harmless to them. It has long been known to occur in wildlife in North America, but cases of AE in humans have been rare.
These human infections occur when a person unknowingly ingests tapeworm eggs—for example, through contaminated food or water. This results in the growth of parasites in the liver.
On an imaging test, the growth looks a lot like a tumor, and when AE progresses to the point where it causes symptoms, they include pain, jaundice, weakness, and weight loss — also indicative of cancer.
The first case of AE in Vermont was incidentally identified in a 36-year-old woman undergoing routine thyroid monitoring. Tests showed her liver enzymes they were high so the doctors did an ultrasound to find out what was going on. That’s when they found a large mass in her liver.
They biopsied the mass, and based on its appearance, her doctors suspected a parasite. She was referred to the infectious disease clinic and finally the diagnosis came back: She had AE and the culprit was a European strain of E. multilocularis.
The second patient, an 82-year-old man, was diagnosed after he developed jaundice and an imaging scan revealed a mass in his liver.
Both patients are now stable, Polish said. Liver masses can often be surgically removed; in the patient’s case, Polish noted, the mass was in a location where surgical removal is too risky. Waiting for a liver transplant.
How exactly the patients became infected with the parasite is not known.
“That’s the trouble incubation period because this parasite is very long,” Polish said.
It can reside in people’s bodies for 10 or 15 years before causing signs or symptoms. At that point, Polský said, it’s very difficult to determine when and how it happened.
Scientists tried to genetically link the cases to a potential “reservoir animal”. They tested stool samples from more than 400 foxes and coyotes in Virginia and found that two foxes had genetic evidence E. multilocularis.
Samples from both animals and both patients showed a close resemblance to the Slovak “E5” strain of the parasite.
How did a European strain get into American foxes?
“That’s the $64,000 question,” Polish said.
The cases may be the first in the United States, but not in North America. Alberta, Canada, recorded its first human case of AE about a decade ago, and the province has since become a “hot spot” for the continent.
He said the story began with veterinarians finding evidence of European strains of E. multilocularis in coyotes and rodents (which have a habit of eating coyote feces). It wasn’t long before the first human case of AE occurred—in a transplant patient whose immune system she was suppressed due to anti-rejection drugs.
Several subsequent patients, Houston said, were also immunocompromised — which could make people more vulnerable to contracting the parasite or speed up the course of the infection.
Like the Poles, Houston said no one knows how the European parasite got into Alberta’s coyotes. But it appears to be “very efficient” at spreading, he noted: In some parts of the province, up to 80% of coyotes are now carrying the parasite.
Houston said people could unknowingly ingest parasite eggs if, say, they ate produce from a garden where a coyote had wandered into. It’s unclear, he noted, whether dogs are an “important bridge.” In theory, however, it is possible: a farm dog, for example, could eat a rodent with a parasite. From there, a person who comes into contact with dog feces could become infected.
According to the Polish team, it happened recent news of two domestic dogs in two US states that have this parasite.
But both doctors emphasized that it’s not something that should keep people up at night. Even in Europe, where human AE cases have been identified over the long term, this is uncommon.
But Houston said it’s important to keep an eye out for diseases in animals and remember that they can be transmitted to humans — something the COVID pandemic has highlighted.
The US Centers for Disease Control and Prevention has more alveolar echinococcosis.
Louis B. Polish et al, The European haplotype of Echinococcus multilocularis in the United States, New England Journal of Medicine (2022). DOI: 10.1056/NEJMc2210000
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