[Ip-health] New strain of H5N1 bird flu emerges in China

[Ira Glazer]

http://www.newscientist.com/article/dn10407-new-strain-of-h5n1-bird-flu-eme=
rges-in-china.html

22:00 30 October 2006
NewScientist.com news service
Debora MacKenzie

A new strain of H5N1 bird flu has emerged in China that is poised to
start yet another global wave of infection.

Nearly three times as many Chinese poultry are infected with H5N1 now
than last year, despite China=92s insistence that all poultry be
vaccinated. In fact, vaccination may be the reason for the increase in
infections, researchers say.

Yi Guan and colleagues at the University of Hong Kong have been testing
poultry in markets across southern China for flu for years, the only
such long-term monitoring in the world. Between mid-2004 and mid-2005
they found 0.9% of market poultry were carrying H5N1, including 2% of
ducks, a major carrier of the virus.

Between then and June 2006, however, they found it in 2.4% of market
poultry on average, a near-threefold increase. It now infects 3.3% of
ducks. The team found the virus in chickens during 11 months of the
year, up from four previously.

The reason, the researchers say, is a new =93Fujian-like=94 strain of the
virus, descended from one first seen in a duck in Fujian, China, in
2005. It caused 3% of poultry infections in September 2005, but 95% by
June 2006.
Unrecognised cases

More infected =96 yet apparently healthy =96 birds in Chinese markets for
more of the year means more risk for humans. All but one of China=92s
reported human cases of H5N1 happened after the Fujian strain started
its rise, and some lived far from any known outbreak in poultry, but
close to urban poultry markets.

There could be many more unrecognised cases. Serious cases of flu in
humans, in China and elsewhere, are only tested for H5N1 if nearby
poultry has suddenly died. But seemingly healthy, infected birds may
cause human cases that are not tested =96 while the spread of the virus in
the poultry also goes unsuspected.

=93If death of poultry is used as the only indication of H5N1 infection,
but the emergence of human cases is ignored, the consequence will be
increased transmission of the virus in poultry,=94 says Guan.

The team has no evidence that the virus is more virulent or more likely
to transmit among humans than previous strains, he says. But it has
caused one human death in Thailand, and the five Chinese cases for which
the team has virus samples. =93As far as I know all 20 human cases
recognised since November 2005 were caused by this virus,=94 Guan told New
Scientist.

Based on what previous H5N1 viruses in China have done, the team warns,
the Fujian strain seems poised to start a third epidemic wave, after the
first in 2004, and H5N1=92s spread across Eurasia in 2005. Fujian virus
has so far spread to Thailand, Malaysia and Laos.
Surging infection

In November 2005 China ordered compulsory vaccination of all poultry.
The law has been imperfectly applied =96 Guan and colleagues found
vaccine-induced antibodies in only 16% of the birds they tested. But
they also found that those vaccine-induced antibodies do not recognise
the Fujian virus, although they do attack the virus strains that Fujian
has now replaced.

This means the Fujian strain has a selective advantage in vaccinated
birds. =93This novel variant may have become dominant because it was not
as easily affected as other strains by the current avian vaccine,=94 says
Guan. That may also be why H5N1 infection in Chinese poultry has surged,
rather than decreased, despite increased poultry vaccination.

Worryingly, the antibodies being used to develop human vaccines for H5N1
have been induced from 2004 strains of the virus =96 these antibodies do
not recognise the Fujian strain. This means the current experimental
pandemic vaccine would not work against any pandemic virus that emerged
equipped with Fujian surface proteins.

Guan and colleagues want comprehensive influenza surveillance in both
people and animals throughout the region, both to provide updates for
vaccine developers and to track the real spread of the virus.

Journal reference: Proceedings of the National Academy of Sciences
(DOI:0:1073/pnas.0608157103)