- From ProMED-mail Source The Statesman Journal
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- For a 3rd straight year, an outbreak of an incurable
disease has forced officials for the Oregon Department of Fish and Wildlife
to destroy rainbow trout being raised at Leaburg Hatchery.
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- Hatchery workers on Wednesday were ordered to kill about
50 000 trout being held at the state hatchery on the McKenzie River off
Highway 126 east of Eugene.
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- As with similar outbreaks in 2002 and 2003, the culprit
is exposure, or infection, of the rainbow trout with infectious hematopoietic
necrosis, commonly known as IHN. In September 2002, almost a quarter-million
trout were destroyed at Leaburg. In October 2003, 33 000 rainbows were
euthanized.
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- IHN is a naturally occurring virus that is endemic throughout
Oregon, Washington and Northern California. It initially attacks the blood-forming
tissues of the kidney. Younger fish suffer the effects of the disease.
External symptoms of the virus include lethargy, darkening of the skin
and bleeding at the base of the fins. According to biologists, adult fish
carry -- and shed -- the virus into the water, but don't die from the disease.
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- In 2002, biologists said that IHN got into the hatchery
from adult steelhead shedding the virus into the water upriver from the
hatchery water in-takes on the McKenzie as a result of a large run of steelhead
and low seasonal flows on the river.
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- Officials at the hatchery said that trout that test non-infected
at the hatchery will be released ahead of schedule -- and at smaller-than-planned-size
-- to prevent them from also contracting the infection.
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- Officials said that the killing of the fish is in line
with Fish and Wildlife's Fish Health Management Policy. The policy lists
procedures and approaches to reduce disease agents and fish losses in the
state.
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- The trout being euthanized have been raised in a pond
where fish were diagnosed in mid-June 2004 with the virus.
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- Past experience -- such as the 2002 outbreak at Leaburg
-- shows that hatchery fish losses can escalate dramatically from this
disease, which has no known treatment. Officials said that hatchery staff,
fish pathologists and other Fish and Wildlife staff members are working
toward a solutions to prevent future outbreaks at the hatchery. Those include
cleaning the ponds where the fish are raised, and trying to prevent the
virus from getting back into the hatchery via the water source.
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- The trout had been scheduled for planting throughout
the Willamette Valley during the fall. Officials said they will evaluate
the impact of the fish losses on trout stocking plans.
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- The rainbow trout are being killed with the chemical
MS-222 (tricaine methane sulfonate). It is in the novocaine family of drugs
and has been approved by the American Veterinary Medical Association panel
on euthanasia as an acceptable and humane way of killing fish that will
not be eaten by people. The fish will be frozen and sent to a landfill
to contain the spread of the disease.
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- Fish pathologists will continue to sample and monitor
the remaining fish at the hatchery.
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- Officials said that if IHN infects more trout, additional
steps will be taken to contain the disease.
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- The hatchery's operations are paid for by the U.S. Army
Corps of Engineers.
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- http://news.statesmanjournal.com/article.cfm?i=82555
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- ProMED-mail promed@promedmail.org
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- This is sad news, as last year it was hoped that the
disease had been eliminated from the hatchery. - Mod.TG
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- Patricia A. Doyle, PhD Please visit my "Emerging
Diseases" message board at: http://www.clickitnews.com/ubbthreads/postlist.
php?Cat=&Board=emergingdiseases Zhan le Devlesa tai sastimasa Go with
God and in Good Health
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