Swine influenza presents a special challenge to genetics researchers because its virus stores its information in RNA, which is more susceptible to mutation and allows viruses to evolve far more rapidly than in DNA. Because of this, it is sometimes hard for an infected host to develop lasting immunity.
Since manipulations commonly done on DNA cannot be performed with RNA, reverse genetics is used to perform a procedure called reverse transcription, in which RNA viruses' genetic material is turned into a DNA state where modifications can be easily introduced. When the DNA is converted back into RNA, these modifications occur in the genome of the RNA virus as well.
Veterinary medical officers at the Agricultural Research Service (ARS)'s virus and prion diseases of livestock research unit are now applying this reverse genetics process to combat the new threat of swine influenza. The process actually creates new flu viruses so that individual components can then be explored. It is hoped these components can in turn become the targets of vaccines.
Reverse genetics has been developed over the past decade for virus studies. "The technology has now advanced to where one can confidently generate influenza viruses entirely from cloned DNA resulting from the process," said veterinary medical officer Kelly Lager.
Animal health scientists in North America used to diagnose almost exclusively only one type of flu virus in pigs: H1N1. This all changed in 1998, however, when pigs started to be diagnosed with H3N2, a strain that up to that time was rarely seen here.
Since then, these H3N2 viruses have combined further with the classical H1N1 viruses, resulting in new H1N2 and H1N1 swine influenza viruses. The increased virulence represented by this new strain has raised concern.