Oregon fish facing tapeworm epidemic


Mar 11, 2001
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Oregon fish facing tapeworm epidemic

Published: September 30, 2001

By John Cramer The Bend Bulletin

Two parasitic tapeworms, including a giant one that can eat its host alive, have been discovered for the first time in some fish and birds in the Deschutes and Crooked river basins.

The tapeworms appear to be emerging as new diseases in Central Oregon and could spread to gamefish and other wildlife, said Barbara Shields, an assistant professor of fisheries science with Oregon State University’s department of fisheries and wildlife.

Scientists also are examining whether the tapeworms could infect people.

Besides their unprecedented appearance in Central Oregon, the tapeworms are exhibiting behavior that has researchers puzzled.

The giant tapeworm, Ligulus intestinalis, has spread to two kinds of fish in which it has never been found before, an indication that it could jump to even more new hosts, Shields said. One of the Ligulus tapeworms was nearly 3.5 feet long and may be the longest such parasite ever discovered in North America.

The other new tapeworm, Schistocephalus solidus, usually infests one fish at a time, but up to 12 of the tapeworms are being found in each infected fish in Central Oregon.

In the last few years, the tapeworms have been found in Mirror Pond in downtown Bend, in irrigation canals between Bend and Madras and in the region’s reservoirs and other waterways, including Lake Billy Chinook. The tapeworms have not been found outside those areas in Oregon.

Researchers are unsure how the tapeworms came to Central Oregon, but they may have hitched a ride inside a migratory bird from Eurasia, a goldfish dumped by a local resident or another host.

The risk of residents contracting the parasites is remote, although similar types of tapeworms have invaded humans in other parts of the world.

“I don’t think it’s a significant risk,” Shields said. “I don’t want anyone to dismiss it, but I also don’t want to incite panic.”

Shields, whose research focuses on how humans alter a region’s aquatic system and the organisms living in them, said many people worry about contracting tapeworms and other parasites.

“I get a lot of calls from the public asking whether they should stop” eating fish and swimming in local waters.”

“I tell them not to worry.”

It’s not known for the tapeworms to infect people, she said, “but we want to examine the relative risk to fish, wildlife and and people, and how to control it without negatively impacting fishermen.”

Shields recommended researchers determine how the tapeworms may affect the region’s food chain and how to reduce their populations and the risk of them spreading to other watersheds, wildlife and people.

“Many species of fish have been introduced that have potentially negative impacts,” she said. “Although managers today make every attempt to assure that fish stocks are disease-free, little thought has been given to how introduced fishes affect local food webs” and alter native diseases and parasites.

The Schistocephalus tapeworm likely arrived in Central Oregon when its host fish, the three spined stickleback, was introduced into the Deschutes basin.

The Ligulus tapeworm has been found in three species of fish — the chiselmouth, the northern pike minnow and the bridgelip sucker — in the lower Crooked River. It is the first time the Ligulus has been found in the chiselmouth and bridgelip sucker.

Shields said the Ligula’s jump to new hosts was a “red flag” for possibly infesting other species, including salmon, trout and other gamefish.

Phil Hager, president of Central Oregon Flyfishers, said the tapeworms could cause severe ecological and economic damage in the region if they jump to gamefish, which are important to local fishermen and restaurants.

“We don’t know very much about it, but we’re very concerned,” he said. “The thought of a tapeworm with no natural enemies in our waters, it can literally explode.”

Hager said the discovery of the tapeworms illustrates why Oregon prohibits live bait, which may carry parasites that jump to native species.

As part of a public education effort, the Central Oregon Flyfishers and other groups teach school children about the fragility of ecosystems and the danger of exotic invaders.

A prominent example of a nonnative species affecting a Central Oregon waterway is the tui chub’s impact on Diamond Lake, where the tiny fish have been a problem since fishermen used them illegally as bait in the 1950s.

The lake recently was closed because of toxic algae that bloomed because the chub are devouring the plankton that control the algae. The plankton, in turn, provide food for insects, which are eaten by trout, which are eaten by bald eagles and osprey.

“Now if a tapeworm threat is brought in on a fish that’s put into local waters, look down the road at the potential ecological effect,” Hager said.

Like all parasites, the tapeworms’ life cycle depends on other creatures for nourishment, protection and transportation.

The Schistocephalus and Ligulus tapeworms spend their lives as eggs, larvae and adults in three hosts — tiny crustaceans, fish and birds, which pass on the tapeworms in their various stages of life.

Scientists from OSU and the Oregon Department of Fish and Wildlife are conducting genetic studies, but Shield’s research is on hold pending approval of several state, federal and private grant applications.

The studies includes examining fish and birds at Crane Prairie, Wickiup, Haystack and other reservoirs, and posting educational displays to keep the public informed about the studies’ findings.

The tapeworm research is part of ongoing studies by state, federal and university scientists examining the impact of non-natives species on native fish, vegetation and wildlife.

In Europe and Asia, the adult Ligula tapeworm sometimes bursts out of the fish’s belly, killing the fish, but some Lake Billy Chinook suckers have lesions suggesting they survived such trauma.

The Ligula was discovered in Central Oregon in 1999 when two OSU researchers were snorkeling in Lake Billy Chinook and saw a sucker fish with a large tapeworm crawling out of an abscess in the fish’s side.

“It was very dramatic,” Shields said.

OSU researchers later found that 98 percent of sucker fish tested in Haystack Reservoir were infected by the Schistocephalus tapeworm. The rate of infection and the number of worms in each fish were unusually large.

“It was horrific to see, but the fish pathologists were very excited,” Shields said.

The Ligulus and Schistocephalus tapeworms infect different types of fish and birds in many parts of the world. The worms sometimes have little impact on the fish, but at other times they cause massive fish kills.

In Asia, the tapeworms cause fish to alter their behavior, such as wiggling in shallow water to make themselves more enticing to hungry birds, thus ensuring the tapeworms’ life cycle goes on.

Shields said scientists have not examined the Central Oregon tapeworms’ potential impact on wildlife that eats infected fish, such as great blue herons and otters.

Another possibility, she said, is the tapeworms infecting people who accidentally swallow water containing the microscopic tapeworm eggs.

In such cases, the parasite burrows out of the person’s stomach because it is inside the wrong host species — a human instead of a fish, bird or crustacean.

Shields herself once contracted a related species of tapeworm.

“I found these things growing on my skin and I thought, ‘My God, what is this, cancer?’ “ she said. “What happens is it crawls through your body, it dies and you get scar tissue, but it could keep growing and wander into your eye or brain or spinal cord, but that’s rare.

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