SCIENCE NEWS
October 30, 2006
New Strain of Bird Flu Takes Over

FLU IN FLUX:  Samples taken from poultry in southern China indicate that the H5N1 bird flu
virus continues to evolve, keeping alive the threat of a global pandemic.
Despite mass vaccinations of poultry in China, the bird flu virus continues to evolve. Samples
collected from poultry markets in southern China over the last year show that a variant of the
virus has spread outward from a single province and supplanted strains in the rest of the
region, researchers report. The result calls into question the steps taken so far to contain
the virus, which public health officials fear could give rise to a deadly worldwide flu
pandemic.
In early 2004 the H5N1 bird flu virus spread from poultry in China to southern Asia and has
since been identified in birds as far away as Europe and north Africa. In principle,
vaccination of domestic chickens and other birds could limit the virus's transmission and
thereby its ability to evolve into a more transmissible form. With that goal in mind, China
announced last November that it would begin vaccinating 14 billion domestic chickens against
H5N1.

Since that time, however, the virus seems to have become even more entrenched in domestic
poultry, report Chinese and American researchers in a paper published online October 30 by
Proceedings of the National Academy of Sciences USA. The team collected samples from over
50,000 seemingly healthy birds between July 2005 and June 2006 at live poultry markets in six
provinces of southern China. They identified H5N1 in 2.4 percent of birds, primarily domestic
ducks and geese, up from 0.9 percent the year before.
To identify the source of the ongoing transmission, the researchers selected 390 virus samples
from infected birds, determined their genetic sequence and compared these sequences with known
variants of the virus. One strain, hailing from the province of Fujian, appeared in only 3
percent of birds collected up to September 2005. Between April and June of 2006, however,
Fujian-like viruses were responsible for 95 percent of infections. "It means that the virus is
still evolving," says co-author Robert Webster of St. Jude Children's Research Hospital in
Memphis. "It means that the problem is not under control." Offshoots of the Fujian variant were
isolated in the 22 human cases of bird flu reported in China since last November, and the
strain has sickened birds in Laos, Malaysia and Thailand, where it also infected people, the
group notes.

A weakness in China's vaccine may have allowed the previously local variant to become
widespread, the researchers surmise. They analyzed serum samples from 76 chickens for signs of
antibodies against three H5N1 variants, including the Fujian-like strain. The presence of
antibodies is a sign that a vaccine has taken effect. Almost all of the samples displayed two
to four times more antibodies to the other two variants than to the Fujian virus, suggesting
that the vaccine given to the chickens was less effective against that strain, the researchers
point out. The result highlights the need to supplement vaccination with other measures, says
veterinary researcher Richard Slemons of Ohio State University. The former can be effective if
part of a broader program of monitoring vaccinated chickens with surveillance afterward, agrees
Webster. Vietnam has vaccinated its poultry and saw no new human cases of bird flu this
year. --JR Minkel

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