Cassidy Armstrong went in for surgery last fall to remove what doctors thought was a tumour on her liver.

She had been diagnosed with a suspected rare cancer that, even with the surgery, would probably have left her with only a few years to live.

Instead, doctors found something even rarer: a grapefruit-sized mass caused by the eggs of a tapeworm.

An MRI of Armstrong's abdomen shows the grapefruit-sized clump was growing on her liver. (Stan Houston/AHS)

Armstrong was still recovering in a Calgary hospital in November when doctors told her she likely had a parasite called Echinococcus multilocularis, previously confirmed in fewer than 20 Canadians, almost all of them in Alberta.

"I was still a little doped up on painkillers," she said. "So I said, 'Is that a good thing?' And they said, 'It's definitely better.'"

It was certainly an improvement on the diagnosis of fibrolamellar carcinoma, a rare form of liver cancer that typically attacks otherwise healthy patients under the age of 40. It wasn't until a pathologist analyzed the mass that the parasite was discovered.

But it's still a dangerous infection — without surgery, she would have died.

A slow-spreading cyst from tapeworm eggs

The parasite lives as a tapeworm in coyotes, foxes and, increasingly, domestic dogs. The tapeworm's eggs are spread to other animals, such as rodents, from the feces of infected animals.

When a person accidentally swallows the microscopic eggs, the infection can lead to cyst-like lesions on the liver. But it will only cause minimal symptoms until the growths reach a significant size.

Echinococcus multilocularis is a rare parasite that forms as cysts on the liver in humans when they accidentally eat microscopic tapeworm eggs spread through canine feces. (Centre for Disease Control website)

The parasite had likely been growing inside Armstrong, 36, for more than a decade.

"It was almost a Christmas miracle," she said. "It could have been a lot worse."

Armstrong had worked physically demanding jobs — she'd been a motorcycle mechanic in Edmonton before moving to Banff last year to work as a stage carpenter — and was in good health, though occasionally noticed she was fatigued.

About two years ago, she felt tenderness in her ribs. X-rays didn't find anything, she said, and eventually the pain subsided.

While in Banff, the pain in her side returned and became almost constant. It was accompanied by a new pain in her shoulder.

She worried she had gallstones and insisted on an ultrasound. That's when the mass was discovered, she said, leading to the cancer diagnosis and grim news that surgery wouldn't guarantee her more than a few more years.

"I would have lived maybe another two to five years. There were a lot of things going through my mind," she said. "Mainly, what's the point?"

Growing number of cases in Alberta

Her cancer surgery was the equivalent of an open-heart operation. Surgeons removed her gallbladder, 65 per cent of her liver and cut several nodes off her lungs, in addition to scraping the cyst off her diaphragm. She has a 14-inch, L-shaped scar on her chest that is still not completely closed, two months after surgery.

Armstrong's parasitic clump is one of the largest physicians have seen in Alberta. And they've seen a few.

"We're definitely the hot spot," said Dr. Stan Houston, an infectious disease specialist at the University of Alberta.

Dr. Stan Houston is one of Canada's leading experts in Echinococcus multilocularis, a parasite spread to humans through tapeworm eggs. (Ariel Fournier/CBC)

To date, there have been 15 cases of Echinococcus multilocularis in Alberta. When Armstrong's case is scientifically confirmed, she will be number 16, he said.

It's believed the strain has been arriving in Canada in dogs brought over from Europe and in foxes imported decades ago for hunting.

It has existed in Europe for around 150 years. There are about 1,800 human cases every year, the majority of which are found in China and Tibet.

A 2012 study found that the parasite was well-established in Alberta's wild animal population, with about one-quarter of the province's coyote population infected with the tapeworm.

The first Canadian human case was diagnosed in 2013.

"[Before the last decade] we never had people with this disease in all of North America," Houston said. "In the last six years, we've had 15 definitely proven cases, just in Alberta."

Since 2014, Canadian researchers have warned that the parasite could easily be misdiagnosed by physicians as another liver disease or ailment.

"About half our cases were found by accident," Houston said. In those cases, imaging revealed an abnormal growth in the liver.

Medication not available in Canada

There's no guaranteed cure for Echinococcus multilocularis. Infected patients must take a parasite medication for the rest of their lives to prevent the tapeworm eggs from causing further growths.

A drug called albendazole, normally used to treat other tropical parasites, can act as a preventive treatment. While it is widely available in Africa, Europe and Asia, the drug company hasn't applied to Health Canada to access the Canadian market.

Houston said he applies for special access to the drug every six months on behalf of his patients.

A spokesperson for Health Canada said there are clinical trials in Canada that may lead to approval in the future.

How to avoid infection

Armstrong doesn't know how she was infected, but suspects it could have come from her work fixing farm equipment or from produce purchased at farmer's markets.

Houston said most patients in Alberta were dog owners, but Armstrong hasn't had a dog at home since she was a kid.

Houston's main advice for prevention is meticulous hand-washing, particularly if you have dogs at home. Regularly de-worming your dog can be helpful as well.

"We're hoping to learn more about the ecology of this disease in Alberta so we can give more precise advice," he said.

After Armstrong's cancer diagnosis, she went on sick leave and moved back to Edmonton to be close to family during her recovery. She is still struggling with pain as her incisions heal.

Armstrong may never know how she got sick, but she believes it is important to raise awareness about the disease.

"It's a scary thing and there's still so much we don't know," she said. "I would like to see more funding for research so more people don't have to go through what I went through."