The H1N1 flu virus that triggered the first influenza pandemic in 40 years seemed to come out of nowhere, but, of course, that wasn't the case. The virus mutated inside a pig before making the leap to human beings, and scientists have traced it back to a strain that first emerged in U.S. factory pork farms back in 1998. Flu-virus experts worry that concentrated, factory-style pork farms — with tens of thousands of animals packed closely together — are the ideal incubators for new viruses and that we may see more such viruses spreading from pigs to people in the future. While agriculture-industry leaders say modern farms are ramping up their biosecurity efforts to prevent new pathogens from crossing to humans, more could be done. To keep ourselves healthy, we first need to keep our animals healthy.