This tiny parasite continues to cause a stir around Ontario. While infections are (apparently) still rare, it’s becoming clear that this nasty worm has somehow stealthily established itself in the province. That presumably means it’s either also in neighbouring provinces and states, or heading there.
Echinococcus multilocularis is a small tapeworm that can cause severe disease. Canids (dogs and wild canids like foxes) are the “definitive hosts,” and when infected these animals can shed tapeworm eggs in their feces. Normally, these eggs are eaten by small rodents, who then develop tumour-like lesions containing an immature life stage of the parasite. Canids then get infected by eating the infected little critters, and the cycle continues.
The normal life cycle of Echinococcus is a problem for the rodents but not for the dogs, because having these tapeworms in just the intestine doesn’t cause any signs of illness. If that’s all there was to the story, it wouldn’t get much attention, but the issue is that other species can develop the tumour-like disease similar to the rodents. This includes people, in whom serious and very difficult-to-treat disease can develop, typically after a very long (5 to 15 years) incubation period .
Now what’s happened is there have been several cases in Ontario of these tumour-like lesions in dogs. While dogs are usually intestinal carriers of the adult tapeworm, they can also occasionally develop these lesions from the immature tapeworms instead, if they swallow large numbers of tapeworm eggs (just like rodents and people) . We’ve now seen 4 cases of this since 2012. Based on what we know of the parasite’s epidemiology in other parts of the world, we know that infections like this in dogs tend to only develop in regions where the parasite is widespread in wild canids. That suggests we might have a big, silent reservoir out there, and that human cases could be on the horizon.
Time will tell.
More information about the latest case, along with a few pictures, can be found in the latest Animal Health Laboratory Newsletter.