A dog in Peterborough has tested positive for a new tapeworm infection in Ontario, but there are still no reported human cases.
The dog contracted something called Echinococcus multilocularis (EM) — a parasite which is a form of tapeworm, usually found in rodents and wild animals like foxes, wolves and coyotes.
It's a newer infection that has become a reportable disease, and pet owners should become educated about it.
How dogs get infected
The animals become infected by consuming an infected rodent, through eggs in the rodent's feces or by spread through the environment after a rodent dies.
Some dogs “scent roll” in foreign material — such as wild animal feces — and may become contaminated this way.
The eggs are “tolerant to cold and freezing temperatures, and under optimal conditions, can survive for prolonged periods — over 12 months — in the environment,” Public Health Ontario said.
“Veterinarians are reminded and encouraged to educate pet owners about the animal and human health risks of EM, particularly those who own dogs that live in or frequently visit higher risk areas of southern Ontario, and whose dogs exhibit other high-risk behaviours such as hunting and consuming small rodents, and consuming or having other contact with feces of coyotes, foxes or other dogs,” the province said in a 2022 document.
How it spreads to humans
The parasite can spread to humans through accidental contact with an infected dog's feces — even if it's around a dog's mouth or on their fur.
People at higher risk include trappers, hunters, veterinarians, or others who have contact with wild foxes or coyotes, said the Centers for Disease Control and Prevention (CDC) in the U.S.
It can also come from unwashed produce or unfiltered surface water in areas where infected dogs or wild canids may have defecated, the University of Saskatchewan said on its website.
EM is also known professionally as E. multilocularis, and human and animal diagnosis became a reportable infectious disease with Public Health Ontario in 2018.
Cases in Ontario
With a fact sheet in 2023, the health agency said “Ontario is now considered an endemic area for E. multilocularis, creating the potential for human exposure.”
Historically, the parasite wasn't seen in Ontario before 2012, the National Institutes of Health said on its website.
“How E. multilocularis tapeworms were introduced into Ontario is unclear,” the Centers for Disease Control and Prevention said in a 2019 report. “However, the spatial pattern of high infection prevalence among wild canids in the southern PHUs that border the northern shores of Lake Erie might indicate a natural northeastern expansion from Michigan — an endemic area.”
Cases in dogs have been detected since then in Ontario, with the most recent reports in 2022, the province said.
So far, there has only been one reported case of a human in Ontario, in 2018.
Established areas
The province said random testing done from wild animals from 2015 to 2017 found that EM was present in 23 per cent of the samples.
The University of Saskatchewan said the parasite is well established in all of Western Canada, especially in the prairie regions. It has been identified in some people living in Alberta.
Symptoms don't show
The problem with identifying the parasite in humans is that symptoms don't often appear until five to 15 years after infection.
Once a human is infected, the eggs hatch immediately and the larvae move to the liver or other target organs, where they form slow-growing cysts.
Human infections have been reported in continental Europe, Russia, China and Alaska.
Can be fatal
It can become more serious, causing something called alveolar echinococcus (AE) — which is fatal if left untreated.
Since Ontario has been keeping records, the AE infection has been diagnosed in five dogs, three privately-owned lemurs and a wild-caught chipmunk near the western shores of Lake Ontario.
Symptoms in humans can include abdominal pain, malaise and weight loss.
Testing and treatment
The parasite is usually diagnosed in humans with a blood sample, but in later stages lesions are apparent in the liver or other organs, and tissue biopsies can show the presence of the parasite.
Currently, blood sampling can't be done in Canada, but Public Health Ontario would facilitate testing in Switzerland, the agency said.
For treatment in humans, surgical removal of parasitic lesions and antiparasitic or chemotherapeutic medications have also been successful.
