Some thoughts from Alex Avery, director of research and education with the Center for Global Food Issues at Hudson Institute:
1. Flu viruses are biological sluts — promiscuous and cover a wide range of species. There are related flu viruses that infect people, cats, pigs, poultry/birds, horses, seals, and even whales. Anytime lots of animals/people cohabitate, there will be risk of swapping these viruses between species.
2. When two different types of flu virus each infect a single host (pig or people or whatever), there is a chance that a merged, more dangerous flu will emerge. Think of it like poker, where occasionally you’ll get a Royal Flush – the perfect card combination.
3. While there are always the granola-cranks who will want to blame this on modern farming [Sorry, Rod! — K-Lo], it is a worse problem in traditional farming where each farmer has a few of many species co-habitating and interacting with the people (and wild waterfowl/animals).