New Swine Flu Has Avian Flu Genes
By Ann Perry
December 19, 2007
Researchers have identified a new strain of swine
influenzaH2N3which 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.
Agricultural Research Service (ARS) veterinarians
Gauger conducted this research with Iowa State University (ISU) visiting scientist Wenjun Ma, ISU
veterinarian Bruce Janke and other colleagues at the
University of Minnesota and
St. Jude Childrens Research Hospital.
The ARS veterinarians work at the agency's
Animal Disease Center in Ames, Iowa.
The group studied an unknown pathogenfirst identified by
University of Minnesota veterinary
diagnostician Marie Gramerthat infected two groups of pigs at separate
production facilities in 2006. Both facilities used pond water frequented by
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 replicatingthe first step in the
onset of influenza infection.
In the newly isolated swine H2N3, the avian H2 and N3 gene segments
mixed with gene segments from common swine influenza viruses. This
exchangeand additional mutationsgave the H2N3 viruses the ability
to infect swine. Lab tests confirmed that this strain of H2N3 could also infect
mice and ferrets.
These 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
swineand livestock workersfor H2-subtype viruses and other
influenza strains that might someday threaten swine and human health.
Results of this study were published online this week in the Proceedings of the National Academy of Sciences of
the United States of America.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.