Syphilis. It's thought that syphilis came from South American "yaws" (actually it's found tropically, including Africa) that when transmitted to Columbus et al, the European dress styles and bathing habits, that is, lack of sunlight on the infected lesions, and minimal washing of both clothes and body, prompting the bacteria to mutate to what is now called syphilis.
Yaws can be transmitted through casual contact as well.
It came from, er, intimate contact with animals, though debate goes on. It's an old, old disease that probably was in existence in humans for time immemorial.
A few years ago I chanced upon a magazine article (can’t remember the publication - sorry) reporting that some university in the upper mid-west had discovered syphilis in the fossilized remains of a bear that died 7000 years ago.
Syphilis can be spread by blood transfusions, so I presume eating raw bear meat can infect a human.