The bacterium that causes tetanus is called Clostridium tetani. The bacterium can survive in a dormant state in soil and animal feces. It's essentially shut down until it discovers a place to thrive.
When the dormant bacteria enter a wound — a condition good for growth — the cells are "awakened." As they are growing and dividing, they release a toxin called tetanospasmin. The toxin impairs the nerves in the body that control muscles.
Risk factors:
The greatest risk factor for tetanus infection is not being vaccinated or not keeping up with the 10-year booster shots.
Other factors that increase the risk of tetanus infection are:
• Cuts or wounds exposed to soil or manure
• A foreign body in a wound, such as a nail or splinter
• A history of immune-suppressing medical conditions
• Infected skin lesions in people living with diabetes
• An infected umbilical cord when a mother isn't fully vaccinated
• Shared and unsanitary needles for illegal drug use
Courtesy: Mayo Clinic