- (ENN) -- A virus believed responsible
for cancerous tumors in Atlantic salmon has been identified by a team
of federal and university researchers.
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- The virus, salmon swimbladder sarcoma,
is not believed to be a human health hazard but could be devastating for
Atlantic salmon populations, according to researchers at Cornell University
College of Veterinary Medicine.
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- The virus is believed responsible for
tumors that killed breeding-stock Atlantic salmon in the U.S. Fish and
Wildlife Service hatchery in North Attleboro, Mass. In the past the disease
was found in commercial aquaculture where salmon were grown in off-shore
pens.
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- A cancer with similar symptoms was reported
in some farm-raised Atlantic salmon in Scotland in 1978, before modern
genetic testing methods were available. At the time, Scottish scientists
reported seeing "virus-like particles" during microscopic examination
of the salmon tumors. To date this disease has not been seen in any commercially
raised Atlantic salmon in the United States.
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- "We don't yet know how this virus
is actually transmitted from one fish to another," said James W. Casey,
a Cornell professor of veterinary microbiology and immunology. "This
could occur through so-called vertical transmission in reproductive products,
the eggs and sperm of breeding salmon; or perhaps through horizontal transmission,
with the virus entering the bodies through the skin or gills, in water
they ingest or on food they eat. Our concern is that the virus is in the
environment, and the levels of infection need to be determined."
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- The virus is not a health hazard to humans,
said to Paul R. Bowser, the Cornell fish pathologist. "There is absolutely
no evidence that this virus is a human pathogen. But infection is a real
problem for the Atlantic salmon. Although tumors are fatal, it appears
that viral infection alone reduces their vitality and reproductive success."
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- The virus causes a slow-growing cancer
that can take two years to produce a noticeable tumor on swim-bladders,
said Bowser. By the time the swimbladder tumor is detectable, from a bulging
in the side of the fish, the salmon are near death. An earlier sign of
swimbladder sarcoma might be blood hemorrhaging from the fins.
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- Salmon swimbladder sarcoma is classified
as a retrovirus, Casey says, because it contains hallmark sequence similarities
to other members of this group. There are many well-studied retroviruses
that cause cancers in chickens, mice, cats and humans, but salmon swimbladder
sarcoma is the first retrovirus of salmon that has been identified.
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- "As natural habitats decline and
investigators more intensively monitor aquatic animal health, additional
tumors like these will be found," said Casey.
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- After their successful identification
of the virus, the Cornell scientists hope to develop a rapid diagnostic
test for the virus. If routinely utilized at the salmon breeding facilities,
such a test could help eliminate infected fish before the disease is transmitted
to others, the Cornell scientists predict.
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- "In the long term, this fish disease
will be an excellent model to study the process of tumorogenesis and provide
information relevant to the prevention of all cancers, whether human or
animal," said Casey.
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