'New bird flu strain adapting to humans'

A genetic analysis of the bird flu virus responsible for at least 11 human deaths in China shows the virus is evolving to adapt to human cells, raising concerns of a global flu pandemic, researchers say.
The study by Masato Tashiro of the Influenza Virus Research Center, National Institute of Infectious Diseases, and Yoshihiro Kawaoka of The University of Wisconsin-Madison and the University of Tokyo examined the genetic sequences of H7N9 isolates from four of the pathogen's human victims as well as samples derived from birds and the environs of a Shanghai market.
"The human isolates, but not the avian and environmental ones, have a protein mutation that allows for efficient growth in human cells and that also allows them to grow at a temperature that corresponds to the upper respiratory tract of humans, which is lower than you find in birds," said Kawaoka, a leading expert on avian influenza.

The findings, drawn from genetic sequences deposited by Chinese researchers into an international database, provide some of the first molecular clues about a worrisome new strain of bird flu, the first human cases of which were reported by the Chinese Center for Disease Control and Prevention.
Although it is too early to predict the virus's potential to cause a pandemic, signs that the H7N9 virus is adapting to mammalian and, in particular, human hosts are unmistakable, said Kawaoka.
Access to the genetic information in the viruses is necessary for understanding how the virus is evolving and for developing a candidate vaccine to prevent infection, he added.

Avian influenza rarely infects humans, but can sometimes adapt to people, posing a significant risk to human health.

"These viruses possess several characteristic features of mammalian influenza viruses, which likely contribute to their ability to infect humans and raise concerns regarding their pandemic potential," Kawaoka and his colleagues concluded in a report published in the journal Eurosurveillance.
Kawaoka explained that the majority of the viruses in the study - from both humans and birds - display mutations in the surface protein hemagglutinin, which the pathogen uses to bind to host cells.
Those mutations, according to Kawaoka, allowed them to easily infect human cells.

In addition, the isolates from patients contained another mutation that allows the virus to efficiently replicate inside human cells.
The same mutation, Kawaoka noted, lets the avian virus thrive in the cooler temperatures of the human upper respiratory system. It is in the cells of the nose and throat that flu typically gains a hold in a mammalian or human host.