In a wide analysis on the genome sequences of different virus strains, scientists have found a unique protein responsible for the high mortality of the ongoing H5N1 bird flu outbreak in Asia and Europe.
The protein works within the infected cells and disrupts key cellular processes, virologists at the St. Jude Children's Research Hospital in Memphis, Tennessee, reported on Thursday.
Their findings were published in the Jan. 26 online edition of the journal Science.
The analysis includes 2,196 bird flu genes and 169 complete genomes culled from various wild bird samples. The researchers combined the genetic data from their sequencing efforts with additional avian, swine, and human influenza sequencing data.
They also applied a new technique called prototyping to the sequence data to identify unique gene variants that may be overlooked in traditional evolutionary trees. This approach enabled them to find key proteins in flu virus evolution.
As to the deadly H5N1 virus, the researchers found, a special protein called NS1 may allow the virus to latch on to and disrupt the activity of certain proteins in its human hosts.
When acting in combination with other avian flu proteins, "NS1 may be very important for the virulence of avian flu viruses when they are introduced into humans," said Clayton Naeve, senior author of the paper.
The NS1 protein in the H5N1 virus has a "bird" origin, while the NS1 proteins in other recent low-mortality flu outbreaks in 1957 and 1968 contain a "human" source that appears to be less capable of interacting with host proteins, the researchers said.
"The recent H5, H7 and H9 outbreaks in Asia were caused by viruses in which the entire complement of influenza genes, including NS, were derived from an avian source," they wrote in the Science paper.
"We propose that the introduction of avian NS1 into human cells can potentially disrupt many cell pathways...while the human NS1 does not."
"Disruption of these pathways at the cellular level may well contribute to the higher mortality rates reported for the recent outbreaks compared to those seen in previous pandemics; though it is clear multiple genes and gene products are involved," said the researchers.
They also suggested that the protein may become a key target for future anti-flu drugs.
"This finding reveals an entirely new means by which avian influenza virus may interact with host cell proteins and these proteins may prove valuable as targets for antiviral therapy," the paper said.
The H5N1 virus has been found in birds for decades but in 1997 it was found to infect people. Since 2003, the virus has infected at least 152 people in Asia and Europe, and killed 83 of them, according to the World Health Organization(WHO).
By now the H5N1 virus has only spread from birds to humans, but scientists warned it could cause a global flu pandemic after acquiring the ability to pass from person to person.