Coyotes in Washington carry tapeworms that can be passed to dogs, humans in rare cases

Researchers in Washington state have found that about a third of the local coyotes studied have a species of tapeworm. These can be passed to dogs, and in rare instances humans. These parasites are also present in foxes and other canid urban wildlife. Domestic dogs can also contract them, and it can be years before the symptoms of the severe disease they cause are detected, making diagnosis and treatment difficult. We talk with Yasmine Hentati, the study’s lead author who recently got her doctorate in environmental and forest science from the University of Washington. She shares more about these parasites and the relative risks for people and dogs.

Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. A tapeworm that can cause serious disease in dogs, foxes and coyotes was recently detected in the Pacific Northwest. The tapeworm was connected to cases in Canada and the American Midwest about 15 years ago, but this study by researchers at the University of Washington was the first to find it in wild animals on the West Coast. And the results weren’t subtle. More than a third of the 100 coyotes surveyed in the Puget Sound region tested positive. What’s more, while it is rare, it’s possible that humans can get sick from these tapeworms as well.

Yasmine Hentati was a lead author of the study. She recently got her doctorate from the University of Washington and she joins us now. It’s great to have you on Think Out Loud.

Yasime Hentati: Hey, thanks for having me.

Miller: What were you hoping to learn when you started this study?

Hentati: That’s a great question, because this result actually happened completely by accident. Part of my PhD project was looking into gastrointestinal parasites of coyotes in general. I wanted to know what worms they had because no one had really looked into that in the Seattle area, and also how those infections related to what they were eating and where they were on the landscape. We weren’t expecting to find this specific parasite. We knew that it was spreading throughout North America, but it wasn’t necessarily on our radar. So imagine our shock when our genetic results came back with this parasite. Echinococcus multilocularis is the name, which I know is a mouthful.

Miller: Yeah, a couple of mouths full. If this tapeworm had only been found in the Pacific Northwest earlier this year and basically wasn’t known to be here until this year, how do you explain the fact that you found it in more than a third of the coyotes that you studied?

Hentati: So in the time that it took for us to analyze our results once we started getting them back, another paper came out that found E. multilocularis in a handful of dogs here in Washington and elsewhere in the Pacific Northwest. So it was really interesting because these authors were able to identify some infected dogs, but they didn’t necessarily know where the parasite was coming from because it has a primarily natural life cycle in the wild. And now we know that coyotes are hosting a really healthy population of this tapeworm, at least here in Western Washington.

And it’s thought throughout the northern hemisphere, where this parasite is present, that it’s potentially in a lot of different places where we don’t know, because people just aren’t looking. It’s not because it’s not there, it’s because no one has necessarily taken the time to look in a lot of different places. And I think that was the case here in the Puget Sound region as well.

Miller: Can you give us a sense for the life cycle of this particular tapeworm? And I should give our lunch eating listeners a warning that this could get gnarly.

Hentati: Yes, definitely. So it’s a complex life cycle, which means that it involves multiple hosts throughout the parasite’s life cycle. Wild canids – so members of the dog family like coyotes, wolves, foxes – they host the adult parasites in their intestines. And these are really tiny worms, like 2 to 3 millimeters long, so they can support thousands of worms in their intestines without showing really clinical signs of being ill. And the worms then shed eggs that are passed in the feces of the canids, which contaminate the environment.

The next host in the life cycle is rodents – think mice and voles. They become infected by eating food that’s contaminated with the eggs. The parasite then migrates to the liver of these rodents and forms tumor-like cysts that can spread throughout the body like cancer. And then the life cycle starts again when our canids, or our coyotes or our wolves, eat these infected rodents.

Unfortunately for humans, if we accidentally consume the eggs of E. multilocularis, we can experience the same symptoms as the rodents with the liver cysts. The disease is called alveolar echinococcosis and it’s considered one of the most important foodborne illnesses globally. About 1 million people worldwide are currently infected with this disease. It’s very, very rare here in North America, but because of that and because of the fact that symptoms can take many years to show up, people sometimes don’t get diagnosed until they’re in advanced stages.

