For an example of that, HIV likely crossed into the US from Haiti via the blood trade[0][1] which acted as both amplifier and transport after haitians had to leave DRC, and some got infected in the time they spent there.

And of course thousands of haemophiliacs in the 80s got infected with HIV and HepC because of contaminated Factor VIII: http://en.wikipedia.org/wiki/Contaminated_haemophilia_blood_...

[0] http://www.onereads.org/spillover-david-quammen?page=0,208

[1] http://lambsbloodblog.wordpress.com/2013/01/11/hemo-caribbea...