New swine flu has avian flu genes
Researchers have identified a new strain of swine
influenza - H2N3 - which belongs to the group of H2 influenza viruses that last
infected humans during the 1957 pandemic. This new strain has a molecular twist:
it is composed of avian and swine influenza genes.
Several Agricultural Research Service (ARS) veterinarians conducted this
research with a group of other scientists from around the country. The
veterinarians of the ARS, the US Department of Agriculture's chief scientific
agency, work at the agency's National Animal Disease Center in Ames,
The research team studied an unknown
pathogen that in 2006 infected two groups of pigs at separate production
facilities. Both groups of pigs used water obtained from ponds frequented by
migrating waterfowl. Molecular studies indicated the unknown pathogen was an
H2N3 influenza virus that is closely related to an H2N3 strain found in mallard
ducks. But this was the first time it had been observed in mammals.
Influenza viruses have eight gene segments, all of which can be swapped
between different virus strains. Two of these gene segments code for virus
surface proteins that help determine whether an influenza virus is able to
infect a specific host and start replicating - the first step in the onset of
In the newly isolated
swine H2N3, the avian H2 and N3 gene segments mixed with gene segments from
common swine influenza viruses. This exchange - and additional mutations - gave
the H2N3 viruses the ability to infect swine. Lab tests confirmed that this
strain of H2N3 could also infect mice and ferrets.
findings provide further evidence that swine have the potential to serve as a
'mixing vessel' for influenza viruses carried by birds, pigs and humans.
It also supports the need
to continue monitoring swine - and livestock workers - for H2-subtype viruses
and other influenza strains that might someday threaten swine and human
â€¢ Agricultural Research Service (ARS)
â€¢ US Department
of Agriculture (USDA)
â€¢ National Animal Disease
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