Who's afraid of the big bad tapeworm?

I have spent my career reporting on issues that centered around risk.

What has always interested me is how poorly we humans deal with risk no matter what our ideological bent is.

For instance, I know many people who will not go into Yellowstone’s backcountry because of their fear of grizzly bears. Camping in grizzly country seems as dangerous to them as sleeping in a war zone.

But millions of people visit Yellowstone without ever being attacked by grizzlies. Thousands camp in the backcountry without ever seeing a bear.

Then there is the whole radioactivity thing. Some activists spend their lives fighting to prevent extremely small levels of nuclear material from escaping into the atmosphere even as they smoke cigarettes.

My kids grew up camping in grizzly country and they know how to keep their camp clean. They sleep soundly just like they don’t panic in traffic.

I can’t say I sleep as easily as they do. And even though I have leaned against barrels of nuclear waste at the Idaho National Laboratory I confess one of the scariest moments of my life was when I was standing in a nuclear reactor during a test at the INL in 1986 and a valve released with a loud bang!

I thought I was sitting in Three Mile Island.

Fears like predators and hidden dangers like radioactivity cut to our racial memory, as Carl Jung called it. We are all still haunted by the attacks of sabertooth tigers on our ancestors.

That’s why the extremely infrequent attacks of wolves on humans remains a part of the debate over their restoration to Idaho and the American West. Now the boogeymen are tapeworms.

Washington State University and Idaho Department of Fish and Game researchers found that more than half of the wolves they tested carried a tapeworm parasite known as Echinococcus granulosus. Hunting activist George Dovel of Garden Valley took the study and widely circulated an article that suggests the wolves were brought in from Canada with the disease, its dangerous to people, game and livestock and yet another curse of the hated wolf reintroduction program.

So is George right? Not exactly.

I talked briefly with William Foreyt, the Washington State University wildlife disease expert who led the study. He said chances wolves will pass the tapeworm on to people and livestock is low. It was around before the wolves got here and is an issue that has long been managed.

Here is what the Idaho Department of Fish and Game and the Idaho Department of Agriculture say:

What is Echinococcus granulosus?

Echinococcus granulosus is a parasitic tapeworm (cestode) that requires 2 hosts to complete its life cycle. Ungulates (deer, elk, moose, domestic sheep, and domestic cattle) are intermediate hosts for larval tapeworms which form hydatid cysts in the body cavity. Canids (dogs, wolves, coyotes, foxes) are definitive hosts where larval tapeworms mature and live in the small intestine. Definitive hosts are exposed to larval tapeworms when ingesting infected ungulates. Adult tapeworms, 3-5 mm long, produce eggs which are expelled from canids in feces. Intermediate hosts ingest the eggs while grazing, where the eggs hatch and develop into larvae.

Can humans get infected with Echinococcus granulosus?
Yes, it is a known zoonotic disease of humans with a worldwide distribution. Humans can be infected by ingesting eggs from canid feces, usually from a domestic dog. The hydatid cyst is not infectious to humans. There are several treatments for the disease in humans.

In humans, hydatid cysts usually develop in the liver or lungs. Symptoms depend on cyst location and size. The disease is readily treated with drugs or surgery. In Idaho, at least three reports of human infections with E. granulosus are known; the earliest dating back to 1938.
Throughout the world, most human cases occur in indigenous people with close contact with infected dogs.

Where the parasite is found in wolves and wild ungulates, most wildlife management and public health agencies acknowledge the presence of the parasite, but consider the public health significance to be low. Appropriate use of gloves when handling dog or wolf feces and when skinning and field dressing wolves, coyotes and foxes is recommended by human health and wildlife agencies.

How do I prevent getting infected with this parasite if I am a hunter, trapper or outdoor enthusiast?

The potential for human exposure to E. granulosus eggs in wolf feces or fecal contaminated hides is relatively low. Wolf hunters are encouraged to wear latex or rubber gloves when field dressing and skinning wolves in line with the recommendations for handling carcasses of other wildlife as outlined in the IDFG Game Care Brochure (2002).

Additionally, wild game meat should always be cooked thoroughly.

Regular deworming of domestic dogs and good hygienic practices (wearing rubber or latex gloves when handling feces and washing hands after handling feces) by humans in contact with dogs and dog feces are the best methods of control and prevention of the tapeworm in humans.
Do not feed uncooked meat or organs of deer, elk, moose or sheep to dogs.

Where is Echinococcus granulosus found? Is it found in Idaho?

The tapeworm has a worldwide distribution with 2 recognized “biotypes” – the ‘northern’ biotype that circulates between canids (wolf, dog) and wild ungulates (moose, caribou, reindeer, deer and elk) is primarily found in northern latitudes above the 45th parallel. In Idaho, above the 45th parallel corresponds with McCall north. The ‘southern’ biotype circulates between dogs and domestic ungulates, especially sheep. It is endemic in most sheep raising areas of the world.

