December 21, 2007

US researchers discover new swine flu with bird flu genes

The Agricultural Research Service (ARS) recently identified a new strain of swine influenza, the H2N3, which belongs to H2 influenza viruses that last infected humans in 1957 pandemic.

Researchers said that the new strain has a molecular twist, it is composed of avian and swine influenza genes.

The US 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. However, 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 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 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.

The 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 calls for continued monitoring of swine and livestock workers for H2-subtype viruses and other influenza strains that might someday threaten swine and human health, ARS explained.