Syphilis-
Pre-Columbian theory. According to Lobdell and Owsley (the latter at Smithsonian Institution), syphilis was present in Europe before discovery of America by Europeans.
Columbian Exchange Theory. Mackenzie, Harper et al., syphilis is a New World disease brought back to Europe by Columbus and Pinzon. The latter has some support from genetic studies of the bacterial group.

The disease is caused by a spirochaetal bacterium, it is not viral.