And dogs are a really interesting host here because they can actually be in both situations. So if they consume infected rodents, they can be hosts of the adult tapeworms, like other canids where they live in their intestine and the dog passes the eggs in their feces. But if they’re exposed to eggs in the environment, they can also be that accidental middle host like us, and they can develop the cysts on their livers and potentially on other organs as well.

Miller: We asked listeners if they had concerns about urban coyotes, given your study, and we got a lot of responses. Several people said that they had no concerns. Others mentioned being afraid for their pets. A few said they were troubled by the human activity that’s affecting coyotes and other wildlife. Michael D. Barton wrote this: “People think they need to post to neighborhood Facebook groups and Nextdoor every single time they spot a coyote and warn others to keep their pets inside, as if those are the only times they’re around. They are around all the time.”

It did make us wonder, given that ubiquity, what advice you have right now for dog owners?

Hentati: Yeah, that listener totally nailed it. They’re everywhere here in Seattle where I live, in the Portland area, even if we don’t see them, they’re there. And the advice that I would have is, especially with your dogs, try not to let them hunt rodents or eat feces. I’m sure there’s many dog owners out there that struggle with their dogs wanting to eat poop, so try not to let them do that. Wash your hands after handling dog waste. And if your dog does have behaviors that you’re concerned about, you can talk to your vet about deworming medications that target tapeworms.

And of course with coyotes, don’t feed them or other wildlife. But generally the biggest concern here is for dogs consuming coyote feces by accident, say, while going for a walk in the park.

Miller: What would it take for humans to get infected?

Hentati: We would have to consume the eggs through a contaminated environment. So this can happen through, for example, if you’re foraging and you eat a fruit or a vegetable that didn’t get washed and it was contaminated with eggs, then you could potentially become exposed. Or if your dog is infected and you don’t know, and you handle their feces, you don’t wash your hands, and you accidentally consume it that way. So those would be, I would say, the most common potential ways.

Miller: But just to be clear, you’re saying the risk of dogs is relatively low and the risk to humans is even lower?

Hentati: Yeah, the risk to humans is quite low. It’s not zero. The bigger concern is definitely for dogs, especially for dogs that tend to have a habit to hunt and kill rodents or to eat poop. But yes, I would say it’s a low risk.

Miller: But you said earlier that the fact that this wasn’t identified until now, likely it’s not that it wasn’t here until now, it’s just that you hadn’t really been looking. We also heard that this has been spreading throughout North America for decades now. Can anything be done to slow the spread of this parasite?

Hentati: That’s a good question. In general, parasites are pretty good at spreading where they want to spread, especially with this type of parasite that has a mostly wild life cycle. That kind of middle host is rodents, there are a lot of different rodent species out there that could be potential hosts. We don’t even know necessarily in Washington which rodent species the coyotes are getting it from – that’s a potential area of future research. And similar with coyotes, dogs and foxes, they can disperse pretty large distances from where they were born.

So I would say instead of focusing the spread of the parasite in the wild, we can focus more on making sure that we don’t get infected and our dogs don’t get infected and kind of reducing that risk through the methods that I talked about.

Miller: Just briefly, how did you become a researcher who wanted to focus on parasites?

Hentati: I grew up on the East Coast in Maryland. When I was a kid, I got Lyme disease. I ended up having it a couple times. And for some reason that got me really interested in kind of the urban interface and wildlife diseases, and how we live with wildlife and potentially become exposed to the same diseases as them. And I ended up working on a tick-borne disease project right after college when I got my degree in wildlife ecology. So that was the first step into urban disease research, wildlife disease research. And my mom did not love that I went and sampled ticks on purpose. [Laughs’ But that’s how I got into it.

Miller: Yasmine, thanks so much.

Hentati: Thank you.

Miller: Yasmine Hentati recently got her doctorate in environmental and forest science from the University of Washington. She’s the lead author of this new tapeworm study.

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