Monday, October 22, 2007

The Final Mutation H5N1 Needs To Become Pandemic Ready

Researcher : The Public "Cannot Do Very Much" To Stop The Pandemic

Some more detail from the research released in early October that claimed to have identified the "key mutation" the H5N1 virus needs to undergo so that it could then "more easily infect and spread among humans".

The key to H5N1 turning into a pandemic ready virus is when it is able to infuse itself into cells in the upper respiratory tract, rather than in just the lungs. The closer the virus can form to the mouth, the more likely it is that it can be passed through close contact amongst people, or become airborne on droplets.


The mutation consists of a single amino acid change...

The change promotes better viral replication at the lower temperatures found in the upper airways of mammals, the press release said. Once the H5N1 virus is established in the upper respiratory tract, infected patients can more easily spread the disease to others through coughing and sneezing, making the infection more contagious.

The authors write that the hemagglutinin protein's specificity for avian- or human-type receptors on airway cells is thought to be a major factor governing the efficient transmission of H5N1 viruses. Yet the disease still doesn't spread easily among humans, though scientists have isolated from humans some H5N1 viruses that had specificity for human receptors.

Kawaoka said in the UW-Madison press release that the H5N1 viruses circulating now are more "mammalian-like" than the ones that circulated in 1997, when the first human infections were identified.

"The viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus," he said.

However, the researchers say in their report that additional genetic changes are probably needed to equip the H5N1 virus with full pandemic potential. "Indeed, multiple amino acid changes have been identified in the so-called Spanish influenza virus, which is thought to be derived from an avian antecedent," they write.

Kawaoka and his team believe it's only a matter of time before the H5N1 virus evolves into a strain that's capable of launching a pandemic, the UW-Madison release says.

"I don't like to scare the public, because they cannot do very much," Kawaoka was quoted as saying in a Reuters news report today. "But at the same time it is important to the scientific community to understand what is happening."

"The billion-dollar question is how many more changes are required and will H5N1 ever achieve this," he said. "We must plan as if it will."

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