Could New Flu Spark Global Flu Pandemic? New Bird Flu Strain Seen Adapting to Mammals, Humans

A study conducted by a group led 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 have conducted a genetic analysis of the avian flu virus and have found that the virus is evolving to adapt to human cells, which is raising concern about its potential to trigger a new global flu pandemic. The researchers have examined the genetic sequences of H7N9 isolates from four human victims and from samples derived from birds as well as the environs of a Shanghai market. The first human cases were reported on March 31 by the Chinese Center for Disease Control and Prevention. The new virus has sickened at least 33 people, killing nine. There are definite signs that the virus is adapting to mammalian and more specifically, human hosts.

"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," says Kawaoka, a leading expert on avian influenza.

 The Influenza virus depends on its ability to attach to and hijack the living cells of its host to replicate and spread. Avian influenza rarely infects humans, but can sometimes adapt to people. Kawaoka explains that a majority of the viruses in the study, both from humans and birds, shows mutations in the surface protein hemagglutinin, which the pathogen uses to bind to host cells. Those mutations are what allow them to easily infect human cells. Samples from patients also contained another mutation that allows the virus to efficiently replicate inside human cells. This same mutation is what allows the avian virus to thrive in cooler temperatures, the human upper respiratory system.

Genetic information in the viruses is necessary for understanding how the virus is evolving and for developing a vaccine to prevent infection. Kawaoka evaluated the response of the new strain of the virus to drugs used to treat influenza. He discovered that one class of commonly used antiviral drugs, ion channel inhibitors, were not effective. The ion channel inhibitors work by effectively bottling up the virus in the cell. Although this has been found, the new strain can be treated with another clinically relevant antiviral drug, oseltamivir.

http://www.sciencedaily.com/releases/2013/04/130412192402.htm