- TORONTO -- A team of Canadian
researchers believes it has unravelled the mystery of how hepatitis C evades
the human immune system to cause chronic disease in about three-quarters
of the people who become infected.
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- Their discovery provides a bright ending to the personal
tragedy of the hepatitis C patient whose blood they studied, a man who
became infected through a medical error in a hospital clinic.
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- The researchers report that the virus escapes detection
because its external coat mimics immunoglobulin, one of the immune system's
warriors. Further, the virus may evolve to maintain or improve its camouflage
as time goes on, they suggest.
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- Because the immune system is set up to attack only things
it considers foreign, it does not attempt to destroy the virus.
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- "If you want to hide in a forest, it's often good
to look like a tree," explained Dr. Earl Brown, a virologist at the
University of Ottawa and senior author of the paper.
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- The team came to its conclusions by studying blood drawn
from the first infected blood donor caught by heightened screening methods
put in place after Canada's tainted blood scandal. The man was so newly
infected with hepatitis C that his immune system hadn't yet responded to
it. As a consequence, the scientists were able to chart that response over
time.
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- "We watched it (the virus) walk into the forest,"
Dr. Brown said, continuing with his metaphor.
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- The blood donor had become infected in an Alberta hospital
in the spring of 2000 while receiving intravenous antibiotics. Now living
in southeastern British Columbia, he's pleased his misfortune may help
science figure out how to foil the virus.
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- "It was such a bizarre sequence of events that I
wanted to see some good come out of it," said Randy, 47, who asked
that his surname not be made public.
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- "This might be something that could potentially
lead to a cure or a better treatment for a lot of people. And that kind
of drives you along on this," said Randy, who was cleared of infection
in 2003 after two courses of treatment with expensive anti-viral drugs.
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- However, Dr. Brown said the findings - reported in this
week's issue of the journal Virology - suggest a vaccine for hepatitis
C may be an elusive, even dangerous target that could backfire by prompting
the immune system to attack itself.
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- The team, which also involves scientists from Canadian
Blood Services and the Alberta provincial laboratory of public health,
compared the genetic codes for the virus's envelope with those of some
components of the immune system, finding areas where the virus appeared
to be mimicking the body's defenders.
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- The findings will influence future research into not
just hepatitis C but other viruses that don't provoke an extended immune
response, Dr. Brown said.
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- "It's going to change the way (scientists) think
in hepatitis C (research) for sure, and probably a bunch of other diseases.
It's impossible for it not to."
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- Others interpreted the findings more cautiously.
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- "It's an intriguing hypothesis but I think at this
point it's really only a hypothesis," said Dr. Jake Liang, chief of
the liver diseases branch of U.S. National Institute of Diabetes and Digestive
and Kidney Diseases.
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- Dr. Liang, an expert in viral hepatitis, said the study
was well done. But he and others believe the whole notion of viral "mimicry"
is overhyped.
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- "A lot of these hypotheses are based on very weak
evidence. It does have some appeal to it. Sounds good. But very few of
them have ever been proved to be causal," Dr. Laing said.
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- Dr. Mel Krajden of the British Columbia Centre for Disease
Control said he doubted the mechanism identified is the full answer to
why some hepatitis C infections become chronic.
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- "I'm sure it's more complex than just this,"
said Dr. Krajden, who heads the centre's hepatitis service.
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- It is estimated that about 240,000 Canadians are infected
with hepatitis C, which causes inflammation of the liver that can lead
to cirrhosis or liver cancer.
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- It spreads from person to person via contact with infected
blood. Shared drug paraphernalia - needles, pipes and straws - are currently
the main vehicle of transmission, though prior to changes in blood screening
methods, blood transfusions were also a key source of infection. The virus
can also be transmitted during sex with an infected person, although the
risk is low.
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- In about 20 or 25 per cent of cases, people will spontaneously
clear the virus. The remainder are chronically infected, though treatment
with anti-viral drugs appears to cure some - though not all - cases.
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