From Information Is Beautiful, the reason we’re so concerned about flus that come from birds and pigs:
The reason most flus seem to come from East Asia, is that its common to raise both pigs and ducks in this region.
And, the reason that most infections don’t work this way is body temperature. Most viruses are linked to a fairly specific body temperature — and when they jump species they fail in the warmer or colder environment. The difference with the flu is its ability to survive in more than one hosts body temperature range.
Can you tell we’re watching Contagion and Outbreak on TV at our house this month?