Vermont researchers report dangerous parasite found in foxes

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Jon Pauling/Pixabay” alt=”Researchers in Vermont are reporting two human cases of the disease, called alveolar echinococcosis (EA), which were caused by a European strain of the E. multilocularis parasite. They also found evidence of the strain in two red foxes in Virginia. Photo of Jon Pauling/Pixabay“/>

Vermont researchers are reporting two human cases of the disease, called alveolar echinococcosis (EA), which were caused by a European strain of the E. multilocularis parasite. They also found evidence of the strain in two red foxes in Virginia. Photo by Jon Pauling/Pixabay

A rare parasitic disease long documented in Europe appears to have taken root in the United States.

Vermont researchers are reporting two human cases of the disease, called alveolar echinococcosis (EA), which were caused by a European strain of the E. multilocularis parasite.

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 only been reported – many years ago – in Alaska and Minnesota. And these had been caused by North American strains of the E. multilocularis parasite, 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 caused by a more harmful European strain.

“We’ve never seen this before in the United States,” said Dr. Louis Polish, an infectious disease specialist at the University of Vermont College of Medicine.

He stressed that no one should worry about their personal risk. “This disease is extremely rare,” Polish said. “But we wanted to flag this so doctors could have it on their radar.”

He and his colleagues describe the cases in a research letter published Thursday in the New England Journal of Medicine.

E. multilocularis is a small tapeworm that infects dogs, often coyotes and foxes, and is apparently quite harmless to them. It has long been known to exist in North American wildlife, but human cases of AE are rare.

These human infections occur when a person unknowingly ingests tapeworm eggs – through contaminated food or water, for example. This results in parasitic growth in the liver.

On imaging, the growth looks a lot like a tumour, and when EA progresses to cause symptoms, they include pain, jaundice, weakness and weight loss – also suggesting cancer.

The first case of IE in Vermont was identified incidentally in a 36-year-old woman who was being routinely monitored for a thyroid condition. Tests showed her liver enzymes were elevated, so doctors performed an ultrasound to see what was going on. That’s when they found a large lump in his liver.

The mass was biopsied and, based on its appearance, her doctors suspected a parasite was to blame. She was referred to an infectious disease clinic, and eventually 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 developing jaundice and imaging 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 that makes surgical removal too risky. She is awaiting a liver transplant.

It is unclear exactly how the patients contracted the parasite.

“The difficulty is that the incubation period for this parasite is very long,” Polish said.

It can stay in people’s bodies for 10 or 15 years before causing any signs or symptoms. At this point, Polish said, it’s very difficult to determine when and how he was contracted.

The researchers 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 of 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 end up in 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, had its first human case of IE about a decade ago, and the province has since become the continent’s “hot spot” for the disease.

“We’ve had over 20 confirmed cases now,” said Dr. Stan Houston, an infectious disease specialist and professor emeritus at the University of Alberta.

He said the story started with vets finding evidence of European strains of E. multilocularis in coyotes and rodents (which habitually eat coyote feces). It wasn’t long before the first case of human IE – in a transplant patient whose immune system was suppressed due to anti-rejection drugs.

Several of the following patients, Houston said, were also immunocompromised — which could make people more vulnerable to getting sick from the parasite or hasten the course of infection.

Like Polish, Houston said no one knows how the European parasite got into coyotes in Alberta. But it appears to be “very effective” at spreading, he noted: In some parts of the province, up to 80% of coyotes now carry the parasite.

Houston said people could unwittingly ingest the parasite eggs if, for example, they ate produce from a garden that a coyote had wandered through. It’s unclear, he noted, whether companion dogs are an “important bridge.” In theory, however, it is possible: a farm dog, for example, could eat a rodent with the parasite. From there, a person who comes into contact with the dog’s feces could become infected.

According to the Polish team, there have been recent reports of two pet dogs, in two US states, having the parasite.

Both doctors stressed, however, that this is not something that should keep people up at night. Even in Europe, where human cases of IE have long been established, it is rare.

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 underscored.

More information

The United States Centers for Disease Control and Prevention has more on alveolar echinococcosis.

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