Strains of avian influenza virus have become increasingly pathogenic
to mammals, according to research published on July 2 in an online edition
of the Proceedings of the National Academy of Sciences (http://www.pnas.org). The findings underscore concerns that the virus
will evolve to spread more easily from person to person, setting the stage
for a human pandemic.
Researchers from China and the United States inoculated chickens and
mice with H5N1 bird flu isolates obtained between 1999 and 2002 from apparently
healthy ducks (a natural reservoir for avian influenza). They found that the
isolates were highly lethal to chickens; in mice, viruses isolated in 2001
and 2002 were significantly more pathogenic than those isolated in 1999 and
2000. An analysis of the viral isolates' genomes, they said, suggests that
progressive mutations may have contributed to an increase in the strains'
Stephenson J. Deadlier Bird Flu?. JAMA. 2004;292(7):794. doi:10.1001/jama.292.7.794-a