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Scientists Reveal Key Protein in H5N1 Bird Flu Virus

Posted on: Friday, 17 March 2006, 09:00 CST

Scientists reveal key protein in H5N1 bird flu virus

LOS ANGELES, March 16 (Xinhua) -- The structure of a key protein of the H5N1 avian influenza virus reveals that certain mutations could ease the deadly virus' spread among people, U.S. scientists reported on Thursday.

In a study published in the March 16 online edition of the journal Science, the researchers led by Ian Wilson at the Scripps Research Institute said they have determined the structure of the hemagglutinin protein.

Hemagglutinin protein, which allows the virus to enter host cells, is the principal antigen on the flu viral surface.

The researchers imaged and analyzed the protein with glycan microarray, after isolating a H5N1 virus sample from a Vietnamese boy who died from the flu in 2004.

The hemagglutinin protein latches on to different cell receptors in avian and human-type flu, which may explain why most bird flu viruses do not spread between humans, according to the researchers.

By now, only three avian influenza viruses have caused pandemics in humans, including the H1N1, the H2N2 and H3N2 strains.

The three viruses aroused flu pandemics in year 1918, 1957 and 1968, respectively, after hemagglutinin of these viruses have become adapted to the human population.

The researchers said both the H2N2 and H3N2 pandemic viruses were avian-human re-assortments, in which some avian gene segments were re-assorted into an already circulating, human-adapted virus.

And the third virus, the H1N1 strain that caused the 1918 Spanish Flu pandemic killing about 50 million worldwide, may have experienced some mutations before jumping from birds to humans.

Although hemagglutinin of the H5N1 virus looked very similar to the H1N1 virus, these mutations do not cause the bird flu virus to prefer human receptor, the researchers found.

"Our conclusion is that the mutations that cause a shift from the avian type to human type specificity on the H1 and H3 frameworks do not cause an equivalent shift in specificity on the H5 framework," the wrote in the Science paper.

However, the researchers noted that some of these mutations may make the H5N1 virus hemagglutinin more likely to bind to human lung epithelial cells, providing a possible "foothold" for the virus in the human population.

"Thus, such mutations provide one possible route by which H5 viruses could gain a foothold into the human population," they said.

With continued outbreaks of the H5N1 virus in poultry and wild birds, further human cases are likely. The potential for the emergence of a human-adapted H5 virus, either by re-assortment or mutation, is a threat to public health worldwide, the researchers said.

Source: Xinhua News Agency - CEIS

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