Small pox is a unique disease and the only one in history to be eradicated by mankind. This disease is caused by the Variola virus which is quite closely related to cowpox. Early symptoms of small pox are fever and fatigue and later rashes and bumps begin to appear. These bumps are raised dots on the body which are filled with puss.
Small pox has existed since 3,000 years but later it was eradicated completely. The last outbreak of the disease was due to a laboratory accident in England in 1978. In 1979, the World Health Organisation declared that the disease had been completely eradicated.
It was a deadly disease which was fatal in 30% of the cases. It spread when people came in contact with each other. The first outbreak of disease was in 753 BC in Rome and it killed the entire civilization due its infectious nature.
Effective vaccination helped in the eradication process. The small pox vaccine was able to prevent infection up to four days after the initial exposure but it was a painstaking process to make that vaccine.
In 1976, Edward Jenner, the pioneer of the small pox vaccine, carried out his famous and most successful experiment. Folklore claimed that milkmaids were immune to smallpox since they got exposed to a virus called cowpox from cows.
So, Edward tested this theory by infusing cowpox in people and later injecting them with the small pox virus and realized that people can beat the disease.
Since smallpox was eradicated, the vaccine is no longer recommended in routine immunization. It is used to protect researchers who work on the Variola virus that causes smallpox and other viruses in the same virus family (known as Orthopox viruses). It could also be used to protect anyone else who is likely to have a huge risk of pox.
The World Health Organisation (WHO) conducts several programs on the disease as they receive data from various countries on how they can prevent it from spreading. The World Health Organisation provides technical and practical information on the outbreak of diseases.
Look at this interesting views which explains the origin and cure of small pox in a nut shell.