Avian Influenza Virus Genome Contains Mutations Favorable for Growth in Humans

A collaborative study conducted by researchers in the United States and Japan analyzed isolates of the A(H7N9) avian influenza virus taken from Chinese patients and from samples derived from birds and the environment in the area of Shanghai.

As of April 20, 2013, there had been a total of 96 laboratory-confirmed cases of human infection with the avian influenza A(H7N9) virus in China, and 18 of the patients had died.

Investigators from the University of Wisconsin (Madison, USA) and the University of Tokyo (Japan) analyzed the genetic sequences of H7N9 isolates from four human flu patients as well as samples derived from birds and the environs of a Shanghai market.

They reported in the April 12, 2013, online edition of the journal Eurosurveillance that while the hemagglutinin (HA) and neuraminidase genes probably originated from Eurasian avian influenza viruses, the remaining genes were closely related to avian H9N2 influenza viruses. Several characteristic amino acid changes in HA and the PB2 RNA polymerase subunit probably facilitated binding to human-type receptors and efficient replication in mammals, respectively, highlighting the pandemic potential of the novel A(H7N9) viruses.

"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 contributing author Dr. Yoshihiro Kawaoka, professor of virology at the University of Wisconsin. "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. Although it is too early to predict its potential to cause a pandemic, signs that the virus is adapting to mammalian and, in particular, human hosts are unmistakable."

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