Scientists Move Closer to Understanding Flu Virus Evolution

By Jason Gale

Aug. 28 (Bloomberg) -- Scientists tracking bird flu moved closer to understanding the evolution of the viruses and the genes that make them more infectious to people in a new study.

About 52 key genetic changes distinguish avian influenza strains from those that spread easily among people, according to researchers in Taiwan, who analyzed the genes of more than 400 A- type flu viruses. The analysis will help scientists trace the mechanism for infection and how the viruses replicate in different species, according to a report appearing in the September edition of Emerging Infectious Diseases.

Interest in influenza viruses has been bolstered by the spread of the H5N1 avian flu strain, which has infected at least 241 people in 10 countries during the past three years, killing 141 of them. The virus may kill millions if it changes into a pandemic form that can be passed from human to human.

``How many mutations would make an avian virus capable of infecting humans efficiently, or how many mutations would render an influenza virus a pandemic strain, is difficult to predict,'' wrote Guang-Wu Chen and colleagues at Taiwan's Chang Gung University.

The researchers analyzed the gene sequences of 306 human and 95 avian influenza viruses to molecularly identify the host species. The data was crosschecked with 15,785 more sequences from the National Center for Biotechnology Information.

Spanish Flu

``It is the type of work that everyone has thought of doing, but no one has had the time to do,'' Ron Fouchier, a virologist at the Erasmus University in Rotterdam, said in an e-mail today. ``The number of mutations in the viruses that correlate with host species is much larger than I initially suspected.''

There are dozens of influenza subtypes, many of which weren't analyzed in the study. This may have influenced findings, Fouchier said.

``Using reverse genetics technology, and with the information collected from the systematic analysis of mutations in published genome sequences as described in this paper, it should now become possible to test the effects of each of the described mutations, and start to understand how avian influenza viruses adapt to the human host,'' Fouchier said.

Experts believe that a pandemic in 1918, which may have killed as many as 50 million people, began when an avian flu virus jumped to people from birds. The study by the Taiwan scientists indicate that the H1N1 virus responsible for the 1918 pandemic, known as Spanish flu, is more closely related to avian influenza than other human influenza viruses.

``As a signature for the first species jump, the study does not offer much new,'' said Ian Jones, a professor of virology at the University of Reading in the U.K. ``As something that adds to understanding the long-term evolution of these viruses, it is useful.''

To contact the reporter on this story: Jason Gale in Singapore at at j.gale@bloomberg.net

Last Updated: August 28, 2006 06:38 EDT