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Public Radio's Environmental News Magazine (follow us on Google News)

Farming the Flu

Air Date: Week of

The H1N1 2009 virus has a mix of genetic material linked to pigs, birds, and humans.

As health officials try to guess where the so-called swine flu will show up next, other researchers are trying to track the H1N1 virus to its origins. And a number of experts suspect large-scale factory farms. Host Jeff Young talks with Johns Hopkins Public Health Professor Ellen Silbergeld who says crowded, filthy conditions at factory farms could speed the mutation and transfer of viruses from pigs to people.


CURWOOD: It’s Living on Earth, I’m Steve Curwood.

YOUNG: And I’m Jeff Young.

World health authorities are on alert, tracking the new flu – now officially called the H1N1 2009 flu. Not as catchy as swine flu maybe, but more accurate since scientists are still working to better understand the connection between the virus and pigs. While heath officials are trying to check the virus’s spread, other researchers working to find its origin. And some of them suspect large-scale factory farms may have played a role.

Ellen Silbergeld.

Ellen Silbergeld teaches environmental health at the Johns Hopkins Bloomberg School of Public Health, where she’s studied the connections between factory farms and disease. Professor Silbergeld says, these intensive industrial scale livestock operations are fertile ground for viruses to mutate. The H1N1 2009 virus has a mix of genetic material linked to pigs, birds, and humans, and Professor Silbergeld says that’s allowed it to take on its troubling characteristics.

SILBERGELD: The aspects of this strain that are troubling to us are, number one: that it has clearly moved from non-human into human hosts. Number two: that it appears to readily infect one human from another human, so its transmissible among us, you don’t have to have contact with pigs or birds to get this virus. And third: that it is quite virulent, that is, it causes serious illness.

YOUNG: Now why do we suspect pigs had some role here and what is it that is special about pigs that makes them a possible conduit for a flu that humans can get?

SILBERGELD: The reason why this is notable is of course that pigs are very close to humans in terms of the immune system. And so an influenza virus that has been able to infect pigs is in some way closer to being conditioned to infecting us.

YOUNG: Why do you suspect these large-scale farms? What is it about this particular method of farming that you think makes it easier for viruses to change and to jump from species to species?

SILBERGELD: Well, this, of course, is not strictly limited to influenza viruses, but is based on observations by us and others in studying bacteria as well as viruses.

These operations contain elements that really are conducive to raising concerns for public health. You have thousands of animals, in the case of pigs usually between two and six thousand animals, held in close confinement under conditions that are not sanitary, that is frankly that they’re housed with their wastes. And therefore you’ve got a lot of hosts available to exchange a pathogen, which is one of the processes by which viruses and bacteria evolve and acquire mutations. And then the way in which these operations are run – and I want to stress that this is a worldwide issue, it is not peculiar or restricted to Mexico.

The spread of the flu has everyone worried. (Photo: Bruce Gellerman)

You have situations that are not bio-secure and also large amounts of waste that are not well regulated in terms of their management or disposal. In terms of bio-security, it’s generally not recognized that these operations have to be high ventilated. When you put two to six thousand animals in side a building, you have to have very high rates of ventilation or that animals will die of heat stress. So several researchers have in fact reported that in the environs of these large operations, you can detect pathogens in the outflow air from these exhaust fans. People have also isolated influenza virus from the legs and feet of flies in the vicinity of these operations. This was noted in some outbreaks of avian influenzas, for example, in Japan. So, the lack of bio-security, the very dense populations, the conditions that are conducive to viral evolution and mutation and the lack of control over disposal of waste from these animals which also contain pathogens are really the elements that have given rise to concern for us and many others as to the public health implications of this manner of food animal production.

YOUNG: So despite their efforts to keep it secure, you can’t stop the flow of air, you can’t stop insects.

SILBERGELD: Well, the issue is most of the bio-security practices that have been developed by the industry – most of them have been to protect the animals from a person bringing in a disease that could be dangerous to the health of the animals. In terms of what we call bio-containment – that is preventing from something that might be in the house from coming out – there’s very, very imperfect and limited protection.

YOUNG: Is there evidence that the people who work at these type farms are more susceptible to catching diseases from the animals and able to spread disease to other people.

SILBERGELD: There’s considerable evidence that workers in these operations, farmers and farm workers are in fact at greater risk of exposure. Studies conducted in Iowa and other places have demonstrated that workers in swine CAFOs have a high rate of infection by swine influenzas. In the same way that we and others have reported that workers in poultry houses have a high rate of being infected by poultry born pathogens. Now – and here’s one of the tricky things – they may not be sick. I’m sure you’ve heard of Typhoid Mary – and the really worrying thing in public health is what we call the asymptomatic carrier, that is a person who’s become infected by a pathogen but does not get sick.

The H1N1 2009 virus has a mix of genetic material linked to pigs, birds, and humans.

YOUNG: So they people then sort of become the bridge for the virus to get out of the farm and out into their broader human population.

SILBERGELD: They are one bridge. But I do want to emphasize these environmental pathways of dispersion through air and waste that may be even more important.

YOUNG: And what would be your recommendations, how could this type of farming be made less likely to produce dangerous diseases?

SILBERGELD: I think in light of this event, there are some things we should do in the short term. First and foremost, we need to recognize the critical role of industrial food animal production in the emergence of new diseases. And we need to direct much more oversight and monitoring as to what’s going on in terms of what’s happening in the animals and also in people who are really at the front line, who are the workers and the farmers and the nearby communities. These groups really aren’t part of our monitoring and surveillance programs at the same time. Second, I think we need to immediately institute much better oversight over the management of waste. Influenzas can survive in wastes for months. And yet there are no requirements for either testing or appropriate management. And this has got to be a very important switch point in this whole process globally speaking.

YOUNG: Ellen Silbergeld is professor of environmental health at Johns Hopkins Bloomberg School of Public Health. Thanks very much for your time.

SILBERGELD: Thank you.

[MUSIC: Tosca “Chocolate Elvis (Boozoo Baju Soul Sufferer Version) from Chocolate Elvis Dubs (G-Stone records 1999)]



For more on Ellen Silbergeld, click here.


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