Protein Change Could Make Bird Flu Deadlier

Scientists have just identified the key change needed to make it easier for the bird flu to spread from person to person, according to news from the University of Wisconsin-Madison (UW-Madison).

While the avian flu virus, known as H5N1, has been highly dangerous to humans who have contracted it, it hasn't yet evolved into a strain that can be easily transmitted from person to person. Of the 250-plus people worldwide who have been infected with the bird flu -- more than 150 of whom have died -- most became ill after being exposed to birds carrying the H5N1 virus, rather than to other people who were sickened.

However, medical researchers studying the virus have long believed the virus could eventually mutate into a form that would make it easier for the disease to spread by person-to-person contact.

A team of scientists at the UW-Madison this month reported finding that a single change to a protein in the H5N1 virus makes it easier for the virus to infect cells in the upper respiratory systems of mammals. Up until now, the virus has sickened people and other mammals mostly by infecting cells in the lower respiratory system, where receptors better enable the virus to establish itself. Temperatures also tend to be warmer in the lower part of the mammalian respiratory system, providing a better breeding ground for the bird flu bug.

But the virus recently shows signs of becoming more effective in targeting mammals, the UW-Madison researchers found.

"The viruses that are in circulation now are much more mammalian-like than the ones circulating in 1997," said Yoshihiro Kawaoka, an international authority on influenza and a faculty member of the UW-Madison School of Veterinary Medicine. "The viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus."

While the protein change Kawaoka and his team identified isn't enough to change the H5N1 virus into an agent capable of creating a worldwide pandemic, it "may provide a platform for the adaptation of avian H5N1 viruses to humans and for efficient person-to-person virus transmission," they found. In other words, the change would allow the virus to be more easily spread among humans by coughing and sneezing.

"This change is needed, but not sufficient," Kawaoka said. "There are other viral factors needed to cause a viral pandemic."

Still, scientists believe it's only a matter of time before such a deadly strain of bird flu evolves.

Flu viruses in the past have occasionally mutated into deadly forms that spread quickly through human populations. The last major pandemic, involving the Spanish flu, killed at least 30 million people around the world in 1918.

Kawaoka's team's findings were published in the most recent edition of the journal, "Public Library of Science Pathogens." Other members of the research team include Masato Hatta, Yasuko Hatta, Jin Hyun Kim, Shinji Watanabe from UW-Madison; Kyoko Shinya of Japan's Tottori University; Tung Nguyen of the Vietnamese National Centre for Veterinary Diagnostics; Phuong Song Lien of the Vietnam Veterinary Association; and Quynh Mai Le of the Vietnamese National Institute of Hygiene and Epidemiology.

The team's research was funded by grants from the U.S. National Institutes of Health and the Japan Science and Technology Agency.

University of Wisconsin-Madison, "Researchers Identify Key Step Bird Flu Virus Takes to Spread Readily in Humans." URL: (http://www.news.wisc.edu/14262)