But still, diseases that infected our ancestors will infect us. Bubonic plague GREATLY reduced the European population in the 14th century, and we have used antibiotics to fight against such diseases in the 20th century. But still, there are cases of bubonic plague in the 21st century. Again, once emerged, a disease will never go away from the human race until the extinction of the race itself! The only way to see the world without sickness is to see the world without the human race. This is one of the reasons people are travelling to the remote places like Ladakh, Tibet, Sahara etc.