At a teleconference with reporters last week timed to coincide with release of a new study, a team of researchers said the H1N1 virus sickening people worldwide could have been circulating undetected in pigs for years.
The results are significant because of fears that current agricultural practices, including so-called concentrated animal feeding operations, or CAFOs, as well as a lack of monitoring of swine for influenza, could be raising the risks of a global flu pandemic. (For a well-sourced argument for why CAFOs may be “a perfect system for manufacturing highly-virulent disease organisms that can be disseminated quickly into a world without walls,” please see this posting at a blog hosted by Nature.com, the publisher of the prestigious science journal Nature.)
“This study reinforces the fact that swine are an important reservoir of influenza viruses with the potential to cause significant respiratory outbreaks or even a possible pandemic in humans, and the results of the study show the global need for more systemic surveillance of influenza viruses in pigs,” said Nancy Cox, a researcher with the Centers of Disease Control and a lead author on the study published in Science. (Click here for the study; here for an excellent summary at ScienceInsider; and here for a transcript of the teleconference at which the results were discussed.)
Pigs are “classic mixing vessels” in which various flu strains can swap genes, creating new and potentially dangerous influenza viruses, says Peter Hotez, president of the Sabin Vaccine Institute at George Washington University. Quoted in a USA Today story, he says the new results are “a wake-up call that we have to have aggressive, ongoing monitoring of flu in pigs,” Hotez says.
But while Canadian pig farmers are currently required to report outbreaks of flu among their herds, Americans are not, according to a story in the New York Times. In fact, the U.S. Department of Agriculture says it analyzes just 500 samples a year from some 100 million American pigs.
The new study shows that the H1N1 virus’s genes represent a mishmash of material from two kinds of swine flu. One of these variations of swine flu is called a “triple reassortment” because it contains genes that came from avian flu viruses and a human virus.
Where did the two forms of swine flu mix to produce the unqiue H1N1 strain that is now making people sick? Nancy Cox addressed that question in the teleconference:
So, we have this unique gene combination within the 2009 H1N1 viruses, and while our analysis shows that all gene segments are derived from swine influenza viruses, at this time, we do not know if the virus entered the human population directly from swine or via an intermediate host, nor do we know for certain the exact host that the viruses might previously have circulated in to obtain its current properties.
Some scientists suspect that the exact host will turn out to be pigs. That point is argued by Marco Salemi in a post to a remarkable new forum for rapid science communication: a public Wiki. It was set up by a group of computational biologists to facilitate rapid dissemination and discussion among scientific peers of research in progress on the influenza outbreak.
In his post, Salemi, a biologist at the University of Florida, summarized the work he and his colleagues have done to pin down the origin of the H1N1 outbreak. Even before the peer-reviewed study in Science appeared last week, Salemi and his colleagues had described the same basic picture of the evolution of the H1N1 virus. And he added this:
By far the most parsimonious explanation for the phylogenetic results here is that the final reassortment between classic swine flu and Eurasian swine flu occurred in a pig infected with both variants.
The new study in Science, as well as the work being conducted by Salemi and his colleagues around the world, should offer fresh impetus for journalists in the United States to investigate how confined animal feeding operations may be serving as breeding hot-houses for all sorts of potentially deadly microbes. But as far as I can tell, so far the results have been reported simply as news, without any contextualization.
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