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New Strain of Deadly Bird Flu Seen Adapting to Mammals, Humans

Experts voice concern about possible pandemic (Apr. 12)

A genetic analysis of the avian flu virus responsible for at least 14 human deaths in China portrays a virus evolving to adapt to human cells, raising concern about its potential to spark a new global flu pandemic.

The collaborative study, led by experts at the National Institute of Infectious Diseases in Japan and at the University of Wisconsin–Madison in the U.S., was published in the journal Eurosurveillance. The group 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 study co-author Dr. Yoshihiro Kawaoka, a leading expert on avian influenza.

Influenza virus depends on its ability to attach to and “commandeer” the living cells of its host to replicate and spread efficiently. Avian influenza rarely infects humans but can sometimes adapt to people, posing a significant risk to human health.

Kawaoka explained that most of the viruses in the study — from both humans and birds — displayed 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, isolates from infected patients contained another mutation that allows the virus to replicate efficiently inside human cells. The same mutation, Kawaoka noted, lets the avian virus thrive in the cooler temperatures of the human upper respiratory system. Flu virus typically gains a hold in the cells of the nose and throat in a mammalian or human host.

Kawaoka and his colleagues also assessed the response of the new avian strain to drugs used to treat influenza. They discovered that one class of commonly used antiviral drugs — ion channel inhibitors — would be ineffective. However, the new strain could be treated with another clinically relevant antiviral drug, oseltamivir, they suggest.

Sources: University of Wisconsin–Madison; April 12, 2013; and Eurosurveillance; April 11, 2013.

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