Deadly liver parasite on the rise in Alberta; canine tapeworms contribute to human spread

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A rare and potentially fatal parasitic disease originating in Europe and transmitted by dogs has taken root in Alberta, now the infection hotspot in North America.

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A recently published review of known cases of human alveolar echinococcosis (EA) found in 17 Alberta between 2013 and 2020, shows research led in part by University of Alberta infectious disease expert Stan Houston.

Only two cases of AE in humans had ever been confirmed in North America: one in Manitoba in 1928 and another in Minnesota in 1977.

“This parasite has now become very widely established in the wild on the Prairies. It has been found in Saskatchewan and British Columbia, but Alberta has had most cases of human disease, ”Houston said in a press release Thursday from the U of A.

“We have on average more cases each year. There has been a lull since COVID-19, but I suspect this reflects a slowdown in testing during the pandemic and that we may soon see a further increase. “

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The strain of EA found in the Alberta cases has been identified by scientists at the Calgary School of Veterinary Medicine as originating in Europe, possibly in dogs brought to the area.

The parasite takes the form of a tiny tapeworm in dogs – typically foxes and coyotes, but potentially companion dogs – and is relatively harmless to them. But when a rodent ingests parasite eggs from dog feces, it contracts a different form of the disease and develops a fatal tumor, or parasitic growth, in the liver. And if the rodent is eaten by a dog, the parasite takes on the form of the tapeworm.

“We humans take the rodent’s place in the life cycle when we accidentally consume the eggs of microscopic parasites – perhaps in strawberries or lettuce from a garden where a coyote has passed, or perhaps a dog if he’s a carrier of the parasite, “Houston said. .

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Dr. Stan Houston, Associate Professor in the Divisions of Infectious Disease Medicine and Internal Medicine at the University of Alberta.  Ed Kaiser / Postmedia, file
Dr. Stan Houston, Associate Professor in the Divisions of Infectious Disease Medicine and Internal Medicine at the University of Alberta. Ed Kaiser / Postmedia, file Photo by Ed Kaiser /Edmonton Journal

The increase in human contact with urbanized coyotes and the number of people in the province with weakened immune systems are likely contributing to the growth of cases in Alberta.

“In Calgary and Edmonton coyotes, more than half of them carry this parasite. So the new strain not only appears to be more virulent when affecting humans, but it also appears to be super effective in wild hosts, ”said Houston.

“The COVID-19 pandemic has once again raised awareness of the number and importance of human diseases transmitted by animals. “

Of the 17 cases from Alberta, 11 patients lived in rural areas, 14 dog owners and six were immunocompromised. The disease progresses faster in patients whose immune systems have been suppressed.

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But the symptoms of AE can be elusive – it can take several years for a patient to start showing signs. Almost half of the cases in Alberta were discovered accidentally while the patient was being tested for another disease. Often it was found after an ultrasound showed abnormalities in the liver, followed by an investigative biopsy. When symptoms do appear, they can include unspecified pain, jaundice, weakness, and weight loss – many of the same conditions expected from a cancerous liver tumor.

Because the parasite is initially asymptomatic, it is often able to grow slowly and by the time it is detected, about two-thirds of patients will be inoperable. In these cases, lifetime antiparasitic drugs are the only option. The most useful drug for controlling AE is not licensed in Canada and is only available through a special application process with the government and the manufacturer.

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If left untreated, the parasite could kill its human host within 10 to 15 years.

Researchers are currently working on a new study examining liver biopsy samples from patients in Alberta where no cancer has been detected, to look for possible cases of previously unrecognized AEs.

“It would give us a better idea of ​​what’s going on, but more importantly, it would give us a chance to give these patients proper therapy,” Houston said.

“We should be careful, but it is still a very rare disease,” he added. “People should keep this in perspective, adopt healthy behaviors and not obsess over it. “

Avoiding the parasite comes down to good hygiene practices like washing your hands after handling a dog, especially if you think they’ve eaten a rodent or spent time in a dog park or in an area frequented by coyotes. It is also recommended to wash products that come from the ground or near the ground thoroughly, such as lettuce or mushrooms.

The study, “Epidemiological and Clinical Features of Alveolar Echinococcosis: An Emerging Infectious Disease in Alberta, Canada,” was published in The American Journal of Tropical Medicine and Hygiene.

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