Bad Neighbors

Tightly packed poultry and pig farms could be incubating the next deadly flu.

- By Tom Philpott

If you're like me, you associate pork with the deliciousness of bacon. But lurking behind the pleasure lies something much less savory to think about: the risk of another pandemic.

That's because humans and pigs easily swap influenza viruses. Worse still, pigs can also pick up influenza strains that circulate among birds, whose viruses aren't well adapted to infecting and spreading among people. Humans don't have the receptors in our throats and noses that avian flus can easily attach to. Our isolation from avian flus is what makes them dangerous-since our immune systems rarely encounter them, we have little innate ability to fight them off. Enter pigs. They can catch flu strains from birds (often carrying them without symptoms), mash them up with genetic material from human-adapted flus, and create novel varieties capable of flummoxing human immunity and generating pandemics. That's why virologists call hogs "mixing vessels" for novel influenza strains.