Echinococcus multilocularis, a small tapeworm with a big name, is causing big concerns in Ontario, an area that was until recently considered free of this parasite. This tapeworm is normally found in the intestinal tract of wild canids (e.g. coyotes, foxes) and can also infect dogs. That itself isn’t a problem, since the intestinal form of the worm doesn’t make these animals sick. The concern arises when something (or someone) ingests tapeworm eggs from the feces of an animal with the intestinal infection, potentially leading to a different form of infection called alveolar echinococcosis (AE). In this form, the parasite causes tumour-like cysts to form in various parts of the body, particularly in the liver, and the condition can be very difficult to treat by the time it is diagnosed.
In the normal life cycle of this tapeworm, wild canids shed eggs in their feces and those eggs are eaten by small rodents, who develop the parasitic cysts in their bodies. When a canid eats one of those infected rodents, the life cycle continues, as the parasite grows into its adult stage in the canid’s gut and produces more eggs.
That’s bad for rodents, but the problem is that this “intermediate host” stage can occur in more than rodents – it can also occur in dogs and people (and occasionally other species).
Alveolar echinococcosis has been diagnosed in a small number of Ontario dogs (with no travel history) since 2012, raising questions about how they got infected. The concern was that this parasite might have become established in our wild canid population, which would result in ongoing and widespread risk to people and other animals, and would be hard to control.
Those concerns have been proven true, by a study just published in Emerging Infectious Diseases (Kotwa et al. 2019). For this study, fecal samples were collected from 460 wild canids in Ontario. An astounding 23% of them were positive for Echinococcus multilocularis, with infection concentrated most heavily in the western-central part of the province.
This remarkable set of results shows that this parasite is by now well established, at least in parts of Ontario, and that there is local exposure risk through direct or indirect contact with wild canid feces. Dogs that are prone to eating feces (I own one of those) or rodents (dead or alive) are at highest risk of exposure. Humans who have contact with coyote feces (e.g. hunters, trappers) are probably also at particularly high risk, but since canids live in such close proximity to people in some areas, including large urban centres, there’s a chance for exposure of lots of people through contact with fecally-contaminated outdoor sites.
What is the status of this disease in people in Ontario?
- We don’t know. The incubation period (the time from ingesting eggs to the time you get sick) is very long (typically 5-15 years). That means we may not really know what’s going on in people for some time. Since we have this parasite in wild canids and it’s spilled over into dogs, it’s almost certain that there are infected people in the province, they just don’t know it yet. That’s not meant to be alarmist, since it’s still going to be a rare disease; however, we won’t know the scope of the problem for some time. Echinococcus multilocularis has also recently been made provincially reportable in Ontario, to help us gather more data.
What can we do?
- Avoid contact with wild canids and wild canid feces as much as possible.
- Do our best to prevent and treat intestinal infection in dogs. In other areas of the world where this parasite is widespread, dog ownership has been identified as a risk factor for human infection, probably because dogs act as a bridge between households and the wildlife cycle of this parasite. We can treat dogs for tapeworms, but this isn’t usually part of routine deworming protocols, so currently only a small percentage of dogs are treated. I’ve been treating my dog with praziquantel monthly for the past couple of years, since emergence of the parasite was identified. I recommend it now, especially for dogs that might have contact with wild canids or that are prone to eating things like feces and small rodents.