Hydatid cysts were found in domestic sheep from Idaho that were sent to California for slaughter in the late 1960’s and early 1970’s.

In Idaho, hydatid cysts were found in a mountain goat in 2006 and in mule deer and elk in subsequent years in several areas of central Idaho. Adult tapeworms were found in 39 of 63 (62%) wolves collected in 2006-2008 from Idaho. Similar prevalence occurs in Montana. Tests for the tapeworm have not been conducted in coyotes and foxes, and the prevalence rate is unknown.

Were wolves examined and treated for Echinococcus granulosus before they were released in Idaho?

All wolves captured in Canada for relocation to Yellowstone National Park and central Idaho were sampled for disease (blood, feces and external parasites) and treated twice for lice (Ivermectin and pyrethrin), roundworms (Ivermectin), and tapeworms (Praziquantel).

What is the significance of Echinococcus granulosus to wildlife and livestock?

Normally, Echinococcus granulosus is not harmful to canids or felids. Heavy infections may be associated with diarrhea or poor body condition. In ungulates, the presence of large numbers of hydatid cysts can lead to respiratory difficulty. The presence of hydatid cysts in livestock at slaughter is generally not of concern, and if present, is trimmed from the edible product.

Wolves n' Worms

Thanks, Rocky:

Good reporting on an important topic. 62% is a big number. I can remember when people laughed about Lyme's Disease, too. Except the ones who got it.

Good luck on keeping the dogs from eating uncooked meat or sniffing butts. And don't forget to wear rubber gloves when petting them afterwards!

It will be interesting to see where this story is by this time next year. Or how many hunters pose with wolf hides while wearing latex.

Relative risks

Great post, Rocky. Thanks for reminding us to consider the relative risks of threats.

We understand the risk of contracting pork tapeworm (Taenia solium), which causes seizures and death. We minimize the risk by thoroughly cooking pork before eating it; we didn't get rid of pigs.

We also know how to minimize the risk of contracting Echinococcus granulosus: make like Walter Mitty and snap on a pair of gloves.

Mitty was too busy fighting the Franco-Prussian War, etc


Like a midair collision with a tugboat

How about Plague?

I have tried to get info about Plague and tape worms from the ID F&G and get no where.

See: http://www.jhnewsandguide.com/article.php?art_id=5511

One of our dog's greatest joy in life is rolling in elk and deer poop - sigh.

Dogs and Poop

Just make sure you cook his meat before he eats it and that you're wearing latex gloves when you pet him.

And, if you get bit my a frothing chipmunk or squirrel, you probably have the plague. Also, if you get bit by a flea or a tick that has been riding around on a frothing chipmunk or squirrel.

Leave her alone, Bob.

Like a midair collision with a tugboat


Have you been bitten by a frothing chipmunk lately, FO?

I can't tell you, Dave.


Like a midair collision with a tugboat

It's OK FO

Dr. Bob Z is cool. I believe he was mixing good advice with some good natured teasing - which I understand and appreciate.

Thanks for being my knight in shining armor.

But seriously, there was a story in the Jackson Hole news not that long ago about a cougar that died of plague, and it mentioned that a boy scout had contracted plague (survived) in Jellystone. I read that a biologist (in Utah?) died from plague. I know its carried by fleas usually on rats and small mammals, but it was the first time I had heard that we had it in the west.

They have Sharks, Bengals, Huricanes...

No tough teams named Tapeworms.

Like a midair collision with a tugboat

Plague and Playgrounds

You're cool too, YPMule. And exactly right with my attempts at mixing a few facts with some humor. Or attempts at humor, anyway.

Squirrels and chipmunks really are a problem with plague, particularly where they routinely mix with people around parks and campgrounds.

We have reported cases of such problems here in Oregon and northern California for the past 20 years or so. Something like 50% of humans will die of plague if it is not treated.




Thanks Dr. Bob!

This is the kind of information I was looking for (and you know what I will do with it...)


According to cdc, there were 7 cases of plague in the entire US in 2007. In the same timeframe, 32 cases of hantavirus (sin nombre) found in deer mouse droppings.

Unfortunately, those rare individuals who do acquire these infections have early symptoms difficult to discern from influenza like illness.

So they are likely to be diagnosed late because it's so low on the list of possible causes for that particular cluster of symptoms.

Plague Stats


The CDC reports an average of 10-15 cases a year in the US, usually rural and often fatal:


In the 1924-25 LA outbreak, 30 people died within two weeks:


How 'bout the tapeworms, though!

Only if they are Maxell Type II tapeworms.

Like a midair collision with a tugboat

Only if they are Maxell Type II tapeworms.

Like a midair collision with a tugboat

Oh well, two is good as Type II tapeworms are scarce now.

Like a midair collision with a tugboat