Bird flu virus could mutate to human form

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CAMBRIDGE, England, June 21 (UPI) -- Avian H5N1 influenza viruses could evolve in nature to become a human-to-human airborne transmissible virus, British researchers say.

Avian H5N1, also known as bird flu, can be transmitted from birds to humans but not from human to human, but researchers say it could become airborne transmissible between mammals, and thus potentially among humans, with as few as five mutations, Cambridge University researchers reported.

Until now, it was not known whether the mutations might evolve in nature, but scientist discovered two of the five mutations seen in experimental viruses in laboratories had occurred in numerous existing avian flu strains.

"Viruses that have two of these mutations are already common in birds, meaning that there are viruses that might have to acquire only three additional mutations in a human to become airborne transmissible," Cambridge researcher Colin Russell said. "The next key question is 'is three a lot, or a little?'"

The scientists used a mathematical model of how viruses replicate and evolve within a mammalian host to determine whether the remaining three mutations could evolve in a single host or in a short chain of transmission between hosts.

"With the information we have, it is impossible to say what the exact risk is of the virus becoming airborne transmissible among humans," Derek Smith, a Cambridge professor of infectious diseases said. "However, the results suggest that the remaining three mutations could evolve in a single human host, making a virus evolving in nature a potentially serious threat."