Smallpox. Human to Human transmission. The WHO announced World-wide eradication of Smallpox on May 8 1980. Smallpox has no animal reservoirs. So Smallpox would not return naturally.
Exposure to case. Since the disease hasn't been found active in the world since 1977, it would be quite a notable event for you to get smallpox. While it was active it was passed person to person.