A woman from Alberta, Canada, who believed she was dying from a rare cancer was subsequently told by doctors that her symptoms were actually being caused by a parasite.

Toward the end of last year, 36-year-old Cassidy Armstrong began feeling severe pain in her ribs and was also experiencing weight loss, Global News reported.

Armstrong took herself to get checked out at the hospital and doctors recommended that she undergo an MRI scan. The scans revealed a large mass in her liver and medical staff subsequently diagnosed her with a rare form of liver cancer.

"I was basically getting ready to just die," Armstrong told Global News. "It didn't look good. It was pretty sad and scary."

After her diagnosis, Armstrong underwent surgery and during the procedure, surgeons removed around 65 percent of her liver, her whole gallbladder and some parts of her lungs.

However, when medical staff analyzed some of the tissue removed from Armstrong's body, they made a surprise finding—her symptoms were actually being caused by the presence of a parasitic tapeworm known as Echinococcus multilocularis.

"[Doctors] said, 'We have some good news for you. We don't think this is cancer. We think this is a parasite,'" Armstrong said. "I was like, 'This is good?' They're like, 'Yes, it's very good. It's much better.'"

Infection with the larva of this tapeworm—which is found primarily in foxes, coyotes, and dogs—can lead to a rare disease known as Alveolar echinococcosis (AE.) It involves the growth of cysts in the liver, or sometimes other organs such as the lungs and brain, according to the Centers for Disease Control and Prevention (CDC.)

These cysts grow at a slow rate, and thus, symptoms may not appear for several years. When they do, patients often report pain or discomfort in the upper abdomen, weakness and weight loss. These are similar to the symptoms reported by patients with liver cancer and liver cirrhosis. If AE is not treated, the disease can be fatal in some cases.

Armstrong may have been infected with Echinococcus multilocularis for around 10 years, doctors said. Medical staff have now prescribed her anti-parasitic medication.

"[Doctors are] saying that I might have a chance at a normal life expectancy, which is great," Armstrong said. "I'm forever grateful."

Humans can become infected with Echinococcus multilocularis after ingesting the eggs of the tapeworm via "hand-to-mouth" transfer or contamination, according to the CDC. For example, an individual could consume food which is contaminated with the feces of foxes or coyotes.

Or they could become infected after handling household dogs and cats which are contaminated with the eggs. These pets may become contaminated after coming into contact with infected rodents—or their feces.

Stan Houston, an infectious disease specialist from the University of Alberta, said that the parasite is seemingly becoming more common in the Canadian province. Fifteen human cases of the parasite have been confirmed in Alberta since 2013.

"This [parasite] is a totally new thing... this didn't used to be here," Houston told Global News.

Nevertheless, AE is found around the world—mostly in northern latitudes—with cases reported in central Europe, Russia, China, Japan, Central Asia and some parts of North America.