( in turn contain terminal sialic acids. ...)Minor mutations in avian flu virus increase chances of human infection

in turn contain terminal sialic acids. Avian viruses prefer binding to ?2-3-linked sialic acids on receptors of intestinal epithelial cells, while human viruses are usually specific for the ?2-6 linkage on epithelial cells of the lungs and upper respiratory tract. Such interactions allow the virus membrane to fuse with the membrane of the host cell so that viral genetic material can be transferred to the cell.

The switch from ?2-3 to ?2-6 receptor specificity is a critical step in the adaptation of avian viruses to a human host and appears to be one of the reasons why most avian influenza viruses, including current avian H5 strains, are not easily transmitted from human-to-human following avian-to-human infection. However, the report did suggest that "once a foothold in a new host species is made, the virus HA can optimize its specificity to the new host."

"Our recombinant approach to the structural analysis of the Viet04 virus showed that when we inserted HA mutations that had already been shown to shift receptor preference in H3 HAs to the human respiratory tract, the mutations increased receptor preference of the Viet04 HA towards specific human glycans that could serve as receptors on lung epithelial cells," Wilson said. "The effect of these mutations on the Viet04 HA increases the likelihood of binding to and infection of susceptible epithelial cells."

The study was careful to note that these results reveal only one possible route for virus adaptation. The study concluded that other, as yet "unidentified mutations" could emerge, allowing the avian virus to switch receptor specificity and make the jump to human-to-human transmission.

The glycan microarray technology, which was used to identify the mutations which could enable adaptation of H5N1 into the human population in the laboratory, could also be used to help identify new active virus strains in the field by monitoring changes in the receptor binding preference profile wh
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Source:Scripps Research Institute

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