While the net is buzzing with talk that the swine flu originated from a factory pig farm, the evidence thus far has been compelling but inconclusive. As Grist's Tom Philpott asks: "...could the swine-flu outbreak have originated literally in the shadows of Granjas Carroll’s hog confinements, and not have some tie to intensive hog farming? That’s a question that health authorities have to vigorously pursue."

Although the Mexican government is testing a million pig farm in Perote, in Veracruz State, so far it has not come up with a smoking gun. The first case of the flu, however, originated in the same area.

The Times reports:

Mexico’s first known swine flu case, which was later confirmed, was from Perote, according to Health Minister José Ángel Córdova. The case involved a 5-year-old boy who recovered. 

But a spokesman for the plant said the boy was not related to a plant worker, that none of its workers were sick and that its hogs were vaccinated against flu.

Smithfield Foods, which owns a half-interest in the Mexican facility, is also trying to distance itself from the flu. In the absence of evidence linking the flu to the operation, you wouldn't expect otherwise.

The WSJ reports (subscription-$): 

"We are very comfortable that our pork is safe," Smithfield president and chief executive Larry Pope said in an interview. "This is not a swine issue. This is a human-to-human issue."

Mr. Pope said Mexican authorities have been on at least some Smithfield farms in Mexico for "several days" testing hog herds to confirm that there is "no incidence of this virus on our farms."

Another opinion piece in the Wall Street Journal by Henry Miller, a former flu researcher and scholar at the Hoover Institution at Stanford, however, clearly implicates - as Philpott does - intensive animal production: 

Intensive animal husbandry procedures that place poultry and swine in close proximity to humans, combined with unsanitary conditions, poverty and grossly inadequate public-health infrastructure of all kinds -- all of which exist in Mexico, as well as much of Asia and Africa -- make it unlikely that a pandemic can be prevented or contained at the source.

Flu viruses can be directly transmitted (via droplets from sneezing or coughing) from pigs to people, and vice versa. These cross-species infections occur most commonly when people are in close proximity to large numbers of pigs, such as in barns, livestock exhibits at fairs, and slaughterhouses. And, of course, flu is transmissible from human to human, either directly or via contaminated surfaces. 

Pigs are uniquely susceptible to infection with flu viruses of mammalian and avian origin. This is of concern for a couple of reasons. First, pigs can serve as intermediaries in the transmission of flu viruses from birds to people. And when avian viruses infect pigs, they adapt and become more efficient at infecting mammals -- which makes them more easily transmitted and dangerous to humans.

Second, pigs can serve as hosts in which two (or more) influenza viruses infecting an animal simultaneously can undergo "genetic reassortment," a process in which pieces of viral RNA (the virus's genetic material, similar to DNA) are shuffled and exchanged, creating a new organism. The influenza viruses responsible for the world-wide 1957 and 1968 flu pandemics -- which killed about 70,000 and 34,000, respectively, in the U.S. -- were such viruses, containing genes from both human and avian viruses.

The Humane Society of the US also has a long, informative article about the relationship between factory animal production and flus, but again, does not have a smoking gun. (Linked by Ethicurean.) Which begs the question, do we need one? Or do we merely need to reduce the chances for this sort of outbreak by preventing conditions that breed them in the first place?

-Samuel Fromartz