Despite your claim, there are several diseases that no longer exist.
Only smallpox and rinderpest have been eradicated and rinderpest is not a human disease. Polio is close at 74 new cases reported in 2015 all of which were type 1. Type 2 cases were last reported in 1999 and the last reported type 3 case was in 2012. Only Afghanistan, Pakistan, and Nigeria are not considered polio free.