The interesting part about World War Z is the beginning 1/3rd where the zombie disease is just a disease. It shows how if any disease from Bird Flu II to whatever, the pressure to quarenteen will just cause people to flow across the borders. People who are already willing to move illegal aliens across any border (that's not just a US/Mexico thing) will be more than happy to take money and transport people possibly infected or not.
To me, that's the scary part. Not shambling dead, but the fact that if disease X pops up somewhere, and goes ripping through the population in an isolated corner of the world, it will be everywhere very very quickly.