Canadian scientists may have found why hepatitis C triggers chronic infection
URL of this page: http://www.nlm.nih.gov/medlineplus/news/fullstory_23117.html
(*this news item will not be available after 03/23/2005)




Canadian Press

Monday, February 21, 2005




TORONTO (CP) - 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.

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.

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.

Because the immune system is set up to attack only things it considers foreign,
it does not attempt to destroy the virus.

"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.

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.

"We watched it (the virus) walk into the forest," Brown said, continuing with
his metaphor.

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.

"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.

"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.

However, 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.

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.

The findings will influence future research into not just hepatitis C but other
viruses that don't provoke an extended immune response, Brown said.

"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."

Others interpreted the findings more cautiously.

"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.

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.

"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," Liang said.

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.

"I'm sure it's more complex than just this," said Krajden, who heads the
centre's hepatitis service.

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.

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.

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.




© The Canadian Press, 2005




Sandra Tara Balduf (Ane)

Frontline Hepatitis Awareness

Support for patients and educational materials

http://frontline-hepatitis-awareness.com

1-866-Hep-GoGo 866-437-4646




[Non-text portions of this message have been removed]