from Grist mag:
‘New Scientist’: Swine flu stems from virus that evolved in U.S. 3 Posted 2:03 PM on 30 Apr 2009
by Tom Philpott
In a pair of articles in New Scientist, Debora MacKenzie links the swine flu virus now spreading across the globe to large-scale pork-raising operations in the United States.
In the first article, titled “Swine flu: the predictable pandemic?,” MacKenzie writes that the “virus has been a serious pandemic threat for years, New Scientist can reveal—but research into its potential has been neglected compared with other kinds of flu.” She writes that the strain now in the headlines has its origins in an earlier outbreak in the United States a decade ago:
This type of virus emerged in the U.S. in 1998 and has since become endemic on hog farms across North America. Equipped with a suite of pig, bird and human genes, it was also evolving rapidly.
Before ‘98, MacKenzie claims, a genetically stable swine flu, in the H1N1 family, regularly visited hog farms, not causing much trouble. It was a relatively benign mutation of the strain that caused the great 1918 pandemic. But in 1998, something changed. Citing the work of Richard Webby of St. Jude’s Children’s Research Hospital in Memphis, MacKenzie writes:
Swine H1N1 hybridised with human and bird viruses, resulting in “triple reassortants” that surfaced in Minnesota, Iowa and Texas. The viruses initially had human surface proteins and swine internal proteins, with the exception of three genes that make RNA polymerase, the crucial enzyme the virus uses to replicate in its host. Two were from bird flu and one from human flu. Researchers believe that the bird polymerase allows the virus to replicate faster than those with the human or swine versions, making it more virulent.
Within a year, the triple-reassortant types became the dominant flu bugs seen on U.S. hog farms. Importantly, “unlike the swine virus they replaced,” the new ones “were actively evolving.” Today, she writes, “There are many versions with different pig or human surface proteins, including one, like the Mexican flu spreading now, with H1 and N1 from the original swine virus.” .........(more)
The complete piece is at:
http://www.grist.org/article/2009-04-30-NS-swine-cafos/