Smallpox
Smallpox is a highly contagious infectious disease that over the centuries has caused millions of deaths around the world. It is due to a virus.
The main symptoms are a high fever and development of pustules all over the body. Even those who survived the disease were often left badly scarred by the pustules. Its name refers to the small size of these pustules, as opposed to the great pox or syphilis.
The work of Edward Jenner, who noticed that people who had caught a disease from cows called cowpox were resistant to smallpox, led to the first vaccine against any disease. The use of vaccines and other health measures has eradicated the disease, and it was declared extinct in 1980. The virus is now only known to exist in a few secure laboratories around the world.