Global 3000 | Flu – global epidemic,local causes?

Spanish flu,Asian flu,bird flu and now swine or Mexican flu. Reports of outbreaks of virus diseases constantly alarm people,but the effects are very varied.They can kill millions,like Spanish flu,or affect only a few. But the pathogens must come from somewhere,mutations of viruses that already exist. In Mexico,suspicion has fallen on a pig fattening farm. Chickens were responsible for the bird flu of a few years ago. Does intensive farming lead to the development of new viruses? Global 3000 finds out.