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," Dr. 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, 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.
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, Dr. 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.
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.
"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.
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 Dr. 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.
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