Apparently H3N2 is the name of a hybrid found in North Carolina (a state with a high concentration of factory hog farms) in 1998. This flu had "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."
I assume that they mean "by 1999" when they say "within a year." So that's where this flu was a decade ago. The article says that hog flus are "poorly monitored" so we don't have the full story of what came next. "But eventually an H3N2 spawn merged with a strain of Eurasian pig flu, producing the swine flu variant that's now infecting humans."
Even if we don't have the complete picture, the article notes that:
At an environmental level, the conditions which shaped H3N2 and H1N2 evolution, and increased the variants' chances of taking a human-contagious form, are well understood. High-density animal production facilities came to dominate the U.S. pork industry during the late 20th century, and have been adopted around the world. Inside them, pigs are packed so tightly that they cannot turn, and literally stand in their own waste.
Diseases travel rapidly through such immunologically stressed populations, and travel with the animals as they are shuttled throughout the United States between birth and slaughter. That provides ample opportunity for strains to mingle and recombine. An ever-escalating array of industry-developed vaccines confer short-term protection, but at the expense of provoking flu to evolve in unpredictable ways.
The human health risks posed by factory farms are so well known that in 2003, the American Public Health Association called for a ban on contained animal feeding operations. The article goes on to say:
As of now, neither swine flu nor its close relatives have been found anywhere. But "that probably says more about the lack of sampling in pig flu than anything else," said Andrew Rambaut, a University of Edinburgh viral geneticist who has studied swine flu. "We don't sample nearly the complete diversity of pig flu around the world. Most outbreaks go unstudied."
The article counters the idea that the link to factory farms is merely a conspiracy theory, saying:
The new swine flu could have emerged in a myriad number of ways, passing between any number of birds and pigs and people, at locations across North America, during its evolutionary journey. It may well prove impossible to pinpoint exactly where it first emerged or became infectious to people. But most of its genes are almost certainly part of a North American industrial virus lineage long expected to produce pandemic variants like this one. |
