Uh-Oh...

Tests show birdflu virus is evolving as expected

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Genetic tests of samples taken from Turkish victims of the bird flu virus show it has made a small change, but probably not enough to make it more dangerous yet, researchers said on Thursday.

The mutation is one of those that would be expected in a highly changeable virus, the experts said -- and is one of those that would be predicted to eventually allow it to cause a pandemic.

H5N1 avian influenza has caused a burst of human infections in Turkey and has been found in flocks of poultry across the country. It has killed at least two children in Turkey, probably three, and infected a total of 18 people, according to Turkish authorities.

Globally it has infected just 147 people and killed 78 of them, according to the tally from the World Health Organization, which only includes four of the Turkish cases.

Samples from two of the first Turkish victims were sent to a WHO-affiliated laboratory in Britain for analysis. Scientists are carefully watching the virus to see if it makes the changes needed to allow it to easily pass from human to human -- which could spark a pandemic that could kill millions.

There were two different strains of virus in the bodies of the teenage victims, said Dr. Ruben Donis, team leader of the molecular genetics team of the U.S. Centers for Disease Control and Prevention's Influenza branch.

"One was a regular virus like we have seen in poultry in Turkey before -- no surprises there," Donis said in a telephone interview.

But half the viruses had a mutation in the a protein called hemagglutinin, which influenza viruses use to attach to the cells they infect. This protein is the "H" in a flu virus's designation.

EXPANDING ITS RANGE

This mutation has been found in the past to allow the virus to infect a greater range of cells via a structure known as sialic acid, Donis said.

"If you have this mutation, you have virus that can bind to more different sialic acid variations," he said.

This is only theoretical, Donis stressed. But when researchers have tested flu viruses in the lab, they found this particular mutation gave the virus a better ability to attach to human-like cells.

A spokeswoman at the World Health Organization said there was no evidence the mutation had much significance in making the virus either more transmissible to people, or more or less dangerous to them.

"It doesn't look as if it has significance regarding transmissibility or pathogenicity because it is not borne out by epidemiological evidence we have so far," WHO spokeswoman Maria Cheng said in Geneva.

Donis said similar mutations have been seen in H5N1, in Hong Kong in 2003, when it first re-emerged in people, and later in Vietnam.

"If this was a wildfire mutation that would have caused the virus to spread like wildfire in a population, we would have seen it more often," he said.

The H5N1 virus remains largely a virus that affects birds. But all influenza viruses mutate and evolve very easily, and regularly change into what are known as pandemic strains, which spread rapidly around the world, infecting and killing unusually large numbers of people.

There has not been a flu pandemic since 1968 and health experts feel the world is overdue.

The H5N1 virus, they say, resembles the H1N1 virus that apparently jumped from birds to humans in 1918, causing an especially deadly pandemic before the virus evolved into a less dangerous form and the human population built up an immunity to it.

Copyright © 2006 Reuters Limited.