playing chicken with the bird flu
- From: "TC" <tunderbar@xxxxxxxxxxx>
- Date: 1 Nov 2006 09:13:41 -0800
http://www.sciam.com/article.cfm?chanID=sa003&articleID=9B6897E7-E7F2-99DF-389770E045273992
October 30, 2006
New Strain of Bird Flu Takes Over
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.
*****
Doesn't inspire a great deal of confidence in those charged with
managing the situation, does it?
TC
.
- Prev by Date: What's in a flu shot?
- Next by Date: Re: Squash?
- Previous by thread: What's in a flu shot?
- Next by thread: SIDS, serotonin and DIET
- Index(es):
Relevant Pages
|
