Hard To Find A Smoking Pig...

...In a factory farm filled with pigs:

Scientists have traced the genetic lineage of the new H1N1 swine flu to a strain that emerged in 1998 in U.S. factory farms, where it spread and mutated at an alarming rate. Experts warned then that a pocket of the virus would someday evolve to infect humans, perhaps setting off a global pandemic.

...“Industrial farms are super-incubators for viruses,” said Bob Martin, former executive director of the Pew Commission on Industrial Animal Farm Production, and a long-time critic of the so-called “contained animal feeding operations.”

...[G]eneticists studying the composition of viruses taken from swine flu victims described it as the product of a DNA swap between North American and Eurasian swine flu strains. ... Six of the genes in swine flu looked to be descended from “H1N2 and H3N2 swine viruses isolated since 1998.”

...H3N2 — the letters denote specific gene variants that code for replication-enhancing enzymes — is the name of a hybrid first identified in North Carolina in 1998, the tail end of a decade which saw the state’s hog production rise from two million to 10 million, even as the number of farms dropped. H3N2 originated in a relatively benign swine flu strain first identified in 1918, but had absorbed new genes from bird and human flus.

These new genes provided replication advantages that allowed the hybrid to permeate densely packed pig farms whose inhabitants were routinely shipped across the United States. That rapid replication rate also increased the chances of strains evolving in ways that allowed them to evade hog immune systems.

Within a year, exposures topped 90 percent in several heartland states. A retrospective news account in Science said that “after years of stability, the North American swine flu virus had jumped on an evolutionary fast track.”

...“We haven’t found evidence of infected pigs,” said Ian Lipkin, a Columbia University epidemiologist and member of the World Health Organization’s surveillance network. “But even if we never find that smoking pig, we can surmise that this is probably where it came from.”