Tapeworms infect wolf packs
60 percent of Idaho, Montana wolves tested had parasite
A Washington State University wildlife researcher said he was “absolutely shocked to see such a high prevalence” of tapeworms found in Rocky Mountain gray wolves.
“Some of these wolves had tens of thousands of tapeworms,” said WSU parasitologist William Foreyt. “They were massively infected.”
Foreyt is the lead author of a study that documented the first instances of the tapeworm Echinococcus granulosus in Montana and Idaho wolves. Published in the October issue of the Journal of Wildlife Diseases, the study found the worms in more than 60 percent of the 60 Montana wolves and 63 Idaho wolves tested.
Finding tapeworms in the wolves was not a surprise, according to one of the study’s authors, veterinarian Mark Drew of the Idaho Department of Fish and Game. The tapeworm has long been known to exist in wolves in Canada and Alaska and to take up temporary residence in game animals such as elk, deer, caribou and moose as part of its lifecycle.
“It’s been around in the wolf-ungulate system forever,” Drew said.
But the cause for the extent of the infection and the route it took into this region is uncertain.
Did the tapeworm ride south in wolves roaming over the Canadian border? Or did it arrive when wolves were transplanted into Yellowstone National Park from Canada beginning in 1995?
Transplanted wolves were dewormed, but whether the medicine was 100 percent effective is uncertain, Drew said.
“In my opinion it was brought here by the wolves that were transplanted to Yellowstone,” Foreyt said, noting that he’s not able to prove it.
The high prevalence of tapeworms found in the wolves increases the possibility that the tapeworm will spread, stirring speculation about possible transmission to humans and livestock in Montana and Idaho.
The eggs of the tapeworms enter the environment through a wolf’s feces. Ungulates such as deer and elk can ingest the eggs by feeding on vegetation next to the feces. The tapeworms hatch in the host’s gut and the embryos search out organs such as the liver and lungs where they form a golf ball- to grapefruit-sized cyst. When wolves kill an infected ungulate and eat the cyst, the cycle begins again.
Tapeworms, viruses, bacteria and diseases are common to wildlife, said veterinarian Deborah McCauley, who worked on the study for the Montana Department of Fish, Wildlife and Parks. She doesn’t believe the Echinococcus tapeworm will have any harmful effect on the state’s elk herds.
“In ungulates it doesn’t cause a significant disease,” she said.
Transmission of the tapeworm to humans or livestock is unlikely, Foreyt said.
“It’s primarily a wild ungulate, wolf or coyote cycle,” he said. “If it would occur in domestic stock I think we would have seen it already.”
A human would have to come into oral contact with a wolf’s feces to contract the tapeworm, Foreyt said.
Eating meat from an infected elk or deer does not pose a threat, Foreyt said, noting, “You could even eat the cyst and it will not infect you. You’d have to eat the eggs in the feces. You have to swallow them.”
To prevent contamination, Drew suggested that wolf hunters take normal precautions such as wearing latex gloves when dressing the animal and washing their hands before eating or smoking after handling a wolf.
“The bigger risk would be for the hunter who brings a carcass home and feeds the dog scraps, or the dog that gets into a gut pile,” he added. “That’s a vet bill waiting to happen.”
How many deer, elk, moose or mountain goats may be infected by the tapeworm in Montana or Idaho is uncertain.
“There are more deer and elk infected than people realize,” Drew said, but no study has been done.
The fact that their study was the first to document the tapeworm’s spread to Montana and Idaho excited Foreyt.
“It’s just something we haven’t seen in this area before,” he said. “I assume we’ll see it eventually in Washington and Oregon. Wherever there are wolves there are Echinococcus.”
Brett French of the Billings Gazette and Rich Landers of The Spokesman-Review contributed to this story.