Why Avian Flu Is So
Lethal To Humans
By Sharon Kirkey
The Ottawa Citizen
The bird flu virus that has raised the spectre of a new flu pandemic causes 10 times as much inflammation in human lung cells as regular flu, according to new research.
The finding could explain why H5N1 avian influenza is so adept at causing fatal pneumonia and respiratory distress in people.
"This is the sort of thing you don't want a human (influenza) strain to have," says University of Ottawa virologist Earl Brown.
Scientists from the University of Hong Kong, working with researchers in Vietnam, looked at the amounts of a group of proteins called cytokines in human lung cells infected with the H5N1 bird flu virus, which has infected at least 125 people so far in Southeast Asia, killing 64 of them.
When a virus or bacterium invades the body, the immune cells kick out inflammatory chemicals called cytokines. But if the immune system is over-stimulated, it can unleash a "cytokine storm," causing massive damage to tissues.
The researchers compared the levels of cytokines produced by strains of the H5N1 bird flu that circulated in Hong Kong in 1997, and in Vietnam in 2004, with a human flu virus.
Twenty-four hours after infection with H5N1, the human lung cells contained 10 times the levels of the inflammatory proteins as lung cells infected with a regular flu.
"This tells you what people (infected with bird flu) are dying from," Mr. Brown said. "It's the same thing people died from with SARS, this cytokine storm."
Finding a way to dampen down the immune response could reduce the risk of life-threatening pneumonia and acute respiratory distress in people infected with H5N1.
The research, published today in the journal Respiratory Research, comes as Vietnam confirmed a 35-year-old man from Hanoi who was hospitalized on Oct. 26 died three days later of H5N1 avian flu. It was Vietnam's first confirmed case since late July. Since mid-December 2004, the country, which is seeing new outbreaks of bird flu in poultry, has reported 65 human cases, of which 22 were fatal.
Earlier this week, Indonesia confirmed two more cases of human infection with H5N1 -- a 19-year-old woman from Tangerang, near Jakarta, who died Oct. 28, and her eight-year-old brother, who was in hospital.
According to an update posted on the World Health Organization website, investigators on the ground found signs of sick and dying chickens in the area where the boy lived.
Meanwhile, the Canadian Food Inspection Agency said yesterday it is still not known what type of bird flu strain has infected wild migratory ducks in Quebec and Manitoba. Preliminary results found the birds were infected with the H5 subtype. Officials are still awaiting tests to determine the "N" type of the virus.
The birds -- 28 in Quebec and five in Manitoba -- were healthy and there is no evidence of flu-related sickness among domestic or wild birds in the areas where they were found.
Flu pandemics result when a bird and human flu mix genes, or when bird flu adapts on its own to spread efficiently from humans to humans.
Understanding what makes H5N1 bird flu so dangerous to people "will lead to new strategies for managing human H5N1 disease and enhance our preparedness to confront pandemic influenza, whether from H5N1 or other influenza A subtypes," the researchers write in Respiratory Research.
© The Ottawa Citizen 2005




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