Tetanus is infection of the nervous system with the potentially deadly bacteria Clostridium tetani (C. tetani).
Spores of the bacteria C. tetani live in the soil and are found around the world. In the spore form, C. tetani may remain inactive in the soil, but it can remain infectious for more than 40 years.
Infection begins when the spores enter the body through an injury or wound. The spores release bacteria that spread and make a poison called tetanospasmin. This poison blocks nerve signals from the spinal cord to the muscles, causing severe muscle spasms. The spasms can be so powerful that they tear the muscles or cause fractures of the spine.
The time between infection and the first sign of symptoms is typically 7 to 21 days. Most cases of tetanus in the United States occur in those who have not been properly vaccinated against the disease.
For more detailes oped the attached pdf file:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001640/
http://en.wikipedia.org/wiki/Tetanus