ProMed Article; May 23, 2009
By sequencing the genomes of more than 50 samples
of the new A (H1N1) influenza virus, researchers
have found that it is distantly related to its
nearest relatives, indicating that its genes have
been circulating undetected for an extended
period. The findings suggest that in the future
pig populations will need to be closely monitored
for emerging influenza viruses.
Rebecca Garten and colleagues sequenced the full
or partial genomes of 2009 A (H1N1) viruses
isolated in Mexico and the United States. They
determined the origins of the virus' 8 gene
segments and found that the combination of these
gene segments has not previously been reported
among swine or human influenza viruses. All of
the segments originated in avian hosts and then
began circulating in pigs at various times in
history, from 1918 through to 1998.
6 of the 8 segments originated from triple reassortant swine
viruses -- which include genetic material from
human, avian and swine viruses' as the result of
these virus' tendency to swap pieces of their
genomes with each other -- that have been
circulating in North America and Asia since
approximately 1998. The other 2 segments are
derived from Eurasian swine viruses.
The sequences for the gene segments did not
reveal the signatures of high transmissibility or
virulence that have been found in other influenza
A viruses, suggesting that other, yet-unknown
sequences are responsible for the new virus'
ability to replicate and spread in humans.
The researchers also took a closer look at the
new A (H1N1) virus's hemagglutinin protein, which
is responsible for the virus' ability to bind to
and infect its host cell. Test-tube experiments
that examined how ferret antibodies reacted
against this protein suggest that the new strain
has antigenic properties that are similar to
those of other swine A(H1N1) viruses but distinct
from seasonal human flu. Researchers will need to
continue to look for changes in the hemagglutinin
protein in the new virus, which may affect the
selection of vaccine candidates, the authors say.
[The reference and abstract of the paper
published in ScienceXpress is reproduced below. - Mod.CP]
 Antigenic & genetic characteristics
Date: Fri 22 May 2009
Source: SciencXpress [edited]
Antigenic and Genetic Characteristics of
Swine-Origin 2009 A (H1N1) Influenza Viruses Circulating in Humans
Since its identification in April 2009 an A
(H1N1) virus containing a unique combination of
gene segments from both North American and
Eurasian swine lineages has continued to
circulate in humans. The lack of similarity
between the 2009 A (H1N1) virus and its nearest
relatives indicates that its gene segments have
been circulating undetected for an extended
period. Its low genetic diversity suggests the
introduction into humans was a single event or
multiple events of similar viruses. Molecular
markers predictive of adaptation to humans are
not currently present in 2009 A(H1N1) viruses,
suggesting previously unrecognized molecular
determinants could be responsible for the transmission among humans.
Current isolates of the novel 2009 H1N1 strain
are antigenically homogeneous, but distinct from
current strains of seasonal influenza virus.
[Byline: Rebecca J. Garten 1
C. Todd Davis 1
Colin A. Russell 2, Bo Shu 1, Stephen Lindstrom
1,Amanda Balish 1, Wendy M. Sessions 1, Xiyan Xu
1, Eugene Skepner 3, Varough Deyde 1,Margaret
Okomo-Adhiambo 1, Larisa Gubareva 1, John Barnes
1, Catherine B. Smith 1,Shannon L. Emery 1,
Michael J. Hillman 1, Pierre Rivailler 1, James
Smagala 1, Miranda de Graaf 4,David F. Burke 3,
Ron A. M. Fouchier 5, Claudia Pappas 1, Celia M.
Alpuche-Aranda 6,Hugo López-Gatell 6, Hiram
Olivera 6, Irma López 6, Christopher A. Myers 7,
Dennis Faix 7,Patrick J. Blair 7, Cindy Yu 8,
Kimberly M. Keene 9, P. David Dotson Jr.10, David
Boxrud 11,Anthony R. Sambol 12, Syed H. Abid 13,
Kirsten St. George 14, Tammy Bannerman 15,Amanda
L. Moore 16, David J. Stringer 17, Patricia
Blevins 18, Gail J. Demmler-Harrison 19,Michele
Ginsberg 20, Paula Kriner 21, Steve Waterman 22,
Sandra Smole 23, Hugo F. Guevara 24,Edward A.
Belongia 25, Patricia A. Clark 26, Sara T.
Beatrice 27, Ruben Donis 1, Jacqueline Katz 1,Lyn
Finelli 1, Carolyn B. Bridges 1, Michael Shaw 1,
Daniel B. Jernigan 1, Timothy M. Uyeki 1,Derek J.
Smith 28*, Alexander I. Klimov 1, Nancy J. Cox 1*
At: The WHO Collaborating Center for Influenza,
Centers for Disease Control and Prevention, USA,
and 27 other Laboratories, as noted in the Source URL, above.
Correspondence to: Derek J. Smith
Nancy J. Cox