The whole situation with Echinococcus multilocularis, an important zoonotic tapeworm from dogs, is evolving and unclear in Canada (and probably the US). It’s becoming increasingly clear that the parasite 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.
Echinococcus multilocularis is a small tapeworm that lives in the intestinal tracts of canids. People can become infected when they inadvertently ingest parasite eggs from canid feces. In people, the parasite can migrate to tissues such as the liver and cause lesions very similar to cancer. Treatment can be difficult and, untreated, mortality rates are high (approaching 100%). One problem with sorting out Echinococcus infections in people is the long incubation period. It can take 5-15 years from exposure to development of disease. That’s good in some ways, but it also means that detection of changes or new problems can be a challenge.
One question we have, as we find this parasite in new areas, is what that means for people. Reporting of human cases can be variable, and even if reported, the long incubation period means that it takes a long time to identify changes. So, if we’re seeing a big change in risk to people from a change in this parasite in canids, we may not know for years. Lack of human cases is sometimes cited as a reason that it’s not a big deal. However, this comes down to the ‘absence of evidence’ vs ‘evidence of absence’ debate.
A recent case in Quebec heightens some concerns. Echinococcus multilocularis infection was identified in a child, and it was believed to have been acquired locally. The child had not travelled outside of Quebec, and the dog they had previously owned was from Quebec. 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. However, it’s one more piece in the puzzle. Ongoing work looking for this parasite in pet dogs will help figure out the risk…more to come on that as the year progresses.
More information about Echinococcus multilocularis can be found in our Resources section.