There's always more to say, but the FAQ section on Disease in the Americas might have a few things of interest to you on this topic.

I recommend reading The Colombian Exchange by Alfred Crosby. It covers the biological exchanges between the "new" and "old" world. Just finished reading it for one of my graduate classes.

Syphilis is a disease sailors brought back from the new world. It didn't have as massive an impact due to the facto that the old world had more animals capable of domestication compared to llamas. Out immune systems were tempered through generations of exposure to colds and flus and pox that come fro. Cows pigs and chickens that the new world population did not have.