Incidents of serious infestations on the
A rare parasitic infection imported from Europe continues to have roots in Alberta, Canada. The province is now the North American hotspot for human alveolar echinococcosis (AE), which occurs in the form of liver growth and causes serious and potentially fatal health complications.
A recent review of known AE cases in Alberta found 17 cases of human AE diagnosed in the province between 2013 and 2020. Before the recent surge, only two cases of human AE had been confirmed in North America – one in Manitoba in 1928 and another in the US state of Minnesota in 1977.
“This parasite is now very widespread in the wild on the prairies. It was found in Saskatchewan and British Columbia, but Alberta had the highest number of human disease cases,” said Stan Houston, an infectious disease expert at the University of Alberta helped guide the course.
“We have more cases on average each year. There has been a lull since COVID-19, but I am suspicious that this reflects a slowdown in testing during the pandemic and we may see a spike again soon.”
According to Houston, the AE strain found in the Alberta cases was identified by scientists at the School of Veterinary Medicine in Calgary as originating in Europe, likely in dogs brought to the area.
The parasite takes the form of a tiny tapeworm in dogs – typically foxes and coyotes, but possibly also dogs – and is considered relatively harmless to them. When a rodent ingests parasite eggs from dog feces, it gets another form of the disease and develops a tumor or parasitic growth in the liver that kills it. When the rodent is eaten by a dog, the parasite reverts to tapeworm form.
“We humans take the place of the rodent in the life cycle when we accidentally consume microscopic parasite eggs – maybe in strawberries or lettuce from a garden where a coyote passed, or possibly a dog if it carries the parasite,” said Houston .
The European AE strain was particularly successful in Alberta and quickly spread in the wild. Increased human contact with coyotes as urbanization progresses, as well as the increasing numbers of people with illnesses or therapies that weaken the immune system, are likely to add to the number of people suffering from the disease.
“Coyotes in Calgary and Edmonton have been found to be more than half carrying this parasite. So not only does the new strain appear to be more virulent when attacking humans, but it also appears to be super effective on wild hosts.” said Houston.
“It has always been important to keep an eye on disease from animals,” he added. “The COVID-19 pandemic has re-raised awareness of the number and importance of animal-borne human diseases.”
Of the 17 cases found in Alberta, 11 patients lived in rural areas, 14 of them owned dogs, and 6 were immunocompromised – of particular concern as the disease progresses faster in those with suppressed immune systems.
The symptoms of AE can be difficult to spot. The infection typically has an incubation period of several years before a patient shows signs of disease. Almost half of the cases in Alberta were discovered accidentally while the patient was being tested for another disease. It’s often found after an ultrasound shows abnormalities in the liver, followed by an exam biopsy. When symptoms do occur, they can include unspecified pain, jaundice, weakness, and weight loss – many of the same conditions expected in a cancerous tumor in the liver.
“In most cases, when people first saw the imaging, the first thing they thought was cancer,” Houston said. “The symptoms would be indistinguishable from many other liver diseases, so a biopsy diagnosis is required.”
If it’s found early enough, treatment may include surgery to remove the mass from the liver. Because the parasite is initially asymptomatic, it can often grow slowly, and when found, about two-thirds of patients are inoperable. In these cases, lifetime anti-parasitic drugs are the only option. The drugs do not kill the parasite, but they do keep it from growing. If left untreated, the parasite could kill its human host within 10 to 15 years.
Currently, the most useful drug to combat AE is not approved in Canada (although it is widely used in most parts of the world) and is only available through a special medical application process from both the government and the manufacturer.
Avoiding the parasite depends on good hygiene practices and simple precautionary measures. Houston said it was a good idea to wash your hands after handling your dog, especially if you suspect he may have eaten a rodent or spent time in a dog park or in an area where coyotes are common. It is also advisable to thoroughly wash products that are close to or close to the ground, such as lettuce or mushrooms.
Researchers are now working on a new study examining liver biopsy specimens from patients in Alberta who were not found to be cancer, to look for possible previously undetected cases of AE.
“That would give us a better picture of what is going on, but more importantly, it would give us the ability to provide adequate therapy to these patients,” Houston said.
“We should be careful, but it is still a very rare disease,” he added. “People should keep this in mind, adopt health behaviors and not be obsessed with them.”
The study “Epidemiological and Clinical Characteristics of Alveolar Echinococcose: An Emerging Infectious Disease in Alberta, Canada” was published in. released The American Journal of Tropical Medicine and Hygiene.
American Journal of Tropical Medicine and Hygiene
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