Nothing has changed about Echinococcus multilocularis (the fox tapeworm) in the past couple of months, but my phone is ringing off the hook following another round of media reports about this parasite. Here’s a recap of the issues:

• Echinococcus multilocularis is a small tapeworm normally found in the intestinal tract of wild canids (e.g. coyotes, foxes) and sometimes dogs. For these animals, having this worm in the gut doesn’t cause a problem. The main concern is when something (or someone) ingests tapeworm eggs that are passed in feces of these canids.  This can result in a condition called alveolar echinococcosis (AE), in which tumour-like parasitic cysts can develop in other parts of the body, particularly in the liver.
• In the normal (wildlife) life cycle of this tapeworm, wild canids shed eggs in their feces which are eaten by small rodents, that then develop AE. When a canid eats an infected rodent, the parasite grows into its adult stage in the canid’s gut and produces more eggs, and the cycle continues.  While that’s bad for the rodents, the bigger problem is that this “intermediate host” stage can occur in more than rodents… including dogs and people.
• Alveolar echinococcosis has been diagnosed in a small number of Ontario dogs (with little to no travel history) since 2012, raising questions about how they got infected. The concern was that this parasite had become established in our wild canid population, which presents an ongoing risk to people and other animals, and is very hard to control.
• Human cases in Canada are rare but are being found and may be underdiagnosed.  Since AE is a very nasty disease, and very difficult to treat, we’re inherently cautious.

The recent news stories picked up on a study published earlier this year in Emerging Infectious Diseases (Kotwa et al 2019), where an astounding 23% of wild canids in Southern Ontario were found to be shedding Echinococcus multilocularis. 

What’s the risk to dogs in Ontario?

• We don’t know. I realize that’s not comforting but it’s the honest answer. We should know a lot more in the next few months as we test samples from pet dogs in the highest risk areas. Until then, it’s hard to say much with confidence.

What should dog owners do?

There are two main approaches to prevention: decreasing the risk of exposure and prophylactic treatment.

We can treat dogs for tapeworms, but this isn’t usually part of routine deworming protocols, so only a small percentage of dogs are treated on a regular basis. I’ve been treating my dog with praziquantel monthly for the past couple of years, since emergence of the parasite was identified, because we’re in a higher risk area and he will eat anything. We live in the country and have a lot of coyotes around. If the parasite is here, it’s quite plausible he would be exposed.

The risk is much lower (or non-existent, potentially) in other regions, and dogs that have less outdoor access are much lower risk. Quantifying that risk is the challenge.

Ultimately, whether or not to treat a dog prophylactically is a case-by-case decision, based on the dog’s risk factors (and the owner’s risk aversion).

More information about Echinococcus multilocularis can be found on the Worms & Germs Resources – Pets page. Also check out emultiontario.com and the updated infographic from the Ontario Animal Health Network.  We’ll provide updates as more information about this parasite becomes available.