A story in yesterday’s New York Times was headlined: In New Theory, Swine Flu Started in Asia, Not Mexico. That sounded pretty interesting. What’s the new evidence? The answer? None. Just speculation. So what’s going on?
Contrary to the popular assumption that the new swine flu pandemic arose on factory farms in Mexico, federal agriculture officials now believe that it most likely emerged in pigs in Asia, but then traveled to North America in a human.
But they emphasized that there was no way to prove their theory and only sketchy data underpinning it.
There is no evidence that this new virus, which combines Eurasian and North American genes, has ever circulated in North American pigs, while there is tantalizing evidence that a closely related ?sister virus? has circulated in Asia.
American breeding pigs, possibly carrying North American swine flu, are frequently exported to Asia, where the flu could have combined with Asian strains. But because of disease quarantines that make it hard to import Asian pigs, experts said, it is unlikely that a pig brought the new strain back West.
?The most likely scenario is that it came over in the mammalian species that moves most freely around the world,? said Dr. Amy L. Vincent, a swine flu specialist at the Agriculture Department?s laboratory in Ames, Iowa, referring, of course, to people. (Don McNeil, New York Times)
This is a theory that comes from the Department of Agriculture, an agency that both regulates and promotes the industry. The fact is the data just aren’t there, one way or another. A Nature article we discussed a couple of weeks ago showed all 8 segments were of swine lineage but that the historical surveillance record was so incomplete in time and geographic regions that it was impossible to say where or when the critical combination came together. The jump to humans may have been as recent as the first of the year, but we don’t know how long the virus has been circulating in animal reservoirs (presumably swine). Something that looks similar (but still differs by a whole segment) was seen in Hong Kong in 2004, but with such a sparse record we have no idea if other similar viruses were also around somewhere, including in North American.
The folks from the Department of Agriculture are frank that they are speculating. But it’s not random speculation. I don’t think it’s an accident that the agriculture folks are blaming humans, while the health community is focusing on the jump from animals, presumably at a place near the outbreak itself. A widespread suspicion factory farming is either to blame or helped stoke the outbreak is vigorously denied by agribusiness, the pork industry and the company widely suspected (Smithfield Farms in Veracruz, Mexico), but the evidence for or against is unclear and the matter is not laid to rest.
So the back and forth continues:
Scientists tracking the virus?s lineage have complained that there is far too little global surveillance of flu in swine. Public databases have 10 times as many human and avian flu sequences as they do porcine ones, said Dr. Michael W. Shaw, a scientist in the flu division of the Centers for Disease Control and Prevention, and there are far fewer pig flu sequences from Asia than from North America and Europe, and virtually none from South America or Africa. ?Something could have been going on there for a long time and we wouldn?t know,? Dr. Shaw said.
But national veterinary officials said they knew of no close relatives of the new virus in the large private North American databases, either. That makes it most likely, they said, that it has been circulating in Asia. (New York Times)
This repeats a pattern we have seen with bird flu. There we have an even more complicated mix. There is a gigantic factory farming related to poultry, with culling millions of birds a common control practice with important economic consequences. There is also an active bird conservation contingent who reacts immediately to any suggestion that wild birds are spreading avian flu. They are (appropriately) concerned that blaming migratory birds will cause countries to clear natural habitats to exclude migratory birds from an area or even incite mass culling. The public health community would rather blame migratory birds than migratory humans.
This controversy often plays out at the level of government agency politics. In China the Ministry of Health and the Ministry of Agriculture are constantly at loggerheads, with the health authorities strong proponents of transparency in new cases while the agriculture folks — well, let’s just say, they’re not advocates of transparency. And in the US, CDC and Department of Agriculture each have their perspectives, not to mention Smithfield Farms and the National Pork Producers Council.
So did swine flu originate outside Mexico? I don’t know. But I think the theory originated outside of science.