Echinococcus multilocularis (EM) is an important zoonotic tapeworm. The situation with this parasite in Canada (and probably the US) is unclear and evolving. It’s increasingly clear that EM is present in a high percentage of wild canids (e.g. coyotes, foxes) in some regions. What this means for human health isn’t clear yet.
This tiny tapeworm lives in the intestinal tracts of canids (both wild and domestic). People can become infected when they inadvertently ingest parasite eggs from canid feces (another good reason to not eat poop). In people, the parasite can migrate to tissues such as the liver and cause lesions very similar to a malignant tumour. This condition is called alveolar echinococcosis (AE). Treatment can be difficult and, untreated, mortality rates are high (approaching 100%). Also, the incubation period in people is long: it can take 5-15 years from exposure to development of disease.
As we find this parasite in new areas, inevitably the question is: what does this mean for people? Reporting of human cases is variable, and the long incubation period means that it takes a long time to identify changes to the risk to human health. So, if people are at higher risk of AE because the parasite is becoming more common in canids, we may not actually know for years. Lack of human cases is sometimes cited as a reason why it’s “not a big deal.” However, as is frequently argued, “absence of evidence” is not the same as “evidence of absence.”
A recent case report heightens these concerns. Alveolar echinococcosis was identified in a child in Quebec in the spring of 2018, and it’s believed the infection was acquired locally as the child had not travelled outside of Quebec, and the dog the family had previously owned was also from within the province. Foxes were a possible source since they were common in the area and exposure to fox feces in the outdoor environment was considered likely. However, differentiation of exposure from a pet dog or environmental exposure to canid feces is impossible.
One case does not make an epidemic, but it’s one more piece in the puzzle. Ongoing work looking for this parasite in pet dogs will help to better define the risk… more to come on that as the year progresses.
More information about Echinococcus multilocularis can be found on the Worms & Germs Resources – Pets page. Or check out the latest update to the EM infographic from the Ontario Animal Health Network.