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A ProMED-mail post
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International Society for Infectious Diseases
Date: Fri 18 Jun 2010
Source: The New York Times online [edited]
Study criticizes swine flu follow-up
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There is too little genetic surveillance of last year's human pandemic flu,
which has gone on to infect pigs in China and is readily mixing with other
flus there, according to a study which was released on Thursday [17 Jun
2010] by researchers in Hong Kong.
No dangerous new strain has emerged, said several experts who saw the
study. But in January [2010] the researchers found a new strain with one of
the pandemic flu's surface proteins -- the outer spikes and knobs it uses
to attach to cells. That was a reminder of how easily another swine strain
capable of spreading among people could emerge.
"Just because we've just had a pandemic does not mean we've decreased our
chances of having another," said Dr Carolyn B Bridges, an epidemiologist in
the flu division of the Centers for Disease Control and Prevention. "We
have to stay vigilant." While there is "a long global history" of testing
humans in many countries to see how human flu strains shift each year,
there are "major gaps" in testing pigs, Dr Bridges said. That is important
because pigs can catch both human and bird flus. Flus easily swap their 8
genes and any new combination might be able to spread among pigs and
eventually reach another human.
Pigs in the giant hog-raising barns of the United States and Western Europe
are tested regularly, but the millions of pigs on small farms and in big
operations in Asia and Latin America seldom are. Commercial hog operations
do constant testing so they can formulate new vaccines and snuff out flu
outbreaks. Flu seldom kills pigs, but it makes them lose weight, which cuts
into profits.
In the new study, published online in the journal Science [abstract
reproduced below], the Hong Kong researchers sequenced viruses they found
by regularly swabbing pigs' snouts at the territory's largest
slaughterhouse, which gets pigs from all over southern China. That testing,
supported by a United States government grant, has gone on for 12 years.
"The message from our paper is not an inevitable disaster around the
corner, but the need for continued vigilance," Malik Peiris, a flu expert
at the University of Hong Kong and one of the study's authors, said in an
email message.
Among the globe-circulating flus that pigs could, in theory, catch are 6
swine flus, several human seasonal ones and at least 2 avian ones. The
latter include the feared H5N1, which has killed 60 per cent of the 500
people known to have caught it since 2003 but thus far almost never spreads
from person to person, and an H9N2, which has been found in about a dozen
humans but caused only mild disease so far.
Last year's pandemic was originally dubbed a "swine flu" because the 8
genes in its makeup had been seen before in American or Eurasian pigs
during the previous 10 years, though never in the exact combination that
was making people sick in Mexico. It has not been found in any stored
samples from people or pigs, so where it came from remains a mystery. It
has now reached 200 countries and is still infecting more people every day,
though most cases are mild to moderate. It is now clear that it is also
circulating freely in pigs in China and sometimes mixing genes with at
least 2 other long-known swine flus.
"The implication of this study is that we have to be very careful," said Dr
Peter Palese, a flu researcher at the Mount Sinai School of Medicine. "On
the other hand, I could argue that it hasn't happened yet. It's not clear
that any of these new swine viruses have the potential to go into humans
and cause problems."
[byline: Donald G McNeil Jr]
--
communicated by:
ProMED-mail
[The paper upon which this article is based was published on 18 Jun: D
Vijaykrishna, LLM Poon, HC Zhu, SK Ma, OTW Li, CL Cheung, et al.
Reassortment of pandemic H1N1/2009 influenza A virus in swine. Science
2010; 328 (5985),
Abstract: "The emergence of pandemic H1N1/2009 influenza demonstrated that
pandemic viruses could be generated in swine. Subsequent reintroduction of
H1N1/2009 to swine has occurred in multiple countries. Through systematic
surveillance of influenza viruses in swine from a Hong Kong abattoir, we
characterize a reassortant progeny of H1N1/2009 with swine viruses.
"Swine experimentally infected with this reassortant developed mild illness
and transmitted infection to contact animals. Continued reassortment of
H1N1/2009 with swine influenza viruses could produce variants with
transmissibility and altered virulence for humans. Global systematic
surveillance of influenza viruses in swine is warranted."
The outcome of this research, depending on one's inclination can be
regarded as alarming (frequent reassortment of influenza pandemic (H1N1)
virus genome sub-units in swine), or reassuring (low risk of generation of
variants pathogenic in humans). An example of the glass half full / glass
half empty paradox. Nonetheless there is a clear need to extend influenza
virus surveillance in swine. - Mod.CP]
[see also:
Influenza pandemic (H1N1) (41): New Zealand 20100618.2042
Influenza pandemic (H1N1) (40): WHO update 104 20100612.1970
Influenza pandemic (H1N1) (39): WHO update 103 20100605.1867
Influenza pandemic (H1N1) (38): WHO 20100603.1841
Influenza pandemic (H1N1) (37): Guillain-Barre syndrome risk 20100602.1837
Influenza pandemic (H1N1) (36): WHO update & seasonal 20100530.1798
Influenza pandemic (H1N1) (35): Singapore 20100530.1795
Influenza pandemic (H1N1) (34): Indian variants 20100525.1741
Influenza pandemic (H1N1) (33): WHO update, corr. 20100527.176
Influenza pandemic (H1N1) (32): WHO update 20100501.1418
Influenza pandemic (H1N1) (31): UK (Scotland) D222G mut 20100422.1310
Influenza pandemic (H1N1) (30): WHO update 20100417.1250
Influenza pandemic (H1N1) (20): China, update 20100303.0702
Influenza pandemic (H1N1) (11): WHO statement to CE 20100126.0289
Influenza pandemic (H1N1) (10): PAHO update 20100121.0240
Influenza pandemic (H1N1) (01): China, 2009 20100105.0040]
...................cp/ejp/sh
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