Dog Parasite Causing Cancer-Like Growths In Humans Is On The Rise In North America

Alveolar echinococcosis, a rare parasitic disorder in humans, occurs after ingestion of eggs of the tapeworm Echinococcus multilocularis. Image credit: Wikimedia Commons

A rare parasite that causes cancer-like growths in peoples' livers has started to become increasingly common in North America over the past decade, especially in certain portions of Canada. 

As reported in the American Journal of Tropical Medicine and Hygiene, a team from the University of Alberta argue that the Alberta province of Western Canada has become somewhat of a North American hotspot for the rare infection, known as human alveolar echinococcosis (AE). Before 2013, just two human cases of the parasitic infection had been confirmed in the whole of North America. In the new study, however, the researcher identified 17 cases in Alberta between 2013 and 2020.

The researchers believe the strain of AE was likely brought to Canada by dogs from Europe, where the disease is rare but well-established, before being spread to urbanized coyotes and humans.

"In coyotes in Calgary and in Edmonton, more than half have been found to be carrying this parasite. So the new strain seems to not only be more virulent when it affects humans, but it seems to be super-effective in wild hosts," Stan Houston, an infectious diseases expert from the University of Alberta who led the study, said in a statement

In its typical lifecycle, the tapeworm-like parasite called Echinococcus multilocularis lives harmlessly in the small intestines of canines, typically foxes and coyotes, but also pet dogs. When the parasites’ eggs are pooped out and eaten by rodents, the disease takes a different form and results in cyst-like tumours in the liver, which eventually kills the animal. 

If humans ingest the parasites' eggs, they too can suffer from this nasty fate. According to the Centers for Disease Control and Prevention, humans with the infection can also get tumours in the liver and lungs, and less frequently in the bones, kidneys, spleen, muscles, and central nervous system. However, the disease is relatively difficult to spot in humans as it can easily resemble other diseases, most notably cancer. Symptoms are also fairly vague, such as unspecified pain, jaundice, weakness, and weight loss.

The parasite can kill a human host within 10 to 15 years if left untreated. If the infection is caught early, then surgery to remove the liver mass is possible, although two-thirds of patients will become inoperable as they didn’t receive a diagnosis promptly enough. For these patients, a lifelong treatment of antiparasitic drugs can help stop the mass from growing, but the parasite will survive. 

Of the 17 cases documented in this study, 11 patients lived in rural areas, 14 of them had pet dogs, and six had a weakened immune system. In nearly half of the cases, the patients were only diagnosed with the parasitic infection while being tested for a different illness.

"In the majority of cases that was the people's first thought when they saw the imaging, that it was cancer," said Houston. "The symptoms would be indistinguishable from many other diseases in the liver, hence the need for a biopsy diagnosis."

To prevent this grim infection, Houston advises people to practise some simple hygiene precautions, such as thoroughly washing any fruit and vegetables that have been on the ground. If you own pets, be sure to wash your hands as much as you can after touching them, especially they’ve come into contact with a rodent or an area where coyotes hang out. 

"We should be paying attention, but it's still a very rare disease," he added. "People should keep that in perspective, adopt health behaviours and not obsess about this."